Location:

Period:

29 Oct 2018 13:41:13 - 29 Oct 2018 21:36:20 (7 hours 55 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.6; 19 km E of Gamut, Philippines; (2 Dec 2023) (9km from the swarm center)

15 swarms found nearby.

2001

PS20010101.1(198.2km)

1 Jan

1 day 0 hours

9 earthquakes

2009

PS20090521.1(88.6km)

21 May

8 hours

5 earthquakes

2014

PS20140530.1(96.7km)

30 May

5 hours

6 earthquakes

PS20140531.1(95.3km)

31 May

1 hours

9 earthquakes

2019

PS20190208.1(150.9km)

8 Feb

9 hours

7 earthquakes

PS20190426.1(143.3km)

26 Apr

15 hours

9 earthquakes

2023

PS20231202.1(62.5km)

2 Dec

5 days 19 hours

107 earthquakes

S20231202.2(40.9km)

2 Dec

4 days 13 hours

158 earthquakes

S20231203.1(48.1km)

2 Dec

3 days 8 hours

49 earthquakes

S20231203.2(22.5km)

2 Dec

5 days 21 hours

67 earthquakes

S20231203.3(16.3km)

2 Dec

3 days 3 hours

41 earthquakes

PS20231212.1(37.4km)

11 Dec

14 hours

5 earthquakes

PS20231224.1(60.3km)

23 Dec

15 hours

5 earthquakes

2024

PS20240803.1(53.3km)

2 Aug

5 hours

7 earthquakes

2025

PS20251010.1(138.1km)

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 PS20181029.1: Analysis of Activity Near Tagbina, Philippines

Seismic swarm PS20181029.1 occurred in the Philippines on 29 October 2018, centered 9 km southeast of Tagbina in Surigao del Sur province on Mindanao island. The sequence began at 13:41 local time and concluded at 21:36, encompassing five earthquakes over 7 hours and 55 minutes. This event provides insight into localized tectonic stress release within a highly active subduction zone.

The Philippines lies at the convergent boundary between the Philippine Sea Plate and the Eurasian Plate. Subduction along the Philippine Trench drives frequent seismic activity, while the left-lateral Philippine Fault Zone accommodates lateral motion across the archipelago. The swarm location near Tagbina sits within this complex tectonic setting, where shallow crustal faults interact with deeper subduction-related structures. Such swarms often reflect fluid migration or stress triggering along fault segments rather than a single mainshock-aftershock sequence.

Event details reveal predominantly shallow foci at 10 km depth for the initial four shocks, with magnitudes ranging from 5.1 to 5.3. These occurred in rapid succession between 13:41 and 14:51, suggesting clustered slip on a shallow fault plane. The final event at 21:36 registered magnitude 4.3 but originated at 89 km depth, indicating possible involvement of the subducting slab. The tight temporal clustering and magnitude similarity underscore the swarm character, distinct from typical aftershock decay patterns.

Historical records since 2000 document only four prior swarms in the immediate region: one each in 2001 and 2009, and two in 2014. This low frequency suggests that swarm-type activity remains episodic rather than routine. The 2018 swarm aligns with this pattern, highlighting intermittent periods of distributed microseismicity amid the broader background of larger events.

A notable regional development occurred on 2 December 2023 with a magnitude 7.6 earthquake located 19 km east of Gamut, approximately 9 km from the 2018 swarm center. This event, one of the strongest in recent years, likely influenced local stress fields and may relate to ongoing strain accumulation along nearby fault segments.

Geological monitoring in the Philippines relies on networks operated by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) alongside international catalogs. Continued observation of swarm parameters aids in distinguishing tectonic from volcanic influences, although no surface volcanic features are directly associated with the Tagbina area.

References

Philippine Institute of Volcanology and Seismology (PHIVOLCS) seismic bulletins
United States Geological Survey (USGS) earthquake catalog
SeismoSight internal swarm classification records