These results might not be immediately intuitive. Using these data, we can estimate which cities with a population greater than 50,000 in the Puget Sound region are expected to experience the strongest shaking.Ĭities with a population greater than 50,000 in the Puget Sound region and their expected shaking. While the peak ground velocity for a city may change from one rupture scenario to another, the relative response between cities is often similar, since shaking is strongly influenced by geologic structure and fault location. Since we do not know where the hypocenter was or the exact slip distribution for the 1700 earthquake, what’s shown in the map is the average peak ground velocity from thirty different rupture scenarios, each considering a different hypocenter and slip distribution. The peak ground velocity describes the maximum speed at which the ground moves during an earthquake and typically correlates well with felt shaking intensity - and damage - during large earthquakes.Īs a point of comparison, a peak ground velocity of 1.1 miles per hour (0.5 meters/second) was strong enough to tip over train cars during the 1906 magnitude-7.0 San Francisco earthquake ( Veeraraghavan et al., 2019). Simulated peak ground velocities from a magnitude-9.0 earthquake on the Cascadia Subduction Zone highlight differences in the effect of such an earthquake throughout the Puget Sound region. Data from Frankel et al., 2018, and Wirth et al., 2018. Results represent the average peak ground velocity from thirty possible rupture scenarios. Estimated shaking in the Puget SoundĮstimated peak ground velocities (PGV) in the Puget Sound region from a magnitude-9.0 earthquake on the Cascadia subduction zone. With these results, we can see which parts of the Puget Sound would experience the strongest shaking during a possible repeat of the 1700 quake. While there are not seismological recordings of the last Cascadia earthquake, seismologists can simulate ground shaking using information about the fault and observations from other subduction zone earthquakes. Knowing how the 1700 event shook the region would provide valuable information about which areas need more preparation before the next great Cascadia earthquake. Most of this urbanization took place prior to the realization of the danger posed by a possible megathrust earthquake.ĭamage in downtown Seattle from the 2001 magnitude-6.9 Nisqually earthquake. Within Washington State’s Puget Sound region, urbanization has transformed muddy tidal flats into the bustling port cities of Seattle, Tacoma and Olympia, which have rapidly grown into huge tech and manufacturing hubs. Since the start of European settlement in the late 19th century, the population of the Pacific Northwest has grown into the millions, and the region is currently experiencing one of the largest population booms in the country. It wasn’t until 20th century researchers compared these records with coastal geology that the source of this tsunami was identified: a magnitude-9.0 earthquake on the Cascadia subduction zone ( Atwater et al., 2005 Satake et al., 2003 Ludwin et al., 2005). Magistrate records from Eastern Japan and Native American oral histories from the Pacific Northwest do, however, suggest a large wave of water swept through these regions around this time. ![]() We therefore do not have direct measurements of how large the earthquake was. The 1700 quake occurred two centuries before seismometers were invented and widely installed. Red shading indicates areas of possible slip on the fault during a magnitude-9.0 earthquake. The Cascadia subduction zone sits just offshore of the Pacific Northwest. ![]() The risk is particularly high in the Puget Sound, where major population centers are growing directly in harm’s way. The region’s last major earthquake was in 1700, when an approximate magnitude-9.0 earthquake ruptured the full length of the fault, which extends from off the coast of Northern California to Vancouver Island in Canada.Ī repeat of the 1700 earthquake today would cause extensive damage throughout the Pacific Northwest. The Really Big One: The Next Rupture of the Cascadia Subduction Zone Will Spell the Worst Natural Disaster in the History of North America
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