发震时深浅构造相互作用导致横向断层致锁的有限元分析

THE FINITE ELEMENT ANALYSIS OF THE NEAR FIELD TRANSVERSE FAULT LOCKED ON ACCOUNT OF THE INTERACTION BETWEEN THE DEEP AND SHALLOW FAULTS DURING A STRONG EARTHQUAKE

本文利用三维有限元方法，研究和计算了大震发生前、发生时、发生后震源断层面与深部同面立接断层之间的相互作用以及发震后促使深部断层发生错动从而对震源区近场横向活动断层致锁的结果，得到以下结果：（１）临近大震前震源断层面端部调整单元下方的深部断层有较高的剪应力水平，造成震时对震源断层面发生底辟作用的条件，即调整单元区对应的深部断层单元首先满足破裂条件并发生破裂。（２）震源端部的调整单元和具有蠕滑能力的横向断层对发震断层的传播有止裂作用。（３）大震时发震断层破裂传播至横向断层时，不能使该横向断层发生闭锁，但发震断层破裂错动可导致深部断层作蠕滑剪切传播，并使与震源断层垂直的近场浅层横向断层扭曲闭锁。同时出现与这一成因有关的测震学指标，即出现由深部断层控制的直线式小震条带。（４）震时由于调整单元让位能力有限造成震后震源端部余震发育。

By using 3-D finite element method,author studied and calculated the interaction betweenthe source fault and the deep upright fault on the same plane before,during and after a strongearthquake and the near field transverse fault which is locked because of the dislocation of thedeep upright fault. The following results are obtained :(1)Before a strong earthquake occurs,the deep fault units under the adjustment units have higher shear strain level with the resultthat the deep fault has a diapirism at the bottom of the seismic source fault during the earth-quake,namely,the deep fauIt units under the a山ustment units first reach the fracture limit andsplit.(2)The adjustment units at the ends of earthquake source and transverse fault with thecreeping capacity might prevent the earthquake faults from splitting.(3)A strong earthquakefault′s splitting spreads to transverse fault, which could not make the transverse fault lockedbut may make the deep fault splitting spread. The shallow transverse fault is twisted andlocked when the deep fault′s splitting spreads to the bottom of the shallow transverse fault.Meanwhile,the seismometry quota concerned with the locked transverse fault appears, thisquota is the very small earthquake belt which is controlled by the deep fault.(4)The resigningcapacity of the adjustment units is limited during a strong earthquake,it may give rise to strongaftershocks the ends of the source fault.