Seismic Swarm Activity in Albania: March 23-24, 2023

Albania occupies a tectonically active segment of the Mediterranean region where the African plate converges with the Eurasian plate. This interaction produces frequent shallow crustal earthquakes along thrust faults and strike-slip structures within the Albanides fold-and-thrust belt. The country’s seismicity is dominated by events at depths of 5–20 km, consistent with the ongoing continental collision that has shaped the landscape since the Miocene.

Between 01:39 UTC on 23 March 2023 and 17:58 UTC on 24 March 2023, a seismic swarm designated S20230323.1 was recorded in Albania. In approximately 40 hours, 51 earthquakes were registered. The sequence began with a magnitude 2.3 event at 5 km depth, followed 4 minutes later by the largest shock of the swarm, magnitude 4.9 at 14 km. Subsequent activity included a magnitude 4.0 event at 10 km and a magnitude 4.5 event at 10 km, with the remaining events ranging from magnitude 1.9 to 3.4. Depths throughout the swarm remained shallow, predominantly between 2 km and 15 km, indicating brittle failure within the upper crust.

The temporal distribution showed the highest rate of events during the first 12 hours, after which activity declined steadily, concluding with a magnitude 2.2 event at 2 km depth. This pattern of rapid onset followed by gradual decay is characteristic of swarm sequences driven by fluid migration or aseismic slip rather than a single mainshock-aftershock cascade.

Historical records maintained since 2000 indicate that four comparable swarms have occurred in Albania. Single swarms were documented in 2010 and 2016, while two separate sequences took place in 2019. The 2023 swarm therefore represents the fifth swarm episode in the instrumental era and the first since 2019.

The geological setting explains the recurrence of such sequences. The external Albanides accommodate north-south shortening through a combination of thrust and transverse faulting. Low-magnitude swarms commonly cluster along these active structures, releasing strain accumulated from regional plate motion estimated at 4–5 mm per year. Shallow focal depths recorded in the March 2023 sequence align with the typical seismogenic thickness of the Albanides crust.

Continued monitoring of microseismicity remains essential for refining hazard assessments in this densely populated region. The March 2023 swarm, although moderate in energy release, underscores the persistent seismic potential along Albania’s convergent margin.

References

• Albanian Seismological Network bulletins (2023)
• European-Mediterranean Seismological Centre event catalogue
• Geological Survey of Albania tectonic maps
• SeismoSight internal swarm classification S20230323.1