| Summary: | 碩士 === 國立成功大學 === 地球科學系專班 === 100 === This study investigated the spatial and temporal stress variations before and after a large earthquake, respectively, 1999 Chi-Chi earthquake and 2011 Tohoku earthquake. For the Chi-Chi earthquake, according to the 7126 focal mechanism solutions from March 1991 to October 2010, we selected seven regions in the Chi-Chi earthquake source area and analyzed stress inversion for different periods. The first period started from 1991 to the time right before Chi-Chi. According to the changes of P axis or T axis, the second period ranged from 43 to 116 days. The end of the second period to 2010 is third period. We analyzed P and T axe of the focal mechanism solutions in the spatial and temporal sequences. Stress inversion results are divided into three periods. The stress inversion results between the various regions are due to different geological structure and earthquake mechanisms. For the Tohoku earthquake, we selected 8269 focal mechanism solutions from February 1997 to March 2012. We used the same approach as the Chi-Chi event to the eight regions of the Tohoku earthquake and analyzed stress inversion for different periods. The first period started from 1997 to pre-Tohoku. According to the changes of P axis or T axis values, the second period ranged from 95 to 263 days. The end of the second period to March 2010 is the third period. The results show that Taiwan and Japan after a large earthquake, their stress behaviors have a similar performance. In addition, since the Chi-Chi earthquake, there are three regions had returned to the state of stress before the earthquake and three other regions are in the ongoing stress accumulation process. Comparison of the behavior of the stress after the earthquakes of Chi-Chi and Tohoku, we find that the stress release process is affected by both the magnitude of the mainshock and the distance from the source.
|
|---|
