On Uncertainty Of Static Coulomb Stress Change Triggering And Its Application

Static Coulomb stress change induced by earthquake slip is used frequently to explain earthquake activities and aftershocks distribution. However, some parameters for the Coulomb stress calculation are unable to be well constrained from laboratory experiments and field observations. Different parameters may directly affect the calculation results of static Coulomb stress. Therefore, it is necessary to do a more comprehensive study on the uncertainty and application of static Coulomb stress change triggering.To investigate uncertainty of static Coulomb stress change induced by earthquake, this study takes the well-studied Wenchuan earthquake as an example. We first build the receiver fault matrices of the study area, with smooth interpolation of fault geometry and rake between the Sichuan and Yunnan`s major active faults data, and take the matrices as a projection plane. Then we calculate the 2D image of static Coulomb stress change of the study areas as a basic model to compare and analysis. To investigate how the parameters affect the calculation results, we change the parameters in turn through modeling and directly compare the results of different calculation parameters. We find that gravity, receiver faults position and strike have little influence on coseismic Coulomb stress change calculation, but other parameters can change the value and sign of the results in various degrees especially around the earthquake rupture plane. Therefore the uncertainty of the static Coulomb stress change induced by earthquake should be taken into consideration in the earthquake hazard analysis.To analyze the influence of the static Coulomb stress change induced by the main shocks on the aftershock distribution, we adopt two ways for quantifying the static Coulomb stress change induced by Wenchuan earthquake associated to its aftershock distribution. We first calculate the static Coulomb stress change on the optimally oriented receiver fault plane; then further calculate the static Coulomb stress change on each aftershock nodal planes with different slip model and apparent fault friction. Through counting the proportion of aftershocks in the stress increased areas to the whole, we find that more than half of the aftershocks were triggered by static Coulomb stress change induced by the main shock with maximum triggered rate 84%. The triggered rate is proportional to the apparent fault friction, which is consistent with the Wenchuan earthquake`s thrust mechanism that usually accompanies with a large apparent friction value.Using the Coulomb stress change as a fast output tool, we compute the Coulomb stress change induced by the 14 April 2010 Ms7.1 Yushu earthquake on optimally oriented faults and its neighborhood faults. Our result shows that the Coulomb stress has increased on the northwest and southeast end of the rapture fault. The earthquake also increased on the northwest and southeast of Ganzi-Yushu, Ziga temple-Deqin, the central segment of Qingshuihe, Zayun-Chumaer, Zhalaqu-Zhexiao and the northwest of Zaduo-Shanglaxiu fault. The calculation results can help to refine the seismic hazard analysis of the region.