关键词: 米林M6.9地震, 破裂模型, 接收断层, 静态库伦破裂应力变化, 墨脱M6.3地震

Abstract: Based on the rupture model of Mainling M6.9 earthquake in Tibet on November 18, 2017, the spatial distribution of static Coulomb failure stress change at different depths are calculated respectively according to two different receiving fault selection schemes. The one scheme is that we set the parameters of receiving fault at different position to be consistent with the main shock; The other scheme is on the assumption that fault's orientation is randomly distributed under the ground, and we select the receiving fault which is most prone to slide under the influence of coseismic stress field produced by main shock. Therefore, the geometrical orientation of receiving fault will vary with space. According to the above two results of static Coulomb failure stress change, we discussed the static Coulomb stress influence produced by the main shock to short-term aftershocks and the Medog M6.3 earthquake in Tibet on April 24, 2019, respectively. The result shows that: 1)When the parameters of receiving fault are same with the main shock, the proportion of aftershocks in the positive zone of static Coulomb failure stress change is small at each depth. The focal mechanisms of aftershocks in the positive zone of static coulomb fracture stress are deemed similar to the main shock. We thought that they are motivated by the continuous rupture of the main shock. 2)Most of the aftershocks are in the negative zone of static Coulomb failure stress change at each depth. We inferred that this phenomenon which may be on account of the focal mechanisms of these aftershocks is quite different with the main shock. From the result of receiving fault to choose the most prone to slide under the coseismic stress field produced by main shock, we can clearly see that all the aftershocks are within the zone of static Coulomb failure stress change greater than the trigger threshold of 0.01MPa at different depths. It indicates that all the aftershocks are likely to be triggered. It was speculated that the aftershocks in the negative zone of static Coulomb failure stress change occurred in the crushed zone caused by violent rupture of the main shock. There are countless cracks in the crushed zone, and the orientation of these cracks is abundant. Perhaps, because most aftershocks occurred on these various cracks, their focal mechanisms are quite different from the main shock. The value of elastic constants will be reduced significantly in the crushed zone. All the results in this paper also indicate that considering the elastic constants difference between in and out of the source region is beneficial to accurately estimate the static Coulomb stress influence between earthquakes in the source region. 3)Different institutes and authors used different data and methods to get several different focal mechanisms of the Medog earthquake. According to these results, we calculated a central focal mechanism solution, which has a minimum difference with these focal mechanisms. On the basis of this central focal mechanism solution, the static Coulomb stress influence of the Mainling earthquake to the Medog earthquake is calculated quantitatively. Result indicates that the magnitude of static Coulomb failure stress change generated by the Mainling earthquake is quite small on both two nodal planes of the central focal mechanism solution of the Medog earthquake, this means that the Medog earthquake is independent of the Mainling earthquake.

Key words: Mainling M6.9 earthquake, rupture model, receiving fault, static Coulomb failure stress change, Medog M6.3 earthquake