Science in China Series D: Earth Sciences

© 2008 SCIENCE IN CHINA PRESS

Springer

Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-10

www.scichina.comearth.scichina.com

www.springerlink.com

Spatio-temporal rupture process of the 2008 great Wenchuan earthquake

ZHANG Yong1,2, FENG WanPeng2, XU LiSheng2†, ZHOU ChengHu3 & CHEN YunTai1,2*

1 School of Earth and Space Sciences, Peking University, Beijing 100871, China; 2 Institute of Geophysics, China Earthquake Administration, Beijing 100081, China; 3 Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China

Focal mechanism and dynamic rupture process of the Wenchaun Ms8.0 earthquake in Sichuan province on 12 May 2008 were obtained by inverting long period seismic data from the Global Seismic Network (GSN), and characteristics of the co-seismic displacement field near the fault were quantitatively ana-lyzed based on the inverted results to investigate the mechanism causing disaster. A finite fault model with given focal mechanism and vertical components of the long period P-waves from 21 stations with evenly azimuthal coverage were adopted in the inversion. From the inverted results as well as after-shock distribution, the causative fault of the great Wenchuan earthquake was confirmed to be a fault of strike 225°/dip 39°/rake 120°, indicating that the earthquake was mainly a thrust event with right-lateral strike-slip component. The released scalar seismic moment was estimated to be about 9.4×1020―

2.0×1021 Nm, yielding moment magnitude of Mw7.9―8.1. The great Wenchuan earthquake occurred on a fault more than 300 km long, and had a complicated rupture process of about 90 s duration time. The slip distribution was highly inhomogeneous with the average slip of about 2.4 m. Four slip-patches broke the ground surface. Two of them were underneath the regions of Wenchuan-Yingxiu and Beichuan, respectively, with the first being around the hypocenter (rupture initiation point), where the largest slip was about 7.3 m, and the second being underneath Beichuan and extending to Pingwu, where the largest slip was about 5.6 m. The other two slip-patches had smaller sizes, one having the maximum slip of 1.8 m and lying underneath the north of Kangding, and the other having the maximum slip of 0.7 m and lying underneath the northeast of Qingchuan. Average and maximum stress drops over the whole fault plane were estimated to be 18 MPa and 53 MPa, respectively. In addition, the co-seismic displacement field near the fault was analyzed. The results indicate that the features of the co-seismic displacement field were coincident with those of the intensity distribution in the meizo-seismal area, implying that the large-scale, large-amplitude and surface-broken thrust dislocation should be responsible for the serious disaster in the near fault area.

Wenchuan earthquake, earthquake rupture process, co-seismic displacement

As reported by China Seismograph Network Center (CSNC), an earthquake of Ms8.0 occurred near Yingxiu town (31.0°N, 103.4°E, focal depth: 15 km) of Wen-chuan County, Sichuan Province, at 14: 28: 04 (Beijing Time), 12 May 2008. The earthquake resulted in large-scale landslides and debris flows, silting of rivers, and more than 3000 barrier lakes (Satellite images in Figures 1 (a), (b) and (c)), and seriously damaged more than one hundred of cities and towns. A large number of

buildings, including houses, roads and bridges (Satellite images in Figures 1(d) and (e)), were destroyed or col-lapsed, causing nearly 90000 dead and missing. Received July 25, 2008; accepted December 2, 2008 doi: 10.1007/s11430-008-0148-7 †Corresponding author (email: xuls@cea-igp.ac.cn) * Equal contributor (email: chenyt@cea-igp.ac.cn) Supported by the National Basic Research Program of China (Grant No. 2004CB418404-4) and the National Natural Science Foundation of China (Grant Nos. 40574025 and 40874026)

2 Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-?

Figure 1 Slides, debris flows and barrier lakes ((b),(c)), damaged towns, a large number of destroyed houses, roads and bridges ((d),(e)) along Long-menshan fault zone caused by the great Wenchuan earthquake shown by the images of MODIS satellite. Light yellow toothed lines in (a) are the thrust faults and the directions of sawtooth denote the dip directions of the faults. 1, Maoxian-Wenchuan fault; 2, Yingxiu-Beichuan fault; 3, Pengxian-Guanxian fault.

Epicenter of the great Wenchuan earthquake is lo-cated in the Longmenshan fault zone, on the eastern edge of Tibet Plateau. The Longmenshan fault zone is a large one striking NE-SW, about 500 km long and 30 km to 50 km wide, and fault movements are dominated by thrust with right-lateral strike-slip component[1]. The Longmenshan fault zone consists of the rear-Longmen- shan fault (Maoxian-Wenchuan fault), middle-Long- menshan fault (Yingxiu-Beichuan fault) and fore- Longmenshan fault (Pengxian-Guanxian fault) from west to east (Figure 2). All these are thrust faults with minor right-lateral strike-slip component, and more right-lateral strike-slip component appears in northeast-ern segment of the Longmenshan fault zone[1]. No major earthquake with magnitude larger than 7 was recorded historically while moderate and small earthquakes (M<7) occurred frequently inside the Longmenshan fault zone

in recent years[2]. In contrast, there were strong seismic activities outside the Longmenshan fault zone, even in Southwest China, with a number of large earthquakes occurring not only in history but also in last decades[3,4]

(Figure 2). However, magnitudes of the earthquakes never exceeded 8, and the largest one was the 1933 Diexi Ms7.5 earthquake. The Wenchuan earthquake was an abrupt energy release after being accumulated within Longmenshan fault zone for many years.

Focal mechanism and rupture process of the Wen-chuan earthquake were quickly determined using long period seismic data from the Global Seismograph Net-work (GSN) in a few hours after the occurrence of the earthquake (http://www.cea-igp.ac.cn/special_issue/ earthquake_situation/preliminary_results(1).pdf) and reported on the second day, which provided important information for rescue work on the field. The inverted

Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-? 3

Figure 2 (a) Epicenter (white aniseed star) location of the 2008 great Wenchuan earthquake, main faults (modena lines) in epicentral area, historical earthquakes (yellow circles), and main cities (white circles) along Longmenshan fault zone. Lilac rectangle denotes the projection on ground surface of the fault plane model adopted in this study. “Beach ball” represents the lower hemisphere projection of focal mechanism (strike 225°/dip 39°/rake 120°) of the great Wenchuan earthquake obtained in this study. (b) The tectonic settings of the great Wenchaun earthquake.

results indicated that the fault was about 300 km long, and rupture initiated at 15 km underneath Yingxiu town of Wenchuan County and stopped at Qingchuan County,

northeast of the epicenter, the earthquake rupture dura-tion time was about 90 s, and the maximum dislocation occurred in vicinity of Wenchuan County and Beichuan

4 Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-?

County. In this article we present the focal mechanism and

dynamic rupture process of the great Wenchuan earth-quake obtained by inverting long period seismic data by means of the inversion method based on a finite fault model[5], and quantitatively analyze the characteristics of co-seismic displacement field of this great earthquake based on the inverted results.

1 Data

Long period P waveform data from the stations with epicentral distances of 55° to 90° was selected and in-verted for focal mechanism and rupture process of the great Wenchuan earthquake. To ensure stations to have evenly azimuthal coverage, we adopted 21 stations (Figure 3) with minimum azimuth interval of about 5°.

Figure 3 Epicenter (white aniseed star) of the 2008 great Wenchuan earthquake and spatial distribution of long period seismic stations (trian-gles) used in this study.

Only P waveforms on vertical components were used in the inversion since horizontal components are con-taminated by noise, and a 3-order bandpass Butterworth filter of 0.002 to 0.2 Hz was applied to the observed

seismic recordings in order to reserve source informa-tion as complete as possible. Green’s functions used were calculated by reflectivity method[6] based on the global standard velocity model[7].

2 Determination of fault parameters

Harvard University (http://www.globalcmt.org/CMT search.html), USGS, (http://earthquake.usgs.gov/ eqcenter/eqinthenews/2008/ us2008 ryan/# scitech) and Chen et al. (http://www.cea-igp.ac.cn/special_issue/ earthquake_situation/preliminary_results(1).pdf) deter-mined and released the seismic moment tensor solution (Table 1) timely after the earthquake. All the three re-sults show consistently that the Wenchuan earthquake was mainly a thrust event with a minor right-lateral strike-slip component. However, those results were ob- tained under the assumption that the source time func-tion was a triangle function, neglecting complexity of source time history. To take into account the complexity of source time history, we adopted a new method devel-oped by Zhang[8] to directly invert waveform data for six elements of the moment tensor and source time function describing the complexity of source time history under a condition of merely assuming the six elements of mo-ment tensor have the same time history, and then deter-mine the fault parameters[9].

The inverted results (Table 1) show that the scalar seismic moment released in the great Wenchuan earth-

quake was about 2.0×1021 Nm, corresponding to a mo-

ment magnitude of Mw8.1. The best double couple solu-tion is strike 220°/dip 32°/rake 118° for nodal plane I, and strike 8°/dip 63°/rake 74° for plane II. This result is in agreement with the global centroid moment tensor (GCMT) solution, but with a slight difference[9].

The striking and dipping directions of the inverted nodal plane I (strike 220°/dip 32°/rake 118°) are con-sistent with the overall trend of Longmenshan fault zone, also with the NE-SW orientation of aftershock distribu-tion; thus this plane is preferred as the causative fault. In the following inversion for rupture process, we will take

Table1 Seismic moment, moment magnitude, fault parameters and principal stress axes parameters of the great Wenchuan earthquakea)

Nodal plane I Nodal plane II T axis B axis P axis Source

M0 (1021Nm)

Ｍw Strike (°) Dip (°) Rake (°) Strike (°) Dip (°) Rake (°) Az (°) Pl (°)

Az (°) Pl (°)

Az (°) Pl (°)

Harvard 0.94 7.9 229 33 141 352 70 63 227 57 2 25 114 9

USGS 0.75 7.9 238 59 128 2 47 45 202 57 36 31 110 16

Liu et al.[9] 2.0 8.1 220 32 118 8 63 74 245 69 16 14 302 6

This study 0.94 7.9 225 39 120 8 57 68 230 69 21 18 103 20 a) Az, azimuth; Pl, plunge.

Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-? 5

this plane as the initial fault model.

3 Equations and inversion parameters

Study on inversion for source rupture process started in the 1980s. In the past 20 years, a number of inversion methods were developed, such as the waveform inver-sion methods proposed by Kikuchi and Kanamori[10] and Hartzell and Heaton[11]. In all these methods time-histo- ries of the sub-faults were assumed a priori, which, to some extent, affects the objectivity in rupture mode and/or rupture propagation velocity. In this study, we take advantage of the method used in the study of the 2007 Ning’er earthquake[5]. In this method, time-histo-ries of the sub-fault are not given a priori, and the inversion scheme is formulated with data equation, spatially smoothing equation, temporally smoothing equation, and scalar seismic moment minimizing equa-tion as following:

00

1

2

3

0[ ],

0

0

GU

Ds

T

Z

(1)

where U is vector of observed data; G, matrix of Green’s functions; s, vector of unknowns, which consists of the source time functions of sub-faults; D, spatially smoothing matrix; T, temporally smoothing matrix; Z,

matrix of minimizing scalar moment. 0, 1, 2 and 3

denote the weights. 0 is usually a sparse matrix while

1, 2 and 3 are scalar constants. The non-negative conjugate gradient method[12] was used to solve eq. (1).

A rectangular area with a length of 510 km (305 km

in NE direction and 205 km in SW direction of epicenter) in strike direction and a width of 50 km in down-dip direction was used as initial fault plane. The fault plane of 510 km×50 km was divided into 51×5=255 sub-faults with length of 10 km and width of 10 km. Initial rupture point was set at the 31st sub-fault in strike direction and the 3rd sub-fault in dip direction in accordance with the hypocentral location (31.0°N, 103.4°E, focal depth: 15 km). Rupture duration time of sub-fault was allowed to be 25 s at most and the rupture velocity was allowed to be 4.5 km/s at most. Besides, no constraints on the source time function of sub-fault, and no initial rupture time of sub-faults were imposed in the inversion[13]. In order to fit or interpret all the observed data, the same weights were imposed on all the station data by adjust-

ing 0 for the maximum amplitude of each seismogram to be around 1. Based on this, other weights can be set

referring to 0. After a number of tests, 1=30, 2=80,

and 3=0.4 were adopted in the inversion. Following the method described in the preceding sec-

tion, we performed the inversion for spatio-temporal rupture process by trial-and-error technique using dif-ferent focal mechanisms started from the initial model (fault plane strike 220°/dip 32°/rake 118°), as mentioned before, and the best-fit fault-plane solution was found to be strike 225°/dip 39°/rake 120° (the 4th line in Table 1 and the beach-ball in Figure 2).

4 Static slip distribution

As shown in Figure 4, the Wenchuan earthquake pro-duced highly heterogeneous slip distribution on the fault plane. There are four slip patches on the fault plane. The first one lies underneath the Wenchuan-Yingxiu area,

Figure 4 Static (final) slip distribution on the fault of the 2008 great Wenchuan earthquake. White aniseed star denotes location of hypocenter (rupture initiation point). White lines and white numbers are contours of the slip and slip values (m), respectively. Arrows on the top show the projected location of cities and counties on the fault trace (intersection of fault plane and ground surface). Different scales are used for abscissa and ordinate in this figure.

6 Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-?

with a length of 180 km in strike direction and a width of 50 km in down-dip direction, and the maximum slip is 7.3 m appearing near the hypocenter (rupture initia-tion point); the second slip patch lies underneath Beichuan County and extends to underneath Pingwu County, with a size of 60 km in strike direction and 35 km in down-dip direction, and the maximum slip is 5.6 m; the third slip patch lies underneath the zone between 120 km and 170 km in southeast to the epicenter, with a maximum slip of 1.8 m; and the fourth, and the smallest, is at northeast of Qingchuan County, with the maximum slip of 0.7 m. The average slip over the whole fault is about 2.4 m.

Based on the static (final) slip distribution (Figure 4), the stress drop on the fault was calculated using Brune

model[14,15]. The results indicate that the maximum and average values over the fault plane are 53 MPa and 18 MPa, respectively. The average value is of the same or-der as the average stress drop for intraplate earthquakes (about 10 MPa), but about twice the stress drops of this value[16]. There is no distinct difference between Wen-chuan earthquake and other intraplate earthquakes in the stress drop.

5 Spatio-temporal variation of rupture process

Figure 5 shows the slip variation with space and time on the fault. In the period of the first 12 s after the rupture initiation, rupture propagation appeared to be bilateral toward NE and SW directions, and moment released

Figure 5 Snapshots of slip variation with time on the fault of the 2008 great Wenchaun earthquake. White aniseed star denotes location of the hypocenter (rupture initiation point). Each rectangle denotes the slip distribution at the time as indicated at its lower left corner on the fault plane. The last rectangle at lower right corner is the static (final) slip distribution at 90 s. Red lines represent the evolution of rupture fronts with time. The figures beside the red lines are the corresponding rupture velocity values (unit: km/s).

Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-? 7

fastest at the 5th s. After this time interval there was a short pause of about 4 s. In the period of 16 to 30 s, a new rupture started 80 km away in the northeast to the epicenter and propagated quickly toward SW direction. In this time interval, the rupture occurred in a larger ex-tent, which was a main stage of the Wenchuan earth-quake. In the period of 30 s to 42 s, there were some weak ruptures distributed in a sparse way in both NE and SW directions. In the following 6 s, rupturing seemed to stop. But, in the time interval of 48 s to 58 s, rupturing occurred successively near zones underneath Beichuan 140 km away in northeast of epicenter and Kangding 150 km away in southwest of epicenter. In the time interval of 60 s to 66 s, only a small patch of rup-turing occurred 200 km away in the northeast of epicen-ter. Later, the rupturing in southwest direction almost ceased while there existed patches of weak rupturing 280 km in northeast of epicenter.

As described above, the source process of the Wen-chuan earthquake is highly complicated and the slip dis-tribution is very inhomogeneous. Red thin lines in Fig-ure 5 emphasize the temporal progression of the rupture fronts. Figure 5 also shows that the speed at which the rupture front is propagating (rupture velocity) was vary-ing with space and time during the whole earthquake rupture process. We estimated the rupture velocities for several typical time intervals and marked the values be-side the red lines in red color in Figure 5. From the fea-tures of the rupture propagating along strike direction of the fault, the average rupture velocities were estimated to be 3.4 km/s in the NE direction and 2.2 km/s in the SW direction, respectively.

6 Source time function

The moment-rate function (source time function) shown in Figure 6 can be obtained based on the spatio-temporal rupture images as shown in Figure 5[5]. The source time

Figure 6 Source time function of the 2008 great Wenchuan earthquake.

function indicates that the scalar seismic moment re-leased in the whole earthquake rupture process was about 9.4×1020 Nm, corresponding to a moment magni-tude Mw7.9. The whole time history of the Wenchuan earthquake is divided into five stages, that is, consists of five sub-events. The first event occurred in the first 14 s after the rupture initiation, releasing 14% of the total scalar seismic moment. The second event, the main event, was from 14 s to 34 s, releasing 60% of the total scalar seismic moment. The third one started at 34 s and ended at 43 s, releasing 8% of the total scalar seismic moment. The fourth occurred in the time period of 43 s to 58 s, releasing 17% of the total scalar seismic moment. And the last one started at 58 s, and ruptured weakly until the end of the whole rupture process (90 s), releas-ing only 6% of the total scalar seismic moment.

7 Displacement field on the ground sur-face and mechanism causing serious disaster in the nearfault areas

Displacement in homogeneous and isotropic elastic half space produced by a rectangular dislocation fault can be

expressed in analytic form[17―19], thus it is possible to

calculate the co-seismic displacement field produced by a finite fault model. The co-seismic displacement field on the ground surface in the epicentral area was calcu-lated (Figure 7) by summing the displacement fields produced by the 255 sub-faults of 10 km×10 km, which were obtained from the inversion of the earthquake rup-ture process. Figure 7 compares the spatial distribution of the co-seismic displacement field with the isoseis-mals[20]. Right-lateral movement can be clearly observed in horizontal component of the displacement field (Fig-ure 7(a)), with the NW block moving toward NE direc-tion while the SE block moving toward SW direction. Also, the hanging wall (NW to the fault strike trace) up-lifting and the foot wall (SE to the fault strike trace) de-ducing can be clearly observed in vertical component of the displacement field (Figure 7(b)). The features of both the horizontal and vertical components of the co-seismic displacement field are in good agreement with those of the isoseismals in the meizoseimal area, with two areas of the maximum displacement just being around Wenchuan County and Beichuan County where there are also two areas of the maximum intensity XI (Figure 7). In Wenchuan County, the maximum hori-zontal and vertical displacements are 3.2 m and 2.8 m,

8 Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-?

Figure 7 Comparison of the co-seismic displacement field and the isoseismals of the 2008 great Wenchuan earthquake. (a) Horizontal displacement; (b) vertical displacement. Black full thin lines represent the isoseismals[20].

respectively, and in Beichuan County, the maximum horizontal and vertical displacements are 2.9 m and 2.6 m, respectively. The maximum displacements all ap-peared where the fault broke the ground surface. The calculated relative displacement or dislocation is about 6.1 m where the maximum displacement appeared (at the 50 km northeast of epicenter), which is also in good agreement with the result of field investigation. All these results suggest that the surface-broken thrusting disloca-tion is the main cause for the serious disaster in the near-fault areas in the great Wenchuan earthquake.

8 Discussion and conclusions

We selected 21 teleseismic stations with evenly azi-muthal coverage of the vertical long period recordings from the GSN, and inverted for the spatio-temporal rup-ture process of the Wenchuan Ms8.0 earthquake on 12 May 2008. Reliability of the inverted results can be re-flected, to some extent, by fitness between observed waveforms and synthetic waveforms. Therefore, we calculated synthetic waveforms for 21 stations based on the inverted model of the spatio-temporal rupture proc-ess and compared the synthetic waveforms with ob-served waveforms. As Figure 8 shows, the fitness of the synthetic waveforms with the observed waveforms is good, with most of them (13 stations) having correlation coefficients of above 0.8 and other 3 being between 0.7

and 0.8. It means that the inverted model of dynamic rupture process well interprets most features of the ob-served waveforms.

The comparison of the feature of the co-seismic dis-placement field calculated from the inverted static slip distribution with the feature of the spatial distribution of disastrous areas from the field investigation indicates that they are very similar: the two areas with the larger displacement values are just where the two meizoseis-mal areas are, reflecting close correlation between the meizoseismal areas and the surface-broken thrusting dislocation of the causative fault.

However, some details in the inverted results require further study. For example, the inverted results clearly show that in northeast of Kangding occurred a slip patch with the maximum slip of about 1.8 m, no surface breakage features have been found yet in field investiga-tion; and the fitness of the synthetic waveforms with the observed waveforms at some stations remains unsatis-factory even though the dynamic model inverted for the great Wenchuan earthquake has well interpreted most features of the observed waveforms.

In this paper, focal mechanism, source time function and spatio-temporal variation of the slip on the fault are obtained, and the co-seismic displacement field in the epicentral area is calculated based on the inverted model of static slip dislocation. The inverted focal mechanism and rupture process indicate that the Wenchuan earth-

Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-? 9

Figure 8 Comparison of the observed seismograms of the Global Seismic Network (GSN) and the synthetic seismograms. In each panel, the upper trace denotes the observed waveform and the lower trace denotes the synthetic waveform. On the left are the maximum amplitude of observed waveform, the correlation coefficients and the maximum amplitudes of the synthetic waveform, respectively. On the right from top to bottom are the station codes, com-ponents names and phase names, respectively.

quake was mainly a thrust event, and the rupture propa-gated mainly toward northeast direction in asymmetri-cally bilateral mode, with the maximum slip of about 7.3 m, and large-scale slip-patches strongly breaking the ground surfaces. The striking coincidence of the features of the co-seismic displacement field calculated based on the static slip model with those of the isoseismals in the

epicentral area indicates that the large-scale, high-am- plitude and surface-broken thrusting dislocation resulted from the earthquake source is the main cause for the serious disaster in the near-fault areas.

The authors would like to express their sincere thanks to the anonymous revewers for valuable suggestions.

1 Chen G G, Ji F J, Zhou R J, et al. Primary research of activity seg-

mentation of Longmenshan fault zone since Late-Quaternary (in

Chinese). Seismol Geol, 2007, 29(3): 657―673

2 Yang Z X, Waldhauser F, Chen Y T, et al. Double-difference reloca-

tion of earthquakes in central-western China, 1992–1999. J Seismol,

2005, 9: 241―264

3 Min Z Q. Historical Strong Earthquake Catalog in China (the 23th

Century BC―1911 AD) (in Chinese). Beijing: Seismological Press,

1995. 1―514

4 Min Z Q. Historical Strong Earthquake Catalog in China (1912

AD―1911 AD) (in Chinese). Beijing: Seismological Press, 1995.

1―636

5 Zhang Y, Xu L S, Chen Y T, et al. Source process of Ms6.4 earthquake

in Ning’er, Yunnan in 2007. Sci China Ser D-Earth Sci, 2008, doi:

10.1007/s11430-009-0016-0

6 Kennett B L N. Seismic Wave Propagation in Stratified Media.

Cambridge: Cambridge University Press, 1983. 1―339

7 Kennett B L N, Engdahl E R. Travel times for global earthquake lo-

cation and phase identification. Geophys J Int, 1991, 105: 429―465

8 Zhang Y. Study on the method of earthquake rupture process inversion

(in Chinese). Dissertation for Doctor Degree. Beijing: School of Earth

and Space Sciences, Peking University, 2008. 1―158

9 Liu C, Zhang Y, Xu L S, et al. A new technique for moment tensor

inversion with applications to the 2008 Wenchuan Ms8.0 earthquake

sequence (in Chinese). Acta Seismol Sin, 2008, 30(4): 329―339

10 Kikuchi M, Kanamori H. Inversion of complex body waves. Bull

10 Zhang Yong et al. Sci China Ser D-Earth Sci | Feb. 2009 | vol. 52 | no. 2 | 1-?

Seism Soc Am, 1982, 72: 491―506

11 Hartzell S H, Heaton T H. Inversion of strong ground motion and

teleseismic waveform data for the fault rupture history of the 1979

Imperial Valley, California, earthquake. Bull Seism Soc Am, 1983, 73:

1553―1583

12 Ward S N, Barrientos S E. An inversion for slip distribution and fault

shape from geodetic observations of the 1983, Borah Park, Idaho,

earthquake. J Geophys Res, 1986, 91(B5): 4909―4919

13 Chen Y T, Xu L S. A time domain inversion technique for the

tempo-spatial distribution of slip on a finite fault plane with applica-

tions to recent large earthquakes in Tibetan Plateau. Geophys J Int,

2000, 143(2): 407―416

14 Brune J N. Tectonic stress and the spectra of seismic shear waves from

earthquakes. J Geophys Res, 1970, 75: 4997―5009

15 Brune J N. Correction. Tectonic stress and the spectra of seismic shear

waves from earthquake. J Geophys Res, 1971, 76: 5002

16 Kanamori H. Mechanics of earthquakes. Ann Rev Earth Planet Sci,

1994, 22: 207―237

17 Chen Y T, Lin B H, Lin Z Y, et al. The focal mechanism of the 1966

Hsingtai earthquake as inferred from the ground deformation obser-

vations (in Chinese). Chin J Geophys, 1975, 18(3): 164―182

18 Chen Y T, Huang L R, Lin B H, et al. A dislocation model of the

Tangshan earthquake of 1976 from the inversion of geodetic data (in

Chinese). Chin J Geophys, 1979, 22(3): 201―216

19 Okada Y. Surface deformation due to shear and tensile faults in a

half-space. Bull Seism Soc Am, 1985, 75(4): 1135―1154

20 National Wenchuan Earthquake Expert Committee. Earth-

quake-Geological Disaster Atlas of Wenchuan Earthquake Area.

Beijing: SinoMaps Press, 2008. 1―105