Integrated Gravity–Seismicity Approach to Fault Mapping in the Suoh Depression, Sumatra

Abstract

Suoh Depression (West Lampung, southern Sumatra) is an active volcanic basin along the Great Sumatran Fault (GSF), characterized by high seismicity and active geothermal manifestations. This study integrates satellite gravity data and regional seismicity to delineate the subsurface fault architecture that controls deformation in Suoh. We used 3,098 gravity points from the GGMPlus model and topographic information from the 30 m SRTM DEM. Earthquake data were compiled from the BMKG catalogue (1900–2024). Gravity processing included calculation of the complete Bouguer anomaly (CBA), separation of regional and residual components, and application of edge-enhancement filters such as horizontal gradients and second vertical derivatives. 2-D forward modelling and 3-D density inversion were subsequently conducted to resolve the geometry of the major fault strands. Seismicity was analyzed to validate gravity-derived structures and identify active segments. The CBA varies from ~35 to ~85 mGal, reflecting major density contrasts across the Suoh basin. The West and East Semangko Faults are the two main strands of the Semangko segment, as shown by derivative maps and inversion results. Additionally, there is a local Penetoh Fault that strikes northwest and extends to a depth of about 6 km. Earthquake clusters coincide with these structures, confirming their current activity. These findings demonstrate that Suoh is an actively deforming pull-apart depression governed by strike-slip kinematics. The updated fault configuration provides critical inputs for seismic-hazard mitigation, geothermal assessment, and land-use planning in West Lampung.