Although the geological structures ofJava Island has been widely studied, but there were still many problems that cannot be explained, especially regarding to the genetic relationship between regional fault structures that developed in this region. There are differences in the pattern of faults that developed within the pre-Tertiary basement rocks and Tertiary sedimentary rocks covers. The main structures which developed in the basementare generally having EW, NE-SW and NS directions; whereas in the Tertiary sedimentary rocks, the structure are generally trending to EW as a thrust folds structure. The exception of the Pelabuhanratu and Citanduy Faults, fault structureswiththe other directions are relativelly localized as tear fault.
The fault structures of NE-SW trending are associated with subduction activity during Cretaceous period. This fault pattern has been reactivated during the Early Tertiary tectonic period which generate fault structures of NS trending. At that time,
the position of the subduction track have been in position as it is now (modern subduct). Subduction activity of the last stage, in addition to activating the old structural pattern has also formed a new fault pattern with EW direction. This fault pattern was then controls the formation of fore arc basin, back arc basin and volcanic ranges. The three of fault patterns above, contribute to the formation of the Tertiary basins in the western part of Java Island (pre-rift).
Pre-rift fault patternswere still active until the Oligocene epoch (Syn-rift). This condition is reflected from the configuration of distribution thePaleogene rocks formation which are bounded by fault structures, and shows the difference in the thickness of rock layers. Therefore, the entire fault pattern that formed in Paleogene sedimentary rocks, were generally involving the basement rocks (thick skin tectonic).
At the end of the Tertiary, the entire of Tertiary age sedimentary rocks have been folded and faulted with generally EW direction (post-rift). This latter fault structures, generally were not directly related to the pattern of old faults but involves only to its rock covers which forms thrust fold structure pattern (thin skin tectonic).