Historical research warns of tsunami danger in the central zone of Chile

RIO DE JANEIRO, BRAZIL – On September 16, 2015, a magnitude 8.4 earthquake offshore Illapel, Coquimbo region, shook north-central Chile. The event was followed by a tsunami on the contact surface between the Nazca plate and the South American plate. A little more than six years after that event, research from the University of Chile evidences the complexity of the rupture that caused the earthquake.

The multidisciplinary study “Complex Rupture of the 2015 Illapel Earthquake Mw 8.3 and Prehistoric Events in the Central Chile Tsunami Gap,” conducted by academics from the Geology Department of the house of studies, compared the impact of the 2015 tsunami in Coquimbo with other historical ones from 1943, 1922 and 1877 to establish its complexity.

WHAT DID THEY FIND?

The 2015 tsunami would be equivalent to two in one, associated with two main seismic ruptures:

• One originating closer to the coast, in front of Caleta Sierra-Puerto Oscuro.
• Another near the tectonic trench, where the Nazca and South American plates meet, farther from the coast and in front of Punta Lengua de Vaca in Tongoy Bay.

“This would explain why the tsunami arrived quickly, about 4-5 minutes after the earthquake, in the closest areas,” geologist and academic Gabriel Easton said.

“Moderate to strong magnitude earthquakes, such as the Illapel earthquake in the Coquimbo region, can generate tsunamis that quickly impact the coast with unexpectedly high inundation altitudes,” he added.

This near-shore seismic rupture, according to the expert, generated a tsunami with an inundation of up to 5-6 meters above sea level, while the near-shore rupture generated a tsunami pulse that produced systematic inundation of up to 10-11 meters on the west coast south of Punta Lengua de Vaca.

In this historical review, the research team considered the most important tsunamis in Coquimbo in 1922 and 1877, with inundation heights of about 7 and 3-5 m above sea level.

Easton, Jose Gonzalez-Alfaro, and Angelo Villalobos, along with the team, posit that the 2015 Illapel earthquake-tsunami event partially filled in the absence of tsunamis in that area.

“For this reason, we call the coastline of the central Chile region, comprising the coast of Los Vilos-Valparaíso-San Antonio-Navidad, as tsunami gap, which can be understood as gap or absence of tsunami (…). We propose that an important tsunami gap is located in front of Taltal, where there are no records of large historical tsunami events generated just in front of that locality, but there are records of large prehistoric events,” he pointed out.