Seismogenic structure and coseismic slip distribution of the 2013 Ms7.0 Lushan earthquake in southwestern China

Qi Liu, Xueze Wen, & Zhigang Shao

Published August 13, 2017, SCEC Contribution #7555, 2017 SCEC Annual Meeting Poster #096

To further understand the tectonic process of the Lushan MS7.0 earthquake, which occurred in southwestern China on April 20, 2013, a 3D fault geometry model was built by integrating the relocated aftershocks distribution and the information of geology and geophysics. Given the proper fault model, the coseismic slip distribution was inversed using the near-field deformation data, such as GPS, leveling and strong motion records as the constraints. Our comprehensive fault geometry model revealed that there existed 5 relevant faults named F1 to F5 underground the seismogenic region. After all possible faults combinations had been tested, the inversion results indicated that the combination of faults F1, F3, F4 and F5 can fit the observation data best, and may be the most probable seismogenic fault model. Most of the coseismic slip distributed around the ramp of the main fault F1 dipping to the NW, and the maximum value was 0.86 m, thrust faulting with the rake of 92.88°, while the slip on the back-thrust faults F3 and F4 were dominated by thrust motion with the max value of 0.37 m and 0.4 m and rake of 119.92° and 97.98° respectively. A shallow décollement named F5 was identified at the depths of 5 to 8 km dipping to the NW. It separated the sedimentary cover from the metamorphic basement, and prohibited the coseismic rupture of F1, F3 and F4 spreading to the shallower layer. When the mainshock occurred, the layer under the NE and SW segments of fault F5 slipped to the NE and the SWW respectively, with the maximum value of 0.25 m to accommodate the compression. The inversion result based on the best faults combination can fit various kinds of surface observation well, and also explain the “incompatibility” between the “sinistral” motion observed by GPS and the pure thrust faulting confirmed by seismological outcomes.

Key Words
Lushan Earthquake, 3D seismogenic structure model, Coseismic slip, Joint inversion

Citation
Liu, Q., Wen, X., & Shao, Z. (2017, 08). Seismogenic structure and coseismic slip distribution of the 2013 Ms7.0 Lushan earthquake in southwestern China. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy