New Zealand Earthquake Reveals Vulnerability of Many U.S. Urban Centers

“The earthquake was actually an aftershock associated with the 7.1 magnitude Darfield earthquake that occurred about 15 km west of Christchurch on Sept. 4, 2010. Since then, aftershocks have been occurring on the Greendale Fault, the causative fault, and progressing toward the Christchurch central business district. The relatively shallow depth of the earthquake below the city shows that even 5 to 10 seconds of strong shaking can have devastating effects.

“Some reasons for the serious damage are the many unreinforced masonry buildings in Christchurch and the occurrence of soil liquefaction throughout the city. Soil liquefaction is the transformation of saturated granular soil into a liquid-like substance from high groundwater pressures triggered by strong shaking. The soil liquefaction in Christchurch has damaged many miles of underground water mains, sewers, and electric power cables, and damaged several bridges.

“Many U.S. cities in areas vulnerable to earthquakes have many unreinforced masonry buildings, like those in Christchurch, and are founded on liquefiable soils.”

–Thomas D. O’Rourke, an expert on the impact of earthquakes on infrastructure and Professor of Civil and Environmental Engineering at Cornell University