INVESTIGATION OF FOCAL MECHANISM AND FRACTAL DIMENSIONALONG THE SUMATRA-ANDAMAN SUBDUCTION ZONE

Abstract

The Sumatra–Andaman Subduction Zone (SASZ) is one of the most seismically active subduction zone which have generated continuously many great earthquakes. The main aim of this research is to investigate focal mechanism and fractal dimension including b value of the frequency-magnitude distribution model. Regarding to focal mechanism, this research focused on two seismotectonic setting which are (i) interplate, 0-50 km-depth and (ii) intraslab, 50-1,000 km-depth. Both settings reveal the mechanisms of fault as oblique and reverse faulting. The average dip angle of the thrust fault is around 45๐. In case of fractal dimension and b value, we analyzed both of spatial and temporal terms and divided two groups of seismicity data which are (i) before and (ii) after earthquake declustering process. The result of Dc in spatial and temporal term was estimated reached 2.0. It means that the seismic pattern is a plane source. . For the spatial distribution of b value, the lowest values are in the vicinity of Yangon and Sittwe, Myanmar and the offshore of Sumatra Island. In the temporal investigation at 6 locations of hazardous earthquakes, the b values are in the range of 0.91 – 0.36 and 0.79 – 0.56, respectively. In addition, all the Dc/b relationship of six specific events along the SASZ was defined as negative relationship.