2016年1月21日青海门源M_s6.4余震序列重定位和主震震源机制解

Relocation of the aftershock sequence and focal mechanism solutions of the 21 January 2016 Menyuan,Qinghai,M_s6.4 earthquake

2016年1月21日01时13分13.0秒(北京时间),青海省海北州门源县发生M_s6.4地震.为了更好地认识这次地震的发震构造,本文利用青海省地震台网和甘肃省地震台网的省级固定地震台站及部分流动地震台站记录到的波形资料,通过重新拾取震相和联合HYPOINVERSE 2000与HypoDD定位方法,对2016年1月21日青海门源地震序列M_L≥1.8的189个地震事件进行了重新定位,并采用gCAP方法分别反演了主震的双力偶机制解和全矩张量解.定位结果显示,主震位置为37.67°N、101.61°E,震源深度为11.98 km;余震序列展布方向为SE和NW两个方向、长度约16 km,震源深度优势分布为4~14 km,断层面倾向为SW方向.利用gCAP方法得到的矩心深度在8~9 km之间.结合野外地质调查结果,认为该次地震事件为一次逆冲型事件,其发震断层可能为北西向冷龙岭断裂与北西向民乐一大马营断裂之间的一条盲断层,推测由于印度板块与欧亚板块的碰撞挤压使得青藏高原北缘与阿拉善地块之间的东西向挤压而造成的断层应力失稳,从而形成门源地震.

An MS6.4 earthquake attacked Menyuan County, Qinghai Province at 01：13：13.0 （Beijing time） on 21 January 2016. In order to better understand the mechanism of this earthquake, we collected seismic waveform data recorded by the Qinghai and Gansu permanent seismic stations and some temporary seismic stations, and re-picked the arrival times of seismic phases. Applying the HYPOINVERSE 2000 and HypoDD algorithms, we relocated 189 aftershocks （ML≥1.8） of this event. We obtained the source mechanism solutions and full moment tensor solutions of the mainshock using the gCAP method. Our relocation results show that the mainshock is located at 37.67°N, 101.61°E with a focal depth 11.98 km, and its aftershocks extend a length about 16 km, and their focal depths range from 4 to 14 km. The spatial distribution of aftershocks demonstrates a southeast and northwest strike and the fault plane dips southwestward. The centroid depth inferred using the gCAP method is 8-9 km. Integrating with geological data, it is suggested that the mainshock is a thrusting event. The seismogenic fault may be a blind one that exists between the NW-SE trending Lenglongling and Minle-Damaying faults. It is assumed that this earthquake may be due to the instability of fault stress resulting from the eastward extrusion of the northern margin of the Tibetan plateau toward the Alxa block associated with the Indo-Eurasian plate collision.