A seismic swarm designated S20221213.1 occurred in the Bali region of Indonesia between 09:56 on 13 December 2022 and 18:58 on 15 December 2022. Over this 57-hour period, 40 earthquakes were recorded. The sequence featured predominantly shallow events with magnitudes between 2.5 and 5.2, clustered at depths of 9–22 km. The strongest shock reached magnitude 5.2 at 10:38 on 13 December, followed by several events above magnitude 4.0, including magnitudes 4.9, 4.4, 4.3, 4.1, and 3.8. Most activity concentrated within the first 24 hours, with activity tapering gradually through 15 December.
This swarm represents a notable cluster of low-to-moderate seismicity typical of the region’s tectonic setting. Bali forms part of the Sunda Arc, where the Indo-Australian Plate subducts beneath the Eurasian Plate at rates of approximately 6–7 cm per year. The resulting compressional regime generates frequent shallow crustal earthquakes and fuels the island’s volcanic centers, including Mount Agung and Mount Batur. Historical records document recurrent seismic swarms linked to fluid migration or stress transfer along local fault systems within this subduction environment.
Since 2000, only one prior swarm has been identified in the same area, occurring in 2018. The 2022 sequence therefore constitutes the second documented swarm in more than two decades, underscoring the episodic nature of such activity. All events remained at shallow depths consistent with upper-crustal faulting above the subduction interface.
The swarm produced no reported damage or casualties, reflecting the moderate magnitudes involved. Continued monitoring by regional seismic networks remains essential given Bali’s high population density and tourism infrastructure. Future analysis of waveform data may clarify whether the sequence resulted from magmatic processes or tectonic stress release.
USGS Earthquake Catalog
Indonesian Meteorological, Climatological, and Geophysical Agency (BMKG) Annual Seismicity Reports
Global Volcanism Program, Smithsonian Institution – Bali volcanic arc overview