Understanding swarm earthquakes in Southeast Aceh, Sumatra

The cause of the swarm earthquakes occurring from September until November 2020 remains unclear. The swarm activities are close to the Tripa active fault but also close to Mt. Bendahara. This study offers the analysis of seismic P and S wave arrivals and relocate the hypocenter of the swarm. We analysed the hypocentre distribution that recorded by Badan Meteorologi Klimatologi dan Geofisika (BMKG) from July 2020 to January 2021. The arrival of P and S-wave from 103 events was used obtain 1-D seismic velocity model. The earthquake used for this study consisted of at least 6 phases of seismic arrivals with the azimuthal gap angle less than 180 degree. The different velocities occurred in the upper and lower of the crustal thickness of 0 – 40 km. The Vp values are about 5.0 – 7.0 km/s and 3.0 – 5.0 km/s for Vs value while the Vp/Vs ratio are ranging from 1.5 to 1.7. Our preliminary results indicate that the potential swarm activities near to Mt. Bandahara maybe triggered by an unknown fault activity as no volcanic activity was reported