采用多层粘弹性模型计算了2008年5月12日汶川Mw7.9地震对周围地区尤其是龙门山断裂带南段的影响,结合地震活动性分析,探讨了2013年4月20日芦山Mw6.6地震的发生机制,并对沿龙门山断裂带芦山地震与汶川地震之间的地震空段进行了分析.计算结果表明,由于下部地壳及上地幔的粘弹性效应,芦山地震震源处对应的汶川地震同震库仑应力变化(△CFS)为-0.1bar以下量级,其后随时间逐渐增加,在芦山地震前增加到了0.4bar(有效摩擦系数为0.4)或0.6bar(有效摩擦系数为0.2)以上.这表明,芦山地震的发生与汶川地震的非弹性触发密切相关.芦山地震与汶川地震之间的地震破裂空段存在1970年大邑M6.2地震的库仑应力阴影区(下降区),汶川地震及芦山地震未能使阴影区发生根本变化,因此,如没有其他不可知因素,该空段短期内整体发生破裂,引发大地震的可能性不大.%Stress changes due to the co-seismic slip on the source fault of the 2008 Mw 7.9 Whenchuan earthquake and delayed response of inelastic deformation in the lower crust and upper mantle have an important role in the seismicity in Longmenshan area.After the Wenchuan earthquake,seismicity shows progressively increasing in a wide region.However,the south segment of the Longmenshan Fault did not show any significant change in seismicity,where positive Coulomb failure stress change (△CFS) was estimated under the elastic half-space model.Under such a background,the 2013 Mw 6.6 Lushan earthquake occurred.This paper presents some preliminary results based on seismicity analysis and stress analysis using lithology models in which the lower crust and the upper mantle are suggested to be viscoelastic.The Wenchuan earthquake resulted in a miner negative coseismic △CFS in the hypocenter region of the Lushan earthquake.As a result of inelastic response the estimated △CFS reached the order of 0.2 ～ 0.4bar,a value sufficient to trigger earthquakes in critically loaded faults.We thus conclude that the Lushan earthquake provides a case of inelastic triggering of the Wenchuan earthquake.The 1970 M6.2 Dayi earthquake caused an obvious Coulomb stress shadow in its source area,which partly overlaps to the seismic gap between the ruptures of the Lushan and Wenchuan earthquakes.The stress shadow still exists although the area has been loaded by both the Wenchuan and Lushan earthquakes.We thus suggest that it is less likely that a great earthquake,which ruptures the entire gap,may occur in the near future if there are no other unknown factors.
展开▼
