【摘要】 2014年3月10日13时18分(北京时间)美国加利福尼亚州西北岸发生Mw6.9级地震,震中位于戈尔达板块内部.本文利用国际地震学研究联合会(IRIS)地震数据中心提供的远场体波数据,通过波形反演的方法来研究此次地震的震源破裂过程,并分析未造成重大人员伤亡及诱发海啸的原因,为该地区地球动力学的研究提供依据.选取19个方位角覆盖均匀的远场P波垂向波形记录和13个近场P波初动符号进行约束,基于剪切位错点源模型确定此次地震的震源机制解.结合地质构造背景资料,确定断层破裂面的走向.在考虑海水层多次反射效应的影响下,采用18个远场P波垂向波形数据和21个远场SH波切向波形数据,利用有限断层模型,将断层面剖分为17×9块子断层单元来模拟破裂面上滑动的时空分布,通过波形反演的方法获得此次地震的震源破裂过程.利用海水层地壳模型,剪切位错点源模型的反演结果为:走向323°,倾角86.1°,滑动角-180°,震源深度为10.6km.有限断层模型的反演结果表明,此次地震的破裂过程相对简单,主要滑动量集中于震源上方35km×9km的区域内,破裂时间持续19s左右,平均破裂传播速度约为2.7km·s-1,较大滑动量均沿着走向分布,最大滑动量为249cm.此次地震为发生在戈尔达板块内部的一次Mw6.9级的陡倾角走滑型地震.此次地震为单纯的走滑型地震,断层面接近竖直方向,且发生在洋壳底部,因此破坏力不大,不会对沿岸城市造成重大损失.陡倾角断层在走滑错动的过程中不会使海底地形发生大幅度变化,不会引起大面积水体的突然升降,因此不会诱发大规模海啸.更多还原

【Abstract】 A strong earthquake(Mw6.9)occurred in the Gorda plate off the northwestern coast of California in March 10,2014(Beijing Time).The rupture process of the earthquake is determined by the waveform inversion method using far-field body waveform records provided by IRIS.Afterthat,we analyze the reason why the earthquake did not cause serious hazards and trigger tsunami,and provide new evidence to the research of dynamics study in the area.The focal mechanism of the earthquake is obtained by dislocation source model utilizing 19far-field P vertical waveform records with uniform azimuth coverage and 13near-field P-wave initial motions.Based on the obtained focal mechanism,we get the strike angle of fault rupture surface combined with the geological structure background.In the following finite fault inversion,the fault surface is divided into 17×9subfaults to simulate the temporal and spatial distribution of the slips,along with the use of 18far-field P vertical waveform records and 21 farfield SH tangent waveform records,then we can retrieve the rupture process of the earthquake using waveform inversion method with the multi-reflection effect under consideration.Based on the seawater-layered model,the focal mechanism solution based on the shear dislocation source model indicates that this event occurred on the rupture plane(strike angle 323°,dip angle 86.1°,rake angle-180°,focal depth 10.6km)is a high-angle strike-slip faulting.The rupture process is rather simple,the distribution of major slips is concentered in the region of35km×9km above the source,the rupture lasts about 19 seconds,the average rupture velocity is about 2.7km·s-1,the larger slips distribute along the strike direction,and the maximum slip is 249 cm.The earthquake is an Mw6.9strike-slip event with steep dip angle that occurs in the Gorda plate.The earthquake is a pure strike-slip faulting event occurring beneath the seabed,the fault surface is nearly vertical,so it did not cause great damage to the cities off the coast.Since the earthquake does not change the topography of the seafloor in the rupture process,so there is no big displacement of seawater,thus,it won′t trigger a large-scale tsunami.更多还原