铲形逆冲断层地震破裂动力学模型及其在汶川地震研究中的启示

2008年发生了汶川地震的龙门山断层带是典型的铲形逆冲断层带.利用二维线弹性有限元模型,得到关于铲形逆冲断层带一些具普适性的认识:(1)如果断层带强度不随深度变化,则地震从断层带转换层附近开始发动,破裂沿断层向上传播,当地震蓄积能量足够大时,破裂可以冲破到地表,如汶川地震.(2)一旦到达地表,其最大同震位错将位于断层带...

Dynamic modeling of thrust earthquake on listric fault and its inference to study of Wenchuan earthquake

The 12 May 2008 M_w7.9 Wenchuan earthquake occurred on the Longmenshan fault, which is a classic listric-reverse fault. Using a 2-D elastic finite element model, we obtain some generic understanding on listric fault, and rupture process of the Wenchuan earthquake: (1) If fault strength does not vary along depth, the earthquake would initiate from a spot near the brittle-ductile transition zone of the fault, and propagate upward. The rupture could reach the surface when there is enough energy stored in the crust around the fault system. (2) Once the earthquake rupture breaks to the surface, the coseismic slip would be peaked at the surface, as the case of the Wenchuan earthquake; the shallower the dipping angle of the fault is, the greater the dislocation at the surface would be. (3) Unlike the maximum coseismic slip, the maximum strain energy release density would be located at downdip near the brittle-ductile transition zone of the fault at more than 10 km depth. (4) The shallower the dipping angle of the fault is, the more complete the release would be for the strain energy accumulated during the interseismic time period, and the greater destruction the quake would result at the surface for the near-field region at the hanging wall. (5) Thrust earthquakes occurred on a listric fault could not release all the energy accumulated during the interseismic time period, and furthermore higher strain energy density would be loaded at two regions: one is under the brittle-ductile transition zone of the fault, at a depth range of 15~22 km within the foot wall, and the other is in the shallow crust of the hanging wall, in a depth range of 0~5 km and at about 10+ km horizontal distance from the surface break point. Spatial concentration of the Wenchuan aftershocks reflected the continued strain energy release in these related regions in addition to the continued rupture around the main rupture plane.