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Abstract:
The Halmahera island belongs to the North Moluccas province (Maluku Utara), Indonesia. This K-shaped island is located in the eastern part of the Moluccas Sea, the only active arc-arc collision complex on the Earth. The western arm of the K forms a volcanic arc due to the former subduction of the Moluccas Sea plate underneath Halmahera. The region is characterized by intense seismic activity at crustal, intermediate depth, and along the subducting plate. At crustal level the Halmahera seismicity along the two eastern arms of the K show strike-slip faulting style. In November 2015 a localized intense and energetic seismic activity started around Jailolo volcano in the West Halmahera Regency. The seismic sequence intermittently lasted until February 2016 and hundreds of events were felt by the population and several buildings were destroyed and damaged by the shaking. The largest shocks of the sequence have been located by global seismicity networks (GEOFON and GCMT) showing normal faulting style. The temporal evolution of the seismicity seems to be more swarm-like type activity instead of mainshock-aftershock sequence. In spring 2016 a research project has been funded by the German's Humanitarian program in collaboration with BMKG, Indonesia, with the goal of understanding the origin of the intense seismic activity and the related hazard. In summer 2016 we instrumented the area with a dense seismic network composed of 29 short period and 6 broad-band seismometers. The instrument deployment aims at characterizing the seismicity of the Jailolo region in relationship with the 2015-2016 seismic activity. The network will help to understand the seismo-tectonic of the area and the relation between seismicity and the volcanic activity at Jailolo volcano and possible link with the 2015-2016 swarm. Should the seismic activity intensify as in November 2015, we can record it and narrow down the underlying physical mechanisms. Waveform data are available from the GEOFON data centre, under network code 7G, and are embargoed until the end of 2021.
