阜阳MS4.3地震震源深度的确定及地震成因分析

摘要

2015年3月14日在安徽阜阳地区发生了MS4.3地震,随后发生3月23日MS3.6余震.主震造成2人死亡13人受伤.房屋倒塌155间,受损1万多间.主震震级不大,而造成的灾害巨大.本文使用CAP方法反演了两次地震的震源机制解和震源深度,结果显示两次地震的震源机制解和深度一致.主震的机制解节面Ⅰ走向110°,倾角75°,滑动角-10°;节面Ⅱ走向202°,倾角80°,滑动角-164°;矩震级Mw4.3,余震矩震级Mw3.7,反演最佳深度均为3 km.最佳深度时波形拟合相关系数较高,表明反演结果是可靠的.使用sPn和sPL深度震相进一步分析了两次地震的震源深度.结果显示,选取的7个台站的sPn震相与Pn震相的平均到时差为1 s,对应的震源深度为3 km.震中距为36 km的利辛台的sPL震相与Pg震相到时差约为1.1s,对应震源深度约3～4 km之间.两种深度震相分析的震源深度与CAP方法的结果一致,表明本文给出的阜阳地震震源深度为3 km左右基本是可靠的.本次地震造成较大灾害的原因很可能与地震震源较浅有关.阜阳地区地壳结构相对稳定,地质构造演化形成3 km厚的沉积层,本次地震可能是区域应力作用下发生在沉积层里的一次地震.%On March 14,2015,an earthquake magnitude in MS4.3 occurred in Fuyang,and then an MS3.6 aftershock followed on March 23.Two people were killed,13 people were injured,155 houses collapsed and more than ten thousands were damaged in the earthquake.Compared to other earthquakes with similar magnitude under the same tectonic background,such as Guzhen MS5.0 earthquake in 1979 and Lixin MS4.1 in 1999,the earthquake brought serious casualties and losses,which may be related to the shallow focal depth.We used CAP method to invert focal depth and mechanism of these two earthquakes and the result of the mainshock is consistent with the aftershock.The double-couple solution is:110°,75°,-10° for strike,dip and rake,respectively,the other nodal plane is 202°,80°,-164° and the centriod depth is about 3 km,with the magnitude of Mw4.3.The sPn and sPL depth phase were also used to invert the focal depth of these earthquakes.The result shows that the average arrival time difference between sPn and Pn recorded by seven stations we chose is 1 s and then we can get the focal depth-3 km by waveform comparison method.The arrival time difference between sPL and Pg of LXT station with the epicentral distance for 36 km is 1 s and the corresponding focal depth is 4 km,w hich is coincident with the result of CAP inversion and sPn depth phase.It indicates the reliable focal depth of MS4.3 earthquake is about 3 km,relatively shallow which maybe bring great losses.According to the analysis of the earthquake in Merkering in southwestern of Australia,Lake Ontario in North America we can know that earthquakes are used to occur in shallow for the reason that the rock in deep is hard.According to the research about the geological structure and seismic activity in Fuyang area and the earthquake reliable focal depth result,we think the earthquake may be an event in the sedimentary layer under the regional stress.