Last week, more than 200 earthquakes had been recorded deep under the Salton Sea in Southern California. The rapid succession of small earthquakes — three measuring above magnitude 4.0 — began rupturing near Bombay Beach, continuing for more than 24 hours.

The temblors were not felt over a very large area, but they have garnered intense interest — and concern — among seismologists. It marked only the third time since earthquake sensors were installed there in 1932 that the area had seen such a swarm, and this one had more than the past two events in 2001 and 2009. The concern is that this small quakes may awaken the mighty San Andreas fault.

The San Andreas fault’s southernmost stretch has not ruptured since about 1680 — more than 330 years ago, scientists estimate. And a big earthquake happens on average in this area once every 150 or 200 years, so experts think the region is long overdue for a major quake. The swarm actually increased the likelihood of a much more major quake in Southern California, at least temporarily.

According to the U.S. Geological Survey, as of Tuesday, the chances of a magnitude 7 or greater earthquake being triggered on the southern San Andreas fault over the next seven days were as high as 1 in 100 and as low as 1 in 3,000. Without the swarm, the average chance for such an earthquake striking on any given week is 1 in 6,000.

A San Andreas earthquake starting at the Salton Sea has long been a major concern for scientists. In 2008, USGS researchers simulated what would happen if a magnitude 7.8 earthquake started at the Salton Sea and then barreled up the San Andreas fault, sending shaking waves out in all directions.

Shakeoutposter_Dontfreakout_Color_2010This is a great reminder for those who haven’t yet signed up to participate in the annual California ShakeOut. This is a great opportunity for those in California to educate, inform and practice what to do to be safe during an earthquake and how to prepare. The ShakeOut website has lots of great information and educational materials you can use in training and exercises. Log on, sign up and get going!