Not Quite the Big One

If anything positive can be said about the strongest earthquake to hit California in 40 years, it's that it chose a relatively good place and time to strike. Sunday's powerful early-morning jolt -- 7.4 on the Richter scale in contrast to 7.1 for the 1989 San Francisco Bay area quake -- shook people from their beds and houses from their foundations and was felt as far away as Colorado and Washington. But it was centered in the sparsely populated Mojave Desert, some 100 miles east of Los Angeles. A second quake, with a Richter rating of 6.5, struck an even more remote region in the San Bernardino Mountains, 20 miles closer to L.A.

Though just one person died last week vs. 62 in the San Francisco quake, that death was particularly poignant. The parents of Joseph Bishop, 3, had traveled across the U.S. from Newburyport, Mass., to visit the town of Yucca Valley for a high school reunion; the little boy was killed when a fireplace tumbled down on him while he slept. The quake also caused more than 400 injuries and $91 million in property damage, along with widespread power outages and temporary disruptions to local water supplies.

While neither of the Sunday quakes hit along the San Andreas Fault, where experts believe the Big One will eventually strike, both were on faults that intersect it. That could put more pressure on the San Andreas and hasten the arrival of a mega-quake -- a devastating prospect, since the San Andreas runs through the populous Los Angeles basin.

Some geologists see last week's quakes as evidence of a new, major fault in the making. The San Andreas marks a dividing line where two continental plates -- rock pancakes tens of miles thick and hundreds or thousands of miles across that make up the earth's surface -- are grinding past each other. As the plate carrying Los Angeles heads north toward Alaska, it scrapes against the plate carrying most of the rest of the U.S., sticking for years and then suddenly spurting forward. Near Palm Springs, the San Andreas Fault makes a jog to the west, suggesting that it may be trying to take a shortcut along a new line of least resistance and that eventually the section near Los Angeles may quiet down. That's the good news. Unfortunately, it's not likely to happen for another 50 million years or so.