摘要
2018年1月23日,在美国阿拉斯加湾海域发生了一次MW7.9地震.震源机制解表明这次地震以走滑为主,可能发生在近东西向或南北向的陡倾角断层上,早期余震并非线型展布.我们利用视震源时间函数分析确定了此次地震的总体破裂方向,并结合余震的空间展布特征构建了相互交叉的双断层模型,进而通过联合反演远场P波和SH波数据获得了此次地震的时空破裂过程.视震源时间函数分析表明总体破裂方向既非东西也非南北,而且反演结果表明,两个断层上都发生了错动,总体破裂时间~50s,释放标量地震矩~8.11×1020 Nm.震源时间函数表现出多事件特征,且两个断层破裂的时间过程也不相同.破裂首先在南北向断层的南端开始,很快触发了东西向断层,最后终止于南北向断层的北端.每个断层都具有相当的时空复杂性,位错分布很不均匀.东西向断层具有三个凹凸体,一个位于震源附近,其他两个位于断层两端.南北向断层有两个凹凸体,均位于断层北段,最大滑动量~5.0m就出现在这里.发生最大位错的南北向断层延伸至阿拉斯加海沟,增加了触发阿拉斯加海沟其他断层发生破裂的可能性.
On January 23,2018,an MW7.9 earthquake occurred in the Gulf of Alaska,USA.As the inverted focal mechanism solution suggests,the event was mainly of strike-slip on steep faults which may run nearly from east to west or from north to south(the N-S fault and E-W fault).The early aftershocks don′t appear to be along a straight line.In this study,we determine the overall rupture direction by analyzing the apparent source time functions(ASTFs),and then,combining the direction with the pattern of the aftershocks,we build a double-fault model,with one crossing with the other,and obtain the tempo-spatial process by jointly inverting the P and SH waveform data.The analysis of the ASTFs shows that the overall rupture direction is neithernorth-to-south nor east-to-west,and the inverted results show,the two faults participate in the event,with a total duration of~50 sand a moment release of~8.11×1020 Nm.Multi-events can be recognized on the inverted source time function,and the two faults have different temporal processes.The rupture starts on southern end of the N-S fault,soon propagates on the E-W fault,and finally stops on northern end of the N-S fault.Each of the faults has quite tempospatial complexity,with highly heterogeneous slip on each of them.There are three slip asperities on the E-W fault,with one near the hypocenter while the others on two ends of the fault.There are two slip asperities on the N-S fault,with both of them on the northern end.Right here appears the maximal slip~5.0 m.The N-S fault stretches into the Gulf of Alaska,so the probability that other faults in this gulf are triggered is believed to have increased.
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