作者：武敏捷
院校：中国地震局地震预测研究所
关键字:震源机制解;应力张量反演;地震序列
学位：硕士
专业：固体地球物理学
摘要：地壳构造应力场是地球动力学研究的核心问题之一，其主要任务是：探讨地壳构造应力场的空间分布形态及其随时间的动态演化，进而追踪地壳构造运动的演化历程，认识现今的地壳构造活动及其发生机制，从而预测地壳构造运动未来的发展演化规律。 地震是由于地球内部的岩体受到构造应力作用，导致岩体突然断裂错动的结果。研究断层附近的应力场有助于了解地震发生的物理过程，目前较为普遍和有效的一种途径是通过震源机制解来推断应力主轴的方向。震源机制参数是推测震源区震前和震后构造应力的重要资料，可以反映震源断层的力学性质和动力学特征，揭示地震破裂的力学机制，给出地震的等效释放应力场。 强震序列的震前、震时和震后，震源区应力场会有一变动过程。根据地震序列震源机制解的时间进程描述应力场释放调整的动态图象，对序列中中小地震震源机制解的变化特征和应力场随时间的变化过程进行研究，归纳提取出强余震发生前应力场变化的共性特征，通过多次震例经验的积累，可为强余震预测提供新的方法和物理力学依据。 1989年、1991年、1999年大同三次地震序列和1998年张北地震序列及唐山地震序列是华北地区重要的地震事件，更是研究首都圈地区地震活动特征不可缺少的重要事件。地震序列中余震是震源区应力场调整的产物，大量中小余震震源机制解携带的应力张量信息，可以描述震源区的应力场状况，认识应力场的时空变化特征，了解区域应力场的积累和调整过程。研究强震前后震源区应力场的时空变化，有助于了解地震孕育的力学过程。 本研究应用Gephart的应力张量反演方法，对地震序列的应力场变化特征采用分时段逐步深入的研究方法，即根据地震序列活动的起伏特征，划分不同的研究时段，以孕育与发震过程中的力学分析为主体，以各时段的特征表现为典型现象进一步分析应力场的总体变化特征，研究各地震序列应力的积累和调整过程以及主震和强余震前的应力场变化规律，归纳总结应力场变化的共性特征。为深刻认识理解区域构造应力场变化的时序特征，结合现今构造活动、前兆异常、地震活动等分析研究地震序列应力场的调整变化过程，并进一步探讨其孕震机理，认识各项变化的物理实质。 本文将应力张量反演方法用于地震序列的研究中，探讨具有相近构造条件、相近序列特
Abstract:
Crustal tectonic stress field is an important question in geodynamic. Its principal task is discussing the spatial distribution shape of crustal stress field and its dynamic evolvement with time, tracing the evolvement course of crustal tectonic movement., knowing nowaday crustal tectonic activity and its generant mechanism, accordingly forecasting the future evolvement rule of crustal tectonic movement. Earthquake occur because of tectonic stress action from the interior of earth, rock suddenly rupture and slip. Studying on stress field of fault help us realize physical process of earthquake occurrence. So far, general and effective method is via focal mechanism to deduce directions of stress principal axes. Focal mechanism parameters are important data to confer tectonic stress in the focal region of earthquakes, it can reflect mechanical properties and kinetic properties of focal fault, and reveal mechanics mechanism of earthquake rock, give us equivalent release stress field of earthquakes. Stress field has a deformation process in the focal region of a strong earthquake sequence. Based on the time course of focal mechanism of an earthquake sequence to describe dynamic image of release adjustment of stress field, and study variable characteristics of moderate-small earthquake focal mechanisms in the earthquake sequence and variable process of stress field with time, conclude common characteristics of stress field before strong aftershock happen. Based on the accumulation of earthquake example knowledge, it can provide new method and physical mechanics gist of strong aftershock. Aftershock in the earthquake sequence is the result of stress field adjustment in hypocenter region, Stress tensor informations of lots of moderate-small aftershocks focal mechanisms can depict stress field status of hypocenter region, understand temporal and spatial variable characteristics of stress field, and realize the accumulation and adjustment process of stress filed. Studying on temporal and spatial variable of hypocenter region stress field of strong earthquakes help us realize mechanics process of earthquake preparation. This study applies stress tensor inversion method by Gephart to study the variable characteristics of stress field of earthquake sequence. It adopts partial periods method. Based on the variable characteristic of earthquake sequence, divide it into different study periods, study the accumulation and adjustment process of earthquake sequence and variable rule of stress field before mainshock and strong aftershock, conclude common characteristics of stress field. In order to understand the time sequence characteristics of tectonic stress field in the region, combining nowaday tectonic