Seismic Swarm PS20010225.1 Near Ternate, Indonesia

The seismic swarm designated PS20010225.1 occurred 127 km west-northwest of Ternate in Indonesia's Maluku Islands. It began at 07:23 on 24 February 2001 and concluded at 00:13 on 25 February 2001, spanning 16 hours and 49 minutes during which five earthquakes were recorded. The sequence commenced with a magnitude 7.1 event at 35 km depth on 24 February at 07:23:48. Subsequent events included a magnitude 5.8 quake at 33 km depth at 16:07:47, followed by a magnitude 6.2 event at the same depth at 16:33:44. A magnitude 5.3 shock occurred at 22:56:45, also at 33 km depth, and the swarm ended with a magnitude 4.0 event at 00:13:18 on 25 February at 33 km depth. Depths remained shallow throughout, consistent with activity in the upper crust of this tectonically complex zone. This swarm reflects clustered seismicity without a dominant mainshock-aftershock pattern, typical of stress redistribution along regional fault systems. The Molucca Sea region experiences such episodes due to interactions among the Philippine Sea, Eurasian, and Australian plates, producing both strike-slip and thrust mechanisms at depths of 30-40 km. The area around Ternate lies within the Ring of Fire and features active subduction along the Halmahera Arc. Historical records show repeated large-magnitude events, underscoring persistent seismic hazard. Since 2000, multiple earthquakes exceeding magnitude 7.0 have struck nearby, including a magnitude 7.1 event on 24 February 2001 just 9 km from the swarm center. Additional strong shocks comprise a magnitude 7.5 on 21 January 2007 (27 km distant), a magnitude 7.1 on 15 November 2014 (68 km distant), a magnitude 7.1 on 14 November 2019 (36 km distant), and a magnitude 7.4 on 1 April 2026 (14 km distant). These events illustrate ongoing tectonic loading and release in a narrow corridor of high strain accumulation. Depths near 33 km align with the brittle-ductile transition zone, where fluids or slab dehydration may facilitate swarm-like sequences. Monitoring such clusters aids in assessing short-term hazard escalation in this densely populated volcanic archipelago.

References

SeismoSight internal swarm classification PS20010225.1.
USGS earthquake catalog for events since 2000.01.01.