The 2009 Manokwari Earthquake Sequence in West Papua, Indonesia

On January 3, 2009, a significant seismic sequence struck the region near Manokwari, Indonesia. The mainshock registered M7.7 and occurred at 19:43 local time, with its epicenter located 140 km WNW of Manokwari at a depth of 17.0 km. This event was part of a cluster of strong earthquakes recorded that day, all within close proximity. Preceding and following the mainshock were two additional events: an M7.4 earthquake 86 km WNW of Manokwari and an M7.6 event near the north coast of Papua, Indonesia. The M7.6 was situated 19 km from the M7.7 epicenter, while the M7.4 lay 55 km away. These occurrences highlight the intense seismic activity concentrated in a limited area on that date. The Manokwari region lies within a complex tectonic setting at the boundary between the Australian and Pacific plates. This collision zone features active subduction, strike-slip faulting, and crustal deformation characteristic of the broader New Guinea fold-and-thrust belt. Such geological conditions make West Papua one of the most earthquake-prone areas in Indonesia, with frequent moderate to large events driven by plate convergence rates exceeding 10 cm per year in places. Historical records indicate recurrent seismicity in this sector of Papua, reflecting ongoing tectonic adjustments. The 2009 sequence aligns with patterns observed in the Sorong Fault system and adjacent structures, where shallow crustal earthquakes often occur at depths under 20 km. No major updates to the fundamental tectonic framework of the region have altered interpretations since 2009, though improved monitoring continues to refine aftershock distributions and fault models.

References

USGS Earthquake Catalog (event parameters and locations). Global CMT Project (focal mechanisms for regional events).