[Strategerist]

Couple of additional articles on the Cascadia threat in the new Geological Society of America Bulletin:

Evidence for possible precursor events of megathrust earthquakes on the west coast of North America

Andrea D. Hawkes, Centre for Environmental and Marine Geology, Dalhousie University, Halifax, Nova Scotia B3H3J5, Canada, et al. Pages 996–1008.

Keywords: precursor, megathrust earthquake, foraminifera, thecamoebian, marsh/forest transition.

For many civic planners, the time frame of 300–500 years as a periodicity for the return time of megathrust earthquakes on the west coast of North America is too long to plan by. However, in this paper, we report a possible precursor mechanism that appears to have a 3–10 year time frame that provides 3–10 years' warning time, which is a realistic time frame for civic planners. The precursor was detected using changes in microfossil assemblages (protozoans that leave a fossil record--in this case, foraminifera and thecamoebians) in cores from Alaska and Oregon. The assemblages change in response to small elevational deviations a few years before mega-thrust earthquakes that occurred in coastal forests and salt marshes along the west coast of North America. This technique provides a reliable and economical tool that could save thousands of lives and millions of dollars of property damage in large cities like Vancouver, British Columbia; Portland, Oregon; or Seattle, Washington.

Tsunami history of an Oregon coastal lake reveals a 4600 yr record of great earthquakes on the Cascadia subduction zone

Harvey M. Kelsey, Department of Geology, Humboldt State University, Arcata, California 95521, USA, et al. Pages 1009–1032.

Keywords: tsunami, Cascadia subduction zone, paleoseismology, plate boundaries, subduction zone.

Earthquakes on the Cascadia subduction zone, which is the offshore fault that runs from northern California to southern Canada, generate destructive tsunamis. When these tsunamis spill over into low-lying coastal lakes, they can leave a record of their disturbance as layers of imported beach sand and wood debris preserved in the lake mud. Using this technique, four paleoseismologists (Harvey Kelsey, Humboldt State University; Alan Nelson, U.S. Geological Survey; Eileen Hemphill-Haley, Humboldt State University and Rob Witter, William Lettis and Associates) have discovered a 4,600-year record of tsunamis that have invaded the southern Oregon coast. During this time, fourteen tsunamis have entered Bradley Lake, an 18–20-foot-high lake dammed behind coastal sand dunes. Each tsunami carries beach sand and marine organisms into the lake. Detailed study of these sand layers in the lake shows that the tsunamis consisted of multiple waves that overtopped the sand dunes. Based on the height of the sand dune dam, the paleoseismologists estimate that the tsunamis were at least 18 to 20 feet high, with the larger tsunamis much higher than this minimum height. Time intervals between tsunamis have been as long as about 1,200 years and as short as a few decades. The tsunamis (and hence accompanying earthquakes) appear to come in clusters; for instance, between ca. 850 BC and 250 AD, there were no tsunamis, yet from AD 250 to AD 950, there were at least four. The most recent tsunami was 300 years ago and was preceded by a 700–800 year time gap with no tsunamis. The tsunami of 300-years-ago, which other geologists have determined was caused by a subduction zone earthquake that broke the seafloor between northern California and southern British Columbia, may be the start of a new cluster of closely spaced-in-time subduction zone earthquakes and tsunamis. Although the tsunamis are documented at this one site, it is likely that each tsunami affected a much larger coastal area, encompassing all or most of the northern California to southern Canada coastline. Also, Cascadia tsunamis can travel across the Pacific Ocean and lead to hazards at other Pacific coast localities.

[clamper1797]

So the wave would take out San Franfreako, Santa Cruz, and LA ... so where's the problem ????

[2banana]

Would each victim get millions of dollars of taxpayer money or would they be relying on insurance that they should have bought...?

[Thud]

ping

[ClearCase_guy]

If an earthquake of magnitude 23 were to hit, the effects would be greater.

If the US accidentally attacked itself with our entire nuclear arsenal, many people would die.

If ...

[IllumiNaughtyByNature]

I'd love to see a map showing how far inland the water would go. I'm about 4 miles inland and might have to get ready to own ocean front property. :o)

[Not A Snowbird]

Cool. My office will be lakefront.

[joebuck]

Congress needs to pass a law prohibiting this from happening.

[joebuck]

Congress needs to pass a law prohibiting this from happening.

[b4its2late]

Other than the UK, what country (s) would step up to come to our aid?

[Tulane]

WE'RE DOOOOOOOMED!!!!!!!!!!!!!!!!!!!!!

[RS]

Homeless, women and children effected most !

[dfwgator]

DOOOMED!

[BlackRazor]

if, against all odds, an errant asteroid plunges into the ocean many miles off California, a monstrous tsunami could drown low-lying lands all up and down the continent's western edge

Well, then I guess I'm not moving there. Way too dangerous.

BTW, what makes the asteroid "errant"? How does the author know the correct course?

[Mack the knife]

"If Big Quake Hits off Coast, Tsunami Could be Gigantic (Washington, Oregon, California)"

A 20 foot wave would not be "Gigantic". I saw a Discover or History program earlier this year that talked about the effects of a huge landslide off of an island off the coast of Africa -- this would result in a 300 FOOT TSUNAMI hitting the East Coast of the US.

Now THAT would be GIGANTIC.

[Veto!]

Oh well.

Veto in Puget Sound

[HitmanLV]

Viva Marina Las Vegas!!!!

[Cold Heart]

Thanks for the reminder about the tsunami flooding Portland too. Tidal affects are found all the way up the Columbia and Willamete rivers past Portland to Oregon City.

[So Cal Rocket]

I don't see a problem here.

[Pagey]

If a giant magnitude 9 earthquake strikes someday along the coast of the Pacific Northwest...

Then the Hollywood Liberals in the Malibu Colony and the Peoples Republic of Santa Monica might finally have something 'real' to whine about.

[followerofchrist]

Publish this in Mexico please. Say it is IMMINENT.