Abstract
The seismicity of Longmenshan fault zone and its vicinities before the 12 May 2008 Wenchuan MS8.0 earthquake is studied. Based on the digital seismic waveform data observed from regional seismic networks and mobile stations, the focal mechanism solutions are determined. Our analysis results show that the seismicities of Longmenshan fault zone before the 12 May 2008 Wenchuan earthquake were in stable state. No obvious phenomena of seismic activity intensifying appeared. According to focal mechanism solutions of some small earthquakes before the 12 May 2008 Wenchuan earthquake, the direction of principal compressive stress P-axis is WNW-ESE. The two hypocenter fault planes are NE-striking and NW-striking. The plane of NE direction is among N50°–70°E, the dip angles of fault planes are 60°–70° and it is very steep. The faultings of most earthquakes are dominantly characterized by dip-slip reverse and small part of faultings present strike-slip. The azimuths of principal compressive stress, the strikes of source fault planes and the dislocation types calculated from some small earthquakes before the 12 May 2008 Wenchuan earthquake are in accordance with that of the main shock. The average stress field of micro-rupture along the Longmenshan fault zone before the great earthquake is also consistent with that calculated from main shock. Zipingpu dam is located in the east side 20 km from the initial rupture area of the 12 May 2008 Wenchuan earthquake. The activity increment of small earthquakes in the Zipingpu dam is in the period of water discharging. The source parameter results of the small earthquakes which occurred near the initial rupture area of the 12 May 2008 Wenchuan earthquake indicate that the focal depths are 5 to 14 km and the source parameters are identical with that of earthquake.
Article PDF
Similar content being viewed by others
References
A Compilation of Sichuan Earthquake Data editorial group (1981). A Compilation of Sichuan Earthquake Data. Sichuan People’s Press, Chengdu (in Chinese).
Chen Y T, Xu L S, Zhang Y, Du H L, Feng W P, Liu C, Li C L and Zhang H X (2008). Report on the great Wenchuan earthquake source of May 12, 2008. http://www.csi.ac.cn/sichuan/chenyuntai.pdf (in Chinese).
Diao G L, Yu L M, Ning J Y, Sun P Q and Zhang Z G (1993). Fracture characteristics of the 1989 Datong earthquake swarm. Chinese J Geophys36(3): 360–368 (in Chinese with English abstract).
Harward (2008). http://neic.usgs.gov/neis/eq_depot/2008/eq_080512_ryan/neic_ryan_hrv.html
Liang S H, Li Y M, Shu P Y and Zhu B D (1984). On the determining of source parameters of small earthquakes by suing amplitude ratios of and from regional network observations. Chinese J Geophys27(3): 249–257 (in Chinese with English abstract).
NEIC (2008). http://neic.usgs.gov/neis/eq_depot/2008/eq_080512_ryan/neic_ryan_cmt.html
Zhao Z, Fan J, Zheng S H, Akira Hasegaw and Shigeki Horiuchi (1997). The crustal velocity structure and accuracy amendment of focal location on the Longmenshan fault zone. Acta Seismologica Sinica19(6): 615–622 (in Chinese with English abstract).
Zhong J M and Cheng W Z (2006). Determinations of directions of the mean stress field in Sichuan-Yunnan region from number of focal mechanism solutions. Acta Seismologica Sinica28(4): 337–346 (in Chinese with English abstract).
Zhu J S (2008). The Wenchuan earthquake occurrence background in deep structure and dynamics of lithosphere. Journal of Chengdu University of Technology (Science & Technology Edition) 35(4): 348–356 (in Chinese with English abstract).
Author information
Authors and Affiliations
Corresponding author
About this article
Cite this article
Zhang, Z., Cheng, W., Ruan, X. et al. The seismicity and tectonic stress field characteristics of the Longmenshan fault zone before the Wenchuan MS8.0 earthquake. Earthq Sci 22, 119–128 (2009). https://doi.org/10.1007/s11589-009-0119-x
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11589-009-0119-x