Mataram Fault – New Active Fault Crosses East-West in the Centre of Yogyakarta City

Abstract

Yogyakarta has experienced two devastating earthquake disasters: May 26, 2006, Mw6.4, and the penultimate event, June 10, 1867 Mw7.7. The active fault that is thought to be responsible for the two earthquake events is the Opak Fault. However, the Opak Fault has still not been thoroughly well mapped yet. The lack of a high-resolution image, dense vegetation cover, high sediment flux from the Merapi volcano, and human activities eroding the original landscape challenge studying the on-land fault in this area. Our recent study, however, indicates that the Opak Fault is not the only active fault that can cause a major disaster, but another fault strand exists in the area. We mapped the fault using the best available data of DEMNAS assisted by more detailed DEM and Orthophoto, developed from drone survey, and we also conducted Earth Resistivity Tomography (ERT) survey. We found that inferred new active fault is oriented East-West across the center of the high-populated city. The fault runs parallel and close to the famous Mataram channel (Selokan Mataram). The fault is likely continue the previously recognized Dengkeng Fault, east of the Opak fault. The fault strand is indicated by morphological lineaments and a few steam offsets. Our ERT 2D sections have revealed the fault zone in several locations along the inferred fault line. The fault line cut the Young Quaternary rocks; hence, it is an active fault. Further studies are needed to get further details of this newly recognized active fault, such as conducting paleoseismological studies, detailed seismological survey, geodetic GPS measurement, and acquiring a high-resolution image acquisition survey (LiDAR – Light Detection and Ranging Survey).