Preliminary Result of Swarm Activities in Toba Region Using Dense Temporary Network

Abstract

For the first time, an earthquake swarm occurred in 2021 in Lake Toba (Indonesia), one of the largest calderas in the world. Although the earthquakes were located in the volcanic environment, the swarm activities could be related to the tectonic activities from the Sumatra fault system. The swarm activities occurred at a very shallow depth and were felt with the intensity of II–IV MMI by local people. The objective of this research was to investigate the characteristics of the earthquake swarm in the Toba Caldera from the waveforms recorded by temporary stations in March – June 2021. A total of 26 seismic stations were deployed for two months in May and June 2021. Automatic detection of seismic waves is important because it can be used for earthquake early warning systems and speeds up analysis of origin time, P-, and S arrival times, and earthquake locations. We found characteristics of spectrum waveform from low to high frequency of a non-swarm earthquake, while high frequency seismograms were generated by the swarm earthquake. Furthermore, we successfully captured the hypocentre that was distributed in the SW – NE direction and may figure out the unknown geological system that is responsible for the swarm activities.