Delineation Of Potential Groundwater Aquifers Using Microtremor HVSR And Two And Three-Dimensional Subsurface Modelling In Gejayan, Banyusidi, Magelang, Central Java, Indonesia

Abstract

Groundwater availability is strongly controlled by subsurface lithology, porosity, permeability, and groundwater saturation. Delineating potential aquifer zones is therefore important for identifying suitable locations for groundwater development, particularly where direct subsurface information is limited. This study investigates the distribution and depth of potential groundwater aquifers in Gejayan, Banyusidi, Pakis, Magelang, Central Java, Indonesia, using the microtremor Horizontal-to-Vertical Spectral Ratio (HVSR) method. Thirty microtremor observation stations were distributed across the study area, with surface elevations ranging from 979 to 1010 m above sea level. HVSR-derived subsurface parameters were interpreted using two-dimensional profiles and three-dimensional models of shear-wave velocity and Poisson's ratio. The three-dimensional model indicates two principal potential aquifer trends along stations 6–10 and 26–30. Two-dimensional analysis provides a more detailed delineation of these zones. The first potential aquifer occurs beneath station 9 at an estimated depth of approximately 40 m and can be traced downward to approximately 60 m, whereas the second potential aquifer occurs beneath station 27 at approximately 30–40 m depth. Both zones are interpreted as potential unconfined aquifers. The results demonstrate that integrating microtremor-derived elastic parameters with two- and three-dimensional modelling can provide an efficient preliminary approach for groundwater exploration. However, the inferred aquifer zones should be validated using geoelectrical, well, drilling, or hydrogeological data before groundwater development.