HYPOCENTER RELOCATION USING DOUBLE-DIFFERENCE METHOD IN THE FAULT SEGMENT OF SIANOK AND SUMANI, WEST SUMATRA

• Main Author: Surya Putra, Ade
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/36878
• Institution: Institut Teknologi Bandung

The Sumatran Fault is a fault with a structure of 1900 km and undergoes a lateral displacement formed by the oblique (oblique) subduction of the Indo-Australian Plate under the Eurasian Plate. Based on the irregularities of the geometry order, this fault is divided into 20 main segments and some of them produce doublet earthquakes, namely in 1926 in the Sianok Segment (M6.8 & M6.5) and 1943 in the Sianok Segment (M7.1 & M7.3). Seismicity analysis needs to be done to evaluate the potential for disasters in the area based on accurate hypocenter distribution. In this study, the initial hypocenter was determined using non-linear methods and hypocenter relocation using a double-difference algorithm in the Sianok and Sumani Segments areas. Arrival times of P and S waves are determined manually from 53 BMKG stations that are spread along the Sumatra Island with the recording period from 2009-2017. 1D velocity model used is the model of global velocity AK135. Total of 336 P and S phases were identified from 61 earthquake events that met the criteria, namely earthquakes having magnitudes of more than 3 (Mw> 3) and recorded at a minimum of 3 stations. Based on Wadati diagram showing the value of the Vp/Vs ratio of 1.74, this value can be used as a reference for the quality of observation data. The results of the initial hypocenter determination based on reference data on residual and residual RMS values describe the distribution patterns of well-clustered events. The event is near the Sianok and Sumani fault lines. Total of 43 events were successfully relocated and showed changes between 1-3 km horizontally and significant changes at depths between 5-10 km. Based on results of the relocation, it can be seen that the events at the time of the study are still related to the earthquake doublet that has occurred, because it describes the location not far away. It can be concluded that the events at the time of the study were still at the source location which was the same field of fault as the earthquake doublet event that had occurred