3D gravity data inversion modeling for subsurface identification of Gondang area, Bojonegoro regency

Abstract

Gondang area had experienced an earthquake of a 4.2 magnitude in the mid-2015, showing that tectonics in the area are active. Also, the Gondang area has a mountain categorized as one of the eleven earth thermal prospects in East Java, i.e., Pandan Mountain. It is exciting to study the subsurface structures of the Gondang area. To date, precedent studies only present geological reviews of the surface. This study presents information on subsurface structure conditions based on gravity. The technique used was 3D inversion modeling with Single Value Decomposition (SVD) inversion. The study ' s primary data were gravity data from 61 points with a study area of 6.9 km x 5.5 km from 3-10 September 2019. Secondary data utilized were Bojonegoro geological map and local geological studies. From 3D modeling results, slicing was conducted for five cross-sections based on density contrast. Then, the subsurface 2D cross-section results were interpreted for each section. Subsurface model results illustrated density distributions in south, northeast, and northwest areas with high densities ranging from 2.8 g/cc to 3.0 g/cc in >500 m depths. Meanwhile, the north, southwest, and southeast areas had low densities ranging from 1.70 g/cc to 2.0 g/cc in >500 m depths. Furthermore, it indicates the continuity of andesite intrusion from the south to the study site in >500 m depths.