A new report has looked at the different ways an earthquake of epic proportions could wreak havoc in the Northwest of America.
Citizens living in the vicinity of the Cascadia Subduction Zone have long been aware a 9.0 magnitude earthquake, which has been branded “The Really Big One”, could hit the region on any given day.
The quake, which is predicted to be the worst natural disaster in the history of the continent, would release damaging and probably deadly shaking in coastal Washington, Oregon, British Columbia and northern California. It is a natural catastrophe which scientists and emergency disaster planners say is a matter of “when” rather than “if”.
The new piece of research carried out by the University of Washington has simulated the 50 different ways the earthquake could unfold. While past reports have looked at one or two scenarios, the study is the first to look at such a wide range of potential outcomes.
But the report, which was presented on 24 October, said: “None of the pictures is rosy”.
It ran simulations using different combinations for three chief factors – the epicenter of the earthquake, how far inland the earthquake will rupture and which areas of the fault will engender the strongest shaking. It found that if the quake were to strike the Cascadia Subduction Zone on Washington’s Northwest tip Seattle could get off comparatively easy compared to if it was instead located far off the coast.
A small tectonic plate called Juan de Fuca has been sliding under the far larger North American plate into the Earth’s mantle for around the last 30 million years. While this tends to take place without anyone noticing at present, the pressure which has built up can potentially be released unexpectedly and disastrously and trigger a gigantic earthquake which would shake the Northwest.
This has not happened since 1700 when a magnitude-9.0 earthquake hit and wrecked the coast of what is now Oregon and Washington. An entire First Nation on Vancouver Island, the Pachena Bay people, died in flooding in the space of just one night, according to one story.
The fact this took place way before seismic instruments were around to record the event means a great deal about the exact consequences of the next rupture remains mysterious and uncertain. Geological clues reveal it jolts roughly once every 500 years and could therefore do so at any potential day.
“We know a magnitude 9.0 earthquake occurred in Cascadia in the year 1700, but we didn’t have any seismometers or recording instruments at the time,” said Erin Wirth, a postdoctoral researcher at the University of Washington.
She added: “There had been just a handful of detailed simulations of a magnitude-9 Cascadia earthquake, and it was hard to know if they were showing the full range.”
“With just a few simulations you didn’t know if you were seeing a best-case, a worst-case or an average scenario. This project has really allowed us to be more confident in saying that we’re seeing the full range of possibilities.”
The new piece of research found the various scenarios for the earthquake were extreme, with models showing the ground shaking for 100 seconds. This is a whole four times longer than it shook during the 2001 Nisqually quake which was magnitude 6.8 and exerted a considerable amount of damage.
The authors of the report hope the newly gathered information will aid planners and emergency managers to get ready.