SAO PAULO (BNO NEWS) — A strong earthquake struck deep underneath western Brazil on Monday morning, seismologists said, but causing no damage or casualties.

The 6.5-magnitude earthquake at 11.18 a.m. local time (1618 GMT) was centered about 127 kilometers (79 miles) east-southeast of Cruzeiro do Sul, a town in the western Brazilian state of Acre. It struck about 580.5 kilometers (360.7 miles) deep, making it a deep earthquake, according to the U.S. Geological Survey.

Because of its depth, no damage is expected and it is unlikely that any moderate or strong tremors were felt by residents.

Deep earthquakes, such as the one on Monday, rarely cause damage because of their distance from the Earth’s surface. They occur only in oceanic lithosphere that has been subducted into the Earth’s mantle.

Monday’s earthquake occurred within the Nazca plate, which currently underthrusts the South American plate at the Peru-Chile Trench, along the west coast of South America. As it descends from the west coast of Peru to eastern Peru, the Nazca plate is seismically active down to depths of about 170 km (105 miles). Between depths of 170 km (105 miles) and 530 km (329 miles), the Nazca plate beneath eastern Peru and western Brazil produces very few shocks.

Beneath western Brazil in the region of Monday’s earthquake, the subducted Nazca plate is again seismically active between depths of 530 km (329 miles) and 650 km (403 miles). The deep part of the Nazca plate, in which Monday’s earthquake occurred, took 10 million years or more to descend from the point at which it initially thrust under the South American plate.

On June 20, 2003, a major 7.1-magnitude earthquake at a depth of 344 miles (553 kilometers) was centered about 70 miles (115 kilometers) east of Cruzeiro do Sul, making it one of the largest earthquakes ever recorded in the region. Also in that earthquake, there were no reports of damage or casualties.

The largest earthquake known to have occurred in the subducted Nazca plate was the Bolivian earthquake of June 9, 1994, which had a magnitude of 8.2. That earthquake was felt over a large area, despite its depth of more than 400 miles (645 kilometers), and caused damage as far as Canada.