智利M_W8.3地震与M_W8.8地震的震源过程及其引起的库仑应力特征

Rupture process and Coulomb stress change of the M_W8.3 earthquake and the M_W8.8 earthquake,Chile

2015年9月17日6时54分32秒(北京时间)智利中部伊拉佩尔附近(震中31.57°S,71.67°W)发生了一次M_w8.3大地震,在此次地震震中以南约500 km处的马乌莱地区曾于2010年2月27日14时34分11秒发生过一次M_w8.8强震(震中36.12°S,72.90°W),两次地震余震分布区之间有约75 km的地震空区.本文利用远场体波与面波波形,基于有限断层模型,反演了这两次地震的震源破裂过程.结果显示这两次地震均为逆冲型大地震,2015年伊拉佩尔M_w8.3地震的平均滑动角度为107°,平均滑动量为2.43 m,平均破裂速度为1.82 km·s^(-1),标量地震矩为3.28×10^(21)Nm,95%的标量地震矩在104 s内得到了释放.最大滑动量约8 m,位于沿走向75 km,深度8 km处.2010年马乌莱M_w8.8地震的平均滑动角度为109°,平均滑动量为4.95 m,平均破裂速度1.90 km·s^(-1),标量地震矩为1.86×10^(22)Nm,95%的标量地震矩在121 s内得到了释放.最大滑动量约12.5 m,位于沿走向100 km,深度21 km处.2015年伊拉佩尔M_w8.3地震浅部更大的滑动量应该是其引起了较大海啸的一个原因.基于破裂滑动分布,我们计算了这两次地震引起的周边俯冲带上静态库仑应力变化,结果显示两次地震均显著增加了周边俯冲带上的库仑应力,2010年马乌莱地震使得2015.年伊拉佩尔地震震源区附近的库仑应力增加了(0.01~0.15)×10~5Pa,从应力积累的角度看,2010年马乌莱地震有利于2015年伊拉佩尔地震的发生,对后者的发生起到了促进作用.

On 17 September 2015 （Beijing Time）, a great （Mw8.3） earthquake ruptured offshore Illapel （31.57°S,71.67°W） ,central Chile, and a MwS. 8 earthquake occurred in Maule （36.12°S, 72.90°W） on 27 February, 2010 which ruptured about 500 km to the south of the 2015 Illapel earthquake, it is a remarkable fact that a seismic gap about 75 km between two aftershocks zones for the two events. The rupture processes of the two events are investigated by finite fault model using far field broadband body waves and surface waves records. The results indicate that two events are thrust earthquakes, the average rake, average slip, rupture duration, average rupture velocity and moment tensor for the 2015 Illapel earthquake are 107°, 2.43 m, 104 s, 1.82 km s^- 1 and 3.28）〈1021Nm, respectively, and with a peak slip of 8 m which located in 75 km （along strike） and 8 km in depth; the average rake, average slip, rupture duration, average rupture velocity and moment tensor for the 2010 Maule earthquake are 109~,4.95 m, 121 s, 1.90 km° s^-1 and 1.86× 10^22Nm, respectively, and with a peak slip of 12.5 m which located in 100 km （along strike） and 21 km in depth. The 2015 Illapel Mw8.3 earthquake generates a larger tsunami, on account of the larger shallow slip. Based on the rupture distribution, we calculate the static Coulomb stress change for the two events and shows that both of them makes an increase in the average stress, furthermore, the increased stress in source region of the 2015 Illapel earthquake caused by the 2010 Maule event is （0.01-0.15））〈 105 Pa, that may indicate a promotion from the 2010 Maule earthquake leading to the 2015 Mw8.3 Illapel earthquake.