Gravity-derived subsurface architecture and structural controls of the Terak and Keretak non-volcanic geothermal areas, central Bangka, Indonesia

Dwi Anggraeni; Ganesha Antarnusa

doi:10.58524/jograv.v1i2.176

Authors

Dwi Anggraeni Department of Physics, Institut Teknologi Sumatera Author
Ganesha Antarnusa Graduate School of Engineering, Gifu University Author

DOI:

https://doi.org/10.58524/jograv.v1i2.176

Keywords:

Satellite gravity, Non-volcanic geothermal, Subsurface structure, Gravity inversion, Central Bangka

Abstract

The Terak and Keretak geothermal areas in Central Bangka represent non-volcanic geothermal manifestations developed within a granitic and structurally deformed geological setting. This study investigates the subsurface density architecture and possible structural controls of these geothermal areas using satellite-derived gravity data. Free-air anomaly and elevation data were processed to obtain the Complete Bouguer Anomaly, followed by spectral analysis, regional–residual anomaly separation, two-dimensional forward modelling, and three-dimensional gravity inversion. The Complete Bouguer Anomaly ranges from approximately 23.7 to 40.9 mGal and shows distinct lateral gravity variations across the study area. Spectral analysis indicates two principal depth domains, with approximate boundaries at 2.7 and 6.8 km, interpreted as representing shallower residual and deeper regional gravity sources. The residual anomaly ranges from approximately −2.9 to 3.4 mGal, whereas the regional anomaly ranges from approximately 24.0 to 39.8 mGal. Two-dimensional and three-dimensional models indicate contrasting subsurface density domains that are consistent with Alluvium, the Tanjung Genting Formation, Klabat Granite, and the Pemali Complex. Higher-density domains are predominantly associated with granitic and basement-related materials, whereas lower-density zones correspond to shallower sedimentary units. The spatial correspondence between gravity gradients, interpreted structural boundaries, and the Terak and Keretak manifestations suggests that fault-related structures may influence subsurface fluid circulation. However, the gravity data primarily constrain density contrasts and structural geometry; therefore, the proposed radiogenic heat source and geothermal-fluid pathways should be regarded as a geological interpretation rather than direct evidence. These results provide a preliminary geophysical framework for understanding the subsurface architecture of the Terak and Keretak non-volcanic geothermal areas and for guiding future integrated geothermal investigations.

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