THE EFFECT OF GRAVITY MEASUREMENT DISTRIBUTION POINTS ON INTERPRETATION OF GRAVITY DATA IN THE GUNUNG ENDUT GEOTHERMAL PROSPECT AREA, INDONESIA

Abstract

The geothermal prospect located at Gunung Endut was investigated in 1980s based onreconnaissance surveys, primarily on geological and geochemical aspects. Then in 2006 a gravitymeasurement with 247 stations was carried out. However, due to the distribution of the gravity station wasless than optimal, interpretation of gravity data was not suitable with the geological situation that supportgeothermal system. To ensure this, we have carried out a new gravity survey with 134 random stationsdistribution but remained concentrated on hot spring locations. Data from both measurements were processedby the same treatment starting from pre-processing with some standar corrections to obtain completeBouguer anomaly, then continue by filtering process to separate regional and residual gravity anomaly usingButterworth filter in a wavenumber domain. Residual gravity anomaly map obtained by random position ofstations is more resemble to the geological features developed in the prospect area. The contrast boundariesof the residual gravity anomaly value coincide with the fault-line structures recorded in the surface geologicaldata. This result is better when compared with previous measurements. This study shows that there is asignificant influence of the distribution pattern of the gravity stations which affects the conformity with thegeological data. Based on the new interpretation result, the structural features in the prospect area arecharacterized by the complex fault structures that intersected each other mainly close to the surfacemanifestations. This intersection area is expected to be an enhanced permeability zone so that thehydrothermal fluid can flow to the surface. The interpretation of new gravity data combined with the resultsof geochemical analysis can be used for more understanding of the geothermal system beneath GunungEndut prospect area.