Earthquake Swarm S20240719.1 in Antofagasta, Chile

An earthquake swarm designated S20240719.1 was recorded in the Antofagasta region of northern Chile between 02:00 on 19 July 2024 and 09:22 on 20 July 2024. Over this 31-hour period, 32 events were detected, providing a detailed snapshot of seismic activity along the Andean subduction zone.

The swarm exhibited magnitudes ranging from 2.5 to 5.0, with the largest event occurring at 02:15:52 on 19 July. Depths clustered between 131 km and 188 km, consistent with intermediate-depth seismicity within the subducting slab. Activity began with several events above magnitude 3.5 in the first hour, followed by a gradual decline in both frequency and size. Smaller events below magnitude 3.0 dominated the later stages, with the final recorded shock measuring 3.1 at 132 km depth.

Antofagasta lies above the contact between the Nazca and South American plates, where the oceanic Nazca plate subducts eastward at approximately 6–7 cm per year. This tectonic setting produces both shallow megathrust earthquakes and deeper intraslab events. The observed depth range of the swarm aligns with the expected location of the slab beneath the coastal cordillera, where dehydration reactions and phase transitions can trigger brittle failure.

Northern Chile has experienced recurrent seismic swarms and aftershock sequences. Historical records document significant activity in 1877 and 1960, while instrumental monitoring since the 1980s has captured numerous clusters at intermediate depths. These swarms often lack a single dominant mainshock and instead reflect distributed stress release along pre-existing faults within the slab.

The 2024 swarm displayed typical characteristics of intraslab sequences: a rapid onset, relatively short duration, and a magnitude-frequency distribution dominated by moderate events. No surface rupture or significant damage was associated with the activity, as expected for events at these depths.

Seismic monitoring networks operated by Chilean institutions continue to track such sequences to refine models of slab geometry and stress transfer. Data from S20240719.1 contribute to ongoing efforts to understand how fluids and mineral transformations influence rupture processes at depths exceeding 100 km.

References

• USGS Earthquake Catalog
• Servicio Nacional de Geología y Minería (SERNAGEOMIN) seismic bulletins
• National Seismological Center, University of Chile (CSN) reports
• Plate boundary studies in the Central Andes (Oncken et al., 2022)