UTILIZATION OF MAGNETIC ANOMALY DATA FOR IDENTIFICATION OF FRACTURED GROUNDWATER AQUIFERS; A CASE STUDY FROM SUMBANG DISTRICT, BANYUMAS REGENCY, INDONESIA

Abstract

This study aims to interpret the distribution of fractured groundwater aquifers in volcanic rock complexes based on local magnetic anomaly data in Sumbang District, Banyumas Regency, Central Java, Indonesia. Geologically, the study area is dominated by lahar and lava deposits originating from Slamet Volcano. The target of the study is to obtain the potential of groundwater resources for irrigation water supply, thereby contributing to food security and agro-tourism development. Magnetic data acquisition was carried out at measurement points with a spatial resolution of 100 m, and produced 256 magnetic intensity data points throughout the study area. The magnetic data were processed through a series of corrections and reductions, resulting in local magnetic anomaly values ​​ranging from –3,089.49 – 1,502.98 nT. Reduction-to-equator (RTE) was applied to the local anomaly data to minimize dipole effects that can complicate interpretation. This procedure resulted in RTE local magnetic anomaly values​ ranging from –2,056.54 – 2,264.55 nT. Furthermore, horizontal gradient analysis was applied to the RTE local magnetic anomaly data to delineate the distribution pattern of fractured groundwater aquifers in the volcanic rock complexes. The calculated horizontal gradient values ranged from 0.24 – 22.72 nT/m. Maximum horizontal gradient values formed ridge-like patterns associated with suddenly changes in magnetization, which indicate lithological boundaries that may represent fractured aquifers. This interpretation is further supported by inversion modeling results, which reveal the presence of numerous fractures and cracks within the subsurface volcanic rock complexes.