Seismic Swarm Near Manatuto, Timor-Leste: April 2008

A seismic swarm designated PS20080419.1 was recorded 66 km north of Manatuto, Timor-Leste, beginning at 03:12 on 19 April 2008 and concluding at 13:01 on 20 April 2008. Over 33 hours and 48 minutes, eight earthquakes were registered, providing a clear example of clustered seismic activity in the region.

The sequence began with a magnitude 6.1 event at 13 km depth, followed by a magnitude 6.0 shock at 10 km depth later that morning. Subsequent events included magnitudes of 5.4, 4.5, 5.0, 5.1, and 5.2 at depths ranging from 5 km to 48 km on 19 April. The swarm ended with a magnitude 5.6 earthquake at 3 km depth on 20 April. These events illustrate typical swarm characteristics, with multiple moderate shocks occurring in rapid succession without a single dominant mainshock.

Timor-Leste occupies a tectonically active zone within the Banda Arc, where the Australian continental margin collides with the Banda Sea plate. This convergence produces thrust faulting and frequent seismicity at shallow to intermediate depths. The island's geology features uplifted sedimentary rocks and ophiolites resulting from this long-term plate interaction, which has shaped the rugged terrain and contributed to ongoing deformation.

Historical records indicate recurrent earthquake activity across Timor since at least the early 20th century, consistent with the island's position along a major plate boundary. Regional monitoring since 2000 has identified limited swarm-type sequences, with one prior episode noted in 2004. Such patterns underscore the value of continuous seismic observation for understanding local stress release.

The 2008 swarm highlights the potential for clustered events to occur without producing widespread damage when magnitudes remain moderate and depths vary. Continued study of these episodes supports improved hazard assessment in Timor-Leste's dynamic geological setting.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Banda Arc tectonic summaries, Geoscience Australia
SeismoSight internal swarm classification data