Valparaiso Earthquake

First Posting | Summary
Posting Date: April 25, 2017, 10:00:00 AM

An M6.9 (USGS) earthquake struck off the western coast of Chile at 5:38 p.m. local time (21:38 UTC) on Monday, April 24. The epicenter of the quake was some 22 miles (35 km) from the coastal city of Valparaíso at a depth of about 15.5 miles (25 km) below sea level.

ShakeMap of the April 24 M6.9 earthquake that struck offshore Valparaíso, Chile. (Source: USGS)

Reported Damage

This shallow earthquake was strongly felt in the Chilean capital, Santiago, about 85 miles (25 km) from the epicenter; it was also felt on the other side of the Andes Mountains in Argentina.  There are, however, no reports of serious damage or casualties. Brief power outages were reported, cell phone service was interrupted, and minor landslides have occurred.

A tsunami warning was issued in Valparaíso. Along the coast people evacuated themselves to higher ground, but as no threat materialized the warning was canceled; the Pacific Tsunami Warning Center reported a tsunami of just six inches (15 cm).

Seismology

Chile is located in an earthquake-prone region that has experienced 79 earthquakes of M1.5 or greater in the past 30 days. At least two aftershocks of magnitudes 5.0 and 5.4 have been recorded in the area of the April 24 temblor; both were felt in Santiago.

The April 24 M6.9 earthquake occurred along the plate interface in the Chilean Trench where the Nazca Plate is subducting under the South American Plate. This event occurred at the southernmost part of the subduction zone fault that was ruptured in the 2010 M8.8 Maule earthquake. This same fault segment has been repeatedly ruptured in large earthquakes; it was also ruptured in the 1985 M8.0 Valparaíso earthquake, which caused significant damage in Santiago, and in the 1906 M8.2-8.5 earthquake. The most recent large earthquake in the immediate vicinity was the 2012 M6.7, whose reported epicenter was a little over 50 km to the north of the April 24 event.

Exposure at Risk

The majority of insured risk in Chile is located in the cities of San Antonio, Valparaíso, and Santiago.  Valparaíso is one of Chile’s most important seaports, and the greater Valparaíso region is the second-largest metropolitan area in the country. Santiago has grown rapidly in recent decades to become one of the largest cities in the Americas. It contains nearly 72% of the country’s exposure and approximately 50% of the construction in the area is less than 25 years old. Chile has developed and enforced some of the world’s most stringent seismic building codes and invested heavily in the structural reinforcement of buildings. Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. High-rise office buildings in Santiago reportedly swayed for about 30 seconds in response to the earthquake, but no damage has been reported.

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Posting Date: April 25, 2017, 10:00:00 AM