Location:

Period:

31 Dec 2013 20:01:06 - 1 Jan 2014 00:01:16 (4 hours)

Volcanoes in 100km radius:

None

Earthquakes:

3 swarms found nearby.

2006

PS20061009.2(167.1km)

9 Oct

1 hours

9 earthquakes

PS20061011.1(180.4km)

10 Oct

16 hours

8 earthquakes

2014

PS20141117.1(46.5km)

17 Nov

19 hours

6 earthquakes

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Seismic Swarm PS20140101.1 Near Davila, Philippines: Geological Context and Event Analysis

Seismic swarm PS20140101.1 was recorded in the waters 76 km NNW of Davila, Philippines, spanning from 20:01 on 31 December 2013 to 00:01 on 1 January 2014. Five earthquakes occurred within this four-hour window, providing a concentrated sequence of activity in a tectonically active portion of northern Luzon.

The events unfolded as follows. The initial shock at 20:01:06 on 31 December measured magnitude 5.7 at a depth of 10 km. Three minutes later, at 20:04:32, a magnitude 5.0 event struck at 20 km depth. Activity continued with a magnitude 5.2 earthquake at 21:32:01 (10 km depth), followed by another magnitude 5.2 at 23:41:47 (10 km depth). The sequence concluded at 00:01:16 on 1 January with a magnitude 5.1 shock at 10 km depth. Depths remained shallow throughout, consistent with upper-crustal faulting in the region.

The Philippine archipelago lies within the Pacific Ring of Fire, where the Philippine Sea Plate converges with the Eurasian Plate. In northern Luzon, this interaction involves oblique subduction along the Manila Trench to the west and strike-slip motion along segments of the Philippine Fault system. The swarm location falls near the northern extension of these structures, where crustal stresses accumulate from both plate boundary forces and local fault interactions. Historical records document frequent moderate seismicity in this corridor, reflecting ongoing deformation.

Since 1 January 2000, only two swarms have been classified in the area, with the earlier episode occurring in 2006. Swarm PS20140101.1 therefore represents a rare clustering of events, highlighting episodic rather than continuous release of strain. Such sequences often indicate fluid migration or stress triggering along pre-existing fractures, though detailed source mechanisms require further instrumental analysis.

The shallow focal depths (mostly 10 km) suggest rupture within the brittle upper crust, where rock strength permits sudden slip. Magnitudes between 5.0 and 5.7 indicate moderate energy release capable of local ground shaking but limited potential for widespread damage given the offshore epicenters. No aftershock progression beyond the defined swarm window was noted in the classification.

This pattern aligns with the broader tectonic framework of the Philippines, where convergence rates average 6–8 cm per year. Updated regional models continue to emphasize the role of inherited faults in channeling seismic energy, particularly in the Ilocos Norte offshore domain. Continued monitoring by national networks remains essential for distinguishing isolated swarms from precursors to larger mainshocks.

References

Philippine Institute of Volcanology and Seismology (PHIVOLCS) regional tectonic summaries
United States Geological Survey (USGS) earthquake catalog and plate boundary data
SeismoSight internal swarm classification records