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Location:
6 km WSW of Kiblawan, Philippines
Period:
15 Dec 2019 06:25:15 - 20 Dec 2019 03:45:52 (4 days 21 hours 20 minutes)
Volcanoes in 100km radius:
Matutum(33km), Apo(42km), Melebingoy(68km)
Earthquakes:
56
3 swarms found nearby.
2002
PS20020306.1(112.0km)
5 Mar
22 hours
6 earthquakes
2019
PS20191029.1(23.1km)
29 Oct
20 hours
10 earthquakes
15 Dec
6 hours
8 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20191215.1: Analysis of Earthquake Activity Near Kiblawan, Philippines

Seismic swarm S20191215.1 occurred in a tectonically active region of southern Mindanao, Philippines, centered 6 km west-southwest of Kiblawan in Davao del Sur province. The sequence began at 06:25 on 15 December 2019 and concluded at 03:45 on 20 December 2019, spanning 117 hours and 20 minutes. During this period, 56 earthquakes were recorded, with magnitudes ranging from 3.5 to 5.0 and focal depths predominantly between 1 km and 38 km.

The swarm exhibited a typical pattern of clustered seismic energy release, featuring multiple events of magnitude 4.5–4.9 within the first 48 hours, followed by a gradual decline in frequency and intensity. Notable peaks included five events of magnitude 4.7 or greater on 15 December alone, with the strongest shocks reaching magnitude 5.0 on 17 and 18 December at depths of 10 km. Shallower events (depths under 10 km) were interspersed throughout, indicating possible involvement of both crustal and near-surface fault structures.

Mindanao lies within the Philippine Mobile Belt, a complex zone of deformation driven by the oblique convergence of the Philippine Sea Plate and the Sunda Plate. The area around Kiblawan is influenced by the Philippine Fault System and subsidiary structures such as the Cotabato Fault, which accommodate left-lateral strike-slip motion and accommodate regional strain. Historical seismicity in Davao del Sur reflects this setting, with frequent moderate earthquakes linked to fault reactivation rather than volcanic processes.

Since 2000, only three swarms have been documented in the immediate vicinity, underscoring the episodic nature of such sequences. One swarm occurred in 2002, while two took place in 2019, suggesting a possible increase in clustered activity during that year. These events typically involve rapid successions of similar-magnitude shocks without a single dominant mainshock-aftershock progression.

The 2019 swarm aligns with broader patterns observed along Mindanao’s western and central fault zones, where fluid migration or aseismic slip may trigger prolonged low-to-moderate energy release. Depths clustered around 10 km for many larger events point to nucleation within the seismogenic crust, consistent with regional fault models.

Monitoring by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) provides essential data for such sequences, aiding in distinguishing swarms from foreshock-mainshock sequences. No significant damage or casualties were associated with this particular swarm, though it highlights the ongoing seismic hazard in southern Mindanao.

References

  • Philippine Institute of Volcanology and Seismology (PHIVOLCS) earthquake catalog and fault maps.
  • United States Geological Survey (USGS) Earthquake Hazards Program regional tectonic summaries for the Philippines.