Horizontal Gradient Analysis for Gravity and Magnetic Data Beneath Gedongsongo Geothermal Manifestations, Ungaran, Indonesia

Abstract

Ungaran Volcano is one of geothermal prospect in the province of Central Java, Indonesia. The main manifestations is located at Gedongsongo area which is appear of fumarole, hot spring and altered zone. The study area was covered by gravity and magnetic survey in order to delineate the subsurface structure and its relation to the geothermal manifestation that spread through the area. An analyzed of horizontal gradient interpretation techniques has been applied to gravity and magnetic data. The results present that the hot springs around Ungaran Volcano are structurally controlled and have depths ranging from 1 to 3 km. Moreover from the magnetic quantitative interpretation result beneath Gedongsongo area are compose of 4 layers. The first layer is sedimentary which consists of breccia, sandstone, pyroclastic deposits, alluvium, and top soil with susceptibility 7.0x10-5 cgs emu, the second layer has susceptibility -1.0x10-2 cgs emu with respectively an alteration of andesite lava,. Third layer is composed of hornblende-augite andesite with susceptibility 1.34x10 2 cgs emu, and the fourth layer has susceptibility 1.35x10-2 cgs emu which is composed of andesite rock. The results of the present study lead to an understanding of subsurface structure may aid in future geothermal exploration of Gedongsongo area.