Seismic Swarm PS20140910.1 in the Molucca Sea

On 10 September 2014, a seismic swarm designated PS20140910.1 was recorded in the Molucca Sea. The sequence began at 02:46:06 UTC and concluded at 11:49:42 UTC, spanning nine hours and three minutes. Five earthquakes were registered during this period, all located within the tectonically complex boundaries of the Molucca Sea.

The events unfolded as follows. The initial shock measured magnitude 6.2 at a depth of 35 km. Roughly two and a half hours later, a magnitude 5.9 event occurred at 30 km depth. Minutes afterward, a magnitude 5.6 earthquake struck at 40 km depth. Later in the morning, a magnitude 5.3 event was recorded at 14 km depth, followed by a final magnitude 4.6 shock at 35 km depth.

Seismic swarms such as this one consist of closely spaced earthquakes without a single dominant mainshock. In regions of intense plate interaction, they often reflect adjustments along multiple fault segments or fluid migration within the crust. The Molucca Sea lies at the junction of the Philippine Sea Plate, the Sunda Plate, and smaller intervening plates, creating a setting of opposing subduction zones. The Halmahera slab subducts westward while the Sangihe slab subducts eastward, producing one of the most intricate convergent margins on Earth.

This tectonic configuration has shaped the region’s geological history for millions of years. Arc volcanism, rapid uplift of adjacent islands, and frequent moderate-to-large earthquakes characterize the Molucca Sea. Historical records document numerous significant events, underscoring the persistent seismic hazard. Since 1 January 2000, only one prior swarm has been identified in the same area, occurring in 2007.

The 2014 swarm adds to the catalog of clustered activity that highlights the dynamic stress regime of the Molucca Sea. Depths ranging from 14 km to 40 km indicate involvement of both the overriding crust and the upper portions of the subducting slabs. Such depth distribution is consistent with the double-arc geometry that defines the region.

Continued monitoring of the Molucca Sea remains essential for understanding short-term clustering and longer-term seismic patterns. The 2014 sequence, though brief, provides additional data points for refining models of plate interaction in this highly active segment of the Pacific Ring of Fire.

References

USGS Earthquake Catalog
Global CMT Catalog
Tectonic summaries from the Geological Survey of Indonesia