Seismic tomography imaging beneath Sinabung Volcano, North Sumatra area, Indonesia

Abstract

The Sinabung volcano is located in Karo Regency, North Sumatra with altitude of 2460 m above sea level. Since the sudden eruption in 2010, Sinabung volcano, which is previously a volcano type B, turned into a volcano type A. Variations in the seismic velocity and earthquake hypocenter distribution can be determined using the Local Earthquake Tomography (LET) to well-describe the subsurface structures. We selected 2,105 volcano-tectonic (VT) event from data catalog of CVGHM from November until December 2013. Updates 1-D initial velocity model for P and S wave were conducted by Joint Hypocenter Determination (JHD) method and then used as input for LET to determine 3-D Vp and Vp/Vs structures. Based on the checkerboard resolution test, seismic velocity structures are reliably imaged only about 1 km around the summit down to depths of about 4 km beneath Sinabung volcano due to the VT events seem clustered at that depth and the lack of stations. The tomographic inversion results showed anomalous of low Vp, Vs, and Vp/Vs around Sinabung Volcano may be related to the presence of a weak zone or crack filled by the hot material, CO2, and steam. The low Vp and Vs anomalies, and high Vp/Vs ratio value coincide with aseismic zone that was identified at a depths of 1-2 km beneath Sinabung volcano may be associated with the intermediate partial melting zone, which may cause Sinabung volcano is very active until now.