汶川地震前十年间龙门山区域顾及断层闭锁的地壳应变场

Crustal strain in the Longmenshan region considering fault locking during ten years before the 2008 Wenchuan earthquake

本文利用1997—2008年5月的汶川M_w7.9地震前川滇地区GPS水平速度场数据,采用负位错理论反演了汶川M_w7.9地震前龙门山断裂带的闭锁程度.在顾及断层闭锁影响下,获得了龙门山断裂带区域震前十年间地壳应变率场.结果表明在汶川地震前龙门山断裂带高度闭锁,在地表以下0~25 km范围内其平均闭锁程度为0.972±0.222,滑动亏损速率约为3 mm·a^(-1).震前龙门山断裂滑脱层的高度闭锁为汶川地震深部同震破裂提供了能量基础;在顾及断层闭锁影响下,龙门山断裂带附近应变积累缓慢,断层附近区域最大主应变率约为3.4~9.6 nanostrain·a^(-1),最小主应变率约为-2.5^-7.1 nanostrain·a^(-1);断层西北侧有明显的应变积累.

In this study, the locking degree of the Longmenshan fault and the strain rates in the Longmenshan region before the 2008 Wenchuan earthquake are inverted from the GPS horizontal velocity field between 1997 and May, 2008 using the negative dislocation theory. The inversion results show that the Longmenshan fault was nearly completely locked before the Wenchuan Mw7.9 earthquake. The mean coupling degree of the Longmenshan fault from the surface to 25 km depth is 0. 972±0. 222, and the slip deficit is about 3 mm · a^-1 The detachment of Longmenshan that was nearly fully locked provided the energy for the Wenchuan earthquake rupture at depth. With consideration of the fault coupling, crustal strain slowly accumulated near the fault, more obviously at the northwest of the fault. The principal tensile strain rates near the fault range from 3.4 to 9.6 nanostrain · a^-1 and the principal compressive strain rates range from -2.5 to -7.1 nanostrain· a^-1, respectively.