日本俯冲带地震发生过程的数值模拟研究

Numerical modeling of earthquake generating processes in the Japan subduction slab

了解地震发生的动力学机制是研究地震发震原因的关键,而数值模拟的方法是高速、有效的手段.2011年3月11日日本东北部宫城县发生9.0级大地震,文中以该次大地震所在的日本俯冲带为研究对象,通过使用黏弹性有限元数值模拟,并引用接触对,建立了研究区二维数值模型,模拟俯冲带与上覆板片之间的滑动、黏滞到再滑动的过程,亦即断层失稳发生地震的过程.模拟结果显示,随着太平洋板块不断俯冲,在俯冲带上自发出现了断层闭锁、解锁到再闭锁的黏滑过程,且这种过程呈现一定的准周期性,大事件主要集中分布在20～30km的深度范围内.根据俯冲带可能在俯冲过程中角度的变化,建立了不同的模型,进行模拟对比研究,结果表明,俯冲带的几何形态,以及俯冲角度变化所在的不同深度,对模拟的结果有不同的影响.

Understanding of earthquake dynamic mechanism is the key of studying the causes of earthquakes,especially the large events.Numerical simulation is a fast and efficient approach to solve this issue.The Mw9.0 earthquake of Miyagi Prefecture,northeastern Japan on 11th March,2011 occurred at the Japan subduction slab.In this article,we take the Japan subduction slab as the study object,and simulate the stick-slip process between the slab and overlying plate as well as the instability processes of the fault by a two-dimensional viscoelastic finite element model.The results show that the underthrusting of the Pacific plate leads to the spontaneous stick-slip processes,characterized by fault locking,fault unlocking and back to fault locking again,which present certain quasi-periodicity in the slab,and big events mainly concentrated in the depth range of 20~30 km.Using different models with varied dip angles of the subduction slab,we make a comparative study of simulations.The results reveal that the geometry of the subduction slab and different depths where the subduction angle changes have different effects on the simulation results.