OPAK FAULT DELINIATION
Agus Sutiono, Bambang Prastistho, C. Prasetyadi and Supartoyo
Geological Engineering, University of Pembangunan Nasional “Veteran” Yogyakarta
Center for Volcanology and Geological Hazard Mitigation, Geological Agency of Indonesia
Abstract
The Opak Fault is famous as known as active fault in the South of Java which particularly is importance because accordingly historical noted, its fault has been experienced 3 times large earthquake events that claimed many victims and is being straddled Bantul regency of Yogyakarta. Usually producing uplifts only a few tens cm at a time, the cumulative effect has been to create in Gunung Kidul mountains range over the last million years. It coincides with producing Bantul basin faults fill including their confinements. The location is a site of intense deformation associated with convergence between plates Australia and Eurasia. However, Opak Fault strike-slip strain tend to be obscured due to draping by young active Volcanic Merapi sediments. In this place is hard to encountering outcrop of quasi-continuous fault segment at approximately 30 km of length that is capable to produce M. 6.3 as such earthquake occurring on May 27, 2006. Since this event, Based on conclusions from the experts, fault-s position and dipping role has being disputed; either fault dipping towards Southwest or Northwest, and fault zone along a ruptures are located toward the East in the vicinity of Gunung Kidul 5 or 10 km from Opak River. On the other hand, indicating from sediments typically accommodate within strike-slip fault system show strands where is suggested to traverse from Parangtritis Bantul Regency towards South Merapi Mountain slope. This Merapi sediments basin fill beneath Bantul regency, is considered to evaluate and drawing of important active fault lines in order to present seismic risk of all faults map in this area. Further, the convenient method was resorted to taking comprehensive features for understanding principle of slope surface motions. It may also is located in the vicinity of Bantul basin fill towards Merapi. This study has identified en echelon areas of curving slope shape by using slope propagation shifting analysis from satellite imagery. The aim of this paper is intended to present result of research in which delineates corridor of Opak Fault zone, where could be bounded by confinements within both of sidewall faults and cross-basin faults system identified. After in the last first stage study of the a comparative Opak Fault review presented before, this is second stage result from total four stages of the entire over all studies, which is important in order to get area for much more focus in highlighting any fractures in between its boundaries of Opak Fault system, where underlying and traverse the thick young Merapi sediments beneath Bantul region in Southwest, striking toward Merapi volcano in Northeast. The research will be continuing into other next 2 stages presented later of morphotectonic properties identification and field mapping to get much more comprehensive overview in the ultimate result of research. The indication keys of strike slip fault properties were identified during this second stage by the following: (1) South
Keywords: Opak fault delineations, fault damage zones, Bantul basin fill, Side wall faults and Merapi slope shifted.
Topic: Geology