Heat flow and gravity anomalies in some presumed hidden geothermal prospects in Java

Abstract

The currently developed geothermal fields in Java are hosted by Quaternary volcanic complexes in the central zone of the island. Those fields have many vigorous thermal manifestations. However, seismic tomography shows the presence of an east-west-trending, low P-wave velocity (Vp) zones along the island. This indicates the presence of some hot, molten mass at depth, and provides the possibility of the existence of subsurface heat energy resource that can be utilized despite the rarity of surface manifestations. We investigate the heat flow and gravity anomalies in the areas lacking thermal manifestations, namely Paguyangan, Candi Umbul-Telomoyo, Pablengan, and Parang Wedang. The first three are associated with Slamet, Telomoyo, and Lawu volcanoes, respectively. Parang Wedang is far from the active Merapi volcano, but close to the Opak Fault – one of the major strike-slip faults of Java. This research is a preliminary effort in exploring those presumed hidden geothermal prospects. The results shows that all the investigated areas have high heat flow anomaly (145 – 160 mW/m2). Their gravity anomaly varies. The highest (>70 mGal) and medium values (12 - 24 mGal) are found in Pablengan, and Candi Umbul-Telomoyo, respectively. The lowest values (< 5 mGal) occur in Parang Wedang.