After last night’s 6.7 earthquake near Vancouver Island, many people have asked if this quake has relieved any built up pressure or is it a possible sign that the “Big One” is just around the corner? Additionally, when the big one does hit, what can we expect in the way of impact and damage?
The 6.7 quake struck at 8:10 PM PST on the west coast of Vancouver Island approximately 210 miles WNW of Victoria British Columbia. The epicenter for the earthquake is approximately 14 miles deep and in the vicinity of what many scientists call the Cascadia Subduction Zone.
Although they may first appear to be consistent with other recent earthquake activity along the Pacific Ring of Fire, University of Washington Geologist Bill Steele dismisses the theory this is a precursor to a major quake. "Don't read too much into it," said Dr. Steele. "I don't think we have any change in the hazard here in Cascadia at all." Last month’s magnitude 8.2 quake in Chile as an example was proceeded by hundreds of smaller precursor quakes, As Dr. Steele points out "In Cascadia we have had virtually none, maybe a couple magnitude three's off the coast of Oregon," It is uncertain at this time if last night’s quake was indeed related to Cascadia.
The Cascadia Subduction Zone is considered one of the most dangerous seismic zones in the world. It is a 900 mile long fault that is located anywhere from 50 -150 miles off the coast of Vancouver Island, Washington and Oregon. This zone has produced 9.0+ earthquakes on an average of every 300-500 years. The last one occurred approximately 9:00 AM on January 28th, 1700. The date and time of this quake is known because of the precise documentation of a tsunami that struck Tokyo Japan that was triggered by this quake.
The Cascadia Region Earthquake Workgroup, a nonprofit coalition of scientist, Emergency Management, Engineers, governmental and business leaders have looked at the possibility of a modern 9.0 earthquake happening along this zone. It is estimated the quake would be in the neighborhood of 9.0 - 9.5 and the shaking could last from 3 ½ - 5 1/5 minutes. When, not if this earthquake happens, it will be among the strongest ever recorded in history.
The “Big One” will also be different in how it is felt. The shaking will be much more intense with larger waves of energy flowing through the ground. Liquefaction of loose soils and fracturing of rock will occur as well as the collapse of buildings, highway bridges and utilities. It is probable that those people who do survive the quake itself will be without power, water and other lifelines for multiple days if not weeks. Finally, approximately 10 - 20 minutes after the earthquake, it is expected that 30-50’ high tsunamis will strike the west coast with multiple waves afterwards that could last for more than a day. Combined with ground deformation (parts of the Washington coastline sunk 6’ in 1700) most of the coastline will see complete and total devastation.
Last night’s quake most likely will have no impact on the threat of our next big quake along the Cascadia zone. When this type of quake ruptures, the energy released is so massive that even a thousand smaller earthquakes would pale in comparison. But is it a reminder that we live in earthquake country? Are you prepared to be on your own for days or weeks when it happens? As Dr. Steele and many other scientists will tell us, it is not a matter of if, but when. It may not be in our lifetime, but our area will again experience the impact of a 9.0+ Earthquake and it may likely be one of the largest ever recorded in the history of our planet.
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