Earthquake Damage to Wood‐Framed Buildings in the ShakeOut Scenario

The M7.8 San Andreas earthquake scenario for the ShakeOut exercise subjects more than a million wood‐framed buildings to loads beyond their elastic capacity. Residential construction from the boom from the 1960's to 1980's relied heavily upon drywall sheathing and stucco for shear walls – more vulnerable than plywood or the gypsum lath and plaster of older buildings. During this same construction boom, many apartment buildings were built with tuck‐under parking, and heavy masonry chimneys were prevalent. Based on HAZUS ®MH modeling we describe, more than 30,000 (mostly older) wood buildings could be red‐tagged or yellow‐tagged in the scenario event. More recent wood‐frames, engineered using plywood shear walls, should perform well, even under the conditions produced by the San Andreas event considered. Cost‐effective retrofit measures exist for some of the weaknesses found in older wood construction, but seismic upgrade of wood‐framed buildings with structural wood panels remains expensive and intrusive.