Risk assessment and risk management in Oregon

This paper presents the first statewide quantitative seismic risk assessment. Oregon is especially vulnerable to earthquake hazards because of its proximity to the Cascadia subduction zone and its many older buildings. Expected ground motions, building damage, and social and economic losses were estimated for (1) a magnitude 8.5 Cascadia subduction zone earthquake off the coast of Oregon, and (2) statewide probabilistic ground motions for a 10% probability of exceedance in 50 years, which is the basis of the seismic design levels in the building code. The analyses were conducted using geographic information system (GIS) based HAZUS97 software. The local soil conditions were modeled using a statewide 1997 Uniform Building Code soil map based on shear wave velocities. Ground motion maps for peak ground acceleration, peak ground velocity and spectral responses were developed. Expected losses for the magnitude 8.5 earthquake show about 35,000 buildings severely damaged, about 12 billion dollars (SUS) of building damage, and over 7,700 casualties. Expected losses from the "design level" earthquake study are over 80,000 buildings severely damaged, over $30 billion of building damage, and over 24,600 casualties. Risk management strategies that help stimulate and prioritize mitigation activities are reviewed.