Descriptions of reservoir basin subsurface structure in UNNES based on microgravity data

Abstract

UNNES reservoir basin as a characteristic of the Conservation University is around 12 years old. This relatively long span of time has never been carried out a physical study of a subsurface structure. This study aims to describe the subsurface layer based on gravity data. The method used is to use gravity by calculating the elevation of each measuring point and by tidal correction and drift correction. Both of these corrections are to reduce the tidal and fatigue effects of the gravimeter. Measurements were done in July 2019 (dry season). The results of the study based on observational gravity data indicate that the value of a large gravity is in the north-south part and the smallest value is in the west part of the reservoir basin. The structure of the first layer which has an average density of 2.7 g/cm3 thick 75 m below the surface. The second layer is dominated by andesite rock with an average rock density of 2.8 g/cm3 thick 50 m below the first layer. While the lowest layer is a layer dominated by basalt rock with an average rock density of 3.1 g/cm3 thick more than 40 m below second layer.