ANALYSIS OF SWARM EARTHQUAKE AUGUST 2019 IN BOGOR REGION, WEST JAVA

• Main Author: Kurnia, Ulfah
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/63718
• Institution: Institut Teknologi Bandung

BMKG earthquake data catalog showed that 69 events have been recorded in Nanggung District, Bogor, West Java from August 10th to 21th, 2019. These events have been categorized as a swarm earthquake. This is because the epicenter distribution pattern is relatively local and it has relative small magnitude (? M 4,0) with relatively high frequency. BMKG has conducted a preliminary analysis and suspects that these swarm earthquake were caused by local fault. However, more detailed study is needed to determine the continuity of the fault which caused these swarm earthquake. It is expected that tighter placement of the seismograph network will provide a better recording of earthquake events. Using seismic waveform signals recorded in the local seismic network, this study discovers the frequency of swarm earthquake. The installation of local seismic network observation is carried out by the collaboration of Institut Teknologi Bandung (ITB) and BMKG. 8 seismographs were placed around the source of the swarm earthquake which were distributed in Sukabumi, Bogor, Pelabuhan Ratu, and Bayah Banten. Based on the manual picking process using Seisgram2K software, 56 P wave phases and 56 S wave phases were identified from 9 earthquake events with criteria earthquake events that had a difference value of ts – tp ? 10 seconds and were recorded at a minimum of 4 stations with clear P and S wave phases. As a controller quality of the observation data, the results of plotting the wadati diagram show the value of the Vp/Vs ratio is 1.686. Based on the determination of the earthquake hypocenter conducted using a non-linear method with the Nonlinloc device, 9 events were at depths ranging from 0.2 Km to 53 Km. Then a waveform cross-correlation was performed to update the arrival time of the P wave. The final step of the data processing was the relocation of the earthquake hypocenter using the HypoDD software with the Double-Difference method. The results of the hypocenter relocation show that used cross-correlation data as input to the double-difference algorithm can give better results, where 7 of the 9 events that were relocated concentrated in locations close to each other and close to the SB08 station. The results of this study can be used as a reference in research related to seismic hazard assessment.