Rupture process of March 10, 2014, M(w)6. 9 Earthquake in the northwestern coast of California

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.