Analysis of gravity anomaly for groundwater basin in Bandar Lampung city based on 2D gravity modeling

Abstract

The research aims to delineate the groundwater basin in Bandar Lampung from gravity anomaly. Field data acquisition was carried out at 403 points with a spacing of 2-3 km, covering the Bandar Lampung and surrounding areas. Data processing through gravity data corrections, namely drift, tide, Free Air, Bouguer and Terrain using Geosoft Oasis Montaj 8.3. The Bouguer density used is 2.67 gr/cm3. For the anomaly separation, spectrum analysis and regional and residual anomaly separation were carried out, whereas 2D modeling was carried out by forward modeling. This basin boundary analysis is based on gravity residual anomaly patterns, gravity Second Vertical Derivative (SVD) analysis, and 2D gravity modeling. There are two low residual anomaly patterns (-22 to -5 mGal), where the boundaries of the basin can be clearly delineated from SVD analysis. This 2D model shows layers with a density of 2.3 gr/cm3 which are the Young Volcano Formation (Qhv) and the Lampung Formation (QTl) which have depths of up to 1.0-1.5 km. This Groundwater Basin correlates well with the hydrological pattern with a water discharge of 5 to 100 l/sec.