A seismic swarm designated PS20220314.1 occurred 77 km west-northwest of Cabra in the Philippines. The sequence began at 21:05 on 13 March 2022 and concluded at 08:05 on 15 March 2022, spanning 34 hours and 59 minutes. During this period, seven earthquakes were recorded, with the largest reaching magnitude 6.4 at a depth of 11 km.
The event timeline shows an initial strong shock followed by several moderate aftershocks clustered at shallow depths around 10 km. Subsequent activity included events of magnitudes 5.1, 5.0, 4.8, 5.2, 5.0, and a final 5.0, all within the same narrow depth range. Such shallow focal depths are characteristic of crustal faulting in the region.
The Philippines lies within the Pacific Ring of Fire, where complex interactions between the Philippine Sea Plate and the Eurasian Plate drive frequent seismicity. The area west of Cabra, part of the Lubang Island group offshore Luzon, sits near the boundary influenced by the Manila Trench subduction zone to the west and strike-slip fault systems associated with the Philippine Fault Zone. These tectonic settings produce both subduction-related and transform-style earthquakes, with historical records indicating recurrent moderate-to-strong events in the central Philippine archipelago.
Swarm activity in this specific offshore zone remains infrequent. Since 2000, only two prior swarms have been documented in the same locale: one in 2008 consisting of a single event cluster and another in 2017 also limited to one swarm sequence. The 2022 swarm therefore represents a notable but not unprecedented episode of clustered seismicity.
Seismic swarms of this type often reflect fluid migration or aseismic slip along faults rather than a single large rupture. In the Philippine setting, they may also relate to volcanic or hydrothermal processes along the arc, although no direct link to nearby volcanic centers was identified in this instance. Monitoring by national agencies continues to track aftershock patterns to assess ongoing hazard levels.