STRESS CONCENTRATION PHENOMENON BEFORE THE 2011 M9.0 TOHOKU-OKI EARTHQUAKE: ITS IMPLICATION FOR EARTHQUAKE PREDICTION

Abstract:

According to rock mechanics, there exists a stage of stress accumulation before final failure, this kind of stage also exists in the seismogenic process, but this kind of stage always hide behind the vast seismicity data . There are 5 large eartquakes (M>7.0) , generalized foreshocks, occurred in the source region of M9.0 Tohoku-Oki Earthquake from 2003 to 2011, and they formed a very narrow belt, which is nearly perpendicular to the strike of the Japan Trench. We performed temporal and spatial analysis to the stresses before and after the mainshock from static stress change and focal mechanism solutions. We derived a tectonic stress field model in the vicinity of the source area of the M9.0 North-eastern Japan Earthquake from modeling seismicity and analyzing earthquake focal mechanisms before and after the mainshock. The results show that the stress field in source region barely had any change before and after each large earthquake prior to the M9.0 mainshock. The stress state did not change in the places where are distant away from the rupture center of the M9.0 mainshock during its occurrence, with the azimuth of the maximum principal stress to be 290º, which is perpendicular to the strike of the Japan trench, and dip angle to be 19º. In comparison, the static stress has significant change in the central part of the source region after mainshock, with the occurrence of numerous normal fault type events. There exists an area with negative stress change in the source area of the M9.0 earthquake after the mainshock, with the P axis rotated from horizontal to vertical, which are responsible for numerous normal faulting events, where was dominated by thrust faulting prior to the mainshock. This pattern indicates a complete stress and strain release or locally stresses regime change. Our results provide a constrain to the stress accumulation- release pattern spatially and temporally for the source region of 2011 Tohoku-Oki earthquake. We suggested that the seismicity pattern, may provide some valuable information on the stages of stress accumulation, and thus may be used for estimation of earthquake risk.

KEYWORDS

Source Region, Stress Change, 2011 Tohoku Earthquake, Earthquake Prediction.