Analysis of Focal Mechanism of the Ning'er Earthquake Sequence

Using the data recorded by the Yunnan Digital Seismic Network,we calculate the focal mechanisms of the Ning'er MS6.2 main shock,the MS5.1 strong aftershock and other 51 aftershocks.The results show that the seismogenic fault was NW-ward and the dip angle was nearly vertical.The fault was right-lateral,strike-slip,which was effected by the nearly horizontal,principal,NS-ward compressive stress.The main shock,strong aftershock and some aftershocks occurred on the same seismogenic fault.The focal mechanism of many aftershocks were consistent with the main shock's,which were the main types of the earthquake sequence.The dip-slip aftershocks inconsistent with the main shock showed the adjustment process of the stress field of the focal region,whereas the nearly horizontal press axes were consistent with the main shock.Because of the right-lateral,strike-slip of the NW-ward fault,the reverse aftershocks occurred in the pressing quadrant while the normal quakes occurred in tensional quadrant.The focal mechanism was consistent with those of other four earthquakes with MS≥5.0 around the Ning'er earthquake stricken area,which showed the consistency in the focal region stress field and regional stress field,and the genesis and occurrence of the Ning'er earthquake were controlled by the regional stress field.