Research Shows Next Cascadia Earthquake Could be 'Biggest Natural Disaster,' Even Bigger Than Sandy and Katrina

In 1700, a massive earthquake struck the west coast of North America. Though it was powerful enough to cause a tsunami as far as Japan, a lack of local documentation has made studying this historic event challenging.

Now, researchers from the University of Pennsylvania have helped unlock this geological mystery using a fossil-based technique. Their work provides a finer-grained portrait of this earthquake and the changes in coastal land level it produced, enabling modelers to better prepare for future events.

And the work points to big danger.

“The next Cascadia earthquake has the potential to be the biggest natural disaster that the Unites States will have to come to terms with — far bigger than Sandy or even Katrina,” said Benjamin Horton, associate professor and director of the Sea Level Research Laboratory at the university . “It would happen with very little warning; some areas of Oregon will have less than 20 minutes to evacuate before a large tsunami will inundate the coastline like in Sumatra in 2004 and Japan in 2011.”

The Cascadia Subduction Zone runs along the Pacific Northwest coast of the United States to Vancouver Island in Canada. This major fault line is capable of producing megathrust earthquakes 9.0 or higher, though, due to a dearth of observations or historical records, this trait was only discovered within the last several decades from geology records.

The 1700 Cascadia event was better documented in Japan than in the Americas. Records of the “orphan tsunami” — so named because its “parent” earthquake was too far away to be felt — gave earth scientists hints that this subduction zone was capable of such massive seismic activity. Geological studies provided information about the earthquake, but many critical details remained lost to history.  

“Previous research had determined the timing and the magnitude, but what we didn’t know was how the rupture happened,” Horton said. “Did it rupture in one big long segment, more than a thousand kilometers, or did it rupture in parcels?”

Horton and other researchers found using core samples that the tectonic plates massively shifted during the 1700 earthquake. 

This level of regional detail for land level changes is critical for modeling and disaster planning.

“It’s only when you have that data that you can start to build accurate models of earthquake ruptures and tsunami inundation,” Horton said. “There were areas of the west coast of the United States that were more susceptible to larger coastal subsidence than others.”

The Cascadia subduction zone is of particular interest to geologists and coastal managers because geological evidence points to recurring seismic activity along the fault line, with intervals between 300 and 500 years. With the last major event occurring in 1700, another earthquake could be on the horizon. A better understanding of how such an event might unfold has the potential to save lives.

Source: University of Pennsylvania

Photo: USGS