USGS Reports Major Earthquake Near Pitaloza Arriba, Panama

A major earthquake struck near Pitaloza Arriba, Panama, on Oct 9 at 12:56 PM local time, according to the US Geological Survey (USGS). The agency's event page lists the magnitude as 7.7, while the title of the linked report refers to it as M7.6.

The USGS says extensive shaking impacts are probable and the disaster is likely widespread. It estimates that about 4.6 million people felt shaking from Moderate (MMI V) to Severe (VIII). MMI is the Modified Mercalli Intensity scale, which rates earthquake shaking by what people feel and what damage it causes, rather than by the energy released.

Panama sits near the meeting point of several major tectonic plates. These are the huge slabs of rock that make up the Earth's outer shell. The Cocos and Nazca plates lie to the west and south, and the Caribbean and South America plates lie to the north and east. Together they surround a smaller piece called the Panama microplate.

Along the southern edge, the Cocos plate slides beneath the Panama microplate. The Nazca plate pushes against it at an angle. Along the northern edge, the Caribbean plate slides beneath it.

The USGS says the quake's focal mechanism, which describes how the rock broke and moved, shows left-lateral strike-slip faulting. In simple terms, two blocks of rock slid past each other sideways. The agency says this fits the kind of movement commonly seen along this complex plate boundary.

Earthquakes are common in the region. Most past activity has been west of this event, along the Panama Fracture Zone, a north-south plate boundary that separates the Cocos and Nazca plates. The USGS notes earlier earthquakes in the broader area, including a magnitude 7.5 in July 1934 and a magnitude 7.2 in July 1962.