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| The April 24, 2013 Changning MS4.8 earthquake: a felt earthquake that occurred in Paleozoic sediment |
| Xiangfang Zeng1, Libo Han2, Yaolin Shi1 |
1 CAS Key Laboratory of Computational Geodynamics, University of Chinese Academy of Sciences, Beijing 100049, China
2 Institute of Geophysics, China Earthquake Administration, Beijing 100081, China |
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Abstract The dense broadband seismic network provides more high-quality waveform that is helpful to improve constraint focal depth of shallow earthquake. Many shallow earthquakes occurring in sediment were regarded as induced events. In Sichuan basin, gas industry and salt mining are dependent on fluid injection technique that triggers microseismicity. We adopted waveform inversion method with regional records to obtain focal mechanism of an Ms4.8 earthquake at Changning. The result suggested that the Changning earthquake occurred at a ESE thrust fault, and its focal depth was about 3 km. The depth phases including teleseismic pP phase and regional sPL phase shows that the focal depth is about 2 km. The strong, shortperiod surface wave suggests that this event is a very shallow earthquake. The amplitude ratio between Rayleigh wave and direct S wave was also used to estimate the source depth of the mainshock. The focal depth (2–4 km) is far less than the depth of the sedimentary layer thickness (6–8 km) in epicentral region. It is close to the depth of fluid injection of salt mining, which may imply that this event was triggered by the industrial activity.
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Received: 27 September 2013
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| Fund:China National Special Fund for Earthquake Scientific Research in Public Interest (201308013), China Postdoctoral Science Foundation (No. 2012M520431), and the National Natural Science Foundation of China Grant No. 41204044 |
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Corresponding Authors:
Yaolin Shi
E-mail: shiyl@ucas.ac.cn
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