1988年澜沧-耿马地震的震源特征及其有限元模拟

THE CHARACTER OF SEISMIC SOURCE AND FEMMODELLING FOR 1988 LANCHANG-GENGMA EARTHQUAKE

本文根据澜沧-耿马地震序列余震分布图像的变化，以及用复合型法反演主震破裂过程的研究结果，提出了澜沧-耿马地区北北西走向顺向雁行型双断层力学模型．用断裂力学有限元方法进行数字模拟研究表明：模型中的两个内端点区之间是主压应力的相对低值区，而剪应力分布在两个内端点区为高值区且以较大梯度向中心衰减，两次７级地震后接连发生的４次近东西走向的６级余震主要发生在这一带．由于压应力的减弱、剪应力的增加，使近东西走向的断层上摩擦力减小，有利于发生剪切错动，引发近东西走向分布的强余震；当区域主压应力方向取北北东向时，断层的理论滑动矢量图显示出右旋走滑性质，与震源机制及地表考查结果一致．当区域主压应力方位取值在ＮＥ２５°附近且北部７．２级震区的弹性模量相对南部７．６级震区足够大时，北部断层１的相对滑动矢量可比南部断层２大，从而导致７．２级地震的震中烈度大于７．６级地震的烈度异常分布．

According to analysis for the aftershock dirstribution of LanChang-Gengma Earthquake sequence and the results of main seismic fault mechanism inversion by compound method,we suggest a mechanical modelof Two fault interaction for Lancliang-Gengma earthquake.The results of FEM simulating shows that the region between two faults tip are low principle pressure stress and high shear stress zone.After two 7M_S earthquakes,four aftershock larger than 6M_S were occur in this region.Low pressure stress and high sliear stress decrease the friction force in the faults and benefit the moving of faults. When the region principle pressure stress is in NNE direction,the moving vector of faults are in right lattral strike.This is cotsistent with the seismic source mechanism and investigation of surface faults moving.When Principle stress are in the NE25 direction and take the Yong' models of north Part of seismic zone larger than the south Part.Our FEM simulation results shows that the intensity of 7.2 M_S earthquake in the north part are larger than the intensity of 7.6M_S earthquake in the south part.