Very strong M7.4 earthquake hits Chile – Argentina border region

A very strong earthquake registered by the USGS as M7.4 hit the Chile – Argentina border region at 01:50 UTC on July 19, 2024 (21:50 LT, July 18). The agency is reporting a depth of 126 km (78 miles). EMSC is reporting the same magnitude and depth.

The epicenter was located 45.5 km (28.3 miles) ESE of San Pedro de Atacama (population 2 000) and 134.3 km (83.5 miles) ESE of Calama (population 143 084), Chile.

184 000 people are estimated to have felt very strong shaking, 161 000 strong, 2 532 000 moderate, and 1 275 000 light.

The USGS issued a Yellow alert for shaking-related fatalities and economic losses. Some casualties and damage are possible and the impact should be relatively localized. Past yellow alerts have required a local or regional-level response.

Estimated economic losses are less than 1% of GDP of Chile.

Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are adobe block and rubble/field stone masonry construction.

Recent earthquakes in this area have caused secondary hazards such as tsunamis and landslides that might have contributed to losses.

Liquefaction triggered by this earthquake is estimated to be significant in severity and (or) spatial extent but the number of people living near areas that could have produced liquefaction in this earthquake is low.

There were no immediate reports of damage.

This quake occurred as the result of normal faulting, according to the USGS. The earthquake occurred at an intermediate depth within the subducted Nazca plate, at a depth of about 120 km (74 miles) under the triple country borders between Chile, Argentina, and Bolivia.

Focal mechanism solutions for the earthquake indicate that rupture occurred on either a steeply or shallowing dipping normal fault within the interior of the subducted Nazca slab. Slip on a fault of either orientation would accommodate the down-dip extension of the Nazca slab as it bends downward beneath South America.

At the location of the earthquake, the Nazca plate moves eastward with respect to the South America plate, subducting at the Peru-Chile Trench along the South America coastline at a velocity of about 74 mm (2.9 inches) per year.

Earthquakes like this event with focal depths between 70 and 300 km (43 and 186 miles) are commonly termed “intermediate-depth” earthquakes. Although the Chilean subduction zone is well known for producing very large earthquakes along the coastline, including the 2010 magnitude 8.8 Maule earthquake and 1960 magnitude 9.5 Valdivia earthquake, large (magnitude 7 and over) intermediate depth within the subduction zone are also relatively common.

Such earthquakes typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distances from their epicenters.

Estimated population exposure to earthquake shaking

Selected cities exposed

Regional seismicity

Featured image credit: TW/SAM, Google