Saturday, February 11, 2012

Large Swarm Of Earthquakes Occurring at Salton Sea, CA

The Salton Sea/Salton Buttes area, approximately 100 miles from San Diego and San Diego County, is experiencing a long duration earthquake swarm along one of the regional fault lines. The quakes are centered at and around the SE shore of the Salton Sea lake, near to some geologically fresh obsidian domes that were erupted in the area around 9,000 years ago.

The area is known for very active seismicity, and it is entirely possible that the quakes on the fault are related to magma dike intrusion, however the quakes are very shallow, indicating this is probably only tectonic in nature, as any magma at shallow depth would produce things like dying crops (the area is heavily agricultural), probable C02 emissions, and eventually ending up in some sort of eruptive activity (possibly phreatic or dome building). This is not occurring at the moment.

Above screenshot from Google Earth with USGS Real-time overlay. This shows the relative distance of the Salton Sea to San Diego, one of California's most populous and affluent cities.

This screenshot from Google Earth with the USGS Real-time overlay shows the largest event in the last few days, a 3.0 quake, at shallow depth.

In the second picture, you can see the tectonic fault as a red line. This is a transform/spreading fault. The quakes occur on a stress point for these faults, so these are probably purely tectonic in nature. The USGS and newly formed CalVO (California Volcano Observatory, formerly LVO, the Long Valley Observatory) does classify this area as a "High to Very High Threat Potential" for future eruption. The statement from their new web page says this:

"The Salton Buttes lie within the Salton Sea Geothermal Field located about 145 km (90 mi) southeast of Palm Springs in Imperial Valley, California. The geothermal system is fueled by heat emanating from zones of partially molten rock (magma) deep below the Earth’s surface. Eruptions occurring about 400,000 years ago were followed by a long lull in volcanic activity until about 18,000 years ago. The most recent eruptions, which took place about 9,000 years ago, started explosively, then progressed to relatively gentle effusion of dense, glassy-looking (obsidian) lava domes. The Salton Sea Geothermal Field, which currently produces enough power to supply about 325,000 homes, has persistent small to moderate earthquakes related to the geothermal system and to movement along regional faults. Monitoring of earthquake activity began in the 1930s, and the dense seismic network installed in the 1970s is operated by the USGS and the California Institute of Technology (Caltech). The available data are insufficient to establish a pattern of volcanic activity to determine the likelihood of eruption. The high heat flow from the area and relatively young age of Salton Buttes, however, attest to the potential for future eruptions."

The region was recently destabilized by a magnitude 7.2 earthquake centered just 40 miles south of the Salton Sea, near Mexico's Cerro Prieto volcano, which also hosts a large geothermal area. Reports from people living near the epicenter told of fountains of sulphuric and foul smelling red water geysers occurring in farmlands during the quake, which ended up contaminating much of the farmland in the Mexicali area. This fault is the same fault line as the Salton Sea, and has seen hundreds of quake occurrences a day since the 7.2 magnitude quake. This, to me, says that this is probably the fault line still in motion, but could coincide with geothermal/magmatic movement.

In any case I will be keeping a close eye on the Salton Sea, and may even pay it a visit since I actually live in San Diego, and it wouldn't be too much of a drive (gas is VERY expensive out here at the moment however, almost at $4/gal)... about two hours or so. Hopefully, this is purely tectonic and the people out there can relax. If anything new occurs, I will update this post. 

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