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Over the past 24 hours, approximately 30 small earthquakes have struck the area around the southeastern edge of the Salton Sea, making this the second swarm of small earthquakes to hit the region in the past month. The last swarm hit the area in late September, and brought with it more than 200 small earthquakes, the largest of which measured was a magnitude 4.3 quake.
So far, most of the earthquakes in this latest swarm have been barely perceptible (to humans, at least) shakers registering below magnitude 3.0. Five, however, have exceeded magnitude 3.0, meaning that if anyone was in the area, they definitely felt the ground move around a bit. We've set some parameters on the U.S. Geological Survey's worldwide earthquake tracking map that focuses right on area currently experiencing the increased seismic activity. Click here to view that map.
Earthquake swarms like this one and the one last month do not necessarily mean "the Big One" is imminent. As scientists repeatedly emphasize to reporters and the public alike, there is no meaningful way to accurately predict exactly when and where an earthquake will occur. When scientists issued a elevated risk warning on September 29, they did so on the basis that any seismic activity in a region also increases the risk of more seismic activity.
That risk subsided by October 6, when the USGS released a statement saying that the "likelihood of a large earthquake on the southern San Andreas Fault near the Salton Sea has returned to the typical long-term level."
Returning to the "long-term level" of risk does not mean that the risk of a large earthquake originating from the San Andreas fault has gone away. By contrast, the southern portion of the San Andreas, including the part closest to where today's earthquake swarm was located, is overdue for a large earthquake. By examining the geologic record, earth scientists have determined the fault typically produces a large magnitude 7.0+ earthquake roughly every 150 to 200 years. Unfortunately for us Angelenos, the last time this portion of the fault moved was roughly 350 years ago.
That micro earthquake swarms, like the one happening right now, occur with regularity should be viewed as reminders of our region's inherent seismic instability. Take the time to put together an earthquake preparedness plan and kit.
