Q-Tomography Beneath Agung Volcano, Bali, Indonesia, Using Local Seismic Network: A Preliminary Result

Abstract:

In November 2017, Mt. Agung showed its activity again after its largest eruption in 1964 which caused more than 1,000 casualties. In this study, we conducted attenuation tomographic inversion to determine Qp and Qs structures beneath Mt. Agung in order to obtain a better understanding of the presence of fluids and hot materials. Seismic data were collected using 39 seismographic network around Mt. Agung and Mt. Batur during December 2018 to September 2019 through a research collaboration program among Bandung Institute of Technology (ITB), Center of Volcanology and Geological Hazard Mitigation Indonesia (PVMBG), and United States Geological Survey’s Volcano Disaster Assistance Program (USGS-VDAP). We selected waveform data from ~350 local earthquakes that occurred around Mt. Agung and Mt. Batur which have ts-tp < 10 s to construct the image of seismic attenuation. The t* values are measured from the amplitude spectrum of ~1,000 P-wave and ~ 2,000 S-wave arrival times with the characteristic of the signals has SNR ≥ 2. The spectral fitting process resulted in 214 P phase and 247 S phase which will be used for the input of the inversion calculation using SIMUL2000 algorithm to image the lateral and vertical variations of Qp and Qs structures beneath Mt. Agung. The 3-D Qp and Qs model used in this study has a uniform horizontal grid spacing of 5 km and the vertical node intervals ranging between 4 to 10 km down to the 30 km depth. Our preliminary result of the attenuation tomographic imaging will provide new information to complement the previous body-wave and ambient noise tomography study results beneath Mt. Agung.