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.
But what if my aunt had b*lls?
Dear God, please leave Morro Bay, Pismo and San Diego.
I'm at the top of Cajon pass. Am I safe?
ALRIGHT! One more block, and I'm waterfront! Woohoo!
What?? Wipe-out half of Blue America? Be still, my heart...
Clearly, such a quake would be a Karl Rove strategy to wipe out blue states (and British Columbia). Why haven't the NYT and CNNCBSABCNBC whined about this? Biden!! Teddy!! We need hearings!!
Blue states sink, and the downside is?LOL.
Have you looked at the action in Alaska today.
For the 6.8 I clicked to get tsunami info and it gave me an update for a 5.something that occurred after.
Would like your insight on the Alaskan action that is hitting 5-6.8 today.
BTW I put your screen name as a tag line untill I can spell it, sometimes I want to ask you something and cannot get ahold of you. Plus you don't answer very often for what ever reason.
If the sun suddenly exploded it would be a catastrophe. If housecats learned to love water then dogs would be in big trouble. If Yawn (t)Revolta stopped in the middle of the intersection, clipped on a bow tie, took off his shoes, chewed a wad of decent tobacco and had a practice spit, hitched up his trousers, set fire to his hair, inserted a couple of metal skewers into his left palm, and filmed the resulting blood loss... it might not be a pretty sight.
The Weather Channel will scare your pants off. Their regular programming is 'Storm Story', but they break in with tsunami warnings, complete with saying, "if you have a friend on the beach in Southern California, and they have a cell phone, call them and tell them to get off the beach". The map they show has the entire US west coastline in red tsunami warning. I missed the times they gave for possible tsunami reaching land, but I assume it's the same as in the official report.
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Not only that, it would be hugh.