A seismic swarm designated S20220114.1 was recorded in the Flores Sea, eastern Indonesia, beginning at 03:53 on 14 January 2022 and concluding at 04:39 on 16 January 2022. Over this 48-hour and 46-minute period, 45 earthquakes were detected, with magnitudes ranging from 2.5 to 5.1 and focal depths between 10 and 31 km. The sequence featured a notable concentration of events on 14 January, including the largest shock of magnitude 5.1 at 16:43, followed by additional moderate events such as magnitude 4.6 at 03:59, 4.5 at 18:47, 4.3 at 11:12 on 15 January, and 4.5 at 20:44 on 15 January. Shallower events clustered around 10 km depth, while many smaller shocks occurred at depths of 20–30 km, illustrating a vertically distributed rupture process typical of swarm activity.
The Flores Sea lies within a tectonically complex region of Indonesia where the Australian Plate converges with the Eurasian Plate along the Sunda subduction zone. This setting produces back-arc thrusting along the Flores Thrust, a north-dipping fault system responsible for much of the regional seismicity. The swarm’s shallow to intermediate depths align with activity along this thrust and associated crustal faults. Indonesia experiences frequent earthquake swarms due to its position on the Pacific Ring of Fire, with the Flores Sea area historically affected by events such as the 1992 magnitude 7.8 Flores earthquake and subsequent aftershock sequences that demonstrated similar thrust-fault mechanisms.
Analysis of the 45 events shows a gradual decay in frequency after the initial peak on 14 January, with events becoming sparser by 16 January. Most shocks remained below magnitude 4.0 after the main phase, consistent with swarm behavior driven by fluid migration or stress transfer rather than a single large mainshock-aftershock cascade. Depths predominantly in the upper crust suggest activation of the Flores Thrust and subsidiary structures without significant deeper slab involvement.
Such swarms contribute to ongoing seismic hazard assessment in eastern Indonesia, where population centers on nearby islands remain exposed to potential ground shaking and secondary effects such as tsunamis. Continued monitoring by regional networks supports improved understanding of fault interactions in this convergent margin.
References:
SeismoSight internal swarm classification S20220114.1 data records.
USGS Earthquake Catalog for Flores Sea regional tectonics and historical events.
Global CMT catalog for thrust-fault mechanisms in the Flores back-arc region.