Temporal variation characteristics of shear-wave splitting for the Rushan earthquake swarm of Shandong Province

The seismicity in Rushan region of Shandong Province is characterized by small swarms after the M_L3.8 Rushan earthquake on October 1, 2013, and this situation continues up to now. Four earthquakes with M_L4.7, M_L4.5, M_L4.1 and M_L5.0 occurred from January of 2014 to May of 2015 cause great social effects. Based on the seismic records from the Rushan station, this paper calculated the shear-wave splitting parameters of 224 small earthquakes of Rushan earthquake swarm. The result shows that the polarization direction of the fast shear-wave is consistent with the principal compressive stress direction of the Shandong peninsula; on the other hand, the time delay has obvious change before and after the four earthquakes, that is, it raised about one month and declined about twelve days before earthquake. All the characteristics can be taken as the precursor indicator for earthquake prediction based on stress.