Location:

Period:

2 Dec 2023 15:38:26 - 8 Dec 2023 12:56:57 (5 days 21 hours 18 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

11 swarms found nearby.

2009

PS20090521.1(74.9km)

21 May

8 hours

5 earthquakes

2014

PS20140530.1(98.6km)

30 May

5 hours

6 earthquakes

PS20140531.1(97.8km)

31 May

1 hours

9 earthquakes

2018

PS20181029.1(22.5km)

29 Oct

7 hours

5 earthquakes

2023

PS20231202.1(49.0km)

2 Dec

5 days 19 hours

107 earthquakes

S20231202.2(20.6km)

2 Dec

4 days 13 hours

158 earthquakes

S20231203.1(29.2km)

2 Dec

3 days 8 hours

49 earthquakes

S20231203.3(29.8km)

2 Dec

3 days 3 hours

41 earthquakes

PS20231212.1(17.0km)

11 Dec

14 hours

5 earthquakes

PS20231224.1(38.2km)

23 Dec

15 hours

5 earthquakes

2024

PS20240803.1(41.6km)

2 Aug

5 hours

7 earthquakes

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Seismic Swarm S20231203.2: Analysis of Earthquake Activity Near Hinatuan, Philippines

A seismic swarm designated S20231203.2 was recorded 67 km east-northeast of Hinatuan in Surigao del Sur, Philippines. The sequence began at 15:38 on 2 December 2023 and concluded at 12:56 on 8 December 2023, spanning 141 hours and 18 minutes. During this period, 67 earthquakes were registered, with magnitudes ranging from 3.0 to 4.9 and focal depths between 1 km and 61 km.

The swarm exhibited typical characteristics of clustered seismicity, featuring an initial sequence of moderate events followed by a gradual decline in both frequency and magnitude. Early activity on 2 December included multiple events above magnitude 4.5 at depths of 38–61 km. Subsequent days showed a mix of deeper and shallower events, with several clusters occurring at depths under 10 km on 3 December. By 7–8 December, activity had diminished to isolated events below magnitude 4.0.

The Philippines lies within the Pacific Ring of Fire, where complex tectonic interactions drive frequent seismicity. The region east of Hinatuan is influenced by the Philippine Sea Plate subducting along the Philippine Trench and strike-slip motion along the Philippine Fault system. These structures accommodate convergence rates of approximately 7–9 cm per year, producing both shallow crustal earthquakes and deeper events associated with the subducting slab. Historical records indicate that the broader Mindanao region experiences recurrent seismic swarms linked to fluid migration or stress transfer within these fault networks.

Since 2000, seven swarms have been documented in the area, occurring in 2009 (1 swarm), 2014 (2 swarms), 2018 (1 swarm), and 2023 (3 swarms). This pattern suggests episodic unrest rather than isolated mainshock-aftershock sequences, consistent with the tectonic regime of the Philippine archipelago.

The December 2023 swarm provides insight into short-term clustering behavior. Events were distributed across a range of depths, indicating possible involvement of both the overriding plate and the subducting slab. No single dominant mainshock was evident; instead, the sequence displayed a diffuse temporal evolution typical of swarm activity driven by aseismic slip or pore-pressure changes.

Such episodes underscore the importance of continuous monitoring in this high-hazard zone. While individual events remained below damaging thresholds, the cumulative energy release and spatial distribution highlight ongoing tectonic strain accumulation along the eastern Mindanao margin.

References

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