Exploring Subsurface Layers in Beruang Kanan Main using Passive Seismic HVSR Survey

A preliminary geophysical survey was conducted at Beruang Kanan Main (BKM) project, Central Kalimantan, Indonesia, using the Passive Seismic Horizontal-to-Vertical Spectral Ratio (HVSR) method. This survey proved to be a cost-effective, time-efficient, and labor-saving approach for large-scale exploration. The objective of the survey was to estimate bedrock depth and characterize geological features in the area to support the planning and development of mineral processing infrastructure. Various H/V peaks observed indicated a complex impedance contrast, reflecting the stratigraphic layers beneath the surface. In addition to estimating the bedrock depth, features such as paleochannels and potential faults were inferred, which are suggested to be verified through geologic mapping. By combining all the HVSR sections and a calibrated velocity of 200 m/s from limited drillhole information, a bedrock interface model was generated, showing that the bedrock was shallower in the southern part of BKM compared to the north, where a thicker regolith layer was present. Complementary drillhole data and HVSR measurements from nearby stations supported the reliability of the survey. However, to improve the depth conversion from HVSR data and enhance the accuracy of the model, more extensive drillhole data is recommended. This would allow for a more refined interpretation of subsurface structure.