Mapping of active major faults in the Mamasa and surrounding areas using satellite gravity data and topographic features

Abstract

The mapping of active faults in Indonesia, especially in areas near the city center is very important to determine the building code. Mamasa Regency, West Sulawesi is one of the areas that have active faults, has not been mapped well in the 2017 seismic hazard book, which is a guidebook in creating building codes in Indonesia. A total of 762 earthquakes occurred in this area from November to December 2018. This study aims to map active faults associated with the source of these earthquakes. TOPEX satellite gravity data were processed to obtain the Complete Bouguer Anomaly. The residual and regional gravity values were separated using a Gaussian filter to identify the lineation of the fault and the existing fracture zone. The multiscale second vertical derivative was also implemented to identify and characterize the fault. Topographic contour mapping was carried out to confirm the presence of fault on the surface as well as to observe the direction of fault movement. We used seven focal mechanism data from Global CMT to support the interpretation result of gravity and topographic data. The result, the main fault is a sinistral strike-slip fault with N164E strike orientation. This strike-slip fault has two sides. The movement of the strike-slip fault on these two sides causes a pull-apart which results in normal faults in the pull zone between the two faults.