DETERMINATION OF MOUNT IJEN VOLCANO-TECTONIC (VT) EARTHQUAKE HYPOCENTERS DISTRIBUTION USING GEIGER METHOD BASED ON EARTHQUAKE DATA FOR AUGUST - SEPTEMBER 2022 PERIOD

• Main Author: Rizal Syarif Amrullah, Ahmad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/77978
• Institution: Institut Teknologi Bandung

Indonesia has 127 active volcanoes spread across Sumatra, Java, Nusa Tenggara, Maluku and Sulawesi. One of the 127 active volcanoes is Mount Ijen, East Java. On January 7, 2023 at 14.00 WIB, the status of Mount Ijen was raised one level from level I (Normal) to level II (Alert). The increase in the status of volcanoes is certainly carried out based on the results of observations of several geophysical methods. One of the geophysical methods that can be applied is the seismic method which can detect volcanic-tectonic earthquakes (VT) on volcanoes. This study determined the distribution of VT earthquakes on Mount Ijen and estimated VTA and VTB earthquake clusters. The data used is seismogram data recorded by seven seismic stations belonging to the Center for Volcanology and Geological Hazard Mitigation (CVGHM) around Mount Ijen between August 2022 to September 2022. Data processing began by picking the arrival time of P and S waves for each event using “Seisgram2k” software, producing 400 VT earthquake event data consisting of 20 VTA earthquake events and 300 VTB earthquake events. Next, the positioning of VT earthquake hypocenters using the Geiger method with “Geiger's with Adaptive Damping (GAD)” software. The results of determining the hypocenter of the VT earthquake on Mount Ijen show that the position of the earthquake hypocenter tends to be centralized south to east of the crater, with the depth of the VTA earthquake hypocenter being at 1.5 – 7.5 km below the crater and VTB earthquakes at a depth of 0-2 km below the crater. The hypocenter of VTB earthquakes tends to be centralized, while the hypocenter position of VTA earthquakes spreads further from the crater. The existence of VTB earthquake clusters close to the crater indicates a fracture arising from the movement of magma that is getting closer to the crater.