Light and Moderate Quakes Shake in Gulf of California

At least four light and moderate earthquakes were registered in the Gulf of California off the northwestern coast of Mexico near the Baja Peninsula on Tuesday, according to the United States Geological Survey. The first earthquake came at 11:44 a.m. local time and was registered as a magnitude 5.9. It was followed a little over an hour later at 12:57 p.m. by and aftershock that measured 4.3, then another aftershock -- 5.0 in magnitude -- at 1:40 p.m. local time. Another aftershock that registered 4.0 occurred at 9:13 p.m.

All four of these earthquakes had shallow depths of between about six and eight miles. The location of all four quakes was in a similar region -- 53, 62, 68 and 74 miles southwest of Las Mochis, Sinaloa, Mexico. The USGS labels earthquakes in the 4.0 to 4.9 range as "light" and those in the 5.0 to 5.9 range as "moderate."

There was no reported damage and no injuries due to these quakes and the website Earthquake-report.com stated that while the strength of these quakes allowed them to most likely be felt by several thousand people living in the region, damage and injury was not expected.

A number of similar-sized quakes shook the same region on March 12 -- one day after the massive 9.0 Tohoku earthquake in Japan.

Mexico as a country is very seismically active due to the country's location on top of three tectonic plates -- the North American plate, the Pacific plate and the Cocos plate. It is the movement of these plates that creates both seismic and volcanic activity in Mexico. The subduction of the Cocos plate beneath the North American plate in southern Mexico created the Mid-American trench along Mexico's southern coast and continues to create volcanic activity and earthquakes. It is a different action of plate tectonics that is responsible for earthquakes in the area of the Baja Peninsula that is located farther north.

In this location lies the Gulf of California on Mexico's northwestern coast where the Pacific and North American plates grind past each other, resulting in a slip fault. This is the southern extension of California's well-known San Andreas Fault. It was ancient motion along this fault that rifted the Baja Peninsula away from the rest of Mexico, thus creating the Gulf of California. This portion of the San Andreas Fault continues to be responsible for earthquakes in the western part of Mexico.

The last sizable earthquake in the Gulf of California/Baja region was on April 4, 2010, when a 7.2 quake shook just 30 miles southeast of Mexicali. This quake was along the same fault line with an epicenter further north than Tuesday's quakes.

Tammy Lee Morris is certified as a Community Emergency Response Team (CERT) member and is a trained Skywarn Stormspotter through the National Weather Service. She has received interpretive training regarding the New Madrid Seismic Zone through EarthScope -- a program of the National Science Foundation. She researches and writes about earthquakes, volcanoes, tornadoes, weather and other natural phenomena.