Pre-seismic and Co-seismic Deformations in the Seismogenic zone of the Lushan MS7.0 earthquake

Yanqiang Wu

Published August 14, 2018, SCEC Contribution #8594, 2018 SCEC Annual Meeting Poster #122

The spatiotemporal deformation response of a seismogenic fault to a large earthquake is of great significance to understanding the nucleation and occurrence of the next strong earthquake. The Longmeshan fault, where the 2008 Wenchuan MS 8.0 earthquake and 2013 Lushan MS 7.0 earthquake occurred, provides an opportunity for us to study this important issue. The results are as follows: 1) during the co-seismic and post-seismic processes of the Wenchuan earthquake, the deformation is dominated by a continuous pattern in the Southern Segment of the Longmenshan Fault (SSLMF), which is different from the dislocation pattern in the middle-northern segment of the LMF. Quantitatively, the compressive strain present between 2008 and 2013 was equal to the strain accumulation of 69 years during the interseismic period in the SSLMF; 2) After the Wenchuan earthquake, the deformation adjustment (especially the shear deformation) in the region that crosses the Maoxian-Wenchuan Fault (MWF) and Beichuan-Yingxiu Fault (BYF) is significantly greater than that the eastern region of the Anxian-Guanxian Fault (AGF). Furthermore, the azimuth angles of the principal compressive strain rate in both regions change fast in the first year of the observation period and then turn into the stable state.

The co-seismic displacement GPS results indicate the thrust rupture is dominant and the laevorotation movement is secondary in the strain release of the Lushan earthquake. Some detailed results are obtainable. 1) The co-seismic displacements reflected by GPS data are mainly located in a region that is 230 km (NW direction) × 100 km (SW direction). 2) On a large scale, the co-seismic displacement shows thrust characteristics, but the associated values are remarkably small in the near field (within 70 km) of the earthquake fault. Meanwhile, the thrust movement in this 70-km region does not correspond with the attenuation characteristics of the strain release, indicating that the rupture of this earthquake does not reach the earth's surface. 3) The laevorotation movements are remarkable in the 50-km region, which is located in the hanging wall that is close to the earthquake fault, and the corresponding values in this case correlate with the attenuation characteristics of the strain release.
In general, the deformation features of the SSLMF reveal that the Wenchuan earthquake promotes the occurrence of the Lushan earthquake.

Wu, Y. (2018, 08). Pre-seismic and Co-seismic Deformations in the Seismogenic zone of the Lushan MS7.0 earthquake. Poster Presentation at 2018 SCEC Annual Meeting.

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Tectonic Geodesy