"seismic Static Stress Triggering The Problem

"Static stress triggering" problem currently is one of the controversy questions in seismic circles. Lots of seismologists claimed that Coulomb stress change produced by earthquake can affect occurrence of subsequent rupture, but there are some violational earthquake examples. And also research on these earthquake examples cannot be systematic. So it's necessary to do some research on "static stress triggering" problem systematically and deeply.In the discussion of "static stress triggering" problem, based on the relationship between the occurred earthquake and "triggered" earthquake, the researches at present can be roughly divided into 3 categories: (1) aftershocks triggered by mainshock; (2) the strong earthquakes triggered by other strong earthquakes; (3) earthquakes triggered by volcano or explosion. The research work of this paper belongs to the second category. Our research on "static stress triggering" emphasizes particularly on two basic questions: firstly, how systematically is applicability of "static stress triggering model" according to a great deal of seismic data, and secondly what kinds of problem need to be solved when "static stress triggering model" is applied to China and its adjacent earthquakes.First of all, we give a research of specific earthquake examples on "stress triggering" relationship between different rupture subevent in one complex earthquake. All these earthquake examples have complex rupture process. As approximation, each earthquake can be described as two or more subevents of rupture with short time interval(several seconds to several days). In recent years, as the development of digital seismology, exact epicenter and seismic mechanism can be obtained. This development provides fundamental data for our research. In order to discuss the relationship between different subevents, we've calculated the static stress changes produced by the first event on fault plane and slip direction of the second event in Xintai, Tangshan, Lancang-Gengma, Gonghe and Lijiang earthquakes. The result suggests that except for Lancang-Gengmaearthquake, the static Coulomb stress changes produced by the first subevents of all the above earthquakes have "triggering" effect on the subsequent subevents which locate in the region where the Coulomb stress change produced by the first event is positive. Or we can say the static Coulomb stress change produced by the first rupture is "in favor of" the occurrence of the second event.We give "static stress triggering model" a test using Harvard CMT seismic catalog from 1976 to 2000. Coulomb failure stress changes(ACF5") produced by former earthquake on fault plane and slip direction of latter earthquake have been calculated. We found that the number of earthquake doublets with positive CFS change is more than that of negative CFS change. The results indicate that the previous events in shallow earthquake doublets do have "triggering" effect on the following event, but the effect is very weak. According to Frohlich(1992), all earthquakes were divided into normal fault, thrust fault, strike-slip fault and odd fault earthquakes, and CFS changes have been calculated. Result shows that "static stress triggering" effect of non-strike-slip fault earthquake doublets is significant, but "triggering" effect on strike-slip fault earthquake doublets is very weak. This indicates that seismic mechanism has great effect on "static stress triggering". Five delayed time scales of more than one day, less than one day, more than 10 days, less than 10 days and between 1 day and 10 days are divided and the static CFS changes are calculated respectively. The result shows "seismic stress triggering" effect doesn't change as delay time changes in short time after earthquakes. The research on earthquake doublets of different tectonic zones shows that triggering effect of subduction earthquake doublets is significant. The result of seismic "static stress triggering effect" is independent of earth tide has been obtained. The CFS changes produced by former ruptures o...