Abstract

Investigating temporal evolution of seismicity in Ambon region we performed template matching algorithm by assigning 237 template waveforms to the five continuous recording stations near the epicentre of main event. Tracing back one year before the mainshock to identify the presence of foreshock, the background seismicity increased four months before the mainshock. A detailed episode of the Ambon earthquake aftershocks contains two large aftershocks series while the second large aftershock of Mw 5.1 comprised of 986 events with 20 seconds inter-event interval.
Aftershock productivity derived from generalized Utsu-Omori relationships quantitatively shows that during three months of observation, aftershock activity behaved to decay exponentially. However, two large aftershocks series implied to the sharp outliner and indicates multi-sequences aftershock series.
Spatially, we observed migration of seismicity to the strike direction of the fault line preceding the mainshock to one hour after the main event. The spatio-temporal of seismic distribution also depict the rupture propagated in the contact surface between two crustal blocks. After considering one year of observation, the Ambon fault consider to be aseismic. Then we propose that the aftershock distribution is caused by the aseismic afterslip.
The observation found a general agreement that the spatio-temporal earthquake rupture propagated to a certain direction was controlled by the tectonic stress regime in the region. Our spatio-temporal evolution of seismic migration was consistent with the crustal motion velocity vector derived from GPS observation from previous studies in the Ambon island. Its leads to the direction of NNE while the strike of the Ambon earthquake focal mechanism inline to the same direction.