3D inversion modelling of gravity and geomagnetic in the coastal aquifer of the Mandalika Lombok

Coastal aquifers are essential for coastal communities worldwide, one of which is in the Mandalika area (Lombok Island, Indonesia). This area is the tourism sector which requires an adequate supply of fresh water. Mandalika is a coastal area dominated by alluvial plains, an excellent rock as an aquifer. However, alluvial plains are also susceptible to seawater intrusion. This study uses a combination of gravity and geomagnetic methods to estimate bedrock potential as aquifers based on a 3D inversion model. Data collection was carried out at 151 measuring points using the loop method. Data processing was conducted using Oasis Montaj, Mag3D, and Grav3D. The data were combined to reduce ambiguity in interpreting rock-type estimates. The modelling results show that aquifer composition consists of sandstone, clay, and gravel with a density of about (1.3 - 2.4) g/cm3, susceptibility (0.00040 - 0.0045) SI at an average depth of 2 - 12 m with a percentage of 54.849% of the total 3D models. These rocks dominate the research location scattered around the coastal area of Kuta, around the Circuit to the Mertak area, and are concentrated in the flat morphology areas.