Following a moderate earthquake on Tuesday, an ongoing swarm of small earthquakes has continued to shake the area around the Salton Sea in southern California.
Right now, this earthquake swarm is getting the attention of seismologists, due to both their frequency and especially their location, which is very close to a segment of the San Andreas Fault that is believed to be overdue for a major earthquake. The Southern California Seismic Network has a report on the swarm up on their main page.
The main response is one of "We need more info." Additional seismographs and other sensors are being emplaced around the area, in order to better determine the location of the quakes and find if there is any pattern to them. (For instance - are the locations of the quakes trending in any direction?) It is important to note that this swarm is not that unusual - a similar swarm occurred in 2001. But it bears watching.
There also seems to be some increased alertness among emergency planners. The California Office of Emergency Services issued a notice yesterday, advising of the earthquake swarm and encouraging officials to review their emergency plans.
This area is very interesting, seismologically. Somewhere near the Salton Sea and heading southeast through the Imperial Valley, the San Andreas Fault becomes less defined, broadening into a rift zone where the North American plate and the Pacific Plate stop sliding past each other and actually start moving away from each other. These quakes are occurring about where this rift zone begins.
For more information:
Southern California Seismic Network
USGS, "Recent Earthquakes in California and Nevada"
Los Angeles Times, "Salton Sea is swarming with earthquake data"
Los Angeles Times, "Study finds troubling pattern of Southern California quakes"