Subsurface architecture of the Enggano forearc revealed by satellite gravity and integrated 2D–3D modeling

Dea Elfira Primasiwi; Ikah Ning Prasetyowati Permanasari; Rahmat Nawi Siregar

doi:10.58524/cesl.v1i2.173

Authors

Dea Elfira Primasiwi Department of Physics, Institut Teknologi Sumatera Author
Ikah Ning Prasetyowati Permanasari Department of Physics, Institut Teknologi Sumatera Author
Rahmat Nawi Siregar Department of Physics, Institut Teknologi Sumatera Author

DOI:

https://doi.org/10.58524/cesl.v1i2.173

Keywords:

Enggano Island, Satellite gravity, Bouguer anomaly, Gravity inversion, Subsurface structure, Sunda subduction zone

Abstract

Enggano Island is located within the forearc of the Sunda subduction system, where the Indo-Australian Plate converges obliquely beneath the Sunda Plate and generates high tectonic and seismic activity. This study investigates the subsurface architecture beneath Enggano Island using satellite-derived gravity data integrated with spectral analysis and two- and three-dimensional gravity modeling. Free-air anomaly and topographic data obtained from the TOPEX dataset were processed to derive the complete Bouguer anomaly, followed by separation of regional and residual gravity components. Spectral analysis was applied to estimate the characteristic depths of gravity sources, while 2D forward modeling and 3D inversion were used to constrain the geometry and density distribution of subsurface structures. The complete Bouguer anomaly ranges from 73.8 to 1350.8 mGal, with relatively high anomalies concentrated in the southwestern part of the study area and lower anomalies toward the eastern and southeastern sectors. Spectral analysis indicates characteristic source depths of approximately 10.35 km for the regional component and 5.98 km for the residual component. The 2D gravity model identifies a high-density oceanic crustal body of approximately 3.43 g/cm³ descending beneath a continental crustal domain with a density of approximately 2.67 g/cm³. The model also resolves the Kemiki, Kuwau, and Malakoni formations together with Quaternary alluvium beneath Enggano Island. Three-dimensional inversion further indicates that the high-density subducting structure becomes recognizable from approximately 4.05 km depth. These results demonstrate that satellite gravity data, combined with integrated 2D–3D modeling, can provide first-order constraints on the subsurface geometry of the Enggano forearc and its relation to the Sunda subduction system.

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