Earthq Sci (2011)24: 107–113 107 doi:10.1007/s11589-011-0774-6 Relocation of aftershocks of the Wenchuan M S 8.0 earthquake and its implication to seismotectonics * Bo Zhao Yutao Shi and Yuan Gao Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China Abstract From 14:28 (GMT+8) on May 12th, 2008, the origin time of M S 8.0 Wenchuan earthquake, to December 31th, 2008, more than 10 000 aftershocks (M≥2.0) had been recorded by the seismic networks in Sichuan and surrounding area. Using double difference algorithm, the main shock and more than 7 000 aftershocks were relocated. The aftershocks distribute about 350 km long. The depths of aftershocks are mainly between 10 km and 20 km. The average depth of aftershocks is about 13 km after relocation. In the southwest, the distribution of aftershocks is along the back-range fault, the central-range fault and the front-range fault of Longmenshan faults. In the middle, the distribution of aftershocks is along the Central-range fault. In the north, the distribution of aftershocks through the Qingchuan-Pingwu fault. Relocations suggest that the Back-range fault mainly induced and controlled the aftershock occurrence in the northern section of aftershocks sequence. The MS8.0 main shock is between Central-range and Front-range of Longmenshan faults and it is near the shear plane of the fault bottom. From the depth distribution of aftershock sequence, it suggests that these three faults show imbricate thrust structure. Key words: earthquake location; double difference algorithm; Wenchuan earthquake; Longmenshan faults CLC number: P315.3 + 3 Document code:A 1 Introduction On May 12, 2008, a large M S 8.0 earthquake oc- curred in Wenchuan county of Sichuan Province. Un- til December 31, 2008, there had been tens of thou- sands of aftershocks, including a total of eight after- shocks with M S ≥6.0, along Longmenshan fault. Surface rupture zone extended over hundreds of kilometers, and the earthquakes caused a large number of casualties and economic losses. Aftershock sequences mainly distribute along the Back-range fault, the Central-range fault and the Front- range fault of Longmenshan faults. In order to obtain relatively accurate seismic source locations, this study used double difference algorithm (Waldhauser and Ellsworth, 2000) to relocate aftershock sequence from * Received 19 August 2010; accepted in revised form 31 December 2010; published 10 February 2011. Corresponding author. e-mail: [email protected]The Seismological Society of China and Springer-Verlag Berlin Heidelberg 2011 May 12, 2008 to December 31, 2008. After the Wenchuan earthquake, some researchers quickly calculated part of aftershock sequence to obtain the relocation results. However, only very limited af- tershock data, events occurring until July 2008, were used in those study (e.g., Zhu et al., 2008; Huang et al., 2008; L¨ u et al., 2008; Chen et al., 2009). In order to determine the main seismogenic fault of Wenchuan earthquake, aftershock distribution and seismotecton- ics, this study uses more aftershock data, from origin time of Wenchuan earthquake, May 12, 2008 to the end of December 2008. 2 Tectonic background, seismic data and method Whenchuan aftershock sequence distribute along Longmenshan thrust fault which is a junction region of Songpan-Garze block and South China block (Figure 1). The trend of Longmenshan fault zone is NE-SW. Its length is about 350 km, and the width is 30–40 km.
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Relocation of aftershocks of the Wenchuan S8.0 earthquake ...web.mst.edu/~gaoyua/2011.EqSci.Relocation-Wenchuan-Ms8...In the Back-range of Longmenshan fault, Wen-chuan-Maoxian fault
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Earthq Sci (2011)24: 107–113 107
doi:10.1007/s11589-011-0774-6
Relocation of aftershocks of the WenchuanMS8.0 earthquake and its implication
to seismotectonics∗
Bo Zhao Yutao Shi and Yuan GaoInstitute of Earthquake Science, China Earthquake Administration, Beijing 100036, China
Abstract From 14:28 (GMT+8) on May 12th, 2008, the origin time of MS8.0 Wenchuan earthquake, to
December 31th, 2008, more than 10 000 aftershocks (M≥2.0) had been recorded by the seismic networks in
Sichuan and surrounding area. Using double difference algorithm, the main shock and more than 7 000 aftershocks
were relocated. The aftershocks distribute about 350 km long. The depths of aftershocks are mainly between
10 km and 20 km. The average depth of aftershocks is about 13 km after relocation. In the southwest, the
distribution of aftershocks is along the back-range fault, the central-range fault and the front-range fault of
Longmenshan faults. In the middle, the distribution of aftershocks is along the Central-range fault. In the north,
the distribution of aftershocks through the Qingchuan-Pingwu fault. Relocations suggest that the Back-range
fault mainly induced and controlled the aftershock occurrence in the northern section of aftershocks sequence.
The MS8.0 main shock is between Central-range and Front-range of Longmenshan faults and it is near the shear
plane of the fault bottom. From the depth distribution of aftershock sequence, it suggests that these three faults