Comparative Study Of Changes In Stress Drop Of Earthquake Sequences Of JingGu M_s6.6 And Ludian M_s6.5

The stress drop values of the earthquakes about two sequences were calculated after taking away the effects due to regional earthquake anelastic attenuation,station site response accurately,noise and instrument response;using waveform data and seismic phase data of earthquake sequences of YunNan GingGu Ms 6.6 and LuDian Ms 6.5 that recorded by the station.These results show that the stress drop with magnitude increases within the scope of this study of magnitude.In order to eliminate the influence of the magnitude,this paper compared to the stress drop of earthquakes with the same magnitude range,it shows that the average value of stress drop in JingGu sequence is higher than LuDian earthquake sequence at the same magnitude range,this may be related to the stress state in different regions.In terms of the changes of time and space of stress drop,before the Ms 5.8 and Ms 5.9 strong aftershock,the stress drop is "slow down-turning up-maintain high value" after the mainshock of the GingGu 6.6 earthquake;meanwhile,almost all the stress drop abnormally high value is distributed around Ms 5.8 strong aftershock,it showed that stress environment in the region is increasing after a relatively short-term adjustment after the mainshock.And after Ms 5.9 strong aftershock,the stress drop rapidly decline to a relatively stable state,it shows that the regional tectonic stress get more fully release,its stress environment began to rapidly reduce,seismic activity tend to be over;For LuDian sequence without strong aftershock occurred,the average stress drop of the aftershocks is reduced by the average stress drop of the same magnitude of the earthquake in the JingGu earthquake sequence,at the same time,the stress drop of the aftershock sequence after the main earthquakes is almost no change in time.Compared with the characteristics of the mainshock energy release,it is inferred that the stress at the source is excessively release in the process of the main rupture,the subsequent stress in the region will gradually returned to normal after mainshock,which may have been one of the possible reasons for the aftershocks of the LuDian earthquake,which is obviously weaker aftershocks and there is no strong aftershocks in the follow-up.The Finally,considering the factors that may produce errors in the process of the calculation of stress drop,the reliability analysis of stress drop in this method,and analyze the actual effect on the calculation results.