B.M. Tri Fristiyan Nanda¹ , N. Heryandoko² , B. Kamaruddin²

¹National Seismological Center, Meterological and Geophysical Agency
²BMKG

Abstract:

At the end of 2015, a seismic swarm occurred in Jailolo region, West Halmahera, Indonesia. GFZ Germany collaborated with BMKG Indonesia to monitor seismic activities in Jailolo by installing a temporary network of 35 seismic stations. Here we present the results of a local earthquake tomographic inversion beneath Jailolo region corresponding to two time periods, June and July 2017. About 6,000 P-wave phases from 567 events were used to invert for the 3-D P‐velocity structure of the crust beneath Jailolo region. The calculations were based on tomographic inversion of P arrival time data using the local earthquake tomography code LOTOS. We performed a thorough analysis of the results in each of the time periods and compared them. The resulting tomographic images shows differences for each period. The June period shows low P-velocity anomalies for depths of 4-14 km with anomaly values up to -6%. However in the July period the anomalies have lower values than the June period, P-velocity anomalies value up to -1.5% in 7-10 km depth. Low P-velocity anomalies can be associated with high content of fluids and partial melts or magma reservoir within the crust beneath long-dormant Jailolo volcano. This magmatic activities are assumed as a source of seismic swarm activities in Jailolo region.