RELATIVE SEISMIC VELOCITY CHANGE ANALYSIS BASED ON AMBIENT SEISMIC NOISE OF AGUNG VOLCANO, BALI, INDONESIA

• Main Author: Iqbal Tawakkal Akbar, Lalu
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/57549
• Institution: Institut Teknologi Bandung

Agung volcano is one of the active volcanoes in Bali, Indonesia. Based on Center for Volcanology and Geological Hazard Mitigation of Indonesia (CVGHM), Agung volcano erupted in 2017, after for more than 50 years dormance. Intriguingly, this eruption phase showed a significant increasing seismic activity in SeptemberOctober (seismic crisis) which then decreased gradually until finally erupted on 21 November 2017. To examine the process and mechanism of Agung's activity and dynamics in contrast to the eruptions, the relative seismic velocity changes calculated using the cross correlation of ambient seismic noise. The velocity variations can be caused by stress perturbations in the medium. Therefore, the stress changes can be retrieved from measured velocity variations in the medium associated with the activity of the magma system below the surface. A total of eight seismometers were used, thus the 28 possible pairs of seismometer trace, will be computed to form a cross correlation function (CCF). The delay time (?t/t) calculation is performed for each of the stacked CCF and its reference, which becomes the input for compute the velocity change (?V/V). Based on the velocity changes obtained, it’s interpreted how the medium changes, before and after the eruption. Although varies spatially, the velocity change can be identified a zone with a negative trend between Agung-Batur before the eruption, which then this tren increasingly recorded in stastion pairs until the eruption. This is interpreted as fracture growth due to magma migration towards Agung Volcano. The migration also produced the velocity change increase surrounds the mountain may be due to the increasing pressure in the shallow magma reservoir. Furthermore, the eruption caused a significant deformation in volcanic edifice affects the velocity change trend being deceased and fluctuated.