S11A-2747
Seismological Segmentation of Halmahera Thrust, Molucca Sea Region, based on Large Earthquake Sequences
Monday, 14 December 2015
Poster Hall (Moscone South)
Hasbi Ash Shiddiqi1, Sri Widiyantoro2, Andri D Nugraha2, Mohamad Ramdhan3, Samsul H. Wiyono3 and Wandono Wandono3, (1)Earth Sciences Graduate Program, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Indonesia, Bandung, Indonesia, (2)Bandung Institute of Technology, Global Geophysics Research Group, Bandung, Indonesia, (3)Agency for Meteorology, Climatology and Geophysics (BMKG), Jakarta, Indonesia, Jakarta, Indonesia
Abstract:
The Molucca Sea region in eastern Indonesia is a complex tectonic region, where the arc-arc collision between the Sangihe and Halmahera arcs takes place. Two recent largest earthquakes occurred in this area are Mw 7.5, January 2007, and Mw 7.2, November 2014, that occurred 90 km to the north from the 2007 earthquake site. Both earthquakes occurred along the Halmahera thrust, however, the aftershock of the two events occurred in separated parts of the same fault. In this study, we aim to investigate the segmentation of the seismogenic zone in Molucca Sea by using seismological analysis. We employed teleseismic double-difference relocation using P- and S-wave arrival times from the Meteorological, Climatological, and Geophysical Agency of Indonesia (BMKG) and the International Seismological Centre (ISC) catalog. We used a 3D velocity model for the Indonesian region. Our relocation result revealed that aftershocks of the two events did not overlap each other. Although they have similar focal mechanisms with NNE-SSW direction, the aftershock patterns were different. While the 2014 event aftershock distribution is consistent with the strike direction inferred from the focal mechanism, the 2007 event aftershocks occurred in NEE-SWW direction. Furthermore we analyzed the spatial variation in b-value for different time ranges. The b-value analysis also showed two separated segments of low b-value anomaly around both events for each time range. We envisage that stress regime directions and geometries of the fault are different for both aftershock clusters. For this reason we analyzed focal mechanism data and found that fault segment around the 2014 event is steeper than that related to the 2007 event. We applied focal mechanism inversion to obtain the direction of stress and fault orientation, and found different stress directions for the two segments. While the northern part segment has maximum stress with SSE direction, the stress in the southern part is rotated in SE direction. We concluded that the central part of Molucca Sea has been segmented as indicated by the difference in the stress direction and fault geometry.
