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Seismogenic Structure around the Epicenter of the May 12, 2008 Wenchuan Earthquake from Micro‐seismic Tomography
Author(s) -
AN Meijian,
FENG Mei,
DONG Shuwen,
LONG Changxing,
ZHAO Yue,
YANG g,
ZHAO Wenjin,
ZHANG Jizhong
Publication year - 2009
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2009.00095.x
Subject(s) - geology , seismology , hypocenter , epicenter , massif , aftershock , fault (geology) , induced seismicity , seismic tomography , geodesy , geophysics , mantle (geology) , geochemistry
A three‐dimensional local‐scale P ‐velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event‐to‐receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of ∼2 km. The high‐resolution P ‐velocity model revealed interesting structures in the seismogenic layer: (1) The Guanxian‐Anxian fault, Yingxiu‐Beichuan fault and Wenchuan‐Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; (2) The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least ∼10 km from the surface; (3) A sharp lateral velocity variation beneath the Wenchuan‐Maoxian fault may indicate that the Pengguan massif's western boundary and/or the Wenchuan‐Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu‐Beichuan and Guanxian‐Anxian faults, and vertical Wenchuan‐Maoxian fault; (4) Vicinity along the Yingxiu‐Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; (5) Two blocks of low‐velocity anomaly are respectively imaged in the hanging wall and foot wall of the Guanxian‐Anxian fault with a ∼7 km offset with ∼5 km vertical component.