Seismic Activity in the Flores Sea Region

The Flores Sea, situated between the islands of Flores and Sulawesi in eastern Indonesia, lies within one of the world's most tectonically active zones. On 14 December 2021 at 03:20 local time, a magnitude 7.3 earthquake struck the area at a depth of 14.2 km. This event highlights the persistent seismic hazards driven by complex plate interactions in the region. The Flores Sea forms part of the Banda Arc system, where the Australian Plate converges with the Sunda Plate. This convergence produces a combination of subduction, collision, and back-arc deformation. The shallow depth of the 2021 event suggests rupture along an active thrust fault, consistent with back-arc thrusting north of the volcanic arc. Regional geology features folded sedimentary basins, volcanic islands, and fault systems that accommodate oblique convergence at rates of approximately 70 mm per year. Historical records document frequent large earthquakes in the Flores Sea and adjacent areas. Since 2000, notable events include the 27 February 2015 magnitude 7.0 earthquake located 150 km NNE of Maumere, Indonesia, approximately 48 km from the 2021 epicenter. That event also occurred at shallow depth and produced strong shaking across Flores and nearby islands. The recurrence of magnitude 7+ earthquakes underscores the high strain accumulation along local fault networks. Geological studies indicate that the region has experienced significant deformation since the Miocene, with uplift of the Outer Banda Arc and subsidence in forearc and back-arc basins. Volcanic activity associated with the Sunda Arc contributes additional hazards, though the 2021 and 2015 events were primarily tectonic. Tsunami risk remains elevated due to the shallow bathymetry and potential for seafloor displacement. Monitoring by regional seismic networks continues to improve early-warning capabilities. The 2021 Flores Sea earthquake caused limited structural damage but served as a reminder of the need for resilient infrastructure in this rapidly deforming margin.

References

USGS Earthquake Catalog (events of 14 Dec 2021 and 27 Feb 2015)
Global CMT Catalog
Indonesian Meteorological, Climatological, and Geophysical Agency (BMKG) reports