Relationship between regional seismic activity and strong earthquake based on the region-time-length algorithm

Taking Wenchuan M_S8.0, Yutian M_S7.3, Lushan M_S7.0, Ludian M_S6.5 and Jinggu M_S6.6 earthquakes as examples, the relationship between spatial anomaly distribution of seismic activities and earthquakes occurrence location was analyzed based on the region-time-length (RTL) algorithm. And the relationship between regional seismic activity and earthquake occurrence time based on the new physical parameter I_RTL which was the surface integral in respect to region-time-length was explored. The results show that seismic quie-scence was detected prior to the three strong earthquakes with M_S≥7.0, and an enhancement of seismic activity was detected before the two M_S>6.0 earthquakes. Spatial anomalies of the above seismic quiescence and enhancement were mainly distributed in the potential causative fault and its surrounding areas near the epicenters. The range and degree of anomalies chronologically changed from small to large, and then to small again. During 1--3 years prior to the earthquakes with M_S≥7.0, I_RTL decreased from the zero value; and when falling to the lowest value, it rebounded. The time length from the lowest point of I_RTL curve to the earthquake occurrence was 9--18 months. Before the Ludian M_S6.5 and Jinggu M_S6.6 earthquakes, I_RTL curve began to increase from the lowest point 1 year and 1.8 years separately, and then reduced after reaching the peak point. The time length from the peak points of I_RTL curve to the earthquakes occurrence were three and nine months for the Ludian and Jinggu earthquakes, respectively. Therefore it is deduced that the lowest point of I_RTL curve in the stage of seismic quiescence and the peak point of I_RTL curve in the stage of enhanced activity may be indicators of earthquake occurrence.