Wednesday 27 July 2011

Earthquakes in the Gulf of California, 26 July 2011.

Just before 11.45 am local time a magnitude 5.9 earthquake struck 10 km beneath the Gulf of California (Sea of Cortez). This was followed by a magnitude 4.3 earthquake slightly before 1.00 pm, then a magnitude 5 quake at 1.40, then a magnitude 4 quake just before 9.45 pm. The quakes occurred roughly 125 NE of La Paz in Baja California State and 100 km SE of Los Mohis in Sinaloa State, Mexico, on the San Andreas Fault. There are no reports of any casualties, and no tsunami warning has been issued.

Map showing the location of the quakes (blue squares) and the San Andreas Fault (red line) in the Gulf of Mexico. From the United States Geological Survey

The San Andreas Fault runs along the length of the Gulf of Mexico, then northward through the US state of California. It is a transform, or strike slip fault caused by two plates (in this case the Pacific and the North American) moving past one another. Faults of this type are not particularly prone to causing tsunamis, but can trigger submarine landslides, which are a tsunami hazard. The main danger from this series of quakes is that by releasing pressure on one part of the fault, they increase it on another; thus the danger of a significant quake in the (populous) US State of California will have now increased.

The San Andreas Fault lies on the border between the north-moving Pacific Plate and the south-moving North American Plate.

The Gulf of Mexico is an extensional basin running along the southern part of the San Andreas Fault. The basin runs on-land as the Imperial Valley of Southern California; for this reason the southern part of the San Andreas Fault is sometimes known as the Imperial Fault. Extensional basins occur where two plates move apart from one-another, in this case the Pacific and North American. Potentially the Gulf of California could one day evolve into a new ocean, though this is not guaranteed, most extensional basins stop expanding before this happens.

See also Torino (Turin) rocked by mild earthquake, Earthquake on the Krygyzstan/Uzbekistan Border and Earthquakes on Sciency Thoughts YouTube.