May 15, 2013
Fossils Help Researchers Learn More About Cascadia Quake Of 1700
Brett Smith for redOrbit.com — Your Universe Online
Scientists have long been baffled by a massive earthquake that struck the western coast of North America in 1700. Since that part of the continent was only sparsely populated by indigenous peoples, the lack of official records has made studying the event quite difficult.
According to a new report in the Journal of Geophysical Research: Solid Earth, a research team from the University of Pennsylvania has discovered new details about the event using a fossil-based technique.
“Previous research had determined the timing and the magnitude, but what we didn't know was how the rupture happened,” said Benjamin Horton, a director of the Sea Level Research Laboratory in the Department of Earth and Environmental Science. “Did it rupture in one big long segment, more than a thousand kilometers, or did it rupture in parcels?”
Before this new study, most of the research on the quake was performed using Japanese records of an “orphan tsunami” that appeared on the island nation´s shores without a noticeable seismic event. While previous research has been able to reveal aspects about the earthquake, many critical details of the event had been unknown. The first American surveys of the region were conducted by Lewis and Clark, some 100 years after the event.
To learn more details about the event, the Pennsylvania team traveled to various sites along the Cascadia subduction zone, a major fault line capable of producing the massive 1700 earthquake. At the sites, the team drilled core samples and collected data from local researchers.
In their report, the scientists focused on tiny fossils known as foraminifera. Using radiocarbon dating techniques and the various locations of foraminifera within the cores, the team was able to recreate a historical picture of the coastline. By comparing the historical state of the coastline with its current state, the team was able to determine how much the tectonic plates had shifted during the seismic event.
“What we were able to show for the first time is that the rupture of Cascadia was heterogeneous, making it similar to what happened with the recent major earthquakes in Japan, Chile and Sumatra,” Horton said. “It´s only when you have that data that you can start to build accurate models of earthquake ruptures and tsunami inundation.
“There were areas of the west coast of the United States that were more susceptible to larger coastal subsidence than others,” he added.
Policymakers and scientists alike are interested in the Cascadia subduction zone because evidence suggests recurring seismic activity along the fault line every 300 to 500 years, with the fault´s last major event being the 1700 quake.
“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,” Horton said. “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.”