Magnitude 8 Earthquake Shakes Mexico City, Chiapas Thursday Night

The United States Geological Survey reports an extremely powerful Magnitude earthquake has hit Mexico City. A tsunami is possible. An 8 earthquake would make it the largest earthquake anywhere on the planet this year, and the second largest earthquake ever to strike Mexico.

The Richter magnitude scale (ML, also Richter scale) assigns a magnitude number to quantify the size of an earthquake. ... As measured with a seismometer, an earthquake that registers 5.0 on the Richter scale has a shaking amplitude 10 times greater than an earthquake that registered 4.0 at the same distance.

An earthquake of a preliminary magnitude of 8.0 struck off the coast of Chiapas, Mexico, late on Thursday local time, the Pacific Tsunami Warning Center (PTWC) said, citing USGS data.

The PTWC said that hazardous tsunami waves were possible within the three hours following the quake along some coasts of Mexico, Guatemala, El Salvador, Costa Rica, Nicaragua, Panama, Honduras and Ecuador.

The National Weather Service didn't expect a tsunami on the U.S. West Coast or Britich Columbia. The quake's depth was at 33 kilometers, or 20 miles, the PTWC said.

"It's a big quake. It's about 70 miles offshore, but it's not an unheard of quake," USGS geophysicist Randy Baldwin told NBC News in a phone interview, noting that the mid-American trench has producing a lot of big quakes in the past.

But he added,"This is a large quake. I'm sure that it will be widely felt and possibly damaging." Reuters reported that people in the capital Mexico City ran into the streets after the quake.