Blackouts, telephone outages and highway damage were reported in northern Chile, and tsunami warnings remained in effect after a massive earthquake struck Tuesday evening off that nation's Pacific coast. 

The U.S. Geological Survey upgraded the earthquake to magnitude 8.2 shortly after it struck at 8:46 p.m. about 50 miles southwest of Cuya, about 950 miles north of the capital, Santiago. 

Major damage was reported to Highway A16 north of Iquique, a major port city of about 182,000 people at the edge of Chile’s copper mining Atacama desert region.

With the exception of Iquique, the regions closest to the epicenter of the quake are remote and sparsely populated. Pisagua, about 65 miles north of Iquique, has fewer than 300 inhabitants, and the town of Arica, about 120 miles north of Iquique, has about 10,600 residents, according to recent census data. The Arica and Parinacota regions where the quake was felt strongly have a combined population of about 215,000.

The Chilean navy’s oceanographic center reported wave heights of 5 feet in Iquique, and of greater than 6 feet in Pisagua.   

Much of the Chilean coast borders the oceanic Nazca plate, which is being pushed under the continental South America plate, creating a geologic hotspot responsible for the creation of the Andes Mountains.

That pressure can produce earthquakes greater than magnitude 9.0, the same class of temblor that caused the 2004 Sumatra and 2011 Japan tsunamis.

Southern Chile produced the most powerful earthquake on record, a magnitude 9.5 earthquake in 1960, which killed thousands around the city of Valdivia, and brought tsunamis to Hawaii, Japan, the Philippines and the U.S. West Coast.

Although the quake is off the northern coast, cities up and down the length of the country were put on high alert, including Talcahuano and Dichato, more than 1,100 miles south, where a magnitude 8.8 earthquake killed 524 people and destroyed 220,000 homes in 2010.

A magnitude 7.1 quake in central Chile struck 11 months later, rattling nerves following the previous year’s devastation, but caused little damage or injury.

Swarms of earthquakes off the northern Chilean coast have followed a  magnitude 6.7 temblor that struck March 16 near Iquique.

“The big question is – is this magnitude 8.1 earthquake the 'big one' that we have been expecting in northern Chile, or is this a foreshock to an even bigger earthquake to come?" said Cornell University structural geologist Rick Allmendinger, who returned recently from studies at the Catholic University of the North in Antofogasta, Chile. 

“As big as an 8.1 is, it probably has not released all of the stored up energy on the subduction earthquake fault in northern Chile. For the sake of all of our friends in the region, we’re hoping that there isn’t a bigger one still to come.”