Location:

Period:

10 Oct 2006 15:05:59 - 11 Oct 2006 07:32:22 (16 hours 26 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

5 swarms found nearby.

2006

PS20061009.2(15.9km)

9 Oct

1 hours

9 earthquakes

PS20061226.1(138.6km)

26 Dec

14 hours

7 earthquakes

2013

PS20140101.1(180.4km)

31 Dec

4 hours

5 earthquakes

2014

PS20141117.1(140.1km)

17 Nov

19 hours

6 earthquakes

2022

PS20220628.1(142.2km)

27 Jun

18 hours

5 earthquakes

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Seismic Swarm PS20061011.1 in the Philippine Islands Region

The Philippine Islands region forms part of the tectonically active Pacific Ring of Fire, where the Philippine Sea Plate converges with the Eurasian Plate along the Philippine Trench and associated subduction zones. This setting produces frequent seismic activity, including both isolated events and clustered sequences. Earthquake swarms, defined as groups of earthquakes occurring in close spatial and temporal proximity without a dominant mainshock, are characteristic of the area due to fluid migration, volcanic processes, and crustal stress adjustments along fault systems.

Swarm PS20061011.1 was recorded between 15:05 UTC on 10 October 2006 and 07:32 UTC on 11 October 2006, spanning 16 hours and 26 minutes. Eight earthquakes were registered during this interval, with magnitudes ranging from 5.0 to 5.7 and focal depths between 10 km and 70 km. The sequence began with a magnitude 5.0 event at 26 km depth, followed by additional events clustered around 10 km depth, including three magnitude 5.2 shocks in rapid succession. The largest event, magnitude 5.7 at 10 km depth, occurred at 06:43 UTC on 11 October. The swarm concluded with a magnitude 5.0 event at 26 km depth.

Such swarms reflect episodic stress release within the complex fault network of the Philippine archipelago. Depths predominantly near 10 km indicate activity within the upper crust, consistent with shallow thrust and strike-slip mechanisms prevalent along plate boundaries. Historical records since 1 January 2000 indicate this as the sole swarm identified in the region, underscoring the relative rarity of swarm-type sequences compared to typical mainshock-aftershock patterns in the area.

Geological studies of the Philippines highlight ongoing subduction-related deformation, with the archipelago experiencing an average of several hundred earthquakes annually above magnitude 4.0. The 2006 swarm aligns with known patterns of clustered seismicity near volcanic arcs and transform faults. Updated monitoring by global networks confirms continued seismic productivity in the region, though no subsequent swarms matching this classification have been noted in the intervening period.

The event provides insight into the dynamics of swarm behavior, where rapid temporal clustering may signal transient changes in pore pressure or aseismic slip. Depths extending to 70 km in one instance suggest possible involvement of the subducting slab interface. Overall, the sequence exemplifies the moderate-magnitude, shallow-to-intermediate depth activity typical of the Philippine Islands tectonic regime.

References

USGS Earthquake Catalog
Philippine Institute of Volcanology and Seismology (PHIVOLCS) Regional Tectonic Summaries
Global CMT Project Focal Mechanism Database