Location:

Period:

2 Dec 2023 14:37:04 - 8 Dec 2023 10:32:39 (5 days 19 hours 55 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

107

M 7.0+:

M 7.6; 19 km E of Gamut, Philippines; (2 Dec 2023) (64km from the swarm center)

16 swarms found nearby.

2009

PS20090521.1(109.2km)

21 May

8 hours

5 earthquakes

2012

PS20120831.1(168.9km)

31 Aug

19 hours

15 earthquakes

PS20120904.1(188.6km)

4 Sep

14 hours

9 earthquakes

2014

PS20140530.1(67.6km)

30 May

5 hours

6 earthquakes

PS20140531.1(67.9km)

31 May

1 hours

9 earthquakes

2018

PS20181029.1(62.5km)

29 Oct

7 hours

5 earthquakes

2019

PS20190208.1(122.4km)

8 Feb

9 hours

7 earthquakes

PS20190426.1(103.4km)

26 Apr

15 hours

9 earthquakes

2023

S20231202.2(56.4km)

2 Dec

4 days 13 hours

158 earthquakes

S20231203.1(63.8km)

2 Dec

3 days 8 hours

49 earthquakes

S20231203.2(49.0km)

2 Dec

5 days 21 hours

67 earthquakes

S20231203.3(76.2km)

2 Dec

3 days 3 hours

41 earthquakes

PS20231212.1(34.4km)

11 Dec

14 hours

5 earthquakes

PS20231224.1(55.2km)

23 Dec

15 hours

5 earthquakes

2024

PS20240803.1(83.6km)

2 Aug

5 hours

7 earthquakes

2025

PS20251010.1(173.8km)

10 Oct

1 day 8 hours

21 earthquakes

AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20231202.1 Near Hinatuan, Philippines

Seismic swarm PS20231202.1 was recorded from 14:37 on 2 December 2023 to 10:32 on 8 December 2023, centered 35 km east-northeast of Hinatuan in Surigao del Sur, eastern Mindanao. Over 139 hours and 55 minutes, 107 earthquakes were detected. The sequence began with a magnitude 7.6 event at 40 km depth and included multiple events exceeding magnitude 6.0, with the strongest aftershocks reaching 6.9.

The first 100 events displayed a characteristic swarm pattern of clustered, moderate-to-large shocks rather than a single mainshock-aftershock decay. Depths ranged primarily between 10 km and 80 km, consistent with activity along crustal faults and the deeper interface of regional subduction. Notable larger events included a pair of magnitude 6.6 shocks on 3 December at depths of 19 km and 63 km, a magnitude 6.0 doublet on 2 December, and a magnitude 6.9 event on 3 December at 20 km depth. Many events clustered in the 5.0–5.8 range, with shallower foci (under 30 km) often following deeper triggering events.

Eastern Mindanao lies within the tectonically active Philippine Mobile Belt, where the Philippine Sea Plate subducts westward beneath the Sunda Plate along the Philippine Trench. This convergence, combined with left-lateral strike-slip motion along the Philippine Fault, produces frequent moderate and large earthquakes. The swarm location aligns with the central segment of the Philippine Fault and its subsidiary structures in Surigao del Sur, an area long recognized for elevated seismicity.

Historical records since 2000 show eight prior swarms in the immediate region: one in 2009, two in 2012, two in 2014, one in 2018, and two in 2019. These episodes indicate episodic swarm behavior superimposed on the background rate of tectonic earthquakes. The 2 December 2023 magnitude 7.6 mainshock, located 64 km from the swarm centroid, fits the established pattern of large events capable of triggering prolonged aftershock sequences and secondary swarms along adjacent fault segments.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) maintains continuous monitoring of the area through a national seismic network. Updated hazard assessments recognize the Surigao segment of the Philippine Fault as capable of generating magnitude 7+ events, with recurrence intervals on the order of several decades to a century. The December 2023 swarm underscores the ongoing seismic hazard in this densely populated coastal region of Mindanao.

References

Philippine Institute of Volcanology and Seismology (PHIVOLCS) earthquake catalog and fault database
United States Geological Survey (USGS) Earthquake Hazards Program
SeismoSight internal swarm classification PS20231202.1