Subsurface Structure of Singkarak Pull Apart Inferred from Magnetic and Gravity Modeling

Abstract

The existence of active faults along the Sumatran fault has an impact on tectonic activities such as earthquakes and the formation of pull-apart along the Great Sumatran Fault (GSF). The Great Sumatran Fault is segmented into 19 segments. Fourteen segments of which are pull-apart. One of the pull-apart amongofthe GSF is the Singkarak pull-apart which is located on the Sumani segment. Magnetic and gravitational methods are appropriate geophysical methods used to determine rock structures below the earth’s surface. The subsurface structure of the Singkarak pull-apart analysis needed to identify potential future basins. Based on the analysis of the low magnetic anomaly closures on both sides of Lake Singkarak, this study has also succeeded in identifying the presence of a less dense Quaternary Coluvium volcanic deposition outcrop and concluded that the displacement of about 18± 3 km was resulted from a strike-slip process in the past. Furthermore, Lake Singkarak is estimated to have experienced an opening as far as 8 ±1 km which is based on the maximum width of the model profile that passes through the middle of Lake Singkarak.