Historic seismicity near the source zone of the great 2008 Wenchuan earthquake: Implications for seismic hazards

Abstract

In the past 500years, 14 historical earthquakes, including one that caused a maximum intensity of IX, occurred over a distance of more than 300km along the Longmen Shan thrust belt, including portions that did not rupture during the devastating Wenchuan earthquake sequence of May 12, 2008. Estimated locations of epicenters and trends of faulting during historical events complement information gathered after the 2008 sequence. In particular, in addition to the two fault splays that ruptured in 2008, there are additional seismogenic faults across the Longmen Shan belt, including those in the hinterland and in the foreland. In the latter case, the occurrence of moderate-sized historical earthquakes and the disproportionally wide region of reported damage in the Sichuan basin from large events within the Longmen Shan belt, probably an effect of low attenuation in the stable basin, calls for attention to the potential of seismic hazard in the heavily populated Chengdu basin. Moreover, long recurrence-intervals of great events, estimated from trenching of colluvium along the ruptures of the 2008 sequence, should not be taken as reliable estimates for somewhat smaller, but nonetheless highly destructive events along the Longmen Shan thrust belt.