Preliminary Study: Density Layer Values Estimation of Volcano Hosted Geothermal Area at Tiris Village, Probolinggo Regency, East Java, Indonesia

摘要

A preliminary study has been conducted using gravity method to estimate the volcano hosted geothermal system at Tiris, Probolinggo Regency, East Java. Gravimeter LaCoste & Romberg type G-1503 used for acquisition data which it collected in grid design with 100 meters per each datum. Complete Bouguer anomaly was obtained through gravity correction methods, then reduced into the flat plane and separated between regional anomalies and residual anomalies using upward continuation method. Complete Bouguer anomaly result had value ranged from 49-63 mGal and residual anomaly values ranged from -8.5-5.5 mGal. Subsurface structure identification for determining geothermal layer system was obtained by making three intersection lines (i.e A-A', B-B' and C-C') on the residual anomaly map and analyzing their cross-sections. Based on the modeling results of A-A', B-B' and C-C' cross-sections in terms of density values, it is estimated that the sub-surface rocks of the research area are composed by Lamongan volcano tuff-breccia rocks, Lamongan volcano breccia-lava rocks, Argopuro volcano andesitic-lava rocks, and old-Tengger andesitic-breccia rocks. The Argopuro volcano andesitic-lava rocks are suspected as the geothermal heat source because it volcanic activity is still detected. Furthermore, the Lamongan volcano breccia-lava suspected as the geothermal reservoir where they have large porosity so that the water passes and heated easily.