Focal mechanisms of the Lushan earthquake sequence and spatial variation of the stress field

Yan Luo1, Li Zhao2, XiangFang Zeng3, Yuan Gao1
1Institute of Earthquake Science, China Earthquake Administration, Beijing, China
2Institute of Earth Sciences, Academia Sinica, Taipei, China
3Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, Beijing, China

Tóm tắt

Using broadband seismic records from regional networks, we determined the focal mechanisms and depths of 37 earthquakes in the 2013 M7.0 Lushan earthquake sequence (3.4⩽M w⩽5.1) by fitting the three-component waveform data. The results show that the earthquakes are predominantly thrust events, with occasional strike-slip mechanisms. Most earthquakes occurred at depths of 10–20 km. We derived the regional distribution of the average stress field in this area using the damped linear inversion method and the focal mechanisms obtained in this study. The inversion results suggest that the Lushan region and the adjacent area are mostly under compression. The orientations of the maximum principal axes trend NW-SE, with some local differences in the stress distribution at different depths. Compared with the distribution of the stress field in the Wenchuan earthquake area, the stress field in the southwest section of the Longmenshan Fault zone (LFZ) share similar characteristics, predominantly thrust faulting with a few strike-slip events and the maximum compression axes being perpendicular to the LFZ.

Từ khóa


Tài liệu tham khảo

Angelier J. 1979. Determination of the mean principal directions of stresses for a given fault population. Tectonophysics, 56: T17–T26

Angelier J. 1984. Tectonic analysis of fault slip data sets. J Geophys Res, 89: 5835–5848

Burchfiel B C, Royden L H, van der Hilst R D. 2008. A geological and geophysical context for the Wenchuan earthquake of 12 May 2008, Sichuan, People’s Republic of China. GSA Today, 18: 4–11

Chen W W, Wang D, Wei S J. 2013. A study on the uncertainties of the centroid depth of the 2013 Lushan earthquake from teleseimic body wave data. Acta Seismol Sin-Engl Ed, 26: 161–168

Chen W W, Ni S D, Wang Z J, et a1. 2012. Joint inversion with both local and teleseismic waveforms for source parameters of the 2010 Kaohsiung earthquake (in Chinese). Chin J Geophys, 55: 2319–2328

Deng Q D, Chen G H, Zhu A L. 2011. Discussion of rupture mechanisms on the seismogenic fault of the 2008 M s8.0 Wenchuan earthquake. Sci China Earth Sci, 54: 1360–1337

Dreger D, Helmberger D V. 1993. Determination of source parameters at regional distances 360 with single station or sparse network data. J Geophys Res, 98: 8107–8125

Gao Y, Wang Q, Zhao B, et al. 2014. A rupture blank zone in middle south part of Longmenshan Faults: Effect after Lushan M s7.0 earthquake of 20 April 2013 in Sichuan, China. Sci China Earth Sci, 57: 2036–2044

Gephart J W, Forsyth D V. 1984. An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence. J Geophys Res, 89: 9305–9320

Guo Q L, Wang C H, Ma H S, et al. 2009. In-situ hydro-fracture stress measurement before and after the Wenchuan M s8.0 earthquake of China (in Chinese). Chin J Geophys, 52: 1395–1401

Hardebeck J L, Michael A J. 2006. Damped regional-scale stress inversions: Methodology and examples for southern California and the Coalinga aftershock sequence. J Geophys Res, 111: B11310

Herrmann R B, Benz H, Ammon C J. 2011. Monitoring the earthquake source process in North America. Bull Seismol Soc Amer, 101: 2609–2625

Kagan Y Y. 1991. 3-D rotation of double-couple earthquake sources. Geophys J Int, 106: 709–716

Li Z W, Xu Y, Huang R Q, et al. 2011. Crustal P-wave velocity structure of the Longmenshan region and its tectonic implications for the 2008 Wenchuan earthquake. Sci China Earth Sci, 54: 1386–1393

Li Z W, Ni S D, Hao T Y, et a1. 2012. Uppermost mantle structure of the eastern margin of the Tibetan Plateau from interstation Pn traveltime difference tomography. Earth Planet Sci Lett, 335–336: 195–205

Li Z W, Tian B F, Liu S. et al. 2013. Asperity of the 2013 Lushan earthquake in the eastern margin of Tibetan Plateau from seismic tomography and aftershock relocation. Geophys J Int, 195: 2016–2022

Liu C, Zhu B J, Shi Y L. 2012. Stress accumulation of the Longmenshan Fault and recurrence interval of Wenchuan Earthquake based on viscoelasticity simulation (in Chinese). Acta Geol Sin, 86: 157–169

Luo Y, Ni S D, Zeng X F, et al. 2010. A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone. Sci China Earth Sci, 53: 1655–1664

Luo Y, Ni S D, Zeng X F, et al. 2011. The M5.0 Suining-Tongnan (China) earthquake of 31 January 2010: A destructive earthquake occurring in sedimentary over. Chin Sci Bull, 56: 521–525

Lu J, Wang X S, Su J R, et al. 2013. Hypocentral location and source mechanism of the M s7.0 Lushan earthquake sequence (in Chinese). Chin J Geophys, 56: 1753–1763

McKenzie D P. 1969. The relation between fault plane solutions for earthquakes and the directions of the principal stresses. Bull Seismol Soc Amer, 59: 591–601

Michael A J. 1984. Determination of stress from slip 393 data: Faults and folds. J Geophys Res, 89: 11517–11526

Michael A J. 1987. Use of focal mechanisms to determine stress: A control study. J Geophys Res, 92: 357–368

Patton H, Zandt G. 1991. Seismic moment tensors of western U S earthquakes and implications for the tectonic stress field. J Geophys Res, 96: 18245–18259

Parsons T, Ji C, Kirby E. 2008. Stress changes from the 2008 Wenchuan earthquake and increased hazard in the Sichuan basin. Nature, 454: 509–510

Qin X H, Chen Q C, Tan C X, et al. 2013. Analysis of current geostress state and seismic risk in southwest segment of Longmenshan fracture belt (in Chinese). Chin J Rock Mech Eng, 32: 2870–2876

Romanowicz B, Dreger D, Pasyanos M, et al. 1993. Monitoring of strain release in central and northern California using broadband data. Geophys Res Lett, 20: 1643–1646

Royden L H, Burchfiel B C, van der Hilst R D. 2008. The geological evolution of the Tibetan Plateau. Science, 321: 1054

Shan B, Xiong X, Zheng Y, et al. 2009. Stress changes on major faults caused by M w7.9 Wenchuan earthquake, May 12, 2008. Sci China Ser D-Earth Sci, 52: 593–601

Shao Z G, Zhou L Q, Jang C S, et al. 2010. The impact of Wenchuan M s8.0 earthquake on the seismicity of surrounding faults (in Chinese). Chin J Geophys, 53: 1784–1795

Shen Z K, Lu J, Wang M, et al. 2005. Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau. J Geophys Res, 110: B11409

Shi Y L, Cao J L. 2010. Some aspects in static stress change calculation-Case study on Wenchuan earthquake (in Chinese). Chin J Geophys, 53: 102–110

Shi Y T, Gao Y, Zhao C P, et al. 2009. A study of seismic anisotropy of Wenchuan earthquake sequence (in Chinese). Chin J Geophys, 52: 398–407

Shi Y T, Gao Y, Zhang Y J, et al. 2013. Shear-wave splitting in the crust in Eastern Songpan-Ganze block, Sichuan-Yunnan block, and western Sichuan Basin (in Chinese). Chin J Geophys, 56: 481–494

Toda S, Lin J, Meghraoui M, et al. 2008. 12 May 2008 M=7.9 Wenchuan, China, earthquake calculated to increase failure stress and seismicity rate on three major fault systems. Geophys Res Lett, 35: L17305

Wan Y G, Shen Z K, Sheng S Z, et al. 2009. The influence of 2008 Wenchuan earthquake on surrounding faults. Acta Seismol Sin, 31: 128–139

Wang C Y, Chang L J, Lu Z Y, et al. 2007. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern. Sci China Ser D-Earth Sci, 50: 1150–1160

Wang Y Z, Wang E N, Shen Z K, et al. 2008. GPS-constrained inversion of present-day slip rates along major faults of the Sichuan-Yunnan region, China. Sci China Ser D-Earth Sci, 51: 1267–1283

Wu Y M, Hsu Y J, Chang C H, et al. 2010. Temporal and spatial variation of stress field in Taiwan from 1991 to 2007: Insights from comprehensive first motion focal mechanism catalog. Earth Planet Sci Lett, 298: 306–316

Xie F R, Cui X F, Zhao J T, et al. 2004. Regional division of the recent tectonic stress field in China and adjacent areas (in Chinese). Chin J Geophys, 47: 654–662

Xie F S, Zhang H Y, Cui X F, et al. 2011. The modern tectonic stress field and strong earthquakes in hina(in Chinese). Recent Dev World Seismol, 385: 4–12

Xu Z H. 2001. A present-day tectonic stress map for eastern Asia region (in Chinese). Acta Seismol Sin, 23: 492–501

Xie Z J, Jin B K, Zheng Y, et al. 2013. Source parameters inversion of the 2013 Lushan earthquake by combining teleseismic waveforms and local seismograms. Sci China Earth Sci, 56: 1177–1186

Yang X P, Jiang P, Song F M, et al.1999. The evidence of the south Longmenshan fault zones cutting late quaternary stratum (in Chinese). Seismol Geol, 21: 341–345

Zeng X F, Luo Y, Han L B, et al. 2013. The Lushan M s7.0 earthquake on 20 April 2013: A high-angle thrust event (in Chinese). Chin J Geophys, 56: 1418–1424

Zhao L, Luo Y, Liu, T Y, et al. 2013. Earthquake focal mechanisms in Yunnan and their inference on regional stress field. Bull Seismol Soc Amer, 103: 2498–2507

Zhao L S, Helmberger D V. 1994. Source estimation from broadband regional seismograms. Bull Seismol Soc Amer, 84: 91–104

Zhan Z W, Helmberger D, Simons M, et al. 2012. Anomalously steep dips of earthquakes in the 2011 Tohoku-Oki source region and possible explanations. Earth Planet Sci Lett, 353–354: 121–133

Zhang P Z, Wen X Z, Xu X W, et al. 2009. The multiple-unit mode of the Wenchuan 8.0 great earthquake occurrence (in Chinese). Chin Sci Bull, 54: 944–953

Zhang P Z. 2013. A review on active tectonics and deep crustal processes of the western Sichuan region, eastern margin of the Tibetan Plateau. Tectonophysics, 584: 7–22

Zheng Y, Ma H S, Lu J, et al. 2009. Source mechanism of strong aftershocks (M s⩾-5.6) of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics. Sci China Ser D-Earth Sci, 52: 739–753

Zheng Y, Ge C, Xie Z J, et al. 2013. Crustal and upper mantle structure and the deep seismogenic environment in the source regions of the Lushan earthquake and the Wenchuan earthquake. Sci China Earth Sci, 56: 1158–1168

Zhu L, Rivera L A. 2002. A note on the dynamic 440 and static displacement from a point source in multi-layered media. Geophys J Int, 148: 619–627

Zhu L P, Helmberger D V. 1996. Advancement in source estimation techniques using broadband regional seismograms. Bull Seismol Soc Amer, 86: 1634–1641

Zoback M L. 1992. First- and second-order patterns of stress in the lithosphere: The world stress map project. J Geophys Res, 97: 11703–11728