PEMODELAN ZONA SUBDUKSI DAN STRUKTUR BAWAH PERMUKAAN JAWA TIMUR BERDASARKAN KAJIAN ANOMALI GRAVITASI

Gravitation field research which covers from North coast of East Java to Java trench has been carried out. The major purpose of this research was to estimate basement model from North coast of East Java to Java trench and also to estimate the Tertiery sedimen structures of East Java. The gravity anomaly data used in this research is a secondary data from digitizing Gravity anomaly map which is produced by Indonesian Geological Research and Development Center (Budiman, 2000). Topography data is obtain from http://topex.ucsd.edu. Digitized Gravity anomaly data size is 71 x 75 grid with 6000 m of grid interval. Further process is projection of gravity anomaly onto regularly gridded horisontal plane using the equivalent source technique (Dampney, 1969). The result of upward continuation is a regional and residual gravitation anomaly, which is located at regular surface on 20 km above spheroid reference. The power spectrum methods is used for discontinuity depth estimation. Subsurface modelling use Talwani methods by Geomodel computational program. The result of modelling show the existence of subduction below the Indonesian ocean, horst-like type structure below the southern coast of East Java, and the basin at the center part of East Java. The inclination of the oceanic crust beneath the outer arc is between 4,50 – 80. There is a anticipation that subduction is correspond to the folding system and volcanism at East Java. The result of modelling show that East Java have a thick Tertiary sedimen up to 6 km