A magnitude 8.5 earthquake off the coast of Oregon would devastate portions of the state, kill thousands of residents, and wrack the economy there for years to come, according to recent analyses by state geologists.
Temblors of such immensity are infrequent but aren’t unknown in the region, says Yumei Wang, a seismic engineer with the Oregon Department of Geology and Mineral Industries in Portland. Sediments show that the Cascadia subduction zone, which runs along the state’s coast, has spawned eight or nine earthquakes with estimated magnitudes greater than 8.0 during the past 8,000 years. These so-called great earthquakes happened at irregular intervals during that period.
The last supertemblor, which shook the region in January 1700, sent a large tsunami racing both to the Oregon coast and across the Pacific to Japan (SN: 11/29/97, p. 348). A tsunami generated by a modern version of that temblor would likely inundate the Oregon coastline and kill at least 3,000 people, says Wang. Statewide, another 2,000 or so residents would die in collapsed buildings and 7,700 more would be injured.
The next great quake could cause at least $12 billion in damage to buildings and more than $490 million in losses to airports, bridges, and highways. More than 100,000 buildings would be damaged–about 37,000 of them severely enough to be condemned–and more than 9.3 million tons of debris would be left in the quake’s wake. The physical and economic recovery in Oregon from such a jolt could take 10 years or more, Wang notes.