Relative Seismic Velocity Change Analysis Using Ambient Seismic Noise on Agung Volcano, Bali, Indonesia Lalu Iqbal Tawakkal Akbar (a*), Zulfakriza (b,d), Shindy Rosalia (b), Andri Dian Nugraha (b,d), David Prambudi Sahara (b), Sri Widiyantoro (b), Devy Kamil Syahbana (c)
a) Undergraduate Program of Geophysical Engineering Program, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Indonesia
*laluakbar[at]students.itb.ac.id
b) Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Indonesia
c) Center for Volcanology and Geological Hazard Mitigation, Geological Agency, Bandung, Indonesia
d) Center for Earthquake Science and Technology, Research Center for Disaster Mitigation, Institut Teknologi Bandung, Bandung, Indonesia
Abstract
Agung volcano is one of the active volcanoes in Bali, Indonesia. According to Center for Volcanology and Geological Hazard Mitigation of Indonesia (CVGHM), Agung volcano erupted in November 2017, after dormant for more than 50 years. Intriguingly, the eruption phase showed a significant increase in seismic activity about two months before (seismic crisis) which then decreased gradually until finally erupted on 21 November 2017. To examine the mechanism of Agung^s magma activity against eruptions, we calculated the relative seismic velocity changes using the cross correlation of ambient seismic noise. Based on the velocity changes obtained, we interpreted how the medium changes caused by stress perturbations in the medium, before and after the eruption. Although it varies spatially, we identify a zone of velocity change with a negative trend between Agung-Batur before the eruption which then increasingly recorded until the eruption. We interpret this as fracture growth due to magma migration towards Agung. The migration also produced the increase in velocity surrounds the volcano that may be related to an increase 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.
