Seismicity and source parameters of local ...

Arab J Geosci DOI 10.1007/s12517-013-0929-y

ORIGINAL PAPER

Seismicity and source parameters of local earthquakes in Bilaspur region of Himachal Lesser Himalaya Ashwani Kumar & Arjun Kumar & S. C. Gupta & A. K. Jindal & Vandana Ghangas

Received: 10 October 2012 / Accepted: 15 March 2013 # Saudi Society for Geosciences 2013

Abstract The pattern of local seismicity (110 events) and the source parameters of 26 local events (1.0≤Mw≤2.5) that occurred during May 2008 to April 2009 in Bilaspur region of Himachal Lesser Himalaya were determined. The digital records available from one station have been used to compute the source parameters and fmax based on the Brune source model (1970) and a high-frequency diminution factor (Boore 1983) above fmax. The epicentral distribution of events within 30 km of local network is broadly divided into three clusters of seismic activity: (1) a cluster located to the south of the Jamthal (JAMT) station and falls to the north of the Main Boundary Thrust (MBT) which seems to reflect the contemporary local seismicity of the segment of the MBT, (2) an elongated zone of local seismicity NE–SW trending, delineated NE of JAMT station that falls in the Lesser Himalaya between the MBT and the Main Central Thrust, and (3) NE–SW trending zone of local seismic activity located at about 10 km east of NHRI station and about 15 km northeast of NERI station and extending over a distance of about 20 km. Majority of events occur at shallow depths up to 20 km, and the maximum number of events occurs in the focal depth range between 10 and 15 km. The entire seismic activity is confined to the crust between 5 and 45 km. The average values of these source parameters range from 3.29×1017 to 3.73×1019 dyne-cm for seismic moment, 0.1 to 9.7 bars for stress drops, and 111.78 to 558.92 m for source radii. The average value of fmax for these events varies from 7 to 18 Hz and seems to be source dependent. A. Kumar : A. Kumar (*) : S. C. Gupta : A. K. Jindal : V. Ghangas Department of Earthquake Engineering, Indian Institute of Technology, Roorkee 247667 Uttarakhand, India e-mail: [email protected]

Keywords Source parameters . fmax . Stress drop . Bilaspur . Himachal Lesser Himalaya

Introduction The nature of seismicity and source parameters provide an opportunity to study the ongoing faulting processes and regional stresses operating in the study area. The Bilaspur region of Himachal Pradesh is located in Lesser Himalaya, is highly seismically active, and lies in seismic zone V (IS: 1893–2002 (Part l): General Provisions and Buildings) as shown in Fig. 1 (index). This region has a great potential for hydropower generation, and a number of small- to largescale hydropower projects are either in operation or are under construction. Several tectonic features of local and regional scales have been mapped in the region around. Many moderate- to large-sized earthquakes have occurred in this region. Five prominent earthquakes have occurred around the study area during the last more than 100 years. The nature of seismicity and source parameters will obviously be helpful to study the seismotectonic interaction in the region and for safe construction of critical structures (like dams, schools, hospitals, communication buildings, etc.) as well as in hazard assessment of the region. In the present study, seismicity and source parameters in the Bilaspur region of Himachal Lesser Himalaya have been estimated and interpreted from local earthquakes (1.0≤Mw≤2.5) that occurred during the period of May 2008 to April 2009. The software Hypo71 (Lee and Lahr 1975) has been used for earthquake location, and software EQK_SRC_PARA (Kumar et al. 2012a) based on the Brune source model and a highfrequency diminution factor (Boore 1983) has been used to estimate the source parameters.

Arab J Geosci

Fig. 1 Map showing the Himalaya along with major tectonic like MCT, MBT, and the Indian plate boundary shown by the cyan line. In the index, the seismic zonation map of India (IS 2002) along with

the study region is also shown. Seismotectonic features are adopted from Khatri et al. (1984) and Walling and Mohanty (2009)

Seismotectonics of the region

dam site are the Drang Thrust and the MBT. The MBT marks the northern boundary of the Siwalik belt and separates sub-Himalayan from the Lesser Himalayan. The Main Frontal Thrust (MFT) has its surface manifestations only at a few places and marks the southern limit of the Frontal Belt. The belt between the MBT and MFT is traversed by several subsidiary thrusts some of which have considerable spatial extent viz. Jawala Mukhi Thrust and Drang Thrust. Evidences of neotectonic activity have been documented at several places along the MBT and in western parts of the Jawala Mukhi Thrust (e.g., Srikanita and Bhargava 1998). The region falls in seismic zone V as per the seismic zoning map of India (IS: 1893–2002 (Part l) General Provisions and Buildings), and many moderate- to largesized earthquakes occurred around this region. The prominent earthquakes that occurred around the study area during the last more than 100 years are (1) the Kangra earthquake of 4 April 1905 (mag.=8.0), (2) the Chamba earthquake of 22 June 1945 (mag.=6.5), (3) the Kinnaur earthquake of 19 January 1975 (mag.=6.2), (4) the Dharamshala earthquake of 26 April 1986 (mag.=5.5), and (5) the Uttarkashi earthquake of 20 October 1991 (mag. 6.7).

Within the framework of new global tectonics, the Himalaya is considered to be the result of continent–continent collision of the Indian and Eurasian plates (e.g., Le Fort 1975; Seeber et al. 1981; Khattri 1987). The Himalaya is divided into four major tectonic and physiographic belts from south to north, namely the Outer Himalaya (Siwalik), the Lesser Himalaya, the Great Himalaya, and the Tethyan Himalaya or Tibat Himalaya (Himadri). Figure 1 shows the Himalaya along with major tectonic like the Main Central Thrust (MCT), Main Boundary Thrust (MBT), and the Indian plate boundary shown by the cyan line. The Himalaya can be subdivided into seven geographical sectors from west to east: Kashmir Himalaya, Himachal Himalaya, Kumaun, Nepal, Sikkim, Bhutan, and Arunachal Himalaya. The Indus–Tsangpo Suture Zone is the northern boundary of the Indian plate. The Tethyan Himalaya and the Great Himalaya are divided by the Trans-Himardi fault. The MCT is a tectonic contact between Great Himalaya and Lesser Himalaya whereas the MBT separates the Lesser Himalaya from the Outer Himalaya (Siwaliks). The Himalaya Frontal Thrust separates the Outer Himalayas from the IndoGangetic Plains. Within the above broad tectonic framework, the area of study is located in the Himachal Lesser Himalayan that constitutes the northwestern part of the Himalayan orogenic belt. This region is marked by the presence of two major tectonic features, the MCT and the MBT, and several other local tectonic features such as the Drang Thrust, the Jawala Mukhi Thrust, and the Brasar Thrust. Besides these tectonic features, some nappe window and lineaments are also present around the study region as shown in Fig. 2. The tectonic features located nearest to the

Data set The local seismological network comprises five recording stations, namely, Bandla (BAND), Jamthal (JAMT), Neri (NERI), Nihri (NIHR), and Sikandra (SKND), and has been installed in the Bilaspur region of Himachal Lesser Himalaya. The layout of the network, having a dimension of about 45×35 km2, is shown in Fig. 2, and the details of recording stations viz., station names, station codes,

Arab J Geosci Fig. 2 Map showing epicenters of events recorded during May 2008 to April 2009 (solid circles). The figure also shows the local seismotectonic features along with seismological instrument locations in the study region. Tectonics after GSI (2000)

geographical coordinates, elevations, rock type lying underneath seismometers, and mode of operation are listed in Table 1. Two types of instrumentation were used to collect local earthquake data. The first type of instrumentation comprised analog microearthquake recorders (MEQ-800). Outputs from two types of short-period vertical-component seismometers namely L-4C and S-7000 were recorded on these analog recorders. The mode of recording was smoked paper. The analog recorders had built-in digital clocks for impinging time marks on the records. To maintain accurate timekeeping, the digital clocks were synchronized with the Indian Standard Time (IST). The second type of instrument is the digital seismograph that includes a 24-bit data acquisition system and a broadband seismometer (KS-2000) manufactured by Teledyne Geotech, USA. The digital data were sampled at a rate of 100 samples per second. A GPS was used to synchronize data samples to UTC or IST.

Analysis of the data The obtained data have been analyzed to estimate the hypocenter and source parameters as discussed below: Estimation of hypocenter parameters For computing hypocenter parameters of local events, three types of data sets are needed viz., phase data of local earthquakes, accurate geographical coordinates along with the elevations of recording stations, and local velocity model of the region covered by the network. In addition to this, a computationally efficient and stable scheme (computer program) is a major requirement to allow inverting the travel time data to estimate hypocenter parameters. The knowledge of the local velocity model of the region covered by the network is not available. Therefore, the local

Table 1 Details of seismological stations installed in the study region SI. no.

1. 2. 3. 4. 5.

Station name

Bandla Jamthal Neri Nihri Sikandra

Station code

BAND JAMT NERI NIHR SKND

Location Lat. (N) Deg. min.

Long. (E) Deg. min.

31–19.98 31–23.94 31–12.66 31–23.70 31–33.30

76–46.20 76–51.89 77–00.08 77–01.38 76–48.84

Rock types

Elevation (m)

Sandstone Quartzite Phyllites Quartzite Slates

1,367 824 1,071 2,129 1,537

Mode of operation

Analog Analog Analog Analog Digital

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velocity model currently being adopted by the DEQ, IITR to locate local earthquakes occurring in the environs of Tehri dam in the Garhwal Lesser Himalaya (Table 2), has been employed to estimate the hypocentral parameters of local earthquakes in the region around the Koldam site because of almost similar geological and regional tectonic structures of the Himachal Lesser Himalaya and the Garhwal Lesser Himalaya.

The source radius and stress drop are estimated following Brune (1970, 1971) as:

Estimation of spectral and source parameters

The estimated values of source parameters are given in Tables 2 and 3.

A data set of 26 local events recorded on three component broad band seismometers at Sikandra (SKND) station with the sampling rate of 100 samples per second during May 2008 to April 2009 has been used to estimate the source parameters. The digital time series of local events have been corrected for baseline correction and for instrument response. For path correction, a frequency-dependent attenuation relation, Qc =110f 1.02 (Gupta and Kumar 2002), developed for the Garhwal Himalayan region from coda waves of local earthquakes, has been applied. From the corrected source spectrum, the values of spectral parameters, viz., Ω0, fc, and fmax were estimated. For this purpose, software EQK_SRC_PARA (Kumar et al. 2012a) has been adopted. A typical example of the time series of local earthquakes along with the estimated and modeled source spectra are shown in Fig. 4. Following Keiles-Borok (1959), the seismic moment is estimated from the value of Ω0 as: Seismic moment; M0 ¼

4pρb 3 R Ω0 R θ φ  Sa

ð1Þ

Here, ρ is the average density (=2.67 g/cm3), β is shear wave velocity in the source zone (=3.4 km/s), R is the hypocentral distance that accounts for geometrical spreading, Rθϕ is the average radiation pattern (=0.63), and Sa is free surface amplification (=2). The moment magnitude has been estimated following Hanks and Kanamori (1979) as: Moment magnitude; Mw ¼

2 logðM0 Þ  10:7 3

ð2Þ

Table 2 Velocity model used for locating local earthquakes P wave velocity (km/s)

Depth to the top of the layer (km)

3.00 5.20 6.00 7.91

0.0 1.0 15.0 46.0

The source radius; r ¼

2:34b 2pfc

ð3Þ

The stress drop; Δσ ¼

7M0 16r3

ð4Þ

Results and discussions The hypocenter parameters of 110 local events simultaneously recorded on analog and digital seismographs have been estimated using the Hypo71 program (Lee and Lahr 1975) from their phase data. The standard errors in the estimation of hypocenter parameters for these events are ≤0.50 s in origin time (RMS), ≤5.0 km in epicenter (ERH), and ≤5.0 km in focal depth (ERZ). The epicenters of these events are given in the Appendix (Table 4) and plotted in Fig. 2. Pattern of local seismicity A map showing the distribution of local seismicity in the Bilaspur region of Himachal Lesser Himalaya based on the epicenters of 110 located events is depicted in Fig. 2, and the following pattern of local seismicity is observed: 1. Several local events forming small clusters are located in the region around Jamthal (JAMT) station. Some of the events form an elongated NW–SE trending cluster south of JAMT station. These events are located in the south of the MBT and seem to signify the contemporary local seismicity of the segment of the MBT passing in close proximity to the dam site. 2. To the northeast of JAMT station, an elongated zone of local seismic activity, trending NE–SW with linear dimensions of about 25 to 30 km, has been delineated. This zone of local seismicity falls in the Lesser Himalaya between the MBT and the MCT. 3. A local seismicity zone trending almost north–south with linear dimensions of about 20 km has been delineated in the lesser Himalaya. This zone of local seismicity is located about 10 km east of Nehri (NHRI) station and about 15–20 km northeast of NHRI station. A small cluster of local events is located to the south of Sikandra (SIKN) station. Apart from the above pattern of local seismicity brought out within a radius of about 30 km

Arab J Geosci Table 3 Source parameters of 26 local earthquakes Δσ (bars)

Lat (° N)

Long (° E)

Depth (km)

fc (Hz)

fmax (Hz)

M0 (dyne-cm)

Mw

r (m)

200805151943 200805161830 200805162000 200805162300 200807050800 200807140800 200807141100 200807231130

31.46 31.50 32.85 32.88 31.37 31.33 31.27 31.31

76.90 77.43 76.20 76.12 76.92 76.90 77.88 76.78

5.89 29.88 9.91 15.53 9.74 10.30 14.73 22.83

5.8 5 2.3 3 2 3.8 9 4

15 10 7 10 7 10 15 15

3.50E+17 4.60E+18 1.57E+19 9.49E+18 2.10E+18 9.46E+17 1.19E+18 1.23E+18

1.0 1.7 2.1 2.0 1.5 1.3 1.3 1.4

192.73 223.57 486.01 372.61 558.92 294.17 124.20 279.46

0.21 1.80 0.60 0.80 0.05 0.16 2.71 0.25

200808040330 200808151430 200808161930 200808170630 200809022030 200809030530 200809130200 200810031100 200810072200 200810170500 200901202200 200903032230 200903161730 200903171430 200904141800 200904162200 200904180130 200904190130

31.40 31.04 31.22 31.29 31.50 30.71 31.43 32.28 30.83 30.77 30.88 31.11 31.69 31.58 31.15 31.10 31.18 32.54

77.22 76.63 77.18 77.15 75.80 76.62 76.93 76.96 78.39 77.78 78.29 77.29 77.11 77.07 76.99 76.32 76.46 75.61

34.15 28.18 42.74 12.08 5.00 7.17 1.73 8.88 16.55 13.4 15.91 11.96 1.01 21.65 18.61 12.64 18.28 16.72

4 5.5 3.6 4.5 4.5 4.6 4 3 3.7 5.5 4.8 10 3.7 5.3 5.2 3 3.8 2.3

10 15 9 10 10 10 12 8 9 15 9 18 10 15 15 10 15 10

2.16E+19 1.89E+18 3.62E+19 3.38E+19 1.11E+19 9.19E+18 1.76E+18 9.32E+18 4.63E+18 2.03E+18 4.70E+18 3.29E+17 3.67E+18 2.49E+18 1.88E+18 2.74E+18 3.73E+19 5.20E+18

2.2 1.5 2.3 2.3 2.0 1.9 1.5 1.9 1.7 1.5 1.7 1.0 1.7 1.6 1.5 1.6 2.3 1.8

279.46 203.24 310.51 248.41 248.41 243.01 279.46 372.61 302.12 203.24 232.88 111.78 302.12 210.91 214.97 372.61 294.17 486.01

4.33 0.98 5.29 9.65 3.16 2.80 0.35 0.79 0.73 1.06 1.63 1.03 0.58 1.16 0.83 0.23 6.40 0.20

S. N.

Date

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

from the dam site, epicenters of several local events fall outside the network. These events occur in two tectonic domains, namely, in the Garhwal Lesser Himalaya about 150 km east–southeast of the dam site (i.e., south and southwest of the Sub-Himalaya). Events occurring in the foredeep are scattered over a broad region but shows a NW– SE trend almost parallel to the MBT and Drang Thrust. The histogram showing the depth distribution of local seismicity based on the estimated focal depth of 110 events is depicted in Fig. 3. Majority of events occur at shallow depths up to 20 km, and the maximum number of events occur in the depth range between 10 and 15 km. There is significant reduction in the occurrence of events having focal depths above 20 km. However, the entire seismic activity is confined in the crust between 5 and 45 km. Characteristics of source parameters In order to study the characteristics of estimated source parameters from 26 events, some plots between them are drawn and discussed as below:

Seismic moments vs. corner frequencies and fmax values The dependence of fc and fmax on seismic moment has been studied by plotting seismic moments and fc and fmax for the Sikandra site. The plot shown in Fig. 4 indicates similar scatter and almost parallel trends for both fc and fmax with increasing seismic moment. Thus, indicating both fmax and fc are dependent on seismic moment and due to source process; however, similar scatter in both spectral frequencies may be attributed to complexity of source processes or site effects. Seismic moment vs. source radius and stress drop The source radii of local events indicate a general increasing trend with increasing seismic moments as shown in Fig. 5. The estimated stress drop values for these events are less than 10 bars. Such observations of low stress drop values have been obtained in earlier studies using microearthquake and small earthquakes in the other parts of Himalaya (e.g., Sharma and Wason 1994; Kumar et al. 1994, 2012b; Wason and Sharma 2000; Paul et al. 2007; Paul and Kumar 2010). Low stress drop events have been occurring almost in the same

Arab J Geosci 100

Bilaspur Region (Himachal Lesser Himalaya) 1046.3 M0-0.106 R² = 0.2756

frequency (Hz)

max =

10

1112.8M0-0.13 R² = 0.2103

c=

1 1.00E+17

1.00E+18

1.00E+19

1.00E+20

Seismic moment (Dyne-cm)

Fig. 5 Plot between seismic moments and corner frequencies and fmax values

Fig. 3 Histogram showing focal depth distribution of events located during May 2008 to April 2009 in Bilaspur region of Himachal Lesser Himalaya

area where high stress drop events occur. Two types of models have been postulated to explain the occurrence of low stress drop events: partial stress drop models (Brune 1970) and low effective stress models (Brune et al. 1986). As explained by Brune et al. (1986), Fig. 4 A typical example, input time history (Mw, 1.0) from Sikandra (SKND) station, and its acceleration and displacement spectra along with modeled spectra. The corner frequency and fmax are shown by + symbols

partial stress drop events occur either due to complex fault geometry or due to asperities or barriers on the fault. On account of this, the fault locks (heals) soon after the rupture passes, and the average slip over the fault cannot reach a value corresponding to average dynamic stress drop over the whole fault. The low effective stress model postulates the occurrence of low stress drop events to availability of low effective stress to accelerate the fault. The plot between stress drop and seismic moment in Fig. 6 shows an increase of stress drop with increasing seismic moments. This increase of stress drop with seismic moment for microearthquakes has also been reported by other investigators (e.g., Dysart et al. 1988; García-García et al. 1996; Wu et al. 1999; Tusa and Gresta 2008; Sule 2010).

Arab J Geosci Stress Drop (bars) 0.01 0

0.10

1.00

10.00

1.00E+19

10

Depth(km)

Seismic Moment (dyne-cm)

1.00E+20

1.00E+18

20

30 1.00E+17 10.00

100.00

1000.00

Source Radius (m)

40

Fig. 6 Plot between source radius and seismic moment Fig. 8 Plot between focal depth and stress drop

Focal depth vs. stress drop The plot in Fig. 7 depicts the variation of stress drop with focal depth. Although the data show large scatter, in general, an increasing trend of upper limit of stress drops with focal depths is obtained and is visible in Figs. 7 and 8. In this study, it is found that fmax has similar behavior as fc to seismic moment. Thus, indicating both fmax and f c is dependent on seismic moments or source process; however, similar scatter in both spectral frequencies may be attributed to complexity of source processes or site effects. The average value of fmax for these events varies from 7 to 18 Hz. The dependence of high-cut frequency (fmax) on source process has been reported in earlier studies (e.g., Tsai and Chen 2000; Purvance and Anderson 2003; Durukal and Catalyurekli 2004; Kumar et al. 2013).

Conclusions The observed seismic activity for a period from May 2008 to April 2009 in Bilaspur region of Himachal Lesser Himalaya shows two well-defined sources of local seismic

Stress Drop (bars)

10.00

1.00

0.10

0.01 1.00E+17

1.00E+18

1.00E+19

Seismic Moment (dyne-cm)

Fig. 7 Plot between stress drop and seismic moment

1.00E+20

activity at distances of about 25 km in north–northeast and 45 km in the north direction, respectively, from the NERI station. In addition, a source of seismic activity at a distance of about 25 km is observed near NHRI station. The epicentral distribution of locatable events within 30 km of the local network is broadly divided into three clusters of seismic activity (1) a cluster located to the south of the Jamthal (JAMT) station and falls to the north of MBT which seems to reflect the contemporary local seismicity of the segment of the MBT, (2) an elongated zone of local seismicity NE– SW trending, delineated NE of JAMT station that falls in the Lesser Himalaya between the MBT and MCT, and (3) NE– SW trending zone of local seismic activity located at about 10 km east of NHRI station and about 15 km northeast of NERI station and extending over a distance of about 20 km. Majority of events occur at shallow depths up to 20 km, and the maximum number of events occurs in the focal depth range between 10 and 15 km. The entire seismic activity is confined to the crust between 5 and 45 km. The 26 local events studied have moment magnitudes between 1.0 and 2.5. The source dimensions in terms of radius of the circular fault vary from about 112 to 560 m. The stress drops of these events are found less than 10 bars. Although the variation of stress drops with focal depth shows large scatter, an increasing upper bound of stress drop with increasing focal depth has been observed. In this study, it is found that fmax has similar behavior as fc to seismic moment. Thus, indicating both fmax and fc are dependent on seismic moment and due to source process; however, similar scatter in both spectral frequencies may be attributed to complexity of source processes or site effects. The average value of fmax for these events varies from 7 to 18 Hz. Acknowledgments The authors are profusely thankful to the National Thermal Power Corporation (NTPC), Koldam, Himachal Pradesh, for funding the project under which data were collected and the Department of Earthquake Engineering, Indian Institute of Technology, Roorkee, for providing the data.

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Appendix Table 4 Hypocenter parameters of events recorded during May 2008 to April 2009 S. No.

Date

Time UTC

Lat. (°N)

Long. (°E)

Depth (km)

Mag.

RMS

ERH (km)

ERZ (km)

1 2 3

20080510 20080510 20080514

16 25 59.21 21 42 41.03 13 43 03.72

31.37 33.13 31.21

78.31 76.90 76.98

13.02 14.57 9.26

2.02 2 0.03

0.41 0.03 0.06

5.4 6.3 0.7

7 0.8 0.7

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

20080515 20080515 20080515 20080515 20080516 20080516 20080517 20080520 20080521 20080522 20080522 20080523 20080523 20080525 20080526 20080528 20080530 20080531

01 07 47.65 01 13 01.33 11 18 49.49 13 28 39.04 00 28 27.42 04 49 06.89 12 28 50.86 13 22 52.76 08 35 07.20 17 24 51.22 17 28 23.35 13 37 18.54 15 37 32.75 08 15 42.22 22 17 32.95 12 54 13.84 20 55 49.78 00 30 40.12

31.47 31.46 32.34 31.22 31.50 32.88 31.48 31.38 31.67 31.49 31.52 31.24 31.47 31.42 31.47 31.46 32.93 32.86

76.86 76.90 75.61 77.07 77.43 76.12 76.81 76.88 77.08 77.28 77.17 77.06 76.86 77.22 77.22 76.82 76.38 76.39

13.46 5.89 18.49 16.56 29.88 15.53 1.31 9.4 30.58 17.67 20.68 9.71 6.49 1.51 10.29 8.44 14.2 14.69

−0.07 0.14 1.39 0.38 2.47 2.15 0.5 0.49 1.77 1.54 0.84 0.31 0.49 0.77 3 −0.07 3.05 2.71

0.07 0.17 0.17 0.19 0.5 0.14 0.16 0.31 0.12 0.25 0.18 0.03 0.2 0.47 0.22 0.12 0.15 0.03

1 1.5 5.6 2.6 2.5 7.8 1.4 2.2 7.3 3.2 2.3 0.4 2 8.3 1.6 3.3 6.6 1.2

1.2 3.9 1.1 2.1 1.5 1.5 0.7 4.9 7.7 6.9 2.7 0.4 2.3 0.9 1.4 5.1 1.9 0.4

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

20080531 20080602 20080602 20080604 20080605 20080608 20080609 20080609 20080609 20080614 20080615 20080616 20080619 20080624 20080630 20080705 20080708 20080714

10 45 37.41 00 28 11.72 01 15 07.68 05 39 48.87 13 17 30.25 12 59 03.16 09 40 00.81 13 09 30.48 22 25 35.91 04 49 50.21 11 19 06.74 07 18 10.62 20 19 16.59 03 30 18.72 14 38 31.96 13 50 40.72 15 40 27.89 13 40 20.69

33.01 30.71 32.95 31.16 31.13 31.69 31.53 31.49 30.90 31.45 31.40 31.62 31.44 30.73 31.47 31.37 31.45 31.33

76.64 78.50 76.71 77.78 77.76 76.78 76.95 76.82 78.08 76.98 77.03 77.09 77.18 78.75 76.83 76.92 76.84 76.90

12.73 13.74 12.44 15.2 15.06 34.61 7.85 1.34 13.74 19.82 14.21 13.03 16.76 21.25 15.62 9.74 6.62 10.3

2.76 1.35 1.82 2.67 1.69 1.48 1.03 0.43 2.71 2.64 1.5 2.46 2 1.95 0.33 0.86 0.49 1.89

0.1 0.61 0.04 0.5 0.78 0.11 0.39 0.37 0.59 0.14 0.08 0.54 0.54 0.46 0.15 0.05 0.23 0.19

5.2 2 1.9 4.3 3 2.9 3.1 2.2 4 2.5 0.9 2.6 2.2 2.1 4.2 0.6 4.5 2.1

1 1.5 0.6 3.7 2.6 3.3 5.1 1 1.9 2.4 0.8 2 1.8 1.6 2.9 1.3 3.3 4.4

40 41 42 43 44 45 46 47

20080714 20080722 20080722 20080723 20080723 20080724 20080724 20080724

16 51 56.40 15 21 04.55 15 23 15.90 13 36 46.57 17 09 39.02 13 32 57.93 14 25 15.87 16 56 54.78

31.27 31.38 31.38 31.50 31.31 31.30 31.35 31.54

77.88 76.83 76.81 76.95 76.78 76.80 76.85 76.92

14.73 13.77 13.41 17.35 22.83 18.84 9.01 12.49

1.79 1.26 1.22 1.13 1.52 1.36 1.7 2.25

0.99 0.13 0.17 0.3 0.6 0.35 0.21 0.19

6.2 1.5 1.9 4.8 2.4 3.8 1.6 2.3

6.8 2 2.3 4.6 1.8 3.1 3 2.4

Arab J Geosci Table 4 (continued) S. No.

Date

Time UTC

Lat. (°N)

Long. (°E)

Depth (km)

Mag.

RMS

ERH (km)

ERZ (km)

48 49 50 51 52 53 54 55 56 57 58

20080726 20080728 20080728 20080729 20080804 20080809 20080815 20080815 20080816 20080817 20080819

16 13 19.20 12 25 43.77 01 53 40.80 14 14 28.39 09 13 06.22 01 44 29.58 17 50 35.56 20 05 14.93 01 06 59.85 12 19 38.41 02 46 06.82

30.61 31.42 31.31 31.32 31.40 31.67 31.35 31.04 31.22 31.29 31.34

78.43 76.88 76.80 76.59 77.22 77.32 77.54 76.63 77.18 77.15 76.90

11.02 2.6 28.45 29.96 34.15 29.51 1.14 28.18 42.74 12.08 27.28

1.91 0.85 1.39 1.01 1.67 2.41 2.23 2.22 2.61 2.74 3.44

0.67 0.34 0.61 0.02 0.2 0.54 0.19 0.89 0.63 0.58 0.03

1.5 0.5 4.9 0.8 2.7 6.9 5.6 1.4 10 2.9 0.8

1.7 6.2 2.1 0.5 2.2 6.7 1.1 2.2 5.1 3.2 0.8

59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

20080829 20080901 20080903 20080903 20080911 20080913 20080913 20080917 20081007 20081011 20081014 20081017 20081024 20081101 20081102 20081103 20081113 20081117

17 12 50.97 13 44 09.08 06 55 50.00 11 18 36.30 03 23 46.54 07 36 26.00 14 24 25.65 21 39 50.05 03 35 04.12 13 28 57.11 14 40 19.72 10 38 54.72 21 04 18.46 19 53 53.37 13 31 27.14 03 15 03.05 15 32 11.19 09 51 05.44

31.38 31.43 31.23 30.71 31.52 31.43 31.34 31.58 30.83 31.47 31.45 30.77 30.80 31.48 31.35 31.63 32.92 30.84

77.18 76.87 76.31 76.62 77.00 76.93 76.98 77.04 78.39 76.95 76.91 77.78 78.31 76.98 76.92 77.22 75.71 77.02

22.74 8.59 0.98 7.17 19.42 1.73 2.97 1.2 16.55 18.95 18.38 13.4 12.4 3.53 3.77 21.43 12.83 13.71

2.76 1.08 1.8 2.6 1.9 1.15 0.75 1.39 1.65 1.27 1.37 2.16 1.62 1.38 1.11 2.16 2.19 1.73

0.81 0.11 0.52 0.24 0.69 0.14 0.28 0.22 0.59 0.18 0.16 0.58 0.56 0.37 0.08 0.4 0.04 0.1

3.8 1.2 2.9 4.5 3.4 0.7 0.7 1.5 2.2 3.2 3 2.8 2 2 0.6 3.2 3.5 2.9

5 2.2 1.1 2.3 2.3 0.6 5.1 0.7 1.9 2.3 2.9 2.3 1 6.9 2.4 2.3 0.6 0.8

77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94

20081130 20081213 20090107 20090109 20090115 20090120 20090203 20090206 20090206 20090208 20090208 20090209 20090210 20090212 20090213 20090216 20090301 20090303

23 10 22.28 02 17 11.57 20 23 29.16 15 14 09.79 17 53 57.87 03 53 17.40 10 35 54.76 20 15 29.26 21 36 47.05 02 05 51.40 08 29 10.54 18 29 57.44 02 10 04.54 07 42 23.69 11 33 44.59 07 47 46.90 02 35 48.60 04 02 06.53

31.48 31.48 29.68 29.09 30.86 30.88 30.88 31.53 30.29 31.32 31.49 31.08 29.97 31.46 31.57 31.68 31.37 31.11

76.60 78.20 77.82 77.20 78.26 78.29 76.77 77.09 77.74 77.19 76.95 78.02 75.75 76.96 77.72 77.08 77.03 77.29

35.06 4.38 30.45 13.05 17.42 15.91 33.53 10.14 34.22 5.39 2.77 12.59 12.52 6.69 3.89 10.67 1.48 11.96

2.08 2.02 2.56 2.66 2.35 2.59 1.85 1.17 2.48 2.15 0.25 1.83 2.17 2.2 1.9 1.33 0.78 1.66

0.16 0.79 0.4 0.21 0.42 0.52 0.05 0.09 0.73 0.25 0.13 0.66 0.12 0.07 0.45 0.32 0.33 0.05

4.2 6.3 3.8 5.5 3.4 2 2.3 1.5 3.6 2.1 2.1 6.3 6.4 1.1 4.3 1.1 4.7 0.9

3.2 5.7 3.5 2.8 9.1 0.7 2.8 2.4 2 7.6 10 2.9 2.1 2.1 5.1 3.1 1.1 0.5

95 96

20090304 20090304

23 48 06.85 23 49 05.39

31.34 31.30

77.18 77.16

4.2 16.07

0.67 1.58

0.49 0.16

1.7 2.9

8.1 3.8

Arab J Geosci Table 4 (continued) S. No.

Date

Time UTC

Lat. (°N)

Long. (°E)

Depth (km)

97 98 99 100 101 102 103 104 105 106 107 108

20090305 20090314 20090314 20090316 20090317 20090323 20090326 20090414 20090416 20090418 20090419 20090423

00 05 41.97 05 47 38.14 21 40 19.37 23 17 27.71 20 24 02.17 23 26 04.01 00 04 28.34 23 57 24.12 03 39 26.27 07 03 43.79 07 27 54.32 20 39 50.36

31.47 31.48 31.07 31.69 31.58 31.55 31.33 31.15 31.10 31.18 32.54 31.54

76.97 77.27 76.42 77.11 77.07 77.04 77.01 76.99 76.32 76.46 75.61 77.06

109 110

20090423 20090423

20 53 48.06 22 42 05.45

31.53 31.55

76.98 77.05

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Mag.

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4.89 15.17 33.8 1.01 21.65 6.32 19.88 18.61 12.64 18.28 16.72 7.06

1.05 2.07 1.65 1.99 2.18 1.12 2.38 1.92 1.75 2.65 2.32 1.75

0.56 0.88 0.08 0.34 0.17 0.18 0.08 0.43 0.55 0.21 0.18 0.33

2.6 3.3 3.9 2.4 1.7 1.5 1 4.4 5.8 0.4 3.4 3.1

7.9 2 4.4 0.6 2.1 4.6 1 3.2 2.5 2.3 0.7 8.1

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