Authorities are warning Southern California residents that a major earthquake could be imminent, and that everyone should be on high alert. The Governor’s Office of Emergency Services has issued the warning after a series of temblors under the Salton Sea, which is on the San Andreas fault.

These warnings are not uncommon, issued once or twice per year. The alert was triggered by 142 temblors that struck at the southern end of the fault near Bombay Beach, registering between 1.4 and 4.3 in magnitude on the Richter scale.

Even in this situation, the risk of a magnitude 7.0 or higher earthquake is only as high as 1 in 100, and may be as low as 1 in 3,000, scientists estimate. That compares to the average risk for an earthquake, which is 1 in 6,000.

Earthquakes only happen once every 300 years on the San Andreas fault, and the last earthquake on the southernmost end of the San Andreas fault was all the way back in 1690.

California is certainly no stranger to earthquakes, however, and officials warn that residents should always be ready in case the “big one” strikes.

“The San Andreas Fault is a continental transform fault that extends roughly 800 miles (1,300 km) through California,” states Wikipedia’s entry on the subject. “It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics and a different degree of earthquake risk, the most significant being the southern segment, which passes within about 35 miles (56 km) of Los Angeles.”