![]() We analyzed of waveform of several swarm events (with largest and smallest magnitude) which are recorded by the nearest BMKG station and show has frequency range of 2 to 8 Hz. The relocated hypocenters are located close to Jailolo volcano area which has focus depths of about 5 – 30 km. A validation through the histogram of travel-time residual depicts good relocation results, in which the residual values are mostly close to zero. The results indicate improvement in hypocenter location, where the initial earthquake focal depths fixed at a depth of 10 km has been updated. We have successfully relocated 108 out of the 130 earthquake swarm from September 27 to Octoby using the BMKG network data through hypocenter double-difference method. To have a further understanding of the complex tectonic activity in this area, our future work will focus on conducting a seismic tomographic inversion to determine the 3D seismic velocities structure around the Molucca Sea collision zone.Ī year after the hundreds of earthquake swarm last year (2015-2016), recent swarm activity in Jailolo, north of Maluku area, Indonesia began to reactivated. The seismicity is related to the Molucca Sea Plate which is dipping into west and east direction beneath Sangihe-Halmahera Arc. The seismicity pattern under the Sangihe Arc deepens to the north and the deep earthquake events increase in number. Our preliminary results show that the seismicity beneath the Molucca Sea collision zone forming a double subduction pattern which is dipping westward under the Sangihe Arc, reaching a depth of ~ 600 km and eastward under the Halmahera Arc, reaching a depth of ~ 250 km. The P- and S-arrival times are used to determine the hypocenter location by applying NonLinLoc method which estimating the probability density function (PDF) using the oct-tree importance sampling algorithm. We repicked the P-and S-phase manually and have been succesfully determined ~17,628 P and ~17,628 S arrival times. We used 1,647 events that recorded by 32 seismic stations. In this study, we have determined hypocenter location around the region using local & regional network of Agency of Meteorology, Climatology, and Geophysics, Indonesia (BMKG). Molucca Sea collision zone is a region which has very complex geology and tectonic setting, producing high seismicity and volcanoes activities.
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