Abstract
Gravity survey in the geothermal area including Mataloko, Nage and Mengeruda, the central Flores Island, eastern Indonesia, was conducted in 1999 to 2001. And the biggest town in the survey area is Bajawa Town. The total number of measurement points amounted to about 800, and about 170 stations were taken at the very short intervals, about 200 meter, in the Mataloko geothermal area. The location and altitude were decided by differential GPS and the accuracy is thought to be within 1 meter accuracy or better. All measured gravity data were referred to the International Gravity Standardization Net 1971 (IGSN71) and the normal gravity values were estimated according to the gravity formula 1980. Terrain corrections were conducted with respect to the distance range up to 60km, by approximating the real topography to an assemblage of annular prisms interpolated by mesh terrain data and random terrain data of gravity points. The effect of the topographic sinking from horizon due to the earth's curvature was taken into consideration. Bouguer corrections within the range of 60km in arc distances were made using a spherical cap crust formula. The density for both terrain correction and Bouguer corrections is chosen to be 2.0 g/cm3 according to the result of surface density estimation. This estimated density is reasonable compared to the geological setting. Because whole measurement area is covered with volcanic sediment or pyroclastic flow and surface layer density is estimated to be low from geological consideration. The features of Bouguer anomalies is characterized by a low anomaly around Mengeruda compared to volcanic sediment or pyroclastic flow of depression area, a steep gradient structure in the west near of Mataloko and a elongated high anomaly area from Bena to Dona were found.
