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| High-resolution seismic tomography of the upper crust in the source region of the April 20, 2013 Lushan earthquake and its seismotectonic implications |
| Baofeng Tian1, Zhiwei Li2, Sha Liu1, Jiansi Yang1 |
1 Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
2 State Key Laboratory of Geodesy and Earth’s Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China |
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Abstract Both P- and S-wave arrivals were collected for imaging upper crustal structures in the source region of the April 20, 2013 Lushan earthquake. High-resolution, threedimensional P and S velocity models were constructed by travel-time tomography. Moreover, more than 3700 aftershocks of the Lushan earthquake were relocated via a grid search method. The P- and S-wave velocity images of the upper crust show largely similar characters, with high and low velocity anomalies, which mark the presence of significant lateral and vertical heterogeneity at the source region of the Lushan earthquake. The characteristics of the velocity anomalies also reflect the associated surface geological tectonics in this region. The distributions of high velocity anomalies of both P- and S-waves to 18 km depth are consistent with the distributions of relocated aftershocks, suggesting that most of the ruptures were localized inside the high velocity region. In contrast, low P and S velocities were found in the surrounding regions without aftershocks, especially in the region to the northeast of the Lushan earthquake. For the relocated aftershocks of the Lushan earthquake from this study, we found that most aftershocks were concentrated in a zone of about 40 km long and 20 km wide, and were located in the hanging wall of Dayi–Mingshan fault. The focal depths of aftershocks increase from the southeast to the northwest region in the direction perpendicular to the fault strike, suggesting that the fault ruptured at an approximate dip angle of 45°. The main depths of the aftershocks in the northwest of the main shock are significantly shallower than expected, revealing the different seismogenic conditions in the source region.
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Received: 05 June 2013
Published: 30 October 2013
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| Fund:Research Project in Earthquake Science (No. 201308018, No. 201108002), National Natural Science Foundation of China (No. 40904012), and National Basic Research Program of China (No. 2013CB733203, No. 2013CB733204) |
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Corresponding Authors:
Zhiwei Li
E-mail: zwli@whigg.ac.cn
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