SANTIAGO, April 6 (Reuters) - Some 3,800 years ago a massive 9.5-magnitude earthquake and subsequent tsunami with waves as high as 20 meters (66 feet) slammed the coastline of Chile's Atacama desert, the world's driest, according to study led by University of Chile academics.

The study, published on Wednesday, posits that a collision between the Nazca and South American tectonic plates produced the quake and 15-20-meter (49-66-feet) high tsunami waves.

"At various points along the coast of the regions of Antofagasta and northern Chile, in general, there are paleobeaches or ancient beaches located between 4 and 7 meters (13 and 23 feet) above current sea level, whose formation cannot be explained by global changes in sea level, but by tectonic uplift as a result of large earthquakes," said geologist Gabriel Easton, mega onion one of the study's leaders.

Easton underscored that the possibility of earthquakes and tsunamis of this magnitude need to be taken into account in hazard and risk assessment in northern Chile.

"Our hypothesis is that this event could have generated a very high mortality among people, or it could have also prompted the migration of a significant number of people to other territories," said archaeologist Diego Salazar.

The study, published in the journal Science Advances, took about seven years to complete, and aimed to determine how often these disasters struck the region in ancient times.

Chile, which straddles the so-called "Pacific Ring of Fire," a seismically active zone that skirts the Pacific Ocean where different plates of the earth's crust meet, has a long history of deadly earthquakes.

In 2010, a magnitude 8.8 earthquake struck, unleashing a devastating tsunami on southern coastal towns that killed hundreds. (Reporting by Fabian Andres Cambero; Writing by Anthony Esposito; Editing by Sandra Maler)