ANALYSIS OF VOLCANO-TECTONIC EARTHQUAKES DISTRIBUTION IN MOUNT AGUNG OCTOBER-DECEMBER 2017

• Main Author: Puspanindyah Rahsetyo, Puput
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/50529
• Institution: Institut Teknologi Bandung

Mount Agung is one of the active volcanoes in Indonesia, located in Bali. Since 1963, Mount Agung has not had any significant activity. The volcano began to reactivate in September 2017 marked by an increase in seismic activity and eruption in November 2017. To understand the dynamics and eruption processes of active volcanoes requires an understanding of the structure of volcanoes, especially the position of the magma chamber and their paths. The depiction of the structure of this volcano can be analyzed by determining the location of the earthquake due to the volcanic activity, especially the volcanic-tectonic earthquake (VT). In this study, the initial stages carried out were the identification of earthquakes in volcanoes such as Volcano-Tectonic type A (VTA), Volcano-Tectonic type B, low frequency, eruption earthquake, blast earthquake and tremor earthquake. Next, determine the location of the VT by using the nonlinear location method for the initial location and hypocenter relocation using the double-difference (DD) method. The initial seismic velocity model used was the Koulakov 1D seismic velocity model and updated with the results of the seismic speed model using the Joint Hypocentre Determination (JHD) method. The results of the identification of events around Mount Agung obtained a VTA event with a frequency range of 7-12 Hz, VTB with a frequency of 4-8 Hz, low frequency with a frequency of ~ 2 Hz, an eruption earthquake with a frequency of 3-5 Hz, an earthquake with a frequency of ~ 3 Hz and tremor with a dominant frequency of ~ 6 Hz. The earthquake distribution shows a weak zone at a depth of 5 to 15 km between Mount Agung and Mount Batur which can be a shallow magma reservoir. And there is a swarm of earthquakes that form a dyke straight up to the southwest of the weak zone. This dyke was formed long before the eruption or in October which has a high number of seismicity. In October 2017 there were several earthquakes with similar waveforms thought to have originated from a fault above the dyke. Whereas in November, the dominant earthquake distribution was towards the top of Mount Agung so that the eruption occurred and in December the dominant earthquake was in the southeast of the summit of Mount Agung which had a very random distribution.