“IDENTIFICATION OF SUBSURFACE ROCKS IN GEOTHERMAL AREA OF NORTH TAPANULI USING HORIZONTAL TO VERTICAL SPECTRAL RATIO METHOD”. EINSTEIN (e-Journal) 14, no. 1 (February 25, 2026): 47–55. Accessed April 24, 2026. https://jurnal.unimed.ac.id/2012/index.php/einsten/article/view/64966.