Seismic Swarm PS20140204.1: Analysis of Activity Near Timor-Leste

A notable seismic swarm, designated PS20140204.1, was recorded in the waters northeast of Timor-Leste. The sequence began at 20:37 UTC on 3 February 2014 and concluded at 01:05 UTC on 4 February 2014. All events were located approximately 217 km northeast of Lospalos. Within a span of four hours and twenty-eight minutes, six earthquakes were registered.

The swarm unfolded in a rapid succession of moderate-magnitude events. The first shock measured 5.2 at a depth of 17 km. Roughly two hours later, the largest event reached magnitude 5.8 at a shallower depth of 7 km. Subsequent shocks included magnitudes 5.0, 5.0, 4.6, and 5.1, most occurring at depths near 10 km. This tight temporal clustering and progressive shallowing of foci are characteristic of swarm behavior, where stress redistribution along nearby fault segments triggers multiple similar-sized events without a dominant mainshock-aftershock pattern.

The Timor-Leste region occupies a tectonically active margin where the Australian Plate converges with the Sunda Plate. This interaction produces a complex system of thrust faults and strike-slip structures associated with the Banda Arc. The area experiences elevated seismicity as the leading edge of the Australian continental margin collides with and underthrusts the arc system. Historical records indicate that such swarms remain infrequent; since 1 January 2000 only one prior swarm has been identified in the immediate vicinity, occurring in 2008.

A significant regional event underscores the ongoing tectonic loading. On 29 December 2021 a magnitude 7.3 earthquake struck 125 km north-northeast of Lospalos, approximately 92 km from the 2014 swarm center. That earthquake, like the 2014 swarm, reflects the persistent convergence and associated crustal deformation in the region.

Seismic swarms in this setting provide valuable insight into short-term stress migration along the plate boundary. Continued monitoring of similar sequences contributes to improved understanding of rupture processes and seismic hazard assessment for Timor-Leste and surrounding maritime areas.

References:
SeismoSight internal swarm classification PS20140204.1
USGS Earthquake Catalog (regional events since 2000)
Geological Survey of Indonesia tectonic framework reports