A strong 6.3-magnitude earthquake struck on Monday in a jungle area near the mountainous border of Brazil and Peru but was barely felt on the surface and caused no damage, US and Brazilian experts said.
The temblor, with its center about 127 kms east-southeast of Cruzeiro do Sul, Brazil, and 328 kms east of Pucallpa, in Peru's Andes, struck at 16:18 GMT, the USGS said.
The quake originated a relatively deep 580 kms under the surface.
A spokesman for the civil defense service in Cruziero do Sul said," the quake almost went unnoticed." Such activity was not unusual in the region, he added.
"This zone suffers a lot of earthquakes, but the last one we really felt was 20 days ago. We didn't register any disorder or damage on the surface from today's quake," he said.
Brazil's Seismological Observatory told AFP the region sat above the South American and Andean tectonic plates, which resulted in a lot of deep-earth seismic activity.
"Generally speaking, quakes more than 500 kms deep don't leave signals in the surface, they are only detected by instruments," one observatory official said.
On Sunday another strong 5.9-magnitude earthquake jolted several regions of Peru including the capital, Lima, with no damage immediately reported, Peru's National Geophysics Institute reported.
That followed 6.0 magnitude earthquake which hit northern Peru early Wednesday some 131 kms north-northwest of the town of Moyobamba.