Quake Predicted for West Coast - Without a Word to US at Risk

How many years have you heard the prediction that southern California is going to shake off its foundations and into the sea, falling to the mother of all earthquakes? Of course that's an exaggeration of fact, though a major quake is a virtual certainty for the area - sooner or later.

On Saturday, though, a much more specific prediction went out to emergency officials in western Canada, warning that a huge quake could be imminent in British Columbia, along the coast. The Globe and Mail reported the prediction Saturday, 4 January 2007, with the note that the Big One was expected sometime in the next week. Maybe.

The article quoted Dr. Gary Rogers (Pacific Geoscience Centre, Vancouver Island) as saying that the probability remains small but nonetheless real. He compared the chances of a big quake to the risk of a collision while driving. When you drive your car every day, he explained, you could be involved in a crash. But when driving in rush hour, the risk escalates. He said Vancouver Island is now in its "rush hour" in terms of seismology.

Notably missing were any comparable alerts to residents of the US northwest, who would also be at risk of damage from any resulting tsunami.

Trembling Subsides Sunday

Canada's earthquake tracking page said Sunday that the Episodic Tremor and Slip event appeared to have ended, after 24 hours without additional recorded "significant tremors." According to Canada's site, the subsidence of tremors likely means the danger has passed, at least for the moment.

Comparable seismic events occur in the area every fourteen to sixteen months. During each of those events, the potential for a major quake rises dramatically.

There is a precedent for predicting a major event. A tsunami struck Japan in 1700 as a result of an estimated magnitude 9.0 quake off of Vancouver Island, in what's known as the Cascadia subduction zone. The zone encompasses a major fault line that stretches from Vancouver southward along the coasts of Washington and Oregon. It's the region where the North American tectonic plate and the Juan de Fuca plate meet and push against one another. In fact, studies show that huge quakes strike the area about every 500 years.

The US Geological Survey page, which tracks and reports quake information worldwide, showed no activity in the immediate vicinity of Vancouver Island last week, but displayed three quakes of 4+ magnitude since January 31 of this year. Several smaller tremors rattled the northern California coastline, just south of the Oregon border. As of the time of this writing, the most recent was a 2.8 magnitude quake that occurred at 10:29am PST.

You Say Quake, I Say Tremor

The episodic tremor and slip events differ slightly from a normal quake, in that they occur at depths where solid rock isn't so solid. The Episodic Tremor and Slip (ETS) activity, recorded at depths between 25 and 40km (approximately 15-25 miles,) occur in areas where heat and pressure creates a degree of elasticity in the rock. That value changes the nature of shaking so it's not considered a true quake. But scientists do know that those non-quake quivers can be harbingers of the real thing - a very big real thing, every so often.

As Vancouver Goes, So Goes The US Coastline

Vancouver Island sits right at the edge of the two major plates, and as the ETS events recur, they change the direction of the island's drift. For a period, Vancouver Island will move toward the mainland; following an ETS, it may begin drifting away, instead.

The island's position makes it especially vulnerable if and when such major quakes occur, though it wouldn't be the sole casualty. The predicted Big Quake will likely involve a segment of the sea floor more than 600 miles long, and could go on for several minutes. The resulting vertical shift of the plates is expected to generate a devastating tsunami that washes over the west coast of Vancouver Island and potentially segments of the northwestern US coast.

Tsunamis have struck US shores in the past, inundating portions of Alaska, Hawaii and California. A 1964 tsunami washed away twenty-nine blocks of Crescent, California, killing eleven people. Just a few days later, a 7.4 magnitude quake in the Aleutian chain sent a 100-foot wall of water that wiped out the city's waterfront and traveled half a mile inland in some areas.

In January of 2005, MSNBC reported that a major quake along the Cascadia subduction zone could inundate the coast of Oregon in as little as thirty minutes.

Pinpointing Location

While the specifics of when are still a bit fuzzy, seismologists are more certain of the where. And that worries them even more in this instance, because they expect the rupture to occur closer in than the previous events, within 75km (46 miles) of the coast.

Vancouver Island and the western coast of the USA are all part of what's known as the "Ring of Fire," a horseshoe-shaped shake zone following the contours of the Pacific Ocean. The Ring of Fire is home to 90 percent of the world's total earthquakes, and 81 percent of the world's largest recorded temblors.