摘要
本文以完整的形式给出拉梅常数不相等情形的半无限弹性介质中任意倾角的矩形滑动断层引起的地震位移场解析表示式。以一些数值结果说明介质的泊松比、断层面的倾角、上界和下界对地面的地震位移场的影响。在比较1966年邢台地震的地形变资料和计算得到的各种走向、倾向、倾角、断层面长度、宽度、震源深度和错距的单个的矩形滑动断层引起的地面位移之后指出,简单的滑动断层错动模式不能同时很好地解释观测到的邢台地震的水平和垂直形变。为了解释观测结果,提出了一个复合的断层模式。这个复合断层模式由六个简单的矩形滑动断层构成。运用网格尝试法,得到了基本上符合观测到的水平和垂直位移场的震源参数。结果是:第一、二、三部分,出露到地面,倾角45°,宽度15公里;第四、五、六部分,倾角82°,宽度30公里。其它参数是:断层面走向N35°E,倾向N125°E,断层总长度50公里,断层各部分的平均走向滑动错距依次为—78、—134、—17、2、—3和1厘米(负号表示右旋走向滑动,正号表示左旋走向滑动),平均倾向滑动错距依次为2、50、88、24、—5和—23厘米(负号表示逆断层,正号表示正断层),地震矩依次为3.2、5.9、3.7、2.0、0.5、1.9×10^(23)达因·厘米,应力降依次为22、42、33、5、1、4巴,应变降依次为3.3、6.4、5.0、0.8、0.2、0.6×10^(-5),释放的总能量的下限为6.1×10^(22)尔格。对比所得结果和6级以上的地震震中分布,表明邢台地震的两个较大的前震及主震和复合断层上部的错动关系较大,而大的余震则和复合断层下面那部分的端部的错动相联系。邢台地震区近半个世纪以来的水准测量资料表明,这个地区下降速率的上限约为5毫米/年。如果认为通过这次地震,积累在主要断层上的应变已基本释放完毕,那么,由这次地震的倾向滑动错距的大小可以估计这个地震断层上的地震复发周期的下限大约是176年。
In this paper,analytical expressions for the earthquake displacement field produced by rectangular strike-slip and dip-slip faults of arbitrary dip in a semi-infinite elastic medium for the case of unequal Lame constants are given in closed forms.Some numerical examples are presented to illustrate the effects of Poisson ratio of the medium,the dip angle,upper and lower boundary of the fault,to earthquake dis-placement field on surface.By comparing the geodetic data of the 1966 Hsingtai earth-quake to the theoretical surface displacements that would be produced by a single rectangular slip fault of various strike,dip direction,dip angle,fault length,width,focal depth,and dislocations,it is shown that the simplified single slip fault model can not explain satisfactorily the observed horizontal and vertical ground deforma-tion.In order to account for the observed data,a compounded fault model which consists of six simple rectangular slip faults,is proposed.By using the grid trial method,the source parameters appropriate to the observed horizontal as well as ver-tical displacement field are obtained.The results are as follows:the upper three simple rectangular slip faults breaking to the surface,have a dip angle of 45°,width 15 km,while the lower three simple rectangular slip faults have a dip angle of 82°,width 30 km.Other source parameters determined are as follows:strike,N35°B;dip direction,N125°E;total fault length,50 km;average strike-slip dislocations respectively,-78,-134,-17,2,-3,and 1 cm(minus stands for the right-lateral strike-slip while plus for the left-lateral strike-slip);average dip-slip dislocations respectively,2,50,88,24,-5,and-23 cm(minus stands for the reverse fault while plus for the normal fault);seismic moments respectively,3.2,5.9,3.7,2.0,0.5,and 1.9×10^(25)dyne·cm,stress drops respectively,22,42,33,5,1,and 4 bars,strain drops respectively,3.3,6.4,5.0,0.8,0.2,and 0.6×10^(-5).Lower limit of strain energy release is 6.1×10^(22)ergs.A comparison of the obtained results with the epicentral distri-bution of earthquakes of magnitudes greater than 6 indicates that,the main shock and two larger foreshocks are related more closely with the dislocation of the upper three portions of this compounded fault,and that the two larger aftershocks are related with the dislocation near the ends of the lower portions of this compounded fault.Results of leveling survey in Hsingtai area since 1920,indicate that the upper limit of the rate of subsidence is about 5 mm/yr.If the strain accumulated in this area is as-sumed to be released entirely by the 1966 Hsingtai earthquake,the lower limit of the recurrence period of earthquakes of magnitudes as high as the 1966 Hsingtai earth-quake can be estimated in terms of the average dip-slip dislocation of this compound-ed fault to be about 176 years.
作者
陈运泰
林邦慧
林中洋
李志勇
CHEN YUN-TAI;LIN BANG-HUI;LIN ZHONG-YANG;LI ZHI-YONG(Institute of Geophysics,Academia Sinica)
出处
《地球物理学报》
1975年第3期164-182,共19页
Chinese Journal of Geophysics
