2010年马乌莱M_(W)8.8地震震后形变三维黏弹性数值模拟

3D numerical model for viscoelastic postseismic deformation following the Maule M_(W)8.8 earthquake in 2010

2010年智利马乌莱M_(W)8.8地震发生在纳斯卡板块与南美板块的板块边界处,引起了显著的同震和震后效应。GPS台网数据显示记录到的同震海向位移最大约5 m,垂向沉降最大约50 cm。在经过对俯冲效应、季节变化等效应的校正后,震后6年的海向最大位移约68 cm,垂向抬升最大约20 cm。马乌莱地震显著的震后形变对该区域的地下三维黏弹性结构有良好的约束。本文建立了智利中南部俯冲带区域的三维有限元模型,黏弹性的地幔楔及海洋地幔均使用伯格斯体材料,并在断层面上设置2 km厚的软弱层以模拟震后余滑。在与GPS台站震后位移数据进行比较后,模拟结果表明,大洋地幔顶部存在约120 km厚,黏度为1×10^(19)Pa·s的软流圈。模拟震后余滑效应的软弱层黏度为5×10^(17)Pa·s,其等效震后余滑的最大值在震后前两年接近2 m,且随着时间的增长而快速衰减。

The 2010 M_(W)8.8 Maule earthquake occurred near the plate boundary between the Nazca plate and the South American plate.The earthquake produced significant coseismic and postseismic deformation.The maximum coseismic motion is about 5 m in the horizontal direction and about 5 cm subsidence.After correcting the GPS data for secular,seasonal and annual trends,the postseismic cumulative motion within the first 6 years after the earthquake include up to about 68 cm in the horizontal direction and up to 20 cm uplift.The three-dimensional(3D)viscoelastic structure can be constrained by the postseismic deformation of the 2010 earthquake.We have constructed a 3D finite element model to study the effects of the rheological structure on the postseismic deformation of the 2010 earthquake.We assume the viscoelastic relaxation of the upper mantle to be represented by the Burgers rheology.And in the paper,a 2 km thick weak shear zone attached to the megathrust is used to simulate the afterslip.Based on the comparison with the GPS observation data,the preferred model determined that a 120 km thick asthenosphere with a viscosity of 1×10^(19) Pa·s at the top of the oceanic upper mantle is required to fit the data.The afterslip simulated by shear zone with a viscosity of 5×10^(7) Pa·s is up to 2 m in the first 2 years and decays rapidly with time.