Location:

Period:

1 Sep 2020 04:09:27 - 1 Sep 2020 21:09:17 (16 hours 59 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

6 swarms found nearby.

2006

PS20060430.1(94.5km)

30 Apr

16 hours

19 earthquakes

S20060501.1(79.2km)

30 Apr

3 days 16 hours

53 earthquakes

2015

PS20151111.1(190.2km)

11 Nov

1 hours

6 earthquakes

2020

S20200901.1(15.1km)

1 Sep

3 days 19 hours

90 earthquakes

2021

S20210704.1(99.6km)

4 Jul

2 days 11 hours

72 earthquakes

2026

S20260313.2(96.2km)

13 Mar

4 days 9 hours

62 earthquakes

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Seismic Swarm PS20200901.1 Near Vallenar, Chile: Event Analysis and Regional Context

On 1 September 2020, a seismic swarm designated PS20200901.1 was recorded 79 km NNW of Vallenar in northern Chile’s Atacama Region. The sequence began at 04:09 UTC and concluded at 21:09 UTC, encompassing 10 earthquakes over 16 hours and 59 minutes. Magnitudes ranged from 5.0 to 6.8, with focal depths between 2 km and 28 km.

The swarm initiated with two events of magnitude 6.8 at 04:09:27 and 04:09:28, followed by a magnitude 6.3 event at 04:30:02. Subsequent activity included five events between magnitudes 5.0 and 5.8 through the afternoon, culminating in a magnitude 6.5 earthquake at 21:09:17. Depths remained predominantly shallow, consistent with crustal stress release along regional fault systems.

This activity occurred within the tectonically active margin where the Nazca Plate subducts beneath the South American Plate at approximately 6–7 cm per year. Northern Chile’s Atacama Region lies above this convergent boundary, producing frequent moderate-to-large earthquakes. The shallow depths observed align with known seismogenic zones in the overriding plate and along the plate interface.

Chile maintains one of the highest levels of seismic hazard globally due to its position on the Pacific Ring of Fire. Historical records document major events such as the 2010 Maule earthquake (Mw 8.8) and the 2014 Iquique earthquake (Mw 8.2), both generated by the same subduction process. The Vallenar area has experienced recurrent moderate seismicity, reflecting ongoing strain accumulation and release.

Since 2000, three swarms have been identified in the region according to internal classification records: two events in 2006 and one in 2015. The 2020 sequence represents the most recent and energetic swarm documented under this framework, highlighting episodic clustering of moderate-magnitude events without a single dominant mainshock-aftershock pattern.

Such swarms provide insight into fluid migration or aseismic slip processes that can modulate stress on nearby faults. Continued monitoring by regional networks supports improved characterization of these transient sequences and their relation to long-term subduction dynamics.

References: USGS Earthquake Hazards Program Servicio Nacional de Geología y Minería (SERNAGEOMIN) Chile Global Centroid Moment Tensor Catalog