Mapping of buried archaeological ruins using magnetic and gravity methods around the 17th-century fort of Gunong Biram, Aceh Besar, Indonesia
摘要
The integrated application of high-resolution gravity and magnetic methods has proven effective in detecting and mapping buried archaeological structures at the Gunong Biram Fortress site in Aceh Besar. The research aims to map subsurface archaeological structures and validate geophysical anomalies through targeted excavations. A CG-5 gravimeter and GSM-19 proton-precession magnetometer were deployed over ~ 5600–5900 m² with 2 m spacing inside the 28 × 28 m fort and 3 m outside. The Complete Bouguer anomaly ranges from 80.5 to 83 mGal, with low values (< 80 mGal) inside the fort, while higher values (> 82 mGal) and steep gradients appear along the southern and eastern edges, aligning with the cliffs formed by the Seulimeum fault. Total magnetic intensity ranges from − 600 to + 600 nT, with higher amplitudes near the preserved fort remains. To clarify the anomalies’ spatial distribution, we applied filters like derivatives, tilt angle, and analytic signal. These highlight edges and linear trends matching the fort-wall geometry and NW-SE trend. Euler deconvolution (SI = 0) shows that most sources cluster between 1 and 3 m in depth, with a few < 1 m, indicating shallow origins. Excavation of six trenches revealed column-like stone features, a buried wall parallel to the remains, and dispersed rubble aligned with the wall, within the upper meters and beyond the visible fort outline. The spatial correlation of anomaly patterns, Euler depths, and excavation results confirms extensive shallow masonry around the fort platform, highlighting the value of combining methods for archaeological prospection in active volcanic terrains.