Sunday, June 7, 2015

Forecasting the next Cascadia Subduction Zone Megaquake and Tsunami

As we quietly sleep; oblivious to the dangers of a Cascadia Subduction Zone Megaquake.
Lions Gate Bridge at Sunset, North Vancouver, BC, Canada





Seismologists say there is a 37 percent chance a gigantic magnitude 8.0 or 9.0 or higher Megaquake along the 1,000km long Cascadia Fault, here, on the West Coast of Canada and North West United States, in the next 50 years; along the Cascadia Subduction Zone.[15] The tsunami produced may reach heights of approximately 30 meters (100 ft).[18] The earthquake is expected to be similar to the 2011 Tōhoku earthquake and tsunami, as the rupture is expected to be as long as the 2004 Indian Ocean earthquake and tsunami.*

The last Cascadia Megaquake occurred at about 9 pm, January 26, 1700.

Studies of past earthquake traces on both the northern San Andreas Fault and the southern Cascadia subduction zone indicate a correlation in time which may be evidence that quakes on the Cascadia subduction zone may have triggered most of the major quakes on the northern San Andreas during at least the past 3,000 years or so. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. The 1906 San Francisco earthquake seems to have been a major exception to this correlation, however, as it was not preceded by a major Cascadia quake.[9]

Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years, suggesting a return time of 300 to 600 years. There is also evidence of accompanying tsunamis with every earthquake. One strong line of evidence for these earthquakes is convergent timings for fossil damage from tsunamis in the U.S. Pacific Northwest and Western Canada and historical Japanese records of tsunamis.[12]
The next rupture of the Cascadia Subduction Zone is anticipated to be capable of causing widespread destruction throughout the Pacific Northwest.[13]
Other similar subduction zones in the world usually have such earthquakes every 100 to 200 years; the longer interval here may indicate unusually large stress buildup and subsequent unusually large earthquake slip.[14]

Forecasts of the next major earthquake

Prior to the 1980s, scientists thought that the subduction zone just did not generate earthquakes like the other subduction zones around the world, but research by Brian Atwater and Kenji Satake tied together evidence of large tsunami on the Washington coast with documentation of an orphan tsunami in Japan (a tsunami without an associated earthquake). The two pieces of the puzzle were linked, and they then realized that the subduction zone was more hazardous than previously suggested. The feared next major earthquake has some geologists predicting a 10% to 14% probability that the Cascadia Subduction Zone will produce an event of magnitude 9 or higher in the next 50 years;[15] however, the most recent studies suggest that this risk could be as high as 37% for earthquakes of magnitude 8 or higher.[16][17]
Geologists and civil engineers have broadly determined that the Pacific Northwest region is not well prepared for such a colossal earthquake. The tsunami produced may reach heights of approximately 30 meters (100 ft).[18] The earthquake is expected to be similar to the 2011 Tōhoku earthquake and tsunami, as the rupture is expected to be as long as the 2004 Indian Ocean earthquake and tsunami.

* Reference from Wikipedia