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Is the seismicity swarm at long-dormant Jailolo volcano (Indonesia) a signature of a magmatic unrest?

Event Type: 
Event Date: 
21 July 2017 - 8:00am
EOS Seminar Room N2-01b-28
Luigi Passarelli
About the speaker: 

Luigi Passarelli graduated in Physics at University of Bologna in 2006, after he completed his PhD at INGV-Italian Institute of Geophysics and Vulcanology, Bologna in statistical volcanology on eruption forecast and volcanic unrests. In 2011 he received a post-doc at Hamburg University in statistical and physical modelling of magma propagation. Since 2012 he has been working at GFZ as researcher in dike-induced seismicity and fluid induced seismicity, i.e. volcanic and non-volcanic seismic swarms.

About the event: 
Magmatic unrests are challenging to detect when there is no close monitoring network and little knowledge about the volcano. Observable parameters like seismicity, deformation, temperature and gas emission can be reliable indicators of ongoing volcanic unrest caused by magma movements. Jailolo volcano is a Holocene volcano belonging to the Halmahera volcanic arc in the Northern Moluccas Islands, Indonesia. Global databases of volcanic eruptions have no records of its eruptive activity and no geological investigation has been carried out to better assess the Jailolo past eruptive activity. In November 2015 an energetic seismic swarm started around Jailolo region and lasted until late February 2016 with four earthquakes with M>5. The normal fault focal mechanisms of these four events clearly depart from the regional strike-slip tectonic regime. However, no geophysical monitoring network was available around Jailolo volcano during the seismic sequence. We obviated the lack of monitoring last summer by installing a dense multi-parametric monitoring network with 36 seismic stations, 6 GPS and 2 gas monitoring stations around Jailolo volcano.
We revised the focal mechanisms of the larger events and used single station location methods in order to exploit the little information available at the time of the swarm activity. Migration of hypocenters and inversion of the local stress field derived by focal mechanisms analysis may indicate magma migration at shallow depth as the source of the 2015-2016 seismicity swarm. Data from our dense network confirms an ongoing  micro-seismic activity underneath Jailolo volcano but there are no indication of new magma intrusion. Our findings seem to indicate of a magmatic unrest occurred at Jailolo volcano and call for a revision of the hazard assessment of the Jailolo volcano.