New analyses by Oregon State University marine geologist Chris Goldfinger and his colleagues have provided fresh insights into the Northwestâ€™s turbulent seismic history â€“ where magnitude 8.2 (or higher) earthquakes have occurred 41 times during the past 10,000 years. Those earthquakes were thought to generally occur every 500 years, but as scientists delve more deeply into the offshore sediments and other evidence, they have discovered a great deal more complexity to the Cascadia Subduction Zone.
â€œWhat weâ€™ve found is that Cascadia isnâ€™t one big subduction zone when it comes to major earthquakes,â€ Goldfinger said. â€œIt actually has several segments â€“ at least four â€“ and the earthquake activity is different depending on where a quake originates. The largest earthquakes occur in the north and usually rupture the entire fault. These are quakes of about magnitude-9 and they are just huge â€“ but they donâ€™t happen as frequently.
â€œAt the southern end of the fault, the earthquakes tend to be a bit smaller, but more frequent,â€ he added. â€œThese are still magnitude-8 or greater events, which is similar to what took place in Chile, so the potential for damage is quite real.â€
Based on historical averages, Goldfinger says the southern end of the fault â€“ from about Newport, Ore., to northern California â€“ has a 37 percent chance of producing a major earthquake in the next 50 years. The odds that a mega-quake will hit the northern segment, from Seaside, Ore., to Vancouver Island in British Columbia, are more like 10 to 15 percent.
â€œPerhaps more striking than the probability numbers is that we can now say that we have already gone longer without an earthquake than 75 percent of the known times between earthquakes in the last 10,000 years,â€ Goldfinger said. â€œAnd 50 years from now, that number will rise to 85 percent.â€
Found via the FuturePundit who asks “Anyone who lives in the northwest made any special preparations for an earthquake? Ready to survive for weeks without electric power or city water?”