RUPTURE KINEMATIC PROCESS OF THE MW 5.9 SERAM EARTHQUAKE IMAGED BY BACK-PROJECTION TECHNIQUE FOLLOWED BY THE TSUNAMI

The 16 June 2021 Seram earthquake occurred at a moderate magnitude of Mw 5.9 along the Banda Arc close to Seram Island, followed by a tsunami with a runup height of 0.51 m. A detailed kinematic study of the earthquake helps us better understand the tectonic environment of the secondary faults and the causes of an unexpected tsunamis after earthquakes, particularly on the island. In this study, we image the rupture processes of this earthquake using a Multiple Signal Classification Back-Projection (MUSIC-BP) method. This method used P-seismic waveforms from teleseismic data recorded by seismic stations across the Australian continent (AU arrays). These waveforms were filtered in the range of 0.5-1.0 Hz to remove unwanted phases. Our results show that the rupture moves bilaterally to southwest and northeast at a relatively slow speed of 1.47 km/s. In this earthquake, the rupture propagated ~35 km away from the epicenter and had a total duration of ~30 s. The maximum peak of the energy released is estimated to be ~15 km from the epicenter. The rupture directivity agrees well with the spatial distribution of aftershock events and the reported focal mechanism solution. According to the result of the rupture kinematics parameter, the tsunami was not caused directly by the earthquake. However, the direction of tsunami propagation is the same as that of earthquake rupture propagation. Furthermore, the results of this study reveal that the seismogenic fault under Seram Island has an SSW- NNE fault orientation.