Research On Aftershock Frequency Based On The Coseismic Coulomb Stress Changes

This paper is mainly about the “direct” aftershock frequency distributionestimation based on static coseismic coulomb stress changes, combining the rate andstate dependent friction law.The results show:1. The effect time of the coulomb stress changes on aftershock activity isassociated with the lower magnitude, which is about15~16months for the aftershocksabove ML4,and close to60months for that above ML3.5.2. The forecast result is lower than the true significantly in the main fracture zone,especially the south of the fracture, because of the decrease of the calculatedcoseismic coulomb stress change.3. In this period, the ratio of the "direct" aftershocks caused by coseismic coulombstress changes lies between44.7%to48.6%, which suggests that, even in the"effective" period of coseismic coulomb stress changes, there is about half of theaftershocks is independent of the coseismic coulomb stress changes in the fracturezone of the mainshock.4. The impact of the model parameters are discussed systemly.The ’value and bvalue are positive correlation with the calculated aftershock number. The simulatedaftershocks number with large parameter values lead to higher values, while the trendof aftershocks spatial distribution stay the same. The rational selection of relatedparameters is necessary for good results.Compared with the previous similar studies, the progress of this essay is findinga new method from abroad, that using the coseismic coulomb stress changes explainthe aftershock spatial distribution quantitatively. Further more, we use the geologicaldata as the receiver fault to calculate the coseismic coulomb stress changes firstly.The significance of this research is that it provides a degree of "predict" ability.