Location:

Period:

17 Nov 2014 13:34:11 - 18 Nov 2014 09:15:53 (19 hours 41 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

4 swarms found nearby.

2006

PS20061009.2(128.4km)

9 Oct

1 hours

9 earthquakes

PS20061011.1(140.1km)

10 Oct

16 hours

8 earthquakes

2008

PS20080401.1(190.2km)

1 Apr

11 hours

5 earthquakes

2013

PS20140101.1(46.5km)

31 Dec

4 hours

5 earthquakes

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Seismic Swarm PS20141117.1: Earthquake Activity 115 km NNW of Pagudpud, Philippines

A seismic swarm designated PS20141117.1 occurred in the waters northwest of the Philippines between 13:34 on 17 November 2014 and 09:15 on 18 November 2014. In 19 hours and 41 minutes, six earthquakes were recorded at a consistent depth of 10 km. The sequence began with a magnitude 5.1 event at 13:34:11 on 17 November, followed by a 5.3 event at 14:01:27, a 4.9 event at 14:04:26, a 5.4 event at 14:13:41, and a 5.0 event at 14:16:31. The swarm concluded with a magnitude 5.3 earthquake at 09:15:53 on 18 November.

The epicentral region lies along the western margin of the Philippine archipelago, where the Eurasian Plate subducts eastward beneath the Philippine Mobile Belt along the Manila Trench. This convergent boundary generates frequent moderate-depth seismicity and is capable of producing both interplate and intraplate events. The 10 km focal depth of the swarm events places them within the upper crust, consistent with shallow thrust or strike-slip faulting commonly observed in the forearc region northwest of Luzon.

The northern Philippines experiences elevated seismic hazard due to the interaction of multiple tectonic plates, including the Philippine Sea Plate to the east and the South China Sea basin to the west. Historical records document recurrent moderate-magnitude sequences in this offshore corridor, often occurring without a single dominant mainshock. Such swarms are interpreted as distributed brittle failure along secondary faults rather than classic mainshock-aftershock sequences driven by static stress transfer.

Since 1 January 2000, four swarms have been identified in the broader area. Earlier episodes occurred in 2006 (two swarms), 2008 (one swarm), and 2013 (one swarm). The 2014 swarm fits within this pattern of episodic, short-duration clusters of magnitude 4.9–5.4 events at shallow depth.

Seismic swarms in subduction forearc settings can reflect fluid migration, aseismic slip on adjacent segments, or stress perturbations from distant large earthquakes. The tightly clustered timing and uniform depths recorded in PS20141117.1 are characteristic of such swarm behavior and do not indicate immediate escalation to a larger rupture.

Ongoing monitoring by regional networks remains essential for distinguishing swarm activity from foreshock sequences in this tectonically complex zone.

References

USGS Earthquake Catalog
PHIVOLCS Seismological Bulletin
Global CMT Catalog