An earthquake with MS5.8 occurred on 10 March 2011 in Yingjiang county,western Yunnan,China.This earthquake caused 25 deaths and over 250 injuries.In order to better understand the seismotectonics in the region,we collected the arrival time data from the Yunnan seismic observational bulletins during 1 January to 25 March 2011,and precisely hand-picked the arrival times from high-quality seismograms that were recorded by the temporary seismic stations deployed by our Institute of Crustal Dynamics,China Earthquake Administration.Using these arrival times,we relocated all the earthquakes including the Yingjiang mainshock and its aftershocks using the double-difference relocation algorithm.Our results show that the relocated earthquakes dominantly occurred along the ENE direction and formed an upside-down bow-shaped structure in depth.It is also observed that after the Yingjiang mainshock,some aftershocks extended toward the SSE over about 10 km.These results may indicate that the Yingjiang mainshock ruptured a conjugate fault system consisting of the ENE trending Da Yingjiang fault and a SSE trending blind fault.Such structural features could contribute to severely seismic hazards during the moderate-size Yingjiang earthquake.
In this paper,we focus on the influences of various parameters in the niching genetic algorithm inversion procedure on the results,such as various objective functions,the number of the models in each subpopulation,and the critical separation radius.The frequency–waveform integration(F–K) method is applied to synthesize three-component waveform data with noise in various epicentral distances and azimuths.Our results show that if we use a zero-th-lag cross-correlation function,then we will obtain the model with a faster convergence and a higher precision than other objective functions.The number of models in each subpopulation has a great influence on the rate of convergence and computation time,suggesting that it should be obtained through tests in practical problems.The critical separation radius should be determined carefully because it directly affects the multiextreme values in the inversion.We also compare the inverted results from full-band waveform data and surfacewave frequency-band(0.02–0.1 Hz) data,and find that the latter is relatively poorer but still has a higher precision,suggesting that surface-wave frequency-band data can also be used to invert for the crustal structure.
