Contribution of site effects and soil-structure interaction to building ...

Proc. ICOSSAR 2005, G. Augusti, G. I. Schueller, M. Ciampoli (eds) / Millpress, Rotterdam, ISBN 90 5966 040 4

Contribution of site effects and soil-structure interaction to building damage in Golcuk, Turkey, during the 1999 Kocaeli earthquake Hiroshi Arai & Nelson Pulido Earthquake Disaster Mitigation Research Center, National Research Institute for Earth Science and Disaster Prevention, Kobe, Japan

Keywords: the 1999 Kocaeli earthquake, building damage, site effect, soil-structure interaction, microtremor ABSTRACT: The effects of the S-wave velocity (VS) profiles on the R/C building damage in Golcuk, Turkey, during the 1999 Kocaeli earthquake are examined considering soil-structure interaction (SSI). Microtremor array measurements were conducted at seven sites, and a joint inverse analysis of observed dispersion curves and horizontal-to-vertical (H/V) spectral ratios accurately results in VS profiles down to seismic bedrock at the sites. With the estimated VS profiles and a source asperity model of the main shock, we performed a strong ground motion simulation at the sites. Based on the simulated ground motions and the observed damage statistics at the sites, simplified SSI analytical models of Turkish R/C buildings groups are identified for evaluating the building damage ratios. The results of parametric studies using the identified buildings models indicate that the damage ratios for 1-7 storied R/C buildings are amplified by a factor of 3-10 or more due to the site effects, however, those for 1-4 storied buildings get smaller by a factor of 0.5-0.8 due to the SSI effects. 1

INTRODUCTION

The Kocaeli earthquake of August 17, 1999 destroyed over 60,000 houses and buildings in the northwest area of Turkey. In Golcuk, in particular, a large number of low- and medium-rise buildings sustained either partial or complete collapse typically of a soft first story. Fig. 1 shows spatial distribution of collapse ratios for the low- and mediumrise reinforced-concrete (R/C) buildings in Golcuk, which is based on the results of reconnaissance survey performed by Architectural Institute of Japan (AIJ) (AIJ et al., 2001). The damage to R/C buildings was concentrated at several areas in the north of Ataturk street, which is the main street running in the east-west (EW) direction. The concentration of building damage could be due to the effects of unknown underground structures on seismic motions, i.e., site effects. In fact, most of the northern area of the main street is located on a plain while the south is on a hill, where the building damage was slight. To evaluate site effects quantitatively, S-wave velocity (VS) profiles of sedimentary deposits should be properly determined down to seismic bedrock. It is, however, too expensive and time-consuming to estimate VS profile using conventional geophysical or geotechnical methods with boreholes. As an economical and practical substitute, microtremor measurements that can be readily performed on the ground surface have been used.

Recent studies, for example, have shown that (1) surface (Rayleigh and Love) waves dominate in microtremors, (2) the frequency-wave number (F-k) spectral analysis (Capon, 1969) of microtremor vertical motions measured with arrays of sensors at a

Figure 1. Map showing microtremor array observation sites (Sites A-G) and distribution of collapse ratios for low- and medium-rise R/C buildings in Golcuk during the 1999 Kocaeli earthquake (AIJ et al., 2001). - 111 -

site can yield dispersion characteristics of Rayleigh waves, and (3) the inverse analysis of dispersion data results in a sedimentary VS structure at the site (e.g., Horike, 1985; Matsushima and Okada, 1990; Tokimatsu et al., 1992). It was also revealed that the horizontal-to-vertical (H/V) spectral ratios (Nakamura, 1989) of microtremors measured with one three-component sensor at a site correspond to those of surface waves and reflect a bedrock VS structure at the site (e.g., Tokimatsu and Miyadera, 1992; Tokimatsu, 1997; Arai and Tokimatsu, 2004). These findings indicate that the joint inverse analysis of both microtremor dispersion curve and H/V spectrum can be promising to estimate the VS profile down to bedrock at a site. The objectives of this article are to introduce the use of the microtremor methods for estimating VS structures and to examine the effects of the VS profiles on the strong ground motions and building damage ratios in Golcuk during the 1999 earthquake, considering soil-structure interaction (SSI). 2

MICROTREMOR MEASUREMENTS

Microtremor measurements using two-dimensional horizontal arrays of sensors were conducted at seven sites, subsequently called Sites A, B, C, D, E, F, and G. As shown in Fig. 1, Sites A-F are located in the heavily damaged areas on the plain and their damage ranks vary drastically depending on the site geological conditions, while Site G is on the hill where the building damage was rarely seen. The measurement system used consists of amplifiers, lowpass-filters, 24-bit A/D converters, and a note-type computer, all built in a portable case; and three-component velocity sensors with a natural period of 1 s. Six sensors were placed on the ground surface to form a circular array with a sensor in the center. The minimum array radius used was 2.5 m at each site, and the maximum ones were 41, 103, 108, 31, 39, 42, 10 m at Sites A-G, respectively. With each array, microtremors were measured simultaneously and digitized at an equal sampling rate. The sampling rate varied from 100 to 500 Hz, depending on the site conditions and array radius used. About 20-40 sets of data segments with 2048 or 4096 points each were selected from the digitized motions, and used for the following spectral analyses. 3

The H/V spectral ratios are also derived for microtremors observed at all the sensors in the arrays used. The definition of microtremor H/V spectral ratio, (H/V)m, used in this study is ( H / V )m =

(1)

where PUD is the Fourier power spectrum of microtremor vertical motion, and PNS and PEW are those of two orthogonal horizontal motions (e.g., Arai and Tokimatsu, 2004). With the H/V spectral ratios at the sensors, their average spectrum and standard deviations are determined for each Site A-G. The resulting H/V spectra at Sites B and E, for example, are shown in Fig. 3 as open circles and thin lines. Using the observed dispersion and H/V data at Sites A-G, the joint inverse analyses are conducted with the theoretical formulas of Rayleigh wave dispersion curve and surface wave H/V spectrum considering the effects of fundamental and higher modes (Tokimatsu et al., 1992; Tokimatsu, 1997; Arai and Tokimatsu, 2004). In the joint inverse analysis, the generalized (non-linear) least-squares method using the adaptive biweight estimation (Tukey, 1974) and the modified Marquardt’s technique combined with the singular value decomposition (e.g., Wiggins, 1972; Yuan and Nazarian, 1993) is employed. The soil structure at each site is assumed to be horizontally stratified and consists of 68 layers in the inversion. Further details of the inverse analysis used in this study can be found elsewhere (Arai and Tokimatsu, 2004).

1000

(a) Site B

(b) Site E

800 600 400 200 0 0.02

Observed Inverted 0.1

Period (s)

1

Observed Inverted 5 0.02

0.1

Period (s)

1

5

Figure 2. Dispersion curves of microtremor vertical motions compared with those of Rayleigh waves theoretically computed for the inverted soil layer models at Sites B and E.

10

(b) Site E

(a) Site B Observed Std. Deviation Inverted

VS PROFILES FROM MICROTREMOR F-K AND H/V ANALYSES

The high-resolution F-k spectral analysis (Capon, 1969) is used to determine dispersion curves of microtremor vertical motions recorded at Sites A-G. The resulting dispersion curves at Sites B and E, for example, are shown in Fig. 2 as open circles.

PNS + PEW PUD

1

0.1 0.02

Observed Std. Deviation Inverted 0.1

Period (s)

1

5 0.02

0.1

Period (s)

1

5

Figure 3. H/V spectra of microtremors compared with those of surface waves theoretically computed for the inverted soil layer models at Sites B and E. - 112 -

S-Wave Velocity (m/s) S-Wave Velocity (m/s) S-Wave Velocity (m/s) 0 500 1000 1500 0 500 1000 1500 0 500 1000 1500 0 (a) Site A (b) Site B (c) Site C 50

Table 1. Asperity parameters of source fault model in the 1999 Kocaeli earthquake (after Pulido, 2004). The number in parentheses is variation coefficient (uncertainty) of the parameter.

100

Rupture Velocity

150

Rise Time Stress Drops of Asperities 1-3 Stress Drops of Segments 1-3 f max

200 250 300 0

(d) Site D

(e) Site E

(f) Site F

a b

50

1 / [1+( f / f max) ]

100

Q=αfβ

150

3.5 km/s West (+/-50%) 4.8 km/s East (+/-50%) 2.5-4.5 s (+/-50%) 140, 148, 271 bar (+/-50%) 22, 92, 128 bar (+/-50%) 5 Hz (+/-20%) a = 7.5 (+/-30%) b = 0.47 (+/-20%) α = 113 (+/-50%) β = 1.2 (+/-30%)

Segment 4 is not used because of its small contribution.

200 250 300

Figure 4. S-wave velocity profiles estimated from microtremor array observations at Sites A-F. At Site G, it is estimated that a base-rock with VS over 1.3 km/s is outcropping.

Figure 5. Multi-asperity source fault model in the 1999 Kocaeli earthquake (after Pulido, 2004; Sekiguchi and Iwata, 2002).

Fig. 4 shows the inverted VS profiles at Sites A-F. At Site G, it is estimated that a base-rock with VS over 1.3 km/s is outcropping. The Rayleigh wave dispersion curves and surface wave H/V spectra for the inverted soil profiles at Sites B and E are shown in Figs. 2 and 3 as solid lines, respectively. The theoretical dispersion curves and H/V spectra show fairly good agreement with the observed ones at the sites, indicating that the inverse analyses have been performed with a reasonable degree of accuracy and that the estimated VS profiles could be reliable. 4

GROUND MOTION CHARACTERISTICS IN THE 1999 KOCAELI EARTHQUAKE

4.1 Strong Ground Motion Simulation To evaluate strong ground motions in Golcuk during the main shock, unknown bedrock outcrop motions at each site are first determined by a broadband frequency seismic motion simulation using a multiasperity source fault model shown in Fig. 5 (Pulido, 2004), which is based on an inverted slip model (Sekiguchi and Iwata, 2002). The asperity parameters

used are listed in Table 1, which were inferred to minimize the misfits between the observed and simulated waveforms at several observation stations. Further details of the simulation procedure used can be found elsewhere (Pulido et al., 2004). Using the simulated bedrock motions at Sites AG, the one-dimensional (1-D) effective stress analyses are then conducted for the estimated VS profiles at the sites. In the analysis, the modified RambergOsgood model is used for the stress-strain relations of soils. The cyclic stress ratios causing liquefaction are inferred from the geological information of Golcuk (AIJ et al., 2001), using the equations proposed by Tokimatsu and Yoshimi (1983). Further details of the effective stress analysis employed in this study can be found elsewhere (Shamoto et al., 1992). Fig. 6 shows the computed ground velocity motions in the north-south (NS) and EW directions at Sites A-G. Figs. 7(a)-(c) show the peak acceleration, velocity, and shear strain profiles, respectively, for the larger NS motions obtained from the effective stress analyses at the sites. The analyses results indicate that little part of subsurface soils liquefied at the sites. However, at the sedimentary sites (Sites A-F), the peak shear strain values of subsurface soils are over 1%, and the peak velocity values on the ground are amplified by a factor of 1.5-2 as compared with those at a depth of 50m. This reveals that the ground motions at Sites A-F are affected significantly by the non-linear soil behavior during the earthquake. 4.2 Comparison with Building Damage Recent studies have indicated that the damage rank of R/C buildings during earthquake is consistent with the acceleration response spectral value, SAE, of strong ground motions at the equivalent-damage periods of the buildings (Sakai et al., 2001). They have also revealed that the equivalent-damage period of R/C buildings is about three times longer than the fundamental (elastic) one. Fig. 8 shows the variation of the R/C building existence ratios in Golcuk (AIJ et al., 2001) with its fundamental period, Tb, which - 113 -

150

(a) NS

Site A Site C

0.4

Site B Site D

Site E Site G

-150 150

T = 0.07N b

0

0.3

Site F

(b) EW

5 4

0.2 2

0

3

6

0.1

-150 0

5

10

15

20

25

Time (s)

30

35

40

45

50

Figure 6. Ground velocity motions in NS and EW directions obtained from strong ground motion simulation for Sites A-G.

0 0

7

N=1 0.2

0.4

89 >9 0.8

0.6

1

1.2

Fundamental Period, T (s) b

Figure 8. Variation of R/C building existence ratios in Golcuk (AIJ et al., 2001) with its fundamental period.

2

Peak Shear Strain Peak Acc. (cm/s ) Peak Vel. (cm/s) -4 -3 -2 -1 0 200 400 600 0 50 100 150 10 10 10 10 0 0 (a) 0 (b) 50

50

50

100

100

100

150

150

150

200

200

200

250

250

250

300

300

300

2000

1500

Site D Site E Site F Site G

(c) Site A Site B Site C Site D Site E Site F Site G

1000

500

Figure 7. Peak acceleration, velocity, and shear strain profiles for NS direction motions computed from 1-D effective stress analyses at Sites A-G.

0 0

Tb = 0.07 N

2000

(2)

1500

where N is the number of building story. In the figure, the most R/C buildings in Golcuk are 2-6 storied and their fundamental periods are about 0.2-0.4 s. Thus, the equivalent-damage periods of the R/C buildings in Golcuk range in about 0.6-1.2 s. Fig. 9 shows the acceleration response spectra (h=5%) of the larger NS ground motions estimated at Sites A-G. Based on the response spectra and the equivalent-damage periods, the SAE values at periods of 0.6-1.2 s are evaluated for the sites and their relationships with the site damage ranks (Fig. 1, AIJ et al., 2001) are illustrated in Fig. 10 as open circles. The evaluated SAE values for Sites A-G are fairly consistent with the observed damage ranks at the sites, indicating that the estimated VS profiles and strong ground motions could be reasonably reliable.

1000

DAMAGE RATIO SIMULATION OF R/C BUILDINGS IN GOLCUK

5.1 Building Damage Statistics In order to examine a possibility for estimating R/C building damage ratios during earthquake, the results of damage investigation by AIJ (AIJ et al., 2001) are first rearranged for Sites A-G. In this study, the

0.2

0.4

0.6

0.8

Period (s)

1

1.2

Figure 9. Acceleration response spectra (h=5%) of NS ground motions estimated at Sites A-G.

is based on the following empirical formula (e.g., Kobayashi et al., 1996):

5

Site A Site B Site C

Simulated (Deterministic) with Src.+Site Errors (Std. Deviation)

E

F

D

B

500

with Src.+Site Errors (Max. Dispersion)

G 0

C

A

1

2

3

4

Damage Rank

5

Figure 10. Acceleration response spectral values at periods of 0.6-1.2 s of ground motions estimated at Sites A-G and their relationships with site damage ranks in Fig. 1 (AIJ et al., 2001).

damage ratios near the sites are determined for two damage criteria, slightly and heavily ones, which are defined as the cases that the R/C building damage grades judged using the EMS-98 (European Seismological Commission, 1998) are over G1 and G3, respectively. In Fig. 11, the R/C building damage ratios for the slightly and heavily criteria near Sites AG are shown as open and solid circles, respectively. The building damage ratios for both criteria are dispersive at any of the 1-7 story numbers. 5.2 Buildings Group Models with Soil-Structure Interaction for Damage Ratio Evaluation Using the observed damage ratios in Fig. 11 and the estimated ground motions at Sites A-G, simplified - 114 -

analytical models of Turkish R/C buildings groups are identified to simulate the observed damage ratios at the sites, based on the earthquake response analysis considering soil-structure interaction (SSI). The procedure of SSI buildings group modeling and identification has been basically proposed by Nagato and Kawase (2001), and the outline is as follows:

1

(29)(104)(110) (97) (148) (76) (12) (0)

(0)

(0)

>G1 (G2+G3+G4+G5) >G3 (G4+G5)

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

1) The multi-degrees-of-freedom (MDOF) building systems with degrading tri-linear forcedisplacement relations and sway-rocking soil springs (e.g., Parmelee, 1970) are inferred to represent standard 1-7 storied R/C buildings with SSI (Fig. 12(a)). In the figure, building yield strength (base shear coefficient), cy, is not determined. The existing probability density distribution for the yield strengths of buildings group is then assumed to be the lognormal one having a reference value of cy0 (Fig. 12(b)), which is based on the results of R/C building investigations by Shibata (1980). This leaves only unknown reference yield strength of buildings group, cy0, to be identified. 2) The strength demands of the 1-7 storied MDOF building systems with SSI, cyD, are computed for the simulated ground motions at Sites A-G. In the analyses, the required displacement ductility demands for the slightly and heavily damage criteria are assumed to be equal to 1.5 and 3.5, respectively (e.g., Sakai et al., 2001). 3) Using the cyD value for each damage criterion and the inferred yield strength distribution, p(cy/cy0), the building damage radio, RD-SSI, is presented as: RD − SSI = ∫

c yD

0

p ( x c y 0 ) dx

0.1 0

3

4

5

6

7

8

9 10

(a)

(b)

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0

(4)

0.5

1

1.5

2

2.5

3

3.5

Normarized Base Shear Coef.

4

Figure 12. R/C buildings group model with SSI. (a) Multidegrees-of-freedom building system with sway-rocking soil springs. (b) Existing probability density distribution for normalized yield strength of R/C buildings (after Shibata, 1980).

Open and solid circles in Fig. 13 show the identified reference yield strengths of the 1-7 storied R/C buildings in Golcuk, cy0, for the slightly and heavily damage criteria, respectively. For both damage criteria, the estimated cy0 values are concentrative and show a distinguishable trend in which they decrease with increasing the number of building story, N. Based on the results, regression curves for standard cy0-N relationships of the 1-7 storied R/C buildings in Golcuk are then determined as

and shown in Fig. 13 as solid and broken lines.

2

Number of Story, N

Figure 11. Variation of R/C building damage ratios near Sites A-G with story number (AIJ et al., 2001). The number in parentheses on the top of the figure is that of total building samples for each story.

(3)

for each story number. The reference yield strength value of buildings group, cy0, is then sought using the iteration analysis to minimize the misfit between the computed damage ratio RD-SSI and the observed one. Repeating the analyses for all the damage ratios data of the 1-7 storied R/C buildings shown in Fig. 11 and averaging the analyses results, thus, the standard models of the 1-7 storied Turkish R/C buildings groups with SSI are finally identified.

c y 0 = 0.78 N 0.39 ± 0.05 (standard deviation)

1

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 Estimated from >G3 (G4+G5) 0.2

>G1 (G2+G3+G4+G5) 0.39 Regression (C =0.78/N )

0.1 0

y0

1

2

3

4

5

6

7

8

Number of Story, N

9 10

Figure 13. Reference yield strengths of R/C buildings with SSI in Golcuk and their regression curves identified using observed damage statistics and simulated ground motions at Sites A-G. - 115 -

Thick solid lines in Fig. 14 show the R/C building damage ratios for the slightly and heavily damage criteria computed from Eq. (3) using the 1-7 storied SSI buildings group models with the identified cy0-N relations in Eq. (4), compared with the observed damage ratios for the criteria at Sites A, B, and G. For each site and damage criterion, the computed building damage rations are fairly consistent with the observed ones, indicating that the identified SSI buildings group models are promising to estimate Turkish R/C building damage ratios during earthquake, and also confirming again that the estimated VS profiles and the simulated strong ground motions at the sites are reasonably reliable.

1

(b) Site A (>G3)

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1 0.9

Observed (>G1)

(a) Site A (>G1) (c) Site B (>G3)

(d) Site G (>G3) Observed (>G3) Simulated (Deterministic) with Bldg. Error with Src.+Site+Bldg. Errors (Std. Deviation) with Src.+Site+Bldg. Errors (Max. Dispersion)

0.8 0.7 0.6 0.5 0.4

5.3 Effects of VS Profiles and Soil-Structure Interaction on Building Damage Ratios Imaging the cases that the sedimentary VS profiles and/or SSI at Sites A-G are missing, the corresponding 1-7 storied R/C building damage ratios, RBD-SSI, RD-FIX, and RBD-FIX, are similarly computed for the slightly and heavily damage criteria, where the superscript B and the subscript FIX indicate the conditions that the VS profile and SSI at the site are ignored, respectively. Fig. 15 shows the variations of the RD-FIX / RBD-FIX values simulated for the slightly and heavily damage criteria at the sites with number of building story, thus, presenting the site effects on the 1-7 storied R/C building damage ratios in Golcuk. In the figure, for the slightly and heavily criteria, the R/C building damage ratios at the sedimentary sites (Sites A-F) are amplified by factors of 1-10 and 3-30 or more, respectively, as compared with those at the rockoutcropping site (Site G). Fig. 16 shows the variations of the RD-SSI / RD-FIX values computed for the both damage criteria at the sites with number of building story, thus, meaning the SSI effects on the R/C building damage ratios in Golcuk. In the figure, for both criteria, the damage ratios for 1-4 storied (low-rise) R/C buildings get smaller by a factor of 0.5-0.8 due to the SSI effects at the sedimentary sites (Sites A-F), however, those for 5-7 storied buildings do not.

0.3 0.2 0.1 0

2

3

4

5

6

7

8

Number of Story, N

9 10

1

2

3

4

5

6

7

8

Number of Story, N

9 10

Figure 14. Simulated R/C building damage ratios computed from Eq. (3) using 1-7 storied SSI buildings group models with identified cy0-N relations in Eq. (4), compared with observed damage ratios at Sites A, B, and G. 1000

(a) >G1 (G2+G3+G4+G5) Site A Site B Site C Site D

100

(b) >G3 (G4+G5)

Site E Site F Site G

10

1

0.1

1

2

3

4

5

6

7

8

Number of Story, N

9 10

1

2

3

4

5

6

7

8

Number of Story, N

9 10

Figure 15. Variations of RD-FIX / RBD-FIX values simulated at Sites A-G with number of building story, thus, site effects on 1-7 storied R/C building damage ratios in Golcuk. The damage ratios at the sedimentary sites (Sites A-F) are amplified by a factor of 3-10 or more due to the site effects, as compared with those at the rock-outcropping site (Site G). 2

(a) >G1 (G2+G3+G4+G5)

Site A Site B Site C Site D

1.5

5.4 Effects of Source, Site, and Structural Uncertainties on Building Damage Ratios To investigate the effects of the uncertainties of seismic source fault, sedimentary soil profile (site), and structural performance on the R/C building damage ratio evaluation in this study, the Monte Carlo simulation is performed. In the simulation, variable coefficient values of the source asperity parameters used, based on seismological considerations, are listed in Table 1 as the numbers in parentheses. Those of the soil layer (site) parameters (thickness, density, initial S-wave velocity, shear strength, reference shear strain, and maximum damping ratio) and the build-

1

Site E Site F Site G

1

0.5

(b) >G3 (G4+G5) 0

1

2

3

4

5

6

7

8

Number of Story, N

9 10

1

2

3

4

5

6

7

8

Number of Story, N

9 10

Figure 16. Variations of RD-SSI / RD-FIX values simulated at Sites A-G with number of building story, thus, SSI effects on R/C building damage ratios in Golcuk. The damage ratios for 1-4 storied (low-rise) R/C buildings get smaller by a factor of 0.50.8 due to the SSI effects at the sedimentary sites (Sites A-F), however, those for 5-7 storied buildings do not. - 116 -

ing yield strengths used in the simulation are 20% and 10%, respectively, which are based on the standard error values of the inverted VS profiles at Sites A-G and those of the identified Turkish R/C building yield strengths shown in Fig. 13. In the simulation, 10 asperity models, 20 soil profiles at each site, and 10 SSI building models for each story number are generated randomly using the uniform probability density distribution. Thus, 200 different strong ground motions are calculated at each site and 2,000 case building damage ratios are computed for each story number at each site. Chained lines and vertical error bars shown in Fig. 10 are respectively the standard deviations and maximum dispersions of the SAE values for the Monte Carlo simulated ground motions at Sites A-G. At the rock site (Site G), probable SAE error ratios of the simulated ground motions are less than 20%. This is due only to the asperity uncertainties. At the sedimentary sites (Sites A-F), however, the SAE error ratios enlarge because of the site uncertainties, and their standard deviations and maximum dispersions are about 20% and 50%, respectively. Broken lines in Fig. 14 show the Monte Carlo simulated R/C building damage ratios at Sites A, B, and G, considering the structural uncertainties only. Chained and thin lines in the figure are respectively the standard deviations and maximum dispersions of the simulated R/C building damage ratios at the sites, with all the physical uncertainties considered. In the figure, the similar trends indicated in Fig. 10 can be again confirmed. Thus, the damage estimation error ratios due to the building uncertainties are less than about 10-20%, however, those adding the source and site uncertainties are further amplified at a maximum of 50-80%. These results indicate that the uncertainties of seismic source and, in particular, sedimentary soil profile have significant effects on the R/C building damage ratio evaluation in this study. The deterministic estimation of VS profiles and ground motions are fairly consistent with the observed damage ranks at the study sites. However, for a prediction analysis in a future earthquake, the large uncertainties in the source asperity location and size might drastically change the input seismic bedrock waveforms (e.g., Pulido et al., 2004), and therefore, the overall damage assessment prediction accuracy. This suggests that the reduction of the uncertainties of the source and site parameters is one of the key components for predicting ground motions and building damage in a future earthquake. 6

CONCLUSIONS

Microtremor array measurements were conducted at seven sites in Golcuk, Turkey, and a joint inverse analysis of observed dispersion and H/V data accurately results in VS profiles down to seismic bedrock

at the sites. With the estimated VS profiles and a source asperity model of the 1999 Kocaeli earthquake, we performed a strong ground motion simulation at the sites. The acceleration response spectral values of the simulated ground motions are fairly consistent with the observed damage ranks at the sites, indicating that the estimated VS profiles and ground motions could be reasonably reliable. Based on the simulated ground motions and the observed damage statistics at the sites, simplified SSI analytical models of 1-7 storied Turkish R/C buildings groups are identified for evaluating the building damage ratios. With the identified buildings models, the effects of the VS profiles and SSI on the R/C building damage ratios are examined parametrically. The examination results indicate that the damage ratios for 1-7 storied R/C buildings at the sedimentary sites are amplified by a factor of 3-10 or more due to the site effects, however, those for 1-4 storied buildings get smaller by a factor of 0.5-0.8 due to the SSI effects. In addition, the effects of the source, site, and structural uncertainties on the building damage ratio evaluation in this study are investigated using the Monte Carlo simulation. The simulation results indicate that the reduction of the uncertainties of the source and site parameters is one of the key components for predicting ground motions and building damage in a future earthquake. ACKNOWLEDGEMENTS The authors would like to express their sincere thanks and appreciation to Prof. Tetsuo Kubo, University of Tokyo, Japan, Assoc. Prof. Ryosuke Uzuoka, Tohoku University, Japan, and Drs. Yalikun Yusufu, Khosrow T. Shabestari, and Kangning Li (formally Earthquake Disaster Mitigation Research Center, National Research Institute for Earth Science and Disaster Prevention, Japan), for their valuable assistance in the microtremor measurements. REFERENCES Arai, H. & Tokimatsu, K. 2004. S-wave velocity profiling by inversion of microtremor H/V spectrum. Bull. Seism. Soc. Am. 94(1): 53-63. Architectural Institute of Japan, Japan Society of Civil Engineers & The Japanese Geotechnical Society. 2001. Report on the damage investigation of the 1999 Kocaeli earthquake in Turkey. 465 pages. Capon, J. 1969. High-resolution Frequency-wavenumber spectrum analysis. Geophysics. 34(1): 21-38. European Seismological Commission (Grunthal, G., Editor). 1998. European Macroseismic Scale 1998 (EMS-98). Luxembourg. Horike, M. 1985. Inversion of phase velocity of long-period microtremors to the S-wave-velocity structure down to the basement in urbanized area. J. Phys. Earth. 33: 59-96. Kobayashi, H. et al. 1996. Evaluation of dynamic behavior of building structures with microtremors for seismic micro- 117 -

zonation mapping. Proc. CD-ROM. 11th WCEE: Paper ID 1769. Matsushima, T. & Okada, H. 1990. Determination of deep geological structures under urban areas. BUTSURI-TANSA. 43(1): 21-33. Nagato, K. & Kawase, H. 2001. Damage evaluation models of reinforced concrete buildings based on the building damage statistics and simulated strong motions. J. Struct. Constr. Eng. AIJ. 544: 31-37 (in Japanese with English abstract). Nakamura, Y. 1989. A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. Quarterly Report of the Railway Technical Research Institute. 30(1): 25-33. Parmelee, R. A. 1970. The influence of foundation parameters on the seismic response of interaction systems. Proc. 3rd Japan Earthquake Engineering Symposium. Pulido, N. 2004. Broadband frequency asperity parameters of crustal earthquakes from inversion of near-fault ground motion. Proc. CD-ROM. 13th WCEE: Paper ID 751. Pulido, N. et al. 2004. Strong ground motion estimation in the sea of Marmara region (Turkey) based on a scenario earthquake. Tectonophysics. 391: 357-374. Sakai, Y. et al. 2001. Investigation on indices of representing destructive power of strong ground motions to estimate damage to buildings based on the 1999 Chi-chi earthquake, Taiwan. J. Struct. Constr. Eng. AIJ. 549: 43-50 (in Japanese with English abstract). Sekiguchi, H. & Iwata, T. 2002. Rupture process of the 1999 Kocaeli, Turkey, earthquake estimated from strong-motion waveforms. Bull. Seism. Soc. Am. 92(1): 300-311. Shamoto, Y., Tokimatsu, K. & Ariizumi, K. 1992. Applicability of a one-dimensional effective stress analysis to an ex-

isting soil deposit. J. Struct. Constr. Eng. AIJ. 433: 113-119 (in Japanese with English abstract). Shibata, A. 1980. Prediction of the probability of earthquake damage to reinforced concrete building groups in a city. Proc. 7th WCEE. 4: 395-402. Tokimatsu, K. 1997. Geotechnical site characterization using surface waves. Proc. 1st Intl. Conf. Earthquake Geotechnical Engineering. 3: 1333-1368. Tokimatsu, K. & Yoshimi, Y. 1983. Empirical correlation of soil liquefaction based on SPT N-value and fines content. Soils and Foundations. JGS. 23(4): 56-74. Tokimatsu, K. & Miyadera, Y. 1992. Characteristics of Rayleigh waves in microtremors and their relation to underground structures. J. Struct. Constr. Eng. AIJ. 439: 8187 (in Japanese with English abstract). Tokimatsu, K., Shinzawa, K., & Kuwayama, S. 1992. Use of short-period microtremors for VS profiling. J. Geotech. Eng. ASCE. 118(10): 1544-1588. Tukey, J. E. 1974. Introduction to today’s data analysis. Proc. the Conference on Critical Evaluation of Chemical and Physical Structural Information. D. R. Lide, Jr. and M.A. Paul (Editors), National Academy of Sciences, Washington, D. C.: 3-14. Wiggins. R. A. 1972. The general linear inversion problem: Implication of surface waves and free oscillations for earth structure. Reviews of Geophysics and Space Physics. 10(1): 251-285. Yuan, D. & Nazarian, S. 1993. Automated surface wave method: Inversion technique. J. Geotech. Eng. ASCE. 119(7): 1112-1126.

- 118 -