Preliminary Geometry, Displacement, and Kinematics ...

Bulletin of the Seismological Society of America, Vol. , No. , pp. –, , doi: 10.1785/0120170329

Preliminary Geometry, Displacement, and Kinematics of Fault Ruptures in the Epicentral Region of the 2016 Mw 7.8 Kaikoura, New Zealand, Earthquake by A. Nicol, N. Khajavi, J. R. Pettinga, C. Fenton, T. Stahl, S. Bannister, K. Pedley, N. Hyland-Brook, T. Bushell, I. Hamling, J. Ristau, D. Noble, and S. T. McColl The Mw 7.8 Kaikoura earthquake ruptured at least 17 faults for a distance of ∼165 km across the New Zealand plate boundary zone in the northeastern South Island. In the epicentral area, the earthquake produced displacement at the surface on The Humps, Leader, Conway-Charwell, and Stone Jug faults, which are the primary focus of this article. Analysis of the surface rupture, aftershocks, focal mechanisms, and Interferometric Synthetic Aperture Radar (InSAR)–derived uplift from the earthquake provides new information on the dimensions, geometries, and kinematics of these faults, which was not previously available from the active faults or bedrock structure. Relocation of the mainshock indicates that it initiated on The Humps fault with rupture mainly propagating to the northeast. The resulting ground ruptures comprise two intersecting sets that strike east-northeast with right-lateral and reverse displacements, and north-northwest to north-northeast faults with left-lateral reverse displacement. Reverse faulting was accompanied by folding associated with differential uplift and bedding-parallel slip. On a regional scale, faulting accommodated transpression consistent with the oblique relative plate motion vector and Quaternary bedrock deformation. Whereas the kinematics of faults that ruptured during the earthquake was predictable, the fault-rupture complexity could not have been anticipated or explicitly incorporated into seismic hazard models.

Abstract

Introduction Historical earthquakes provide key information about the earthquake and tectonic processes that form plate boundaries (e.g., Reid, 1910; Ellsworth et al., 1981; Stein et al., 1997; Beavan et al., 2012; Schwartz et al., 2012). The quantity and quality of these data have increased dramatically over the past 10 yrs with the densification of Global Positioning System (GPS) and seismograph networks and the advent of remote sensing datasets including light detection and ranging (lidar) and Interferometric Synthetic Aperture Radar (InSAR) (e.g., Beavan et al., 2012; Oskin et al., 2012; Duffy et al., 2013; Gold et al., 2013; Hamling et al., 2017). These datasets provide unprecedented detail of earthquake processes, fault geometries and kinematics, and regional tectonics. Lidar and InSAR data have been particularly useful for documenting the November 2016 M w 7.8 Kaikoura earthquake, which ruptured an array of faults within the New Zealand plate boundary zone in the northern South Island (Clark et al., 2017; Hamling et al., 2017; Hollingsworth et al., 2017; Wang et al., 2017; Kearse et al., 2018; Langridge et al., 2018; Litchfield et al., 2018; Williams et al., 2018) (Fig. 1). The Kaikoura earthquake produced signifi-

cant displacement at the ground surface on at least 17 active faults, with some active faults in the same area apparently bypassed by the rupture process. Although the complexity of the rupture is accepted, the precise number of surfacerupturing faults can vary and depends on the resolution of the fault-displacement data, the size of fault incorporated into the analysis, and whether intersecting near coplanar faults with different names (e.g., Needles, Kekerengu, Jordan thrust, and upper Kowhai faults) are considered separate structures or a single fault (e.g., Litchfield et al., 2018, indicate that 20 faults ruptured, but if the Needles, Kekerengu, Jordan thrust, and upper Kowhai faults are considered as a single structure, this number decreases to 17). Many aspects of the earthquake were unexpected, including the number and geometric complexity of faults and the propagation of the rupture obliquely across the plate boundary, which resulted in up to a ∼12-m slip at the ground surface (Hamling et al., 2017; Kearse et al., 2018; Litchfield et al., 2018). The earthquake ruptured active faults with variable displacement rates and in two different tectonic domains, the mainly strikeslip Marlborough fault system (MFS) that accommodates 1

2

A. Nicol et al.

scarps forming four primary faults that are here referred to as The Humps, Leader, Conway-Charwell, and Stone Jug faults. These four faults are the primary focus of this article (Figs. 2 and 3). Analysis of the surface rupture, aftershocks, focal mechanisms, and InSAR-derived uplift from the earthquake constrain the dimensions, geometries, and kinematics of these faults. In this article, information from the earthquake has been used to provide additional constraints on Quaternary deformation and transpressional tectonics in the epicentral area (NCD), which was not previously recognized from historical seismicity, GPS records, active faulting, or bedrock structure. The faults that ruptured during the earthquake form a hard-linked system dominated by east-northeast (The Humps and Conway-Charwell faults) and northnorthwest–north-northeast (Leader and Stone Jug faults) striking structures. We examine how these fault sets interact kinematically and what influence these interactions have had on earthquake rupture. The implications of our observations for earthquake hazard assessment and the frequency of Kaikoura-type earthquakes are also briefly considered.

(b) (a)

Figure 1. Maps showing the plate boundary setting of the Kaikoura earthquake. (a) New Zealand plate boundary. AF, Alpine fault; ChCh, Christchurch; HT, Hikurangi trough; Well, Wellington. (b) Geology (gray, Torlesse Supergroup Basement; orangebrown, Late Cretaceous–Cenozoic strata; yellow-green, Quaternary deposits; Rattenbury et al., 2006), active faults (black lines from Langridge et al., 2016), and faults that ruptured in the 14 November 2016 M w 7.8 Kaikoura earthquake (red lines with fault names) in the northeastern South Island. The Pacific plate motion vector relative to the Australian plate is from Beavan et al. (2002). The epicentral locations of the Kaikoura earthquake (blue star) and large historical Cheviot and Motunau earthquakes (Downes and Dowrick, 2015) in the North Canterbury Domain are indicated. Onshore topographic hillshade digital terrain model is from Land Information New Zealand and bathymetry is from the National Institute of Water and Atmosphere (NIWA). MFS, Marlborough fault system; NCD, North Canterbury domain. ∼40 mm=yr relative plate motion and the transpressional North Canterbury domain (NCD) with regional shortening rates of 2–3 mm=yr (Nicol et al., 1994; Barnes, 1996; Litchfield et al., 2003, 2014, 2018) (Fig. 1). To understand better the factors that contributed to the complexity of the earthquake, we document the surface rupture characteristics and present a preliminary analysis of the geometry and kinematics of faults that ruptured during the Kaikoura earthquake in the epicentral area (Fig. 2). The study area covers ∼750 km2 enclosing the epicenter in the northern NCD immediately south of the Hope fault (Figs. 1 and 2). To date, more than 150 km of fault-scarp length has been mapped in the study area, with the majority of these

Kaikoura Earthquake Geological Setting

The M w 7.8 Kaikoura earthquake produced displacement on faults that accommodate the transition from subduction beneath the North Island to continental collision and strike slip on the Alpine fault in the South Island of New Zealand (Fig. 1a). Onshore in the South Island, ≥ 80% of the ∼40 mm=yr relative plate motion is transferred from subduction toward the Alpine fault via strike slip on the MFS (e.g., Holt and Haines, 1995; Beavan and Haines, 2001; Pondard and Barnes, 2010; Wallace et al., 2012). Offshore and east of the Kaikoura earthquake surface ruptures, plate boundary deformation is accommodated by a subduction thrust and accretionary prism complex (e.g., Ansell and Bannister, 1996; Barnes and Audru, 1999; Pondard and Barnes, 2010; Williams et al., 2013). The accretionary prism and eastern MFS are underlain by the Pacific plate, which, based on seismic tomography and focal depths of historical seismicity, extends to a depth of at least 200 km beneath the northern South Island (Ansell and Bannister, 1996; Eberhart-Phillips and Bannister, 2010; Eberhart-Phillips and Reyners, 2012; Williams et al., 2013). In the epicentral area, the top of the subducted Pacific plate is

Preliminary Geometry, Displacement, and Kinematics of Fault Ruptures in the Epicentral Region

3

Figure 2. Geological map of rock units, active faults that did not rupture during the earthquake (dark gray lines), and surface ruptures from the Kaikoura earthquake (solid and black lines Global Positioning System [GPS] surveys and light detection and ranging [lidar] mapping, and dotted lines are ruptures inferred from deformation recorded by Interferometric Synthetic Aperture Radar [InSAR], e.g., Fig. 8), in the study area (Rattenbury et al., 2006; Langridge et al., 2016). Red and black lines represent northeast and more northerly striking faults, respectively, that ruptured during the 2016 Kaikoura earthquake. Refer to Williams et al. (2018) for rupture information on the Hundalee fault. Strike and dip of bedding in Torlesse rocks is from Rattenbury et al. (2006). See Figure 1 for location of study area. Inset stereonets depict fault planes (great circles) and slip vectors (white filled circles) for The Humps, Leader, Conway-Charwell, and Stone Jug faults from field measurements. Strike-slip movement sense shown by arrows along with upthrow (U) and downthrow (D) on fault traces. Locations V, W, X, Y, and Z are describing The Humps and Leader faults. Locations of Figures 3a–e, 5, and 6 are indicated in the figure. at a depth of ∼20–30 km beneath the surface ruptures (Eberhart-Phillips and Bannister, 2010; Williams et al., 2013) and may define the lower limit of the upper-plate faults. The Kaikoura earthquake is the largest historical earthquake to have ruptured onshore in the northeast South Island (Downes and Dowrick, 2015; Nicol et al., 2016). The earthquake produced a complex network of at least 17 strike-slip, reverse-slip, and oblique-slip faults that ruptured the ground surface and seabed with resolvable displacement (Fig. 1) (Clark et al., 2017; Duputel and Rivera, 2017; Hamling et al., 2017; Wang et al., 2017; Kearse et al., 2018; Langridge et al., 2018; Litchfield et al., 2018; Williams et al., 2018; this study). The complexity of the Kaikoura earthquake is partly reflected in the oblique focal mechanism (Fig. 4), which displays approximately equal components of thrusting/reverse and right-lateral slip (e.g., Bai et al., 2017; Cesca et al., 2017; Kaiser et al., 2017; Wang et al., 2017). The mainshock ini-

tiated at a focal depth of ∼14 km, and the rupture generally propagated northward for about 165 km from an epicenter in the northern NCD (Cesca et al., 2017; Duputel and Rivera, 2017; Hamling et al., 2017; Kaiser et al., 2017; Wang et al., 2017). The resulting surface ruptures vary in strike from eastwest to north-northwest. The east-northeast-striking faults are primarily right-lateral strike slip, and the northerly striking faults have left-lateral reverse displacement (Litchfield et al., 2018). The earthquake ruptured a number of previously mapped active faults, including the Needles, Kekerengu, Fidget, Jordan thrust, and Hundalee faults (Stirling et al., 2017; Litchfield et al., 2018). In addition to the mapped surface faults, the spatial extent of coastal uplift and widespread occurrence of tsunami up to ∼250 km from south of Kaikoura have been interpreted to indicate slip on the subduction interface and/or a blind upper-plate thrust(s) within the accretionary prism complex (e.g., Bai et al., 2017;

4

A. Nicol et al. 173˚

174˚ −42˚

−42˚

M 4 5 6

Mainshock

7 8

20 km

−43˚ 173˚

−43˚ 174˚

Figure 4.

Map showing the locations and focal mechanisms of the mainshock and aftershocks from 14 November 2016 to 17 February 2017. Focal mechanisms generated automatically for the GeoNet regional moment tensor solution catalog.

Figure 3. Photographs of surface ruptures in the study area (see Fig. 2 for locations). (a) The Humps fault crossing the Inland Road (photograph by Jarg Pettinga); (b) displaced fence line showing ∼1:6 0:1 m of right-lateral slip on The Humps fault, Emu Plain (photograph by Kate Pedley); (c) Waiau Wall locality on the Leader fault looking northward where the scarp height is 3.5 m (photograph by Kate Pedley); (d) oblique aerial view of the Leader fault looking north on Mendip Hills Station, where the scarp height is ≤ 2 m (photograph by Simon Cox); and (e) oblique aerial view looking northeast along the Conway-Charwell fault with a maximum scarp height from the earthquake of ∼1 m (photograph by Matt Cockcroft). Clark et al., 2017; Furlong and Herman, 2017; Hamling et al., 2017; Power et al., 2017; Wang et al., 2017). The role of such subsurface faults and their contribution to the seismic moment budget remains a point of debate. Active faulting and Quaternary deformation has been widely reported in the NCD (Fig. 1) prior to the Kaikoura earthquake (e.g., Nicol et al., 1994; Barnes, 1996; Pettinga et al., 2001; Rattenbury et al., 2006; Forsyth et al., 2008; Barrell and Townsend, 2012; Vanderleest et al., 2017). Whereas in the south of the NCD, the main faults dip steeply to the southeast with associated northwest-verging folds (e.g., Nicol

et al., 1994; Barnes, 1996), in the epicentral area and farther northeast, the fault dips are to the northwest, consistent with the fault dip direction in the subduction complex offshore (e.g., Barnes and Audru, 1999; Wallace et al., 2012). This change of fault dip direction within the NCD at the ground surface may partly reflect the increasing influence of the subduction system on faulting to the northeast. The NCD accommodates transpression and is dominated by northeast-striking oblique-slip faults with components of right-lateral and reverse displacements (e.g., Nicol and Wise, 1992; Nicol et al., 1994; Barnes, 1996; Pettinga et al., 2001; Vanderleest et al., 2017). These faults typically separate footwall synclines and hanging-wall anticlines, which are manifest in the topography as Quaternary basins and ranges. Whereas Late Cretaceous to Pliocene strata that predate the onset of Quaternary deformation occupy the basins, the ranges are often cored by steeply bedded and complexly deformed Torlesse Supergroup basement (Fig. 1; e.g., Nicol and Wise, 1992; Warren, 1995; Rattenbury et al., 2006; Forsyth et al., 2008). Basin-and-range topography primarily reflects crustal contraction and provides little evidence for a component of strike slip on the northeast to east-northeast-trending faults (Litchfield et al., 2003). Many of the faults mapped in the NCD are associated with active fault traces, which attest to the ongoing earthquake activity on these structures (e.g., Pettinga et al., 2001; Rattenbury et al., 2006; Forsyth et al., 2008; Barrell and Townsend, 2012). Quantitative data constraining the displacement rates and recurrence intervals of these faults are limited. The majority of displacement rates of faults in the NCD are estimated to be < 2 mm=yr with recurrence intervals of thousands to tens of thousands of years (Pettinga et al., 2001; Barrell and Townsend, 2012). Due in part to these long recurrence intervals, the faults in the study area


5

Table 1 Geometries and Kinematics of the Primary Faults Examined in This Study Geometry

Fault Name

The Humps West The Humps East Leader ConwayCharwell Stone Jug

Kinematics

Mean Strike (°)

Mean Dip (°)

Rupture Length (km)*

077

75 ± 10 S

18–22

055

60 ± 10 NW

14–18

020

70 ± 10 W

25–32

052

80 ± 10 NW

4–6

165

85 ± 5 E

18–20

Fault Type†

Right-lateral reverse Reverse right lateral Left-lateral reverse Reverse right lateral Left-lateral reverse

Maximum Horizontal (m)‡

Maximum Vertical (m)‡

Mean H:V Ratio§

Mean Slip Vector∥

Mean Shortening Axis#

3.9 ± 0.4

1.2 ± 0.2

085/21

126/05

2.0 ± 0.2

3.5 ± 0.5

283/50

308/12

2.5 ± 0.15

3.5 ± 0.5

354/51

314/17

0.5 ± 0.2

1.5 ± 0.2

263/73

310/30

0.7 ± 0.1

0.3 ± 0.1

2.6 ± 1.0 (N 150) 0.5 ± 0.5 (N 4) 1.4 ± 1.0 (N 39) 0.8 ± 0.3 (N 10) 1.65 ± 0.6 (N 2)

162/30

106/15

Data measured or derived from surface ruptures. S, south; NW, northwest; W, west; E, east. *Assuming along-strike continuity between intermittent surface ruptures. † Dominant slip type listed first. ‡ Surface rupture displacements. §Mean and standard error for all measurements on each fault. Number of measurements (N) indicated in brackets. ∥ Derived from the mean fault-plane orientation, the slip sense, and the mean horizontal-to-vertical (H:V) ratio. # Mean shortening axis orientations derived using slip sense and mean slip vector and the graphical technique of Marrett and Allmendinger (1990).

that ruptured in November 2016 were either not known to be active, or their lengths were poorly defined before the earthquake. The Kaikoura earthquake is the only historical event to have produced surface rupture in the NCD, although the 1901 Mw 6.8 Cheviot and the 1922 Mw 6.4 Motunau shallow (< 25 km depth) earthquakes may have produced surface folding due to fault displacement at depth (see Downes and Dowrick, 2015, for descriptions of the earthquakes and Fig. 1 for their locations).

Methods and Data Field mapping of surface ruptures, together with interpretation of lidar, InSAR, earthquake aftershock locations, and earthquake focal mechanisms, forms the core data in this article. Field mapping of surface traces generated by the earthquake commenced in the week following the event and is ongoing. Approximately, 150 km of rupture traces has been mapped in the field using hand-held differential GPS and Real Time Kinematic (RTK) GPS equipment (Fig. 2 and Table 1). The resolution and coverage of field mapping varied along individual fault traces and among faults. In relatively low-relief areas covered with grass and crops, fault displacements of sub-20 cm were routinely observed and recorded; however, on steeper slopes or in areas of dense vegetation cover, fault scarps < 1 m high were not always identified and surveyed. Field mapping of fault traces was augmented by interpretation of orthophotos and lidar digital elevation model (DEM) and hillshade models processed from data collected during December 2016 (i.e., 2–4 weeks after the earthquake). The lidar data (source: GNS Science; New Zealand Transport Authority [NZTA]; Land Information New Zealand [LINZ]; Environment Canterbury [ECan],

and AAM NZ Ltd.) were reprocessed to produce submeter resolution DEMs and hillshade models for mapping. The lidar data have horizontal and vertical accuracies of 0:5 and 0:1 m, respectively. The lidar data were used to map fault scarps with heights as small as about 0.1 m (Figs. 3 and 5). In cases when orthophotos showed these scarps to be accompanied by fresh fracturing of the ground surface, they were mapped as rupturing in the November 2016 earthquake (Fig. 5). Fault rupture mapping was augmented by differential lidar modeling for part of The Humps fault constructed by subtracting pre- and postearthquake lidar data (i.e., 2013 ECan and 2016 GNS Science lidar surveys) (Fig. 6). The differential lidar model was classified in 0.2-m vertical intervals, providing sufficient vertical resolution to map fault traces that were neither visible during field mapping nor from the postearthquake lidar images. All surface ruptures mapped during fieldwork were remapped using the remote datasets (e.g., orthophotos, lidar, and differential lidar) and are in good agreement, particularly along low-relief sections of The Humps fault. The majority of fault traces in steep terrain were remotely mapped using lidar. In such areas, lidar was essential for discriminating between tectonic fault scarps, which are relatively linear and cut across topography, and gravitational slope failures (e.g., landslide and slope creep). Outcrop and the interplay of topography with fault surfaces constrain the orientations of faults in the near surface (e.g., < 500 m depth). To estimate the location and geometries of faults at depths of up to 30 km in the crust, the mainshock and aftershocks for the Kaikoura earthquake recorded by GeoNet seismograph stations were relocated. The aftershock relocations use the hypoDD relative earthquake location algorithm (Waldhauser and Ellsworth, 2000) and the New Zealand 3D velocity model (Eberhart-Phillips et al., 2010)

6

A. Nicol et al.

Figure 5. Maps showing lidar-derived hillshade model of Kaikoura earthquake surface ruptures on the (a) Conway-Charwell and (b) The Humps faults. Surface ruptures (black lines) interpreted from a combination of field mapping, lidar, and orthophotos (see text for further discussion). Locations of maps are shown in Figure 2.

routinely used by GeoNet for locations. A total of 731 events were recorded from 14 November to 31 December 2016 for the area in Figure 7. These were relocated using P and S arrival-time picks, 98,926 phase-derived differential times, and 27,098 cross-correlation-derived differential times calculated between event pairs. Relocated aftershocks are expected to have relative location errors about 10 times smaller than the original catalog locations (Waldhauser and Ellsworth, 2000). The mainshock was relocated separately, using new manually picked P phases, and employing the probabilistic nonlinear global-search NonLinLoc approach of Lomax et al. (2009). The epicenter of the relocated mainshock presented here is up to 8 km northwest of the original location given by U.S. Geological Survey and GeoNet. Uncertainties in the depth and latitude–longitude position of the relocated mainshock are in the order of several kilometers. Displacements of the ground surface and fault displacement during the earthquake have been determined from field measurements, lidar, and InSAR DEMs (e.g., Figs. 7 and 8) and are presented in Figures 9–12. Strike-slip and vertical-

slip magnitudes were measured in the field using linear cultural features as displacement markers (e.g., fence lines, farm tracks and road margins, or center lines). These slip data were collected using tape measure and RTK GPS surveying of the displacement markers. Measurements of strike slip typically include both the discrete slip on the fault and the near-fault (< 30 m from the fault) distributed shear. RTK GPS measurements collected along strike-slip markers up to 150 m from the surface rupture indicate that on alluvial surfaces a small proportion (< 10%) of the distributed strain may occur beyond the region of tape measurements. Uncertainties on individual measurements of strike slip and vertical displacement are typically 0:1–0:3 m for both tape and GPS measurements. These measurements have been augmented by fault-scarp height measurements from lidar DEMs and across-fault differences in vertical motion from InSAR. In this study, InSAR uplift estimates were derived from the Sentinel-1A ascending (3 November 2016–15 November 2016 and descending 5 September 2016–16 November 2016) azimuth and range offsets (Hamling et al., 2017; see


7

(a)

172°56'40"E

172°57'20"E

172°58'0"E

172°58'40"E

42°38'20"S

42°38'0"S

(b)

0.5 km Legend -2.5 - -2.4

-2 - -1.8

-2.4 - -2.2

-1.8 - -1.6

-2.2 - -2

-1.6 - -1.4

-1.4 - -1.2 -1.2 - -1 -1 - -0.8

-0.8 - -0.6 -0.6 - -0.4 -0.4 - -0.2

-0.2 - 0 0 - 0.2 0.2 - 0.4

0.4 - 0.6 0.6 - 0.8 0.8 - 1

1 - 1.2 1.2 - 1.4 1.4 - 1.6

1.6 - 1.8 1.8 - 2 2. - 2.2

2.2 - 2.4 2.4- 2.6

Mapped from Differential lidar Mapped by GPS in the field

Figure 6. (a) Uninterpreted and (b) interpreted differential lidar digital elevation model (DEM) generated using pre- (2013) and post(2016) Kaikoura earthquake lidar-derived DEMs. Differential images were generated by comparing elevation values that are not strongly impacted by strike-slip motion because the fluvial plains on the map area are relatively flat (i.e., elevation differences of the ground surface over distances of ≤ 3 m are generally < 0:3 m). Location of map area shown in Figure 2 and corresponds to location B in Figure 10.

their supplementary material). The resulting uplift ranges from 1–1.7 m immediately north of The Humps fault to 1–3 m along the Mt. Stewart range in the immediate hanging wall of The Humps fault (Fig. 8). Vertical, strike-slip, and net displacement profiles have been constructed for each of the faults studied (Figs. 10– 12). For cases in which displacements accrued on multiple subparallel strands, they were summed along sample lines oriented normal to the average fault strike. Net displacement values have been estimated for sites where both strike slip and vertical displacements were measured with calculations assuming the average fault dips presented in Table 1. The resulting profiles are preliminary (because more data are being collected) and provide a first-order indication of how displacement during the earthquake varied along each fault. In addition to recording displacement magnitudes, slip orientations have also been measured at locations where fault

planes crop out at the ground surface (e.g., Fig. 3c). The obliquity of slip has also been documented at individual sites where both the horizontal (H) and vertical (V) components of displacement could be measured using cultural piercing points (e.g., road margins, drainage channels, fence lines, and farm animal tracks) (see Fig. 3). Where components of horizontal and vertical slip were measured, horizontal-tovertical (H:V) ratios have also been calculated (Fig. 9). In cases in which both displacement and fault orientations are available, we used the graphical technique of Marrett and Allmendinger (1990) to estimate the orientations of the principal strain axes for surface-rupturing faults. These data were augmented by P axes derived from focal mechanisms generated automatically for the GeoNet regional moment tensor solution catalog (Fig. 4). The available focal mechanism data were recorded between 14 November 2016 and 17 February 2017 and provide a first-order indication of fault kinematics.

8

A. Nicol et al.

fault as “definitely active” (∼2 km) and “likely active” (∼13 km) east of the Waiau township (Fig. 2) using fault scarps identified on aerial photos. An extension of the fault to the west of Waiau was considered possible, although it could not be mapped with confidence (Barrell and Townsend, 2012). Postearthquake fault-scarp mapping on lidar DEMs confirms the presence of previously mapped fault scarps and the existence of additional pre-earthquake fault scarps on the Late Quaternary alluvial plains (i.e., Emu Plains) west of Waiau (Fig. 2). These plains comprise terrace surfaces that vary in altitude above the modern rivers and are inferred to be mainly 71 ka or younger in age (i.e., Q2 and Q4 of Rattenbury et al., 2006). Preearthquake scarp heights of up to 7 m have Figure 7. (a) Mainshock and aftershock locations and (b,c) cross sections showing been recorded on these surfaces and indisubsurface fault geometry of The Humps fault. Events recorded by GeoNet permanent cate one or more surface-rupturing earthand temporary seismograph stations were relocated using the hypoDD relative earthquakes on The Humps fault following quake location algorithm (Waldhauser and Ellsworth, 2000) and phase-two automatic formation of the terrace surfaces; the numP arrival-time picks along with the New Zealand 3D velocity model now used by Geober and timing of these earthquakes are Net for routine locations (see The Humps Fault section for further discussion). (a) Locations of cross sections A–A′ and B–B′. Red lines indicate surface ruptures from the poorly defined and are the subjects of onKaikoura earthquake. (b) Star indicates the projected location of the mainshock hypogoing investigations. center, and the blue dashed line connects the hypocenter with surface rupture. (b) Red The Humps fault forms a zone comdots and (c) red line show the location of the top of the subducted Pacific plate from prising a segmented array of faults that Williams et al. (2013). Color contours in (b,c) show the crustal velocity structure. Verrange in average strike from ∼090° in the tical and horizontal units for both cross sections are in kilometers. west to ∼050° in the east. The fault can be divided into two main sections, here referred to The Humps West and The Humps East, based Fault Rupture Geometries and Displacement on changes in its strike and dip (Fig. 2 and Table 1). The Surface ruptures in the study area comprise four main Humps West is primarily restricted to the western ∼25 km faults (The Humps, Leader, Conway-Charwell, and Stone of the fault, where it crosses alluvial plains, strikes east to Jug faults), each with many short (≤ 4-km) discontinuous east-northeast, and dips to the south. The Humps East section traces accommodating mainly strike-slip, oblique reverse, of the fault is within, or defines the southeastern and eastern and reverse displacements. The first-order geometries and boundary of, the Mt. Stewart range and mainly strikes displacement of the faults at the ground surface are described northeast with a dip to the northwest. in this section. In addition, the geometry of The Humps fault The Humps fault consists of five primary segments at depth and its relation to the mainshock are discussed. The (labeled segments 1–5 in Fig. 2; segments 4 and 5 both comgeometric relationships between the main faults, which interprise parts (a) and (b), which are separated by the boundary sect each other at the surface, are also presented and together between the west–east sections of The Humps fault), which with the displacement data constrain the kinematic model for are separated by left and right steps of 0.5–1 km width the earthquake in the study area. (Figs. 2, 5b, and 6). Within segments 1 and 2, fault traces often form left and right stepping en echelon arrays associated with pop-up and pull-apart structures, respectively, The Humps Fault consistent with the fault accommodating a component of right-lateral slip (Figs. 2, 5b, and 6). Segments 4 and 5 form The Humps fault is the southwest-most surface rupture discontinuous traces that map into the western side of the of the Kaikoura earthquake. It strikes east to northeast and Mt. Stewart range and have a separation of up to 3 km normal extends for ∼36 km from a free tip on the western margin of to fault strike. Segment 5 forms a trace that bounds the the Emu Plains to its junction with the Leader fault at the southeastern margin of the Mt. Stewart range, mainly separatbase of the Mt. Stewart range in the east (Fig. 2 and Table 1). ing Torlesse basement and Neogene strata (Figs. 2 and 10). Prior to the Kaikoura earthquake, insufficient information The Kaikoura earthquake initiated on The Humps fault. was available to define the active fault length or its sense Early estimates of the nucleation location of the mainshock of slip. Barrell and Townsend (2012) mapped The Humps

172°55'0"E

173°0'0"E

173°5'0"E

173°10'0"E

173°15'0"E

173°20'0"E

9

173°25'0"E

ne J Sto

Legend -2.5 - -2 -2 - -1.5 -1.5 - -1 -1 - -0.5 -0.5 - 0 0 - 0.5 0.5 - 1 1 - 1.5 1.5 - 2 2 - 2.5 2.5- 3 3 - 3.5 3.5 - 4 4 - 4.5

Lea

ault

fault

ug f

der

A

42°35'0"S

42°30'0"S

42°25'0"S


ault

ps f

The

Hum

B

800

e

Le

fault

lin

tic

an

5 km e lin

No data

nc

sy

B

A

2

600

1

400

200 0

3

0

Pre-EQ topography InSAR vertical displacement 5

10

Distance (km)

15

20

-1 25

Vertical displacement (m)

Altitude (a.s.l.) (m)

42°40'0"S

The Humps

ad

er

fa u

lt

No data

Figure 8. Map of uplift in meters calculated from InSAR data in Hamling et al. (2017). Locations of active faults that did not rupture during the earthquake (black lines) and surface ruptures from the Kaikoura earthquake (solid red lines surveyed and dashed red lines inferred from the values of InSAR uplift) are shown together with fold hinges mapped from bedrock structure (Rattenbury et al., 2006). Profile A–B compares the long-term topographic pattern with the uplift caused by the Kaikoura earthquake. The locations of bedrock folds on the profile are also shown.

placed it ∼8 km south of The Humps Fault (see Data and Resources and Kaiser et al., 2017), raising the possibility that it initiated on a fault that did not rupture the ground surface during the earthquake. However, relocation of the mainshock in this study shifts the epicenter to latitude −42.656° and longitude 172.982°, ∼2:5 km south of The Humps fault and within the aftershocks attributed to the fault (Figs. 2 and 7), indicating that the Kaikoura earthquake initiated on The Humps fault. The geometry of the surface trace, aftershocks, and the location of the mainshock hypocenter south of the surface rupture indicates that the fault-dip direction changes along strike. In general, the western section of The Humps fault (Fig. 2) dips steeply to the south, with dips of 71° S and 80° S measured from the surface trace (a third measurement of 73° northwest was taken from the margins of a pop-up and is interpreted to be of local significance only) (see Fig. 2 inset stereonet for The Humps fault). These observations are comparable with the dip angle of 80° S estimated from the line of best fit on the fault-normal profile of aftershocks and to the

dip of 80° 5° estimated by assuming a constant dip between the surface trace and the location of the mainshock at 14 2 km (Fig. 7 section A–A′ blue dashed line). By contrast, The Humps fault eastern section appears to dip steeply to the northwest (see Fig. 2 inset stereonet for The Humps fault). Where measured at the surface, the dip is 60° northwest; however, the distribution of aftershocks (Fig. 7 section B–B′) most clearly defines deformation on a south-dipping plane at depths of > 10 km. Although the details of the aftershock data have not been analyzed in this article, the locations of the aftershocks can be interpreted to suggest that the south-dipping part of The Humps fault extends at depth to at least the Mt. Stewart area. In addition, both cross sections in Figure 7 show aftershocks that extend to at least the top of the Pacific plate oceanic crust at a depth of at least 25 km, consistent with rupture of The Humps fault to the plate interface during the earthquake (also see discussion in Litchfield et al., 2018). Rupture to at least 20 km depth on The Humps fault is supported by slip modeling (see fig. 3d of Wang et al., 2017),

10

A. Nicol et al.

(a) 10

Oblique slip


Dip slip 1

0.1

Strike slip

0.01 0.01

0.1

1

10

Horizontal displacement (m) Conway-Charwell

PMV

(b) 10

(N = 10)

Humps (N = 156)

8 Leader (N = 39)

H:V ratio

Stone Jug (N = 2) 6

4

2

0 0

30

60

90

120

150

180

Fault strike (°)

Figure 9. Plots of (a) vertical versus horizontal slip and (b) horizontal-to-vertical (H:V) ratio versus fault strike for all fault sites where both vertical and horizontal slip could be measured. Data from The Humps, Leader, Conway-Charwell, and Stone Jug faults are differentiated using different filled circles (see the legend in b). Error bars indicate uncertainties on slip measurements. (a) Dip slip (green), oblique slip (white), and strike slip (yellow) polygons are separated by V:H ratios of 1:3 and 3:1, respectively. (b) The vertical line shows the trend of the plate motion vector (PMV) from Bevan et al. (2002).

although it is presently not clear whether the interface between the Pacific oceanic crust and overriding plate in the epicentral area accrued displacement during the earthquake. The Humps fault is primarily right lateral (The Humps fault west) to reverse right lateral (The Humps fault east) (Table 1 and Fig. 10). Vertical, horizontal, and net displacement during the earthquake have been recorded along the length of the fault with the majority of measurements from the western ∼25 km where it crosses alluvial plains. Right-lateral strike displacement, vertical displacement, and net displacement are up to 4 0:3, 3:5 0:5, and 3:9 0:3 m, respectively (Fig. 10). Displacement measurements across the alluvial plains (Humps fault west section) display significant variation in both horizontal and vertical displacement. For example, between distances of 5 and 18 km in Figure 10, horizontal displacement varies from ∼0:5 to > 2 m at length scales of < 2 km. These differences are observed for both GPS survey and tape measurements and cannot be accounted for by measurement technique. Many of the strike-slip displacement lows are located at steps or branch points along

the fault trace, indicating that some of the fluctuations in displacement may reflect fault segmentation (in Fig. 10, compare the locations of displacement lows at A–D in the profiles and fault geometries on the map). One possible explanation for the coincidence of displacement lows and segment boundaries is that these are sites of elevated off-fault deformation, which is not fully sampled by our displacement measurements. In addition, at some fault-segment boundaries, along-strike changes in the magnitude of horizontal displacement locally coincide with an increase in vertical displacement. For example, the strike-slip displacement lows at locations C and D coincide with highs in south-side-up vertical displacement (positive value) and at location B with a high in vertical north-side-up displacement (negative value) (Fig. 10). These local highs in vertical displacement occur at pull-apart basins between fault traces where strike slip is transferred to dip slip (see Fig. 6). In addition to the short wavelength fluctuations in the magnitude of displacement, the profile in Figure 10 shows an eastward change in the direction of fault upthrow. On the alluvial plains, at distances of < ∼19:5 km along the fault, the vertical displacement is generally up to the south, but at > 19:5 km, throw is primarily up to the north. The change in throw direction along the fault appears to coincide with a change in its dip direction at the ground surface, from mainly south at distances < 19:5 km to northwest at distances > 19:5 km. Because of this change in dip direction, the fault accommodates a component of reverse displacement along its entire length. Vertical displacement reaches a maximum of up to ∼4 m along the Mt. Stewart range area, where strike slip is typically lower than the vertical (Fig. 10). The high vertical displacement (and associated low in horizontal displacement) occurs where the obliquity of the fault strike and the trend of the relative plate motion vector (∼260°) are at a maximum (∼050°) (see the Discussion section for further information on the relationships between fault kinematics, relative plate motion, and regional tectonics). Leader Fault The Leader fault has an overall strike of north-northeast and exhibits primarily left-lateral reverse with throw up to the west (Table 1; Figs. 2 and 11a). The fault extends for ∼28 km along strike from a free tip in the south to its intersection with the Conway-Charwell fault in the north (Figs. 2 and 11a). A complex array of mapped traces ruptured the Leader fault during the earthquake, forming a zone of up to ∼3:5 km wide, with strike varying through 180°, and dips from 80° east to 25° west (Fig. 2 Leader fault inset stereonet and Fig. 11a). A bedrock fault within, or bounding, Neogene siltstone was previously mapped south of location V in Figure 2; however, no fault was mapped north of this point (Warren, 1995; Rattenbury et al., 2006). Along the Leader fault, no active fault scarps were identified prior to the earthquake; however, postearthquake examination of 1950 vintage black and


(a)

172°55'0"E

173°0'0"E

173°5'0"E

173°15'0"E

The Humps East

1 42°40'0"S

173°10'0"E

The Humps West

11

4b 4a

Free tip

Emu Plains

2

4b

5b

2

2 3 A 1

(b)

B

D

C

West

4

5 km

5b

5a

East

No data

Displacement (m)

3

2

1

0

Horizontal (N = 103) Vertical (N = 113)

-1

(c) Net displacement (m)

N = 97

No data

4

3

2

1

0

0

10

10

15

20

25

30

35

Distance along fault (km)

Figure 10.

(a) Surface rupture map and displacement profiles for total (b) vertical and horizontal (right lateral) and (c) net displacements on The Humps fault. Horizontal and vertical displacements were measured in the field using linear cultural features as displacement markers (e.g., fence lines and road margins or center lines). Displacement data were collected using tape measure and Real Time Kinematic (RTK) GPS survey of the displacement markers (see The Humps Fault section for further discussion). Vertical displacements have been augmented by lidar data. Measurements of strike slip typically include both the discrete slip on the fault and the near-fault (< 30 m from the fault) distributed deformation. Displacements were summed along sample lines normal to fault strike oriented. The resulting displacement profiles provide an indication of the total resolvable horizontal, vertical, and net displacement across each fault. Uncertainties on horizontal and vertical displacements are 0:2 − 0:5 m for both tape and GPS measurements. Vertical displacements are positive for north side up and negative for south side up. Dotted lines indicate the locations of steps, branch lines, and/or basins along the fault—labeled A–D. Numbers on the map indicate the segment numbers referred to The Humps Fault section.

white aerial photos has revealed many (> 5) short (< 1 km) fault scarps, which subsequently ruptured during the 2016 earthquake. These scarps indicate at least one prehistoric earthquake on the Leader fault, although the timing, slip type, and maximum displacement of this event(s) is not known. Two first-order geometric sections (north and south of location X in Fig. 2) define the Leader fault. The southern section is about 18 km long and, on average, strikes northnortheast with mainly low-dipping (20°–40°) fault surfaces

subparallel to Cretaceous–Cenozoic bedding. The southern section of the fault has irregular rupture-trace geometries, which in part reflect the interplay between the low fault dips and topography. These faults are often approximately located at the contact between basement and Cretaceous–Cenozoic cover rocks (Fig. 2). For example, immediately south of the step in the fault trace at location X, the main surface rupture appears to define the contact between basement and Late Cretaceous cover rocks, which dips westward at ∼30°. Therefore, parts of the Leader fault appear to accommodate

12 173°10'0"E

173°10'0"E

(a)

A. Nicol et al. 42°35'0"S

42°30'0"S

173°15'0"E

into three parts labeled W, Y, and Z, which vary in strike. North of location X, the Y main ruptures are contained entirely withV in Torlesse basement and strike subparallel to basement bedding (Fig. 2). Therefore, X W the geometry of the Leader fault, both at the surface and in the subsurface be5 km neath Late Cretaceous–Cenozoic cover (b) 4 stratigraphy, may be partly controlled by N = 88 Gravity-driven vertical the locations and geometries of planes of displacement? 3 weakness in the basement. Further south Waiau Wall in the area of location V, the Leader and 2 The Humps faults intersect. This zone of intersection comprises numerous (> 10) 1 fault traces with a mixture of right-lateral, left-lateral, reverse, and normal displaceVertical (Insar) Vertical (lidar, Field, RTK) ments that connect the primary fault 0 (c) 4 surfaces. N = 30 The Leader fault primarily accommodated left-lateral reverse displacement, 3 with vertical and horizontal components ranging up to 3.5 and 3 m (including 2 uncertainties), respectively (Fig. 11b,c). Measurements of displacement on the 1 Leader fault are less numerous than on The Humps fault and show spatial vari0 ability for both horizontal and vertical dis4 (d) N = 30 placement of up to 2–3 m over distances of < 1 km (Fig. 11b,c). Although some of 3 these variations may be due to incomplete sampling of displacement, it is also pos2 sible that they reflect local changes in fault strike or locally elevated vertical displace1 ments due to gravitational processes. As North South appears to be the case with The Humps 0 0 5 10 15 20 25 30 fault, the relative importance of horizontal Distance along fault (km) and vertical displacement during the earthquake varies with fault orientation. Parts Figure 11. (a) Surface rupture map, (b) vertical, (c) horizontal (left lateral), and of the Leader fault striking north-northeast (d) net displacement profiles for the Leader fault. Displacement data were collected usto northeast mainly accommodate vertical ing tape measure, GPS, lidar, and InSAR models. As with data from The Humps fault, displacement (H:V ratio = 1:5–1:10) displacements were summed across multiple fault traces with total uncertainties of 0:2–0:5 m. Letters on the profile correspond to letters on the map in Figure 2 and on bedding-parallel thrust surfaces, but are discussed in the Leader Fault section. north-northwest- to north-northeast-striking parts of the fault with steep dips accrued approximately equal amounts of left-lateral and bedding-parallel slip perhaps associated with flexural-slip vertical displacement. Given that landslides are common folding of the Late Cretaceous–Cenozoic sequence. The along the Leader fault (Dellow et al., 2017; Massey et al., southern section also comprises a short (< 2:5 km) fault seg2018), it is also possible that vertical displacement was loment that includes the Waiau Wall locality (Fig. 3c) and cally increased by slope failure. The Waiau Wall site (Fig. 3c) strikes to the north with a steep easterly dip (> 80°). The is one locality where gravitational failures are common and geometry of this north-striking part of the fault is anomalous the vertical displacement on the fault is significantly above and could be influenced by the strike and steep dip of background values (Fig. 11b). Based on the elevated disTorlesse basement bedding in the subsurface. placements at the Waiau Wall site (Fig. 11b,c), it is possible The northern section of the Leader fault (north of point that up to 2 m of vertical displacement here reflects gravitaX on the fault trace, Fig. 2) appears to dip steeply, generally tional rather than tectonic processes. This gravitational interstrikes to the north and is ∼10 km in length. It can be divided pretation is consistent with the orientation of slickenside Net displacement (m)

Left-lateral displacement (m)


±

173°20'0"E

Z


Figure 12.

Vertical, horizontal, and net displacement profiles for the (a) Conway-Charwell and (b) Stone Jug faults. Horizontal displacement on the Conway-Charwell fault is right lateral and on the Stone Jug fault is left lateral. Displacement data were collected using tape and lidar measurements.

13

The Conway-Charwell fault surface rupture produced a trace with two relatively straight segments separated by a left step about 0.5 km wide containing at least 20 secondary fault traces (Fig. 5a). At the scale presented in Figure 2, fault strike varies from 30° to 60°, with a fault dip of 80° northwest measured in a single outcrop (see Fig. 5a for location). Aftershock data provide no subsurface information on fault dip and whether it intersects the Hope fault at depth (Fig. 7). The proximity of the Conway-Charwell fault to the Hope fault and the comparable strike and dip of the two faults are consistent with the view that the Conway-Charwell fault is part of the Hope fault zone and that the two merge at depth. If this hypothesis is correct, it is possible that the Hope fault also ruptured at depth during the 2016 earthquake. The Conway-Charwell fault is primarily downthrown to the southeast, with a component of right-lateral strike slip. Vertical and horizontal components of displacement range up to 2.2 and 0.75 m (including uncertainties), respectively (Fig. 12a). Along the southwestern 1.5 km of the displacement profile (Fig. 12a), vertical displacement is typically at least a factor of 2 greater than horizontal displacement, but toward the northeast, the two components have comparable values. These variations at least partly reflect fault geometry with high values of uplift along more northerly striking sections of the fault. In addition, the highest vertical slip occurred on the alluvial terrace surfaces above (and immediately east of) the deeply incised Conway River (for location see Fig. 5a), which suggests that vertical displacement could have been locally enhanced by gravitational movement toward the river valley along some fault surfaces. Stone Jug Fault

striations, which have more dip slip on the lower 2 m of the fault surface at the Waiau Wall. This increase in dip slip may indicate an increase in gravitational slip on the fault surface as movement progressed. Despite the local variations in displacement, there seems to be a general northward increase in vertical displacement along the fault, but the greatest left-lateral slip occurs on the southern half of the fault. Therefore, the fault has a greater component of strike slip in the south and becomes more dip slip in the north (Fig. 11b,c). Conway-Charwell Fault The Conway-Charwell fault is subparallel to, and located 1–2 km southeast of, the Hope fault (Fig. 2). It has an average strike of 052° and a trace length of 6.5 km and appears to terminate against the Leader and Stone Jug faults at its southwest and northeast tips, respectively (Table 1). The fault accommodates right lateral and reverse slip, primarily displacing Torlesse basement and Late Quaternary alluvial terraces (Rattenbury et al., 2006). Prior to the earthquake, the fault was marked by an active trace ∼4 km long with a mainly south-facing scarp up to ∼6 m high where it crosses terrace surfaces ranging up to ∼170 ka in age (Bull, 1991; Rattenbury et al., 2006).

The Stone Jug fault extends for ∼17 km between the Conway-Charwell and Hundalee faults (Fig. 2 and Table 1). Unlike the other fault surface ruptures mapped in this article, the Stone Jug fault predominantly comprises a single fault trace at the scale of Figure 2. Overall, the fault strikes northnorthwest (335°) and, where observed, a near-vertical dip (Fig. 2 and inset stereonet). The fault changes in strike southward from northwest to north–northwest. It is primarily left lateral with the upthrown side of the fault changing alone strike (Fig. 2). The northern 5 km of the surface rupture was mapped as active and occupies a pre-existing fault scarp up to ∼5 m high (down to the east) formed across a Late Quaternary alluvial terrace ≤ 29 ka in age (Bull, 1991; Rattenbury et al., 2006). The fault-scarp height indicates multiple surface-rupturing earthquakes at the northern end of the fault since the formation of the alluvial terrace, although the timing of these events is unconstrained. South of the alluvial terrace, the fault displaces Late Cretaceous sandstone and Torlesse basement for a strike length of ∼11 km (Fig. 2). Five kilometers from the northwestern tip of the fault, the left-lateral finite displacement of a steeply dipping Cretaceous-Torlesse basement contact is no more than a few hundred meters, and the finite strike-slip displacement on the

14

A. Nicol et al.

fault is minor. As is the case for the Leader fault, the Stone Jug fault strikes and dips steeply (85° east) subparallel to basement bedding (Fig. 2), which may control the fault location and orientation. Torlesse bedding along the rupture trace dips steeply (e.g., > 60°) east and west, and fault dip may also vary along strike. Aftershock data provide little information on the fault dip. Vertical and horizontal components of displacement have been measured for the northern 10 km of the Stone Jug fault, where they range up to 1.1 and 0.8 m (including uncertainties), respectively (Fig. 12b). We have only three horizontal and net displacement measurements on the fault, and these are generally within a factor 2 of vertical displacement at the same sites, although the relative importance of the two components can vary among locations. The vertical displacements are generally too small to significantly impact the uplift contours derived from InSAR for the earthquake (Fig. 8a). Instead, the Stone Jug fault cuts obliquely across a region of uplift that trends to the northeast and may have primarily formed in response to slip on the Hundalee fault at depth (see Williams et al., 2018).

Discussion Kinematics of Regional Deformation Preliminary analysis of the displacements and geometry of surface ruptures during the Kaikoura earthquake indicates that both can be highly variable over short distances along individual faults (< 1 km) (Figs. 2, 5, 6, 8, and 10–13). Faulting is dominated by oblique slip (Fig. 2 inset stereonets and Fig. 9), with the relative importance of strike-slip and dip-slip dependent on fault strike (Figs. 13 and 14). For faults striking 060°–100°, right-lateral strike slip dominates, but faults striking between 0° and 060° generally accommodate more reverse displacement than strike slip (Figs. 9b and 13). Reverse displacements on the primary faults were accompanied by regional scale folding manifest as differential uplift (e.g., Fig. 8) and bedding-parallel slip. The epicentral region accommodated transpression during the Kaikoura earthquake. The study area is deforming in response to oblique convergence across the plate boundary with a relative plate motion vector trending at ∼260° (Beavan et al., 2002). Oblique convergence is consistent with slip vectors on faults in the MFS and NCD (Van Dissen and Yeats, 1991; Nicol and Wise, 1992) and with a regional principal horizontal shortening (PHS) direction of about 120° determined for the NCD in the present study (Figs. 4 and 14b) and from previous work (e.g., Nicol and Wise, 1992). Assuming that the PHS direction is parallel to the trend of the maximum horizontal stress (Balfour et al., 2005; Sibson et al., 2011; Townend et al., 2012) and using an average strike of 060° for the plate boundary, the study area would accommodate transpression at an α angle of about 060° with greater shortening than strike slip (Fig. 14c). The orientations and geometric relationships between different types of faults and the maximum principal stress

Figure 13. Histograms showing relationships between fault strike and slip type. Fault strikes were measured using ArcGIS software for sites where displacement has been measured. Faults dominated by right-lateral, left-lateral, normal, and reverse displacements are plotted on different histograms. The vertical dashed line shows the orientation of the regional principal horizontal shortening (PHS) direction (120° 19°). Light gray polygons show the predicted strikes of faults in the general transpressive model of Figure 14c. (σ 1 ) are consistent with the transpressive model (after Dewey et al., 1998) in Figure 14c, which forms in association with the right-lateral displacement and shortening. In this model, the strikes of reverse and normal faults are perpendicular and parallel to σ 1 , respectively, but strike-slip faults form a conjugate pair symmetrically disposed about the σ 1 . In Figure 14, the margins of the transpressional zone are oriented at 060°, but the σ 1 trends at 120° approximately parallel to the PHS plate boundary, and the filled polygons show the average orientations of right-lateral faults, left-lateral faults, reverse faults, and folds formed during the Kaikoura earthquake (see Fig. 2 inset stereonets and Fig. 13 for supporting data). The strike of predominantly right-lateral and reverse-fault displacement and the trend of folding during the earthquake are compatible with the predictions of the transpression model in Figure 14c. By contrast, the strike of normal and left-lateral faults from the Kaikoura earthquake does not match the model. Faults with predominantly normal displacement show a wide range of strikes with no preferred


(a)

173°0'0"E

173°20'0"E

Fault rupture kinematic summary SJ

pe

Ho

U D

lt

fau

U

Up lif

t

42°3'"00S

F

Mean PHS (120±19°)

D

U D

F TH LF

U

42°40'0"S

D

D

U e

lin

c yn

HF

ne

li tic

An

10 km

S

(b)

(c) PHS data

Transpression model

Kaikoura RL flts

1

PH S

12

0±

Kaikoura Rev flts

19

°

Kaikoura LL flts 1

Focal mechanism P-axis (N = 33) Shortening axis (N = 18)

Kaikoura folds

Figure 14.

(a) Schematic map showing the geometries and slip of faults, orientations folds, and regional PHS for faults that ruptured during the Kaikoura earthquake in the study area (black fault traces ruptured during the earthquake and dark gray fault traces did not). THF, The Humps fault; LF, Leader fault; CCF, Conway-Charwell fault; SJF, Stone Jug fault. (b) Stereonet shows shortening axes determined from fault-slip orientations measured in the field and determined using the technique of Marrett and Allmendinger (1990), and P axes from the focal mechanisms presented in Figure 7. (c) Summary schematic diagram for right-lateral transpression showing the expected structures and their orientations relative to trend of the maximum principal stress (σ 1 ). The transpression model is after Dewey et al. (1998) with the trend of the zone approximately parallel to the plate boundary and the σ 1 parallel to the PHS in the study area. The expected strike of reverse (lines with white triangles), normal (lines with white rectangles), and strike-slip (arrows) faults, and trend of folds (lines with black triangles) are indicated. Filled polygons show the average orientations of reverse faults (Rev), folding and strike-slip faulting (LL, left lateral; RL, right lateral) observed for surface ruptures in the Kaikoura earthquake.

orientation (Fig. 13). The variation in the strike of normal faults may partly reflect the fact that (1) the formation of these faults was influenced by gravitation processes and local slope orientations, which are also highly variable, and/or (2) normal faults at releasing stepovers or bends on strikeslip faults may strike oblique to the PHS direction. Similarly, the strike of left-lateral faults generally varies by ∼25°–45° from left-lateral faults in the model (Fig. 14c). In this case, the more northerly strike of left-lateral faults (compared with the transpressional model) may partly reflect their reactivation of basement heterogeneity (e.g., bedding surfaces and pre-existing faults) with an approximate north–south strike (Fig. 2) rather than striking northwest to north-northwest as might be expected for transpression in homogeneous

15

crust. Such heterogeneity may also locally control the strike of the Hundalee fault and the average strike of the Whites fault (Litchfield et al., 2018; Williams et al., 2018), which also ruptured during the earthquake. Transpressional strain during the earthquake is consistent with Quaternary shortening in the NCD recorded by structures in the bedrock and by the topography, which is interpreted to be a proxy for the 1–2 Ma pattern of uplift (e.g., Nicol et al., 1994, 2017). Comparison of the InSAR-derived uplift with topography suggests that vertical motion during the earthquake is in places consistent with the longer term deformation pattern (i.e., the highest values of uplift coincide with topographic ranges and lower values are observed in the basins and valleys; see profiles in Fig. 8). In particular, the uplift of the Mt. Stewart range is compatible with the mainly right-lateral slip in the west and oblique reverse slip in the east on The Humps fault during the November 2016 earthquake (Fig. 14). These observations indicate that earthquakes on The Humps fault with kinematics similar to the 2016 event may have occurred repeatedly during the Quaternary. Five hundred earthquakes with a maximum vertical displacement of 4 m and recurrence intervals of about 4000 yrs would be required to produce a 2-km finite vertical displacement on The Humps fault estimated from outcrop geology along the Mt. Stewart range front (Warren, 1995; Rattenbury et al., 2006; Fig. 2). For such a model, the uplift of the Mt. Stewart range would be accompanied by about 2 km of right-lateral displacement on The Humps fault where it crosses the Emu Plains in the west (Fig. 2). In contrast to The Humps fault, the topographic expression of the Leader and Stone Jug faults is limited and does not closely match the InSAR-derived uplift patterns. At the Waiau Wall locality, for example, whereas the Kaikoura earthquake produced a scarp height of up to 3.5 m on the Leader fault, topographic relief across the fault scarp is low (< 100 m) and provides few clues to the existence of the fault or its Quaternary displacement history (see Fig. 3c). Therefore, vertical displacements in excess of 1 m on the Leader fault were sufficiently rare to preclude the building of topography on the west side of the fault. The subdued topographic evidence for the Leader fault together with the suggestion that The Humps fault may have ruptured repeatedly during the Quaternary leads us to conclude that earthquakes that corupture both faults are rare (i.e., if they always ruptured together with meter-scale vertical displacements, both the Leader and The Humps faults would have strong topographic expressions). The Kaikoura earthquake ruptures in the study area form a network of faults dominated by two sets with different strikes. Within the resolution of the mapping, these fault sets intersect each other at the ground surface. These intersections promote the transfer of displacements between faults and across the plate boundary zone. In particular, north–southstriking faults may transfer of displacement between the dominant northeast-striking faults (e.g., Hope, Hundalee, and Humps faults), each of which are separated by distances

16

A. Nicol et al.

of 10–30 km normal to strike. Global compilations of historical earthquakes suggest that these across-strike distances are sufficiently large to terminate dynamic rupture propagation (e.g., Biasi and Wesnousky, 2016). Therefore, the presence of north–south-linking faults could have promoted rupture propagation and facilitated displacement transfer across the plate boundary zone in the northeastern South Island. Similarly, the plate interface may also have played a role in promoting synchronous rupture of upper-plate faults and northward rupture propagation (see Litchfield et al., 2018, for further discussion).

Implications for Earthquake Hazard The Kaikoura earthquake has implications for the identification and characterization of seismic sources for seismic hazard analysis. Prior to the earthquake, knowledge of the locations, geometries, and paleoearthquake histories of the faults that ruptured was variable. North of the Hope fault within the MFS, most of the main faults (e.g., > 1-m slip) that ruptured during the earthquake had already been identified as active prior to the earthquake and incorporated into the National Seismic Hazard Model (NSHM; Stirling et al., 2012, 2017). By contrast, in the NCD, most of the faults were either not known to be active (Leader fault) or had poorly defined lengths compared with the 2016 ruptures; 20% of the Stone Jug fault, < 40% of The Humps fault, and 60% of the Conway-Charwell fault were known to be active before the earthquake. Therefore, independent of whether these faults generally rupture together or separately, their previously assigned active fault lengths would produce minimum estimates of the earthquake magnitude. Sparse prior knowledge of fault activity in the NCD may reflect the combined effects of low fault-slip rates (e.g., < 1 mm=yr) and the post Last Glacial Maximum age (< 29 ka) of many of the faulted landscape elements (compare with Nicol et al., 2016). Pre-existing fault scarps in the study area are often best preserved where they cross pre-Holocene fluvial surfaces (Rattenbury et al., 2006). The Conway-Charwell and Stone Jug faults had scarps of 3–5 m high on the Last Glacial Maximum surface (∼12–29 ka: Bull, 1991; Rattenbury et al., 2006) prior to the Kaikoura earthquake, suggesting that these faults may have average vertical-slip rates of ∼0:1–0:4 mm=yr (Barrell and Townsend, 2012; this study). Given the sub-0:4 mm=yr displacement rates and vertical displacement of > 1 m during individual earthquakes, earthquake recurrence intervals of thousands to tens of thousands of years are possible but poorly constrained for these faults. The present New Zealand seismic hazard model contains over 530 individual faults and generally treats these as discrete sources (Stirling et al., 2012). Since the completion of the NSHM fault source model in 2010, the Darfield and Kaikoura earthquakes and numerical models suggest that multifault ruptures are possible and should be included in the model (Field et al., 2014; Stahl et al., 2016; Stirling et al.,

2017; Litchfield et al., 2018). Although the 2010 NSHM includes the possibility of multifault rupture in the area of the greatest seismic energy release during the Kaikoura earthquake, its full complexity had not been recognized as a viable event. The absence of complex ruptures similar to the Kaikoura earthquake in the NSHM is in part because some of the faults that ruptured were not known to be active. Estimates of recurrence intervals for faults in the study area suggest a minimum value for the recurrence interval of Kaikoura events of at least ∼6000 yrs (i.e., this is the longest recurrence interval of the faults that ruptured; Litchfield et al., 2018). Although Kaikoura events appear to occur infrequently, it remains possible that multifault ruptures in general are much more common than presently represented in the NSHM, a view supported by the 1987 Edegcumbe, 2010 Darfield, and 2016 Kaikoura earthquakes, which all produced displacement on at least five faults (Beanland et al., 1989; Beavan et al., 2012; Litchfield et al., 2018). Therefore, future versions of the NSHM could include more multifault ruptures by identifying a greater number of faults that may rupture together and by raising the maximum magnitude of background seismicity from M w 7.2 to at least M w 7.8 to account for events on faults not known to exist (Nicol et al., 2016). In either case, it will be necessary to continue to calibrate outputs from the NSHM using historical, prehistorical, and synthetic seismicity data.

Conclusions In the epicentral area, faulting accommodated transpression with components of right-lateral and shortening arising from oblique convergence across the plate boundary. The faults that ruptured are predominantly oblique slip and comprise two main sets that strike east to northeast and northnortheast to north-northeast, both with mainly steep dips (60°–80°). The more northerly striking faults were largely unknown prior to the earthquake, appear to use steeply inclined bedding in Torlesse basement, and accommodated predominantly left-lateral reverse displacement (Leader and Stone Jug faults with net slip of ≤ 4 and ≤ 1 m, respectively). East- to northeast-striking faults (The Humps and Conway-Charwell faults with net displacements of ≤ 4 and ≤ 2 m, respectively) are parallel to the MFS and accrued right lateral to oblique reverse displacement. Kinematics of surface ruptures during the earthquake is consistent with Quaternary bedrock deformation, the regional ∼120° PHS and the ∼260° trending relative plate motion vector. Intersection of the main fault sets may have facilitated the complexity of rupture, the northeast transfer of displacement, and northward propagation of the earthquake. The earthquake highlights the importance of unidentified active faults and multifault earthquake sources for future iterations of the NSHM in New Zealand and elsewhere.


Data and Resources The earthquake focal mechanisms in Figure 4 are from GeoNet (http://quakesearch.geonet.org.nz/, last accessed August 2017). A 1:250,000 scale map of the surface ruptures can be downloaded from the New Zealand active faults database (https://data.gns.cri.nz/af/, last accessed September 2017). Initial estimates of the location of the hypocenter are from U.S. Geological Survey (USGS) 2016 (https://earthquake.usgs .gov/earthquakes/eventpage/us1000778i#executive, last accessed September 2017) and GeoNet 2016 (https://www. geonet.org.nz/earthquake/2016p858000, last accessed September 2017). The remainder of datasets used come from published sources listed in the References section. P-axes orientations were derived from focal mechanisms data (https://github. com/GeoNet/data/blob/master/moment-tensor/GeoNet_CMT_ solutions.csv, last accessed September 2017).

Acknowledgments This research was funded by the University of Canterbury (UC); the UC Earthquake Commission (EQC) Capability Fund; and the Ministry of Business, Innovation and Employment (MBIE) response funding, provided through the Natural Hazards Research Platform (Grant Number 2017-GNS01-NHRP). The authors thank the farmers of North Canterbury for granting them full access to their land during difficult times. Mike Oskin and Nicola Litchfield are thanked for their constructive and insightful reviews, which helped improve the article. Simon Cox and David Barrell (both GNS Science—Dunedin) provided valuable information and advice during field reconnaissance and mapping. Field assistance was provided by Andrea Barrier, Alan Bischoff, Josh Borella, Matt Cockcroft, Fiona Fenton, Chris Grimshaw, Virginia Toy, Marlene Villeneuve, and Anekant Wandres. Thank you to Land Information New Zealand, New Zealand Transport Authority, AAM NZ Ltd., and GNS Science for providing light detection and ranging (lidar) data.

References Ansell, J. H., and S. C. Bannister (1996). Shallow morphology of the subducted Pacific plate along the Hikurangi margin, New Zealand, Phys. Earth Planet. In. 93, 3–20. Bai, Y., T. Lay, K. F. Cheung, and L. Ye (2017). Two regions of seafloor deformation generated the tsunami for the 13 November 2016, Kaikoura, New Zealand earthquake, Geophys. Res. Lett. 44, no. 13, 6597–6606, doi: 10.1002/2017GL073717. Balfour, N. J., M. K. Savage, and J. Townend (2005). Stress and crustal anisotropy in Marlborough, New Zealand: Evidence for low fault strength and structure-controlled anisotropy, Geophys. J. Int. 163, 1073–1086, doi: 10.1111/j.1365-246X.2005.02783.x. Barnes, P. M. (1996). Active folding of Pleistocene unconformities on the edge of the Australian-Pacific plate boundary zone, offshore North Canterbury, New Zealand, Tectonics 15, 623–640. Barnes, P. M., and J. C. Audru (1999). Quaternary faulting in the offshore Flaxbourne and Wairarapa basins, southern Cook Strait, New Zealand, New Zeal. J. Geol. Geophys. 42, 349–367. Barrell, D. J. A., and D. B. Townsend (2012). General distribution and characteristics of active faults and folds in the Hurunui District, North Canterbury, GNS Science Consultancy Report 2012/113, 45 pp. Beanland, S., K. R. Berryman, and G. H. Blick (1989). Geological investigations of the 1987 Edgecumbe earthquake, New Zealand, New Zeal. J. Geol. Geophys. 32, 73–91.

17

Beavan, J., and J. Haines (2001). Contemporary horizontal velocity and strain-rate fields of the Pacific-Australian plate boundary zone through New Zealand, J. Geophys. Res. 106, 741–770. Beavan, J., M. Motagh, E. J. Fielding, N. Donnely, and D. Collett (2012). Fault slip models of the 2010–2011 Canterbury, New Zealand, earthquakes from geodetic data and observations of postseismic ground deformation, New Zeal. J. Geol. Geophys. 55, 207–221. Beavan, R. J., P. Tregoning, M. Bevis, T. Kato, and C. Meertens (2002). Motion and rigidity of the Pacific plate and implications for plate boundary deformation, J. Geophys. Res. 107, no. B10, doi: 10.1029 /2001JB000282. Biasi, G. P., and S. G. Wesnousky (2016). Steps and gaps in ground ruptures: Empirical bounds on rupture propagation, Bull. Seismol. Soc. Am. 106, 1110–1124. Bull, W. B. (1991). Geomorphic Responses to Climate Change, Oxford University Press, New York, New York, 326 pp. Cesca, S., Y. Zhang, V. Mouslopoulou, R. Wang, J. Saul, M. Savage, S. Heimann, S.-K. Kufner, O. Oncken, and T. Dahm (2017). Complex rupture process of the M w 7.8, 2016, Kaikoura earthquake, New Zealand and its aftershock sequence, Earth Planet. Sci. Lett. 478, 110–120. Clark, K., E. Nissen, J. Howarth, I. Hamling, J. Mountjoy, W. Ries, K. Jones, S. Goldstein, U. Cochran, P. Villamor, et al. (2017). Highly variable coastal deformation in the 2016 Mw 7.8 Kaikōura earthquake reflects rupture complexity along a transpressional plate boundary, Earth Planet. Sci. Lett. 474, no. 605, 334–344, doi: 10.1016/j.epsl.2017.06.048. Dellow, S., C. Massey, S. Cox, G. Archibald, J. Begg, Z. Bruce, J. Carey, J. Davidson, F. Della Pasqua, P. Glassey, et al. (2017). Landslides caused by the Mw 7.8 Kaikōura earthquake and the immediate response, Bull. New Zeal. Soc. Earthq. Eng. 50, 106–116. Dewey, J. F., R. E. Holdsworth, and R. A. Strachan (1998). Transpression and transtension zones, in Continental Transpressional and Transtensional Tectonics, R. E. Holdsworth, R. A. Strachan, and J. F. Dewey (Editors), Geol. Soc. Lond. Spec. Publ. 135, 1–14. Downes, G. L., and D. J. Dowrick (2015). Atlas of Isoseismal Maps of New Zealand Earthquakes, 1843–2003, Second Ed., Institute of Geological & Nuclear Sciences Monograph 25 (issued as a CD), Institute of Geological & Nuclear Sciences, Lower Hutt, New Zealand. Duffy, B., M. Quigley, D. J. Barrell, R. Van Dissen, T. Stahl, S. Leprince, C. McInnes, and E. Bilderback (2013). Fault kinematics and surface deformation across a releasing bend during the 2010 Mw 7.1 Darfield, New Zealand, earthquake revealed by differential LiDAR and cadastral surveying, Geol. Soc. Am. Bull. 125, nos. 3/4, 420–431. Duputel, Z., and L. Rivera (2017). Long-period analysis of the 2016 Kaikōura earthquake, Phys. Earth Planet. In. 265, 62–66. Eberhart-Phillips, D, and S. Bannister (2010). 3-D imaging of Marlborough, New Zealand, subducted plate and strike-slip fault systems, Geophys. J. Int. 182, 73–96, doi: 10.1111/j.1365-246X.2010.04621.x. Eberhart-Phillips, D., and M. Reyners (2012). Imaging the Hikurangi plate interface region, with improved local-earthquake tomography, Geophys. J. Int. 190, no. 2, 1221–1242. Eberhart-Phillips, D., M. Reyners, S. Bannister, M. Chadwick, and S. Ellis (2010). Establishing a versatile 3-D seismic velocity for New Zealand, Seismol. Res. Lett. 81, no. 6, 992–1000, doi: 10.1785/gssrl.81.6.992. Ellsworth, W. L., A. G. Lindh, W. H. Prescott, and D. G. Herd (1981). The 1906 San Francisco earthquake and the seismic cycle, in Earthquake Prediction, D. W. Simpson and P. G. Richards (Editors), American Geophysical Union, Washington, D.C., doi: 10.1029/ME004p0126. Field, E. H., R. J. Arrowsmith, G. P. Biasi, P. Bird, T. E. Dawson, K. R. Felzer, D. D. Jackson, K. M. Johnson, T. H. Jordan, C. Madden, et al. (2014). Uniform California Earthquake Rupture Forecast, version 3 (UCERF3)—The time-independent model, Bull. Seismol. Soc. Am. 104, 1122–1180. Forsyth, P. J., D. J. A. Barrell, and R. Jongens (2008). Geology of the Christchurch area, Institute of Geological and Nuclear Sciences Geological Map 16, GNS Science, Lower Hutt, New Zealand, 1 sheet + 67 pp., scale 1:250,000.

18 Furlong, K., and M. Herman (2017). Reconciling the deformational dichotomy of the 2016 Mw 7.8 Kaikoura New Zealand earthquake, Geophys. Res. Lett. 44, no. 13, 6788–6791, doi: 10.1002/ 2017GL074365. Gold, R. D., W. J. Stephenson, J. K. Odum, R. W. Briggs, A. J. Crone, and S. J. Angster (2013). Concealed Quaternary strike-slip fault resolved with airborne lidar and seismic reflection: The Grizzly Valley fault system, northern Walker Lane, California, J. Geophys. Res. 118, no. 7, 3753– 3766. Hamling, I., S. Hreinsdóttir, K. Clark, J. Elliott, C. Liang, E. J. Fielding, N. Litchfield, P. Villamor, L. Wallace, T. J. Wright, et al. (2017). Complex multifault rupture during the 2016 Mw 7.8 Kaikoura earthquake, New Zealand, Science 356, no. 6334, doi: 10.1126/science.aam7194. Hollingsworth, J., L. L. Ye, and J. P. Avouac (2017). Dynamically triggered slip on a splay fault in the M w 7.8, 2016 Kaikoura (New Zealand) earthquake, Geophys. Res. Lett. 44, 3517–3525. Holt, W. E., and A. J. Haines (1995). The kinematics of northern South Island, New Zealand, determined from geological strain rates, J. Geophys. Res. 100, 17,991–18,010. Kaiser, A., N. Balfour, B. Fry, C. Holden, N. Litchfield, M. Gerstenberger, E. D'Anastasio, N. Horspool, G. McVerry, J. Ristau, et al. (2017). The 2016 Kaikoura (New Zealand) earthquake: Preliminary seismological report, Seismol. Res. Lett. 88, no. 3, 727–739, doi: 10.1785/0220170018. Kearse, J., T. A. Little, R. J. Van Dissen, P. Barnes, R. Langridge, J. Mountjoy, W. Ries, P. Villamor, K. Clark, A. Benson, et al. (2018). Onshore to offshore ground-surface and seabed rupture of the Jordan– Kekerengu–Needles fault network during the 2016 Mw 7.8 Kaikoura earthquake, New Zealand, Bull. Seismol. Soc. Am. 108, no. 3B, doi: 10.1785/0120170304. Langridge, R. M., W. F. Ries, N. J. Litchfield, P. Villamor, R. J. Van Dissen, D. J. A. Barrell, M. S. Rattenbury, D. W. Heron, S. Haubrock, D. B. Townsend, et al. (2016). The New Zealand active faults database, New Zeal. J. Geol. Geophys. 59, 86–96, doi: 10.1080/00288306 .2015.1112818. Langridge, R. M., J. Rowland, P. Villamor, J. J. Mountjoy, C. Madugo, D. B. Townsend, W. R. Ries, K. J. Clark, T. A. Little, A. J. Canva, et al. (2018). Coseismic rupture and slip on the Papatea fault and its role in the 2016 Kaikōura, New Zealand, earthquake, Bull. Seismol. Soc. Am. (in this issue). Litchfield, N. J., J. K. Campbell, and A. Nicol (2003). Recognition of active reverse faults and folds in North Canterbury, New Zealand, using structural mapping and geomorphic analysis, New Zeal. J. Geol. Geophys. 46, no. 4, 563–579. Litchfield, N. J., R. J. Van Dissen, R. M. Langridge, P. Villamor, K. R. Berryman, M. W. Stirling, A. Nicol, S. Nodder, G. Lamarche, D. J. A. Barrell, et al. (2014). A model of active faulting in New Zealand, New Zeal. J. Geol. Geophys. 57, no. 1, 32–56, doi: 10.1080/00288306 .2013.854256. Litchfield, N. J., P. Villamor, R. Van Dissen, A. Nicol, P. Barnes, D. Barrell, J. Pettinga, R. Langridge, T. Little, J. Mountjoy, et al. (2018). Surface fault rupture from the M w 7.8 2016 Kaikōura, New Zealand, earthquake and insights into factors controlling multifault ruptures, Bull. Seismol. Soc. Am. (in this issue). Lomax, A., A. Michelini, and A. Curtis (2009). Earthquake location, direct, global-search methods, in Complexity in Encyclopedia of Complexity and System Science, Part 5, Springer, New York, New York, 2449– 2473, doi: 10.1007/978-0-387-30440-3. Marrett, R., and R. W. Allmendinger (1990). Kinematic analysis of fault-slip data, J. Struct. Geol. 12, 973–986. Massey, C., D. Townsend, E. Rathje, K. Allstadt, Y. Kaneko, B. Lukovic, B. Bradley, J. Wartman, N. Horspool, I. Hamling, et al. (2018). Landslides triggered by the Mw 7.8 14 November 2016 Kaikoura, New Zealand, earthquake, Bull. Seismol. Soc. Am. 108, no. 3B, doi: 10.1785/0120170305. Nicol, A., and D. U. Wise (1992). Paleostress adjacent to the Alpine fault of New Zealand: Fault, vein and stylolite data from the Doctors Dome area, J. Geophys. Res. 97, 17,685–17,692.

A. Nicol et al. Nicol, A., B. V. Alloway, and P. J. Tonkin (1994). Rates of deformation, uplift and landscape development associated with active folding in the Waipara area of North Canterbury, New Zealand, Tectonics 13, 1321–1344. Nicol, A., H. Seebeck, and L. Wallace (2017). Quaternary tectonics of New Zealand, in Atlantis Advances in Quaternary Science: Landscape and Quaternary Environmental Change in New Zealand, J. Schulmeister (Editor), Atlantis Press, Paris, France, 1–34, doi: 10.2991/978-946239-237-3_1. Nicol, A., R. Van Dissen, M. Stirling, and M. Gerstenberger (2016). Completeness of the paleoseismic active fault record in New Zealand, Seismol. Res. Lett. 86, no. 6, doi: 10.1785/0220160088. Oskin, M. E., J. R. Arrowsmith, A. H. Corona, A. J. Elliott, J. M. Fletcher, E. J. Fielding, P. O. Gold, J. J. G. Garcia, K. W. Hudnut, J. Liu-Zeng, et al. (2012). Near-field deformation from the El Mayor–Cucapah earthquake revealed by differential LIDAR, Science 335, no. 6069, 702–705. Pettinga, J. R., M. D. Yetton, R. J. Van Dissen, and G. Downes (2001). Earthquake source identification and characterisation for the Canterbury Region, South Island, New Zealand, Bull. New Zeal. Soc. Earthq. Eng. 34, 282–317. Pondard, N., and P. M. Barnes (2010). Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard, J. Geophys. Res. 115, no. B12320, doi: 10.1029/2010JB007781. Power, W., K. Clark, D. King, J. Borrero, J. Howarth, E. Lane, D. Goring, J. Goff, C. Chague-Goff, J. Williams, et al. (2017). Tsunami runup and tide-gauge observations from the 14 November 2016 M 7.8 Kaikōura earthquake, New Zealand, Pure App. Geophys. 174, 2457–2473. Rattenbury, M. S., D. B. Townsend, and M. R. Johnston (2006). Geology of the Kaikōura area, Institute of Geological & Nuclear Sciences 1:250,000 Geological Map 13, 1 sheet + 70 pp., GNS Science, Lower Hutt, New Zealand. Reid, H. F. (1910). The mechanics of the earthquake, in The California Earthquake of April 18, 1906, Report of the State Investigation Commission, Vol. 2, Carnegie Institution of Washington, Washington, D.C., 16–28. Schwartz, D. P., P. J. Haeussler, G. G. Seitz, and T. E. Dawson (2012). Why the 2002 Denali fault rupture propagated onto the Totschunda fault: Implications for fault branching and seismic hazards, J. Geophys. Res. 117, no. B11304, doi: 10.1029/2011JB008918. Sibson, R., F. Ghisetti, and J. Ristau (2011). Stress control of an evolving strike-slip fault system during the 2010–2011 Canterbury, New Zealand, earthquake sequence, Seismol. Res. Lett. 82, no. 6, 824–832. Stahl, T., M. C. Quigley, A. McGill, and M. S. Bebbington (2016). Modeling earthquake moment magnitudes on imbricate reverse faults from paleoseismic data: Fox peak and forest creek faults, South Island, New Zealand, Bull. Seismol. Soc. Am. 106, 2345–2363. Stein, R., A. Barka, and J. Dieterich (1997). Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering, Geophys. J. Int. 128, 594–604. Stirling, M. W., N. J. Litchfield, P. Villamor, R. J. Van Dissen, A. Nicol, J. Pettinga, P. Barnes, R. M. Langridge, T. Little, D. J. A. Barrell, et al. (2017). The Mw 7.8 Kaikōura earthquake: Surface rupture, and seismic hazard context, Bull. New Zeal. Soc. Earthq. Eng. 50, 73–84. Stirling, M. W., G. McVerry, M. Gerstenberger, N. Litchfield, R. Van Dissen, K. Berryman, P. Barnes, L. Wallace, B. Bradley, P. Villamor, et al. (2012). National Seismic Hazard Model for New Zealand: 2010 update, Bull. Seismol. Soc. Am. 102, 1514–1542. Townend, J., S. Sherburn, and R. Arnold (2012). Three-dimensional variations in present-day tectonic stress along the Australia–Pacific plate boundary in New Zealand, Earth Planet. Sci. Lett. 353, 47–59. Van Dissen, R., and R. S. Yeats (1991). Hope fault, Jordan thrust and uplift of the Seaward Kaikōura range, New Zealand, Geology 9, 393–396. Vanderleest, R. A., D. M. Fisher, D. O. S. Oakley, and T. W. Gardner (2017). Growth and seismic hazard of the Montserrat anticline in the North

Preliminary Geometry, Displacement, and Kinematics of Fault Ruptures in the Epicentral Region Canterbury fold and thrust belt, South Island, New Zealand, J. Struct. Geol. 101, 1–14. Waldhauser, F., and W. L. Ellsworth (2000). A double-difference earthquake location algorithm: Method and application to the northern Hayward fault, California, Bull. Seismol. Soc. Am. 90, 1353–1368. Wallace, L. M., P. Barnes, J. Beavan, R. Van Dissen, N. Litchfield, J. Mountjoy, G. Lamarche, and N. Pondard (2012). The kinematics of a transition from subduction to strike-slip: An example from the central New Zealand plate boundary, J. Geophys. Res. 117, no. B02405, doi: 10.1029/2011JB008640. Wang, T., S. Wei, X. Shia, Q. Qiu, L. Lia, D. Peng, R. J. Weldon, and S. Barbot (2017). The 2016 Kaikōura earthquake: Simultaneous rupture of the subduction interface and overlying faults, Earth Planet. Sci. Lett. 482, no. 2018, 44–51. Warren, G. (1995). Geology of the Parnassus area, Institute of Geological and Nuclear Sciences Geological Map 18, GNS Science, Lower Hutt, New Zealand, 1 sheet + 36 pp., scale 1:50,000. Williams, C. A., D. Eberhart-Phillips, S. Bannister, D. H. N. Barker, S. Henrys, M. Reyners, and R. Sutherland (2013). Revised interface geometry for the Hikurangi subduction zone, New Zealand, Seismol. Res. Lett. 84, 1066–1073. Williams, J. N., D. J. A. Barrell, M. W. Stirling, K. M. Sauer, G. C. Duke, and K. X. Hao (2018). Surface rupture of the Hundalee fault during the 2016 M w 7.8 Kaikōura earthquake, Bull. Seismol. Soc. Am. (in this issue).

Department of Geological Sciences University of Canterbury Private Bag 4800 Christchurch 8140 New Zealand [email protected] (A.N., N.K., J.R.P., C.F., T.S., K.P., N.H.-B., T.B., D.N.)

GNS Science P.O. Box 30-368 Lower Hutt 5040 New Zealand (S.B., I.H., J.R.)

Physical Geography Group Massey University Private Bag 11222 Palmerston North 4442 New Zealand (S.T.M.)

Manuscript received 2 November 2017

19

Preliminary Geometry, Displacement, and Kinematics ...

Preliminary Geometry, Displacement, and Kinematics ...

Suggest Documents

robot geometry and kinematics

Numerical Algebraic Geometry and Algebraic Kinematics

Numerical Algebraic Geometry and Algebraic Kinematics - CiteSeerX

robot geometry and kinematics - Penn Engineering

Avian Wing Geometry and Kinematics - AIAA ARC

Kinematics of conjugate shear zones, displacement partitioning and ...

Topic 3: Kinematics – Displacement, Velocity, Acceleration, 1- and 2 ...

Page 1 Geometry, kinematics and Scaling properties of faults and ...

Geometry, kinematics and fracture pattern of the ...

Study on geometry and kinematics of spherical single ... - SAGE Journals

Geometry and Kinematics with Uncertain Data - Institut fÃ¼r Informatik

To what degree the geometry and kinematics of accretionary wedges

Geometry and kinematics of inversion tectonics Geological Society ...

Active Fault Geometry and Kinematics in Greece: The ...

Geometry, Kinematics, and Rigid Body Mechanics in Cayley-Klein ...

Geometry, kinematics and rates of deformation ... - Wiley Online Library

Geometry, kinematics and tectonic models of the ...

Geometry, kinematics and tectonic models of the Kazakhstan Orocline ...

Geometry, kinematics, and acoustics of Tamil liquid consonants

Instantaneous spatial kinematics and the ... - TU Wien-Geometry

Geometry and kinematics of dog ribs - University of Pennsylvania

Geometry, kinematics and rates of deformation ... - Wiley Online Library

The geometry of continental displacement and its ... - Springer Link

Preliminary Design Considerations for Variable Geometry Radial