【摘要】 2006年7月4日,在距离北京100km左右的文安地区,发生了Mw=5.1级地震,引起了北京地区的强烈震感.为了更好的认识区域构造,我们利用近震及远震波形反演的方法得到了此次文安地震的震源机制.选择了北京数字地震台网的9个地震台,震中距小于600km,台站的方位角覆盖较好.为了更好地利用信号相对较弱的P波信号,对于一个地震记录,本文分别截取出P波和面波两个部分,分别给予不同的权重进行反演,结合格点搜索的方法,得到了与记录P波及面波三分量对应较好的地震的方位角、倾角和滑移角.同时考虑到北京西北地区地壳较厚,本文在利用F-K方法计算近震理论波形的时候,对不同的方位角,采用了不同的地壳速度模型.随后结合远震信号中的直达P、pP、sP波形得到了分辨率较高的地震震源深度.反演结果表明,此次文安地震是一个较为典型的走滑型地震,方位角为210°,倾角80°,滑移角-150°,地震的深度为14～15km,地震的震级为(Mw=5.1).反演结果与断层的几何分布、余震分布及北京地区北北东向应力场有很好的一致性.更多还原

【Abstract】 On July 4,2006,a magnitude 5.1 earthquake occurred at Wen’an,~100 km south of Beijing,which was felt in Beijing metropolitan area.To better understand the regional tectonics,we have inverted local and teleseismic broadband waveform data to determine the focal mechanism of this earthquake.We selected waveform data of 9 stations from the recently installed Beijing metropolitan digital Seismic Network(BSN).These stations are located within 600 km and cover a good azimuthal range to the earthquake.To better fit the lower amplitude P waveform,we employed two different weights for the P wave and surface wave arrivals,respectively.A grid search method was employed to find the strike,dip and slip of the earthquake that best fit the three-component records of P and surface waveforms recorded(the tangential component of the P-wave arrivals was not used).Synthetic waveforms were computed with an F-K method.Two crustal velocity models were used in the synthetic calculation to reflect a rapid east-west transition in crustal structure observed by seismic and geological studies in the study area.The 3D grid search results in reasonable constraints on the fault geometry and the slip vector with a less well determined focal depth.As such we combined teleseismic waveform data from 8 stations of the Global Seismic Network in a joint inversion.Clearly identifiable depth phases(pP,sP)recorded by the teleseismic stations obviously provided a better constraint on the resulting source depth.The results from the joint inversion indicate that the Wen’an earthquake is mainly a right-lateral strike slip event(-150°)which occurred on a near vertical(dip,~80°)NNE trending(210°)fault.The estimated focal depth is 14~15 km,and the moment magnitude is 5.1.The estimated fault geometry here agrees well with aftershock distribution and is consistent with the major fault systems in the area which were developed under a NNE-SSW oriented compressional stress field.更多还原