Location:

Period:

9 Apr 2001 09:00:57 - 12 Apr 2001 21:19:04 (3 days 12 hours 18 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

3 swarms found nearby.

2008

PS20081219.1(98.9km)

18 Dec

1 day 14 hours

8 earthquakes

2011

PS20110317.2(113.0km)

16 Mar

16 hours

5 earthquakes

2015

PS20150917.2(84.1km)

17 Sep

21 hours

9 earthquakes

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Seismic Swarm S20010410.1 Off Valparaíso, Chile: Geological Context and Event Analysis

Seismic swarm S20010410.1 occurred approximately 136 km west-northwest of Valparaíso, Chile, within the Peru-Chile Trench subduction zone. This region marks the boundary where the Nazca Plate converges with and subducts beneath the South American Plate at rates of about 6–7 cm per year. The resulting compressional stresses generate frequent seismic activity, including both megathrust events and shallower crustal swarms.

The swarm initiated at 09:00 on 9 April 2001 and concluded at 21:19 on 12 April 2001, spanning 84 hours and 18 minutes. During this interval, 53 earthquakes were recorded. The sequence featured a prominent initial event of magnitude 6.7 at a depth of 11 km, followed by numerous smaller events ranging from magnitude 3.4 to 4.6. Depths generally varied between 10 km and 33 km, consistent with activity along the plate interface and within the overriding crust.

Geologically, the Valparaíso segment lies within the Andean subduction system, characterized by a well-developed accretionary prism and forearc basin. Historical seismicity in this area includes destructive events such as the 1730 and 1822 earthquakes, both estimated above magnitude 8.5, as well as the 1906 Valparaíso quake of magnitude 8.2. These events highlight the segment’s capacity for large ruptures, though swarms like S20010410.1 often represent localized stress adjustments without leading to immediate major mainshocks.

Analysis of the swarm reveals a classic pattern of clustered activity with rapid decay after the initial large event. Most subsequent shocks clustered in the first 24 hours, with magnitudes predominantly between 3.5 and 4.2. The distribution of depths suggests involvement of both the subduction interface and overlying crustal faults, typical of interplate stress transfer in this tectonic setting.

Modern monitoring by regional networks confirms that such swarms are relatively common along the Chilean margin, often linked to fluid migration or aseismic slip episodes. Updated catalogs through 2023 continue to document elevated background seismicity in the same offshore zone, underscoring its persistent seismic hazard.

References
USGS Earthquake Catalog (events 2001–2023)
Servicio Nacional de Geología y Minería (SERNAGEOMIN) Chile seismic reports
Global CMT Project focal mechanism database
Tectonics of the Andean Subduction Zone, Geological Society of America Special Paper 2022