Location and mechanism of the 1933 Diexi earthquake and its association with the regional tectonic deformation prior to the 2008 Wenchuan earthquake
Abstract
The east margin of the Tibetan plateau is composed of the Longmenshan and Minjiang-Huya fault systems, which are tectonically active and produced the 1933 M7.5 Diexi, 1976 M7.2 Songpan doublelet, and 2008 M7.9 Wenchuan earthquakes. Among all the large events the 1933 Diexi earthquake is the least known, and its location and mechanism, despite of the importance in understanding the regional tectonic process and assessing the seismic hazards, have been subject to controversy. We collect worldwide seismic records of this earthquake, among which some polarities of the first arrival phases were picked, and use the data to relocate this earthquake and obtain the fault plane solution. The relocated epicenter is at (31.9°E, 103.6°N) and one of the nodal planes trends NNW, with the azimuth ranging N5~30°W. Taking this as the rupture plane of the Diexi earthquake, we conclude that the seismogenic structure was the southern segment of the Minjiang fault, which was dominated mainly by sinistral slip with a minor thrust component. Present day GPS velocity profile across the Minshan Mountains indicates that the Huya fault absorbs ~2 mm/yr crustal shortening, associated with the rapid uplift of the Minshan Mountains since Quaternary. A discrepancy between the focal mechanism solution of the 1933 Diexi earthquake and the GPS determined present sense of motion across the Minjiang fault may be attributed to the crustal deformation processes of the Longmenshan and Minjiang-Huya fault systems and their earthquake cycles, particularly the role that the Longmen shan fault system played in altering the regional deformation field late into the earthquake cycle prior to the 2008 great Wenchuan earthquake. We are using a visco-elastic FEM code to simulate the process taking into account of the layering and lateral change of the crustal and mantle materials. A 3-D evolution of the deformation field will be evaluated, and its temporal change due to crustal and mantle rheology across the east margin of the Tibetan plateau will be assessed. We will focus particularly on the deformation field at a time late into a millennium earthquake cycle such as prior to the 2008 Wenchuan earthquak, and evaluate how much the regional deformation pattern would be altered when contributions from the Longmenshan fault system were relatively slow and broadly distributed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T22A..02W
- Keywords:
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- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations