Next subduction quake will rock our world

A little perspective: In 1869 bearded men in tall black hats whacked in a golden spike completing the Transcontinental Railway at Provo, Utah, establishing the first sit-down transportation between the East Coast and San Francisco. In January of the following year a magnitude 9 earthquake set off a flood that drowned Native coastal villages from mid California to the northern tip of Vancouveer Island. In short, it was a whopper; but almost completely unrecognized for over 100 years.

In January 1700, the offshore portion of that fault fractured along 700 miles from northern Vancouver Island to Northern California. The shake from that quake has been estimated at a magnitude 9 or greater. (For perspective, the Great Earthquake that nearly destroyed San Francisco in 1906 was 30 times weaker and the 2001 Nisqually Quake that tumbled much of Pioneer Square in Seattle was 900 times weaker.)

But until the late 1980s, the now infamous subduction fault off our coast was thought by geologists to be unlikely to produce major earthquakes. Then a vacationing West Coast geologist found evidence of an “orphan tsunami” in Japanese temple journals that corresponded and explained sand in deposits mud cores along the Washington coast and Native stories of their canoes being carried away and nest 20 feet up in cedar trees.

Later, a well researched story in the New Yorker magazine included a quote from a high federal official saying, “Everything west of I-5 will be toast.”

Now there is a level of fear way beyond the level of threat. Yes, the Juan de Fuca subduction fault is one of the largest on our planet. Research has shown that this fault tends to rupture along its entire 700-mile length, generating massive shock waves. When it does fracture, the damage can be extreme ... in some particularly vulnerable places.

Shaking from a subduction fault fracture is unlike any other earthquake. The disturbance is long, complexly changing and damaging because of its relentless attack by different kinds of wave forms.

La Conner is within the massive shake zone of a subduction generated earthquake. Some places and situations in our wee hamlet are more at risk than others.

Some places may suffer heavy damage and others little or nothing. Sometimes the difference lies in how a building or house is built. Sometimes the relative damage has more to do with the soils underneath the structure. Houses on the hill, particularly those anchored to the rock beneath, will survive better than those in the flats on old river delta soils. And more often than not, suffered damage differences can’t be explained.

It’s still not possible to predict when or where an earthquake will strike, but it’s now possible to deploy an early warning system using the same technology as the amber alerts on our cell phones. Here’s how it works: earthquakes spread through the ground by different kinds of waves that travel at different speeds. The first waves, the first shaking, while noticeable, is not usually damaging and comes seconds before the stronger, more damaging waves. Seismographs arrayed all around earthquake-prone areas “see” these first waves and issue an automated warning: “Earthquake imminent. Take Cover!” There will be only seconds to respond, but those seconds could save lives and minimize injuries.

Jerry George chairs the La Conner Emergency Management Commission.