It has been 12 years since the last strong earthquake struck California.

On three separate occasions over the past 35 years, significant release of tension along the San Andreas fault has led to disruptive earthquakes in Southern California. In 1971, a temblor registering 6.6 on the Richter scale struck in the San Fernando region. Eighteen years later, I happened to have arrived in Pasadena the day a temblor rippled through San Francisco—Oct. 17, 1989. It was a fearful sight watching the images of roads and bridges whipping in the air like so much spaghetti as the pent-up energy released along the great San Andreas fault rippled across the Bay area. Although that quake registered 7.1 on the scale, its epicenter was in a sparsely populated area. Thankfully the damage was not too substantial.

The most destructive of the three occurred in the early hours of the morning of Jan. 17, 1994. A earthquake registering 6.7 hit Northridge, Calif. It was the most damaging quake to strike the U.S. since the great 1906 San Francisco earthquake. That 1994 quake is rated one of the worst natural disasters in U.S. history in terms of total financial loss, comparable to Hurricane Andrew in 1992.

Since then, although no significant quakes have occurred in areas of high population density within the region, the tension continues to build underneath the surface of the Earth. Registrations along the southern end of that great fault line have added to the most recently expressed concerns that Southern California is well overdue for “the Big One.”

Studies indicate that a major quake could strike that region any time—even today. According to the U.S. Geological Survey, for years scientists have predicted “that a magnitude 6.7 or larger earthquake is nearly twice as likely to happen as not to happen. This is a substantial increase, since in 1988 scientists thought the chance for such an earthquake was 50 percent (just as likely to occur as not to occur) within 30 years.”

Although the three earthquakes mentioned here were significant in their scope, scientists agree that the last really major release of energy along the San Andreas fault occurred over 250 years ago and that the region is essentially primed for a major quake to occur any time.

bbc reported Professor Yuri Fialko, of the Scripps Institution of Oceanography in La Jolla, Calif., as stating that the conclusions of the most recent studies reveal that “The southern section of the fault is fully loaded for the next big event” (June 22). The bbc report continued, “Quakes are predicted to occur on the southern part of the fault every 200 to 300 years. And according to Professor Fialko, the observed movement on the fault is on a par with the maximum amount of shift the fault has ever experienced between quakes” (ibid.).

What is of particular concern in respect to this most recent study is the indication that “given average annual movement rates in other areas of the fault, there could be enough pent-up energy in the southern end to trigger a cataclysmic jolt of up to 10 meters [32 feet]” (Reuters, June 21). This compares with a movement of 21 feet in the great San Francisco quake of 1906. “A sudden lateral movement of 7 to 10 meters would be among the largest ever recorded” (ibid.).

Sooner or later, indications are that the groaning, pent-up energy accumulating along the great San Andreas fault line must be released. Obviously, given the location of Los Angeles County at the southern end of the fault line, a teeming area of some 10 million souls, such an occurrence, if it were to impact that region, could rate beyond the catastrophic.