Saving lives through better design standards

Abstract

Over the past 30 years, scientists have put together a more complete picture of how the ground shakes during earthquakes. They have learned that shaking near the source of earthquakes is far more severe than once thought and that soft ground shakes more strongly than hard rock.This knowledge has enabled engineers to improve design standards so that structures arebetter able to survive strong earthquakes. When the 1989 Loma Prieta earthquake struck, 42 people tragically lost their lives in the collapse of a half-mile-long section of the Cypress structure, an elevated double-decker freeway in Oakland, California.Yet adjacent parts of this structure withstood the magnitude 6.9 temblor—why? The part that collapsed was built on man-made fill over soft mud, whereas adjacent sections stood on older, firmer sand and gravel deposits. Following the collapse, scientists set out instruments in the area to record the earthquake's many strong aftershocks. These instruments showed that the softer ground shook more forcefully than the firmer material-even twice as violently