Aftershocks Still Felt From ’94 Quake

The more we know about Southern California’s intricate seismology, the more it seems we don’t know. Just last week, for instance, scientists suggested that the puzzling damage patterns of the Northridge earthquake--particularly in Sherman Oaks and Santa Monica--were caused by a geologic structure deep within the Earth that focused shaking in certain areas.

Until now, many believed that liquefaction of surface soil played a big role in localized damage. But scientists now question the role of liquefaction in the 1994 quake. Although the results are preliminary--and still subject to the normal give and take of scientific discourse--they are enough to make already worried homeowners further doubt much of the conventional wisdom about everything from insurance rates to readiness.

If the research proves correct, it could change the way policymakers think about safety precautions. For instance, builders in liquefaction zones are required to take special steps to make their projects safer. Insurance rates are based partly on surrounding geology. Both may be misguided. Four years after the earthquake’s shaking woke the San Fernando Valley, its aftershocks continue to be felt.