April 19, 2001

Ground Motion From Nearby Earthquakes Hazardous For Flexible Structures

LIVERMORE, Calif. — Information gathered from recent major earthquakes such as those in Turkey and Taiwan in 1999 shows that large ground displacements near dislocating faults can have potentially damaging effects on flexible structures such as long-span bridges and high-rise buildings.
The flexible nature of such structures could make them vulnerable to the kind of relatively slow-developing, long-period ground motion pulses and permanent ground displacements observed in recent quakes.

The findings will be presented at the Seismological Society of America Annual Meeting in San Francisco today by a team of researchers from Lawrence Livermore National Laboratory; the University of California, Berkeley; and the United States Geological Survey.

The team had long suspected that near-fault ground motions could have significant impact on long-period structures due to the researchers’ extensive seismic modeling work using massively parallel computers.

Team researchers entered data on earthquake physics and topographical and geological characteristics for specific geographical areas into computers to generate simulated earthquakes. They then applied the forces produced by these virtual earthquakes to computerized models of real structures, such as bridges, highways and buildings. The response of the structural models to the simulated shakers showed the potential vulnerability of long-span bridges to long-period ground motions near a rupturing fault.

The recent earthquakes in Taiwan and Turkey vividly demonstrated through data collected at the scene that such longer-period near-field pulses occur near (i.e. within approximately 20 Km) of earthquake faults.

The research team focused their study on long-period pulses partly because of the existence of a number of major long-span bridges within 10 to 15 kilometers of major active earthquake faults in the Bay Area, including the nearby Hayward Fault (considered the most dangerous of San Francisco Bay Area faults).

"These bridges are essential transportation links and critical lifelines for the economy of this seismically active region," said David McCallen of Lawrence Livermore Lab’s Engineering Directorate.

"To ensure the performance and safety of these structures in future earthquakes, it is essential to thoroughly understand the significance of long-period and permanent ground displacements."

The research team includes David McCallen, Larry Hutchings and Shawn Larsen of Lawrence Livermore National Laboratory; Abolhassan Astaneh-Asl of the University of California, Berkeley; and Mehmet Celebi of the United States Geological Survey.