At fifteen minutes after midnight local time (7.15 am, GMT) on Thursday 12 April 2012 the Gulf of California was shaken by an Earthquake close to the Beja California side of the Gulf, recorded by the United States Geological Survey as measuring 6.9 on the Richter Scale, and occurring at a depth of 10.3 km. The quake caused significant shaking both on the Bejan and Sonoran sides of the Gulf, but is not thought to have caused any significant damage or casualties at this time.
The location of the 12 April 2012 Gulf of California Earthquake, and the areas worst effected. USGS.
The Gulf of Mexico lies on the boundary between the Pacific and North American Plates. These plates are moving past one another, the Pacific Plate moving northward and the North American southward; this is called a transform (or transverse) plate margin. This plate margin continues northward under the US State of California, where it is known as the San Andreas Fault. Friction between the two plates can cause Earthquakes in both the Gulf and State of California.
Movement on the plate margin beneath the Gulf of California. Monterey Bay Aquarium Research Institute.
There is also a degree of spreading starting to occur on this plate margin, to the south it becomes a spreading plate margin, the East Pacific Rise, generating new seafloor on the Rivera, Cocos and Nazca Plates, and feeding the subduction zones off the coasts of Central and South America.
The transform fault beneath the Gulf of Mexico becomes the East Pacific Rise spreading center to the south. Monterey Bay Aquarium Research Institute.
The San Andreas Fault passes out from underneath California near San Francisco, becoming the Mendocino Fracture Zone, which separates the Pacific Plate from the Gorda, Juan de Fuca and Explorer Plates to the north. These are remnants of an ancient ocean plate, the Farallon Plate, which is breaking up as it is being subducted beneath North America.
North of California the San Andreas Fault becomes the Mendocino Fracture Zone. USGS.
See also Oaxaca region of Mexico struck by second major Earthquake in two weeks, Chile struck by large Earthquake, Understanding the subduction zone beneath Mexico, Mexico shaken by major Earthquake and Earthquakes on Sciency Thoughts YouTube.
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