Ecology, Environment and Conservation Paper

Vol. 28, Aug Suppl. Issue 2022; Page No.(S27-S35)


M. IrhamNurwidyanto, Tony Yulianto, Gatot Yulianto and Sugeng Widada


The earthquake that happened on 27th May 2006 in Yogyakarta and its surrounding caused terrible damageas well as thousands of dead victims. Such an earthquake was caused by horizontal Opak’s Fault activationand it triggered the emergence of Dengkeng’s Fault movement located at the eastern part of the northernOpak’s Fault. To mitigate the disaster that might occur in the future, the channel and the condition underDengkeng’s Fault need to be mapped. One of the methods that could be used to recognize the under surfacecondition is the gravity method which is based on the measurement of gravity field variation on the earth’ssurface. The existence of a fault would change the condition of rocks in such fault channel zone so that itinfluences the local gravity change. Therefore, on this opportunity, research of Dengkeng’s Fault is carriedout using the gravity method. The measurement of the gravity field has been done in 94 points using LacosteRomberg Gravitymeter type G-1118 MVR. The height of the measurement point was measured usingGPS Altus APS-3 differential, and the research coordinate was measured using GPS Garmin III Plus. Dataon the gravity field that had been obtained was corrected so that complete anomaly Bouguer (ABL) isobtained. Further, the regional component of the ABL value is separated from its local component using anupward continuation method. The target that would be identified is shallow so that the local anomaly thatwould be analyzed uses the second vertical derivative (SVD) and modeled in 3 dimensions using OasisMontaj software. Second vertical derivative type of fault. 3-dimensional modeling was used to identify theunder surface structure of the research area comprehensively. The result of the analysis using the secondvertical derivative shows that Dengkeng’s Fault is a strike-slip fault with the west-east direction. To clarifythe under the surface condition from the 3-dimensional modeling, incisions were made to the Z-axis direction(vertically) and X-axis direction. Z-axis direction modeling shows that the fault in the research area starts tobe seen at the depth of 500 meters to 3500 meters to the west-east. X-axis direction modeling shows that thefault was located at Easting 444500 meter and Northing 9141000 meters to the Easting 456250 and Northing9139000. Based on the modeling result, it could be seen that the southern part block of Dengkeng’s movedto the east, while the northern part block moved to the west.