The Cascadia subduction zone is a 600-mile-long offshore earthquake fault that runs from northern California to southern British Columbia. And that fault has a serious tale to tell. Geologists have found sand deposits up and down the Pacific coast along this zone, the result of a tsunami a little over 300 years ago.

Three hundred years is a long time and that bit of trivia in and of itself may not seem threatening, but pair it with what scientists now know about earthquake patterns, and the Pacific Northwest Coasters should be trembling in fear – or at least preparing for an impending disaster in the very near future.

“I think all subduction zones are guilty until proven otherwise,” Dr. Kerry Sieh told National Geographic in their February 2012 issue. Sieh, director of the Earth Observatory at Singapore’s Nanyang Technological University, is one of the world’s leading paleoseismologist. He spends his days obsessing over geologic records for evidence of ancient earthquakes and tsunamis, and identifies what he calls, “supercycles” or clusters of big earthquakes that occur at regular and predictable intervals.

While the most recent tsunami may have hit that region more than 300 years ago, recent evidence from seafloor sediment cores suggests that about 40 earthquakes have occurred along the Cascadia fault zone over the past 10,000 years, with an alarming average of one every 250 years; although some researchers estimate the recurrence interval at 500 years.

Scientists may not be in total agreement on the recurrence interval, but where there is a meeting of the minds is in their confidence that when the fault does rupture, the earthquake (or earthquakes) could be as large as the one that hit Japan in March just last year, and that the tsunami could reach the Oregon coast in 20 short minutes.

If that horrific event were to occur during prime summertime tourist season, it is expected to create widespread devastation and a massive numbers of casualties.

The most populated area of Washington State is Seattle, insulated on Puget Sound behind the Olympic Peninsula and likely harboring it from major harm. Alarmingly however, geologists are now discovering smaller, shallower cracks in the crust that extend under Puget Sound. They are unclear on how often those earthquakes occur but are suspecting the most recent occurred a thousand years ago. Those new-found cracks are especially disturbing in that a comparatively moderate tsunami starting off Seattle could be more damaging than a giant one off the main coast.

Washingtonians can hardly be in the dark with evacuation signs, information booklets and broadcast towers spotting their landscape. Even so, evacuation centers are rare and many residents do not have access to high ground – and would ultimately perish if such a disaster were to hit their coast. The smartest action to take is to prepare for the worst disaster – and do it now.

We are approaching the 1-year anniversary of the devastating tsunami that rocked Japan and the pacific rim. While countries affected by the massive disaster continue to struggle to recover, we can’t help but turn out thoughts closer to home and worry about the impact of a Pacific Coast tsunami.

Here is a list of a few link resources to help outline how you can start disaster planning for your coastal area for a tsunami-related event:

Southern California info: