2016年11月13日新西兰南岛M_(W)7.8地震的同震粘滑震相研究

The study of the co-seismic stick-slip phase of the M_(W)7.8 earthquake in the South Island,New Zealand on 13 November 2016

实验室内的岩石粘滑错动实验表明,粘滑错动过程一般可分为预滑、粘滑和止滑3个阶段,且往往不是一次、单点错动,而是由多次、多点粘滑错动组成,表现为在断层的不同部位、不同时间、多点、多次粘滑错动的特征。在天然地震观测中,破裂前的预滑过程激发出的信号较弱,一般不易被观测到。但破裂后的同震粘滑和止滑过程激发出的信号较强,容易被观测到。2016年11月13日新西兰南岛发生M_(W)7.8地震后,全球数字地震仪台网(GSN)中的100个台记录到同震粘滑过程激发出的粘滑震相Xs和止滑过程激发出的长周期勒夫型面波XsQ和长周期瑞雷型面波XsR。观测结果表明,此次地震在破裂开始后的同震粘滑错动过程由4次较大的子粘滑事件构成。据此认为,M_(W)7.8地震是断层粘滑错动和弹性破裂共同作用的结果,是一种粘滑错动+弹性破裂的机制。还给出4个子粘滑震相P+Xs1、Xs2、Xs3和Xs4以及止滑面波震相XsQ和XsR的走时关系。在地震记录图上识别出粘滑震相Xs,有助于认识地震的粘滑错动过程,识别出止滑震相XsQ和XsR,有助于预判地震次生灾害。

The results of rock stick-slip dislocation experiments in the laboratory show that one stick-slip dislocation process includes three stages generally pre-slip stage,stick-slip stage,and stop-slip stage.Usually,a stick-slip dislocation process is not a one-time single-point process;instead,it is composed of multi-time and multi-point stick-slip dislocation processes,showing the characteristic of multi-time and multi-point stick-slip dislocation in the different parts of a fault.A strong earthquake of magnitude M_(W)7.8 occurred at the South Island,New Zealand,on 13 November 2016.The pre-slip phase is too weak to be recorded well,but the co-seismic stick-slip dislocation phase and stop-slip phase are stronger and recorded perfectly by the digital seismographs of the Global Seismographic Network(GSN).We analyzed the recordings of 100 stations of GSN.We identified co-seismic stick-slip dislocation phase Xs,stop-slip phase XsQ and XsR.According to this result,we infer that the M_(W)7.8 earthquake mainly consists of 4 sub-stick-slip dislocation events.The four times of sub-stick-slip dislocation events took place during the process of stick-slip dislocation during the main earthquake.Hence,the M_(W)7.8 earthquake may be a result of the stick-slip dislocation of the fault and elastic failure.It is a mechanism of“stick-slip dislocation+elastic failure”.The XsQ phase and XsR phase are long-period surface wave phases that may be excited by the stop-slip process.The travel time relationships of P+Xs1,Xs2,Xs3,Xs4,Xsm,XsQ,and XsR phases are given.Identifying the Xs phase from seismic recordings will be helpful for understanding the process of stick-slip dislocation of main earthquakes.Identifying the XsQ and XsR phases will be helpful for judging disaster loss of great earthquakes.