Preparing for the next megathrust earthquake

[OKIsItJustMe]

http://www.nrcresearchpress.com/doi/story/10.4141/news.2013.06.11.138

[font face=Serif][font size=5]Preparing for the next megathrust earthquake[/font]

[font size=4]Canadian Journal of Earth Sciences
12 June 2013
Direct link to article

Canadian scientists apply new methods to better understand Pacific coast earthquakes[/font]

[font size=3]Understanding the size and frequency of large earthquakes along the Pacific coast of North America is of great importance, not just to scientists, but also to government planners and the general public. The only way to predict the frequency and intensity of the ground motion expected from large and giant “megathrust “ earthquakes along Canada’s west coast is to analyze the geologic record. A new study published today in the Canadian Journal of Earth Sciences presents an exceptionally well-dated first record of earthquake history along the south coast of BC. Using a new high-resolution age model, a team of scientists meticulously identified and dated the disturbed sedimentary layers in a 40-metre marine sediment core raised from Effingham Inlet. The disturbances appear to have been caused by large and megathrust earthquakes that have occurred over the past 11,000 years.

One of the co-authors of the study, Dr. Audrey Dallimore, Associate Professor at Royal Roads University explains: “Some BC coastal fjords preserve annually layered organic sediments going back all the way to deglacial times. In Effingham Inlet, on the west coast of Vancouver Island, these sediments reveal disturbances we interpret were caused by earthquakes. With our very detailed age model that includes 68 radiocarbon dates and the Mazama Ash deposit (a volcanic eruption that took place 6800 yrs ago); we have identified 22 earthquake shaking events over the last 11,000 years, giving an estimate of a recurrence interval for large and megathrust earthquakes of about 500 years. However, it appears that the time between major shaking events can stretch up to about a 1,000 years.

“The last megathrust earthquake originating from the Cascadia subduction zone occurred in 1700 AD. Therefore, we are now in the risk zone of another earthquake. Even though it could be tomorrow or perhaps even centuries before it occurs, paleoseismic studies such as this one can help us understand the nature and frequency of rupture along the Cascadia Subduction Zone, and help Canadian coastal communities to improve their hazard assessments and emergency preparedness plans.”

“This exceptionally well-dated paleoseismic study by Enkin et al., involved a multi-disciplinary team of Canadian university and federal government scientists, and a core from the 2002 international drill program Marges Ouest Nord Américaines (MONA) campaign,” says Dr. Olav Lian, an associate editor of the Canadian Journal of Earth Sciences, professor at the University of the Fraser Valley and Director of the university’s Luminescence Dating Laboratory. “It gives us our first glimpse back in geologic time, of the recurrence interval of large and megathrust earthquakes impacting the vulnerable BC outer coastline. It also supports paleoseismic data found in offshore marine sediment cores along the US portion of the Cascadia Subduction Zone, recently released in an important United States Geological Survey (USGS) paleoseismic study by a team of researchers led by Dr. Chris Goldfinger of Oregon State University.

…[/font][/font]

http://dx.doi.org/10.1139/cjes-2012-0150

[Auggie]

1. I haven't heard the term "megathrust" before ...

even in context with the 2011 quake and tsunami off Japan. And I've lived in the Bay Area for over 33 years.

It's really frightening -- a 9.0 shake lasting anywhere from 4 to 10 minutes.

[FBaggins]

2. Where you live is why you haven't heard of them.

You live along another type of fault ... one that slips sideways rather than thrusting upwards.

But the 2011 quake in Japan was of that type.

[Auggie]

4. Guess so. I believe we once had subduction faults ...

about 150 million years ago. That's what helped create much of California.

[CreekDog]

5. So now you've decided to mislead that person into thinking subduction zones aren't off the CA Coast?

even though she's in Northern California?

you're willing to lie to that member because you are concerned that any discussion of a coastal megathrust earthquake in California, or effecting California will somehow lead to a discussion about our two coastal nuclear facilities?

you're willing to lie to her and say that subduction zones don't matter to us, HERE IN NORTHERN CALIFORNIA, because we lack subduction zones --except we HAVE THEM. they have produced large earthquakes and a mega quake in the Northwest has a good chance of rupturing the entire subduction zone, which stretches well down into Northern California and would be expected to produce a massive tsunami.

it is amazing how shamelessly you can attempt to mislead on a separate topic in order to avoid talking about the risks to nuclear facilities in another topic.

[FBaggins]

7. You think the poster is 300 years old?

You're arguing that something is possible (to cover for your far larger error implying that it's the norm)

Auggie would have no experience with such quakes because that isn't what the Bay area gets the VAST majority of the time (and for the poster's entire life).

Your desperation is showing.

[OKIsItJustMe]

3. In the past, they have resulted in major tsunamis

The tsunami in 1700 hit Japan: http://en.wikipedia.org/wiki/1700_Cascadia_earthquake

“… Geologists have also determined the Pacific Northwest is not prepared for such a colossal quake. The tsunami produced could reach heights of 80 to 100 feet (24 to 30 m).”

[FBaggins]

9. In the past?

I don't understand the implication formed by that statement and the (1700) example you chose.

They've killed hundreds of thousands of people in the last decade alone.

[OKIsItJustMe]

10. 1700 was the last Cascadia megathrust

This was the topic of the OP:

Understanding the size and frequency of large earthquakes along the Pacific coast of North America is of great importance …

[FBaggins]

11. That was the topic of the OP

But the post you replied to was just trying to figure out what they were (and specifically mentioned Japan's recent quake).

It would seem to make more sense to confirm the connection so that the scale of the potential damage would have better context than something that happened hundreds of years ago. I thought it could be particularly confusing when you mentioned that the 1700 quake impacted Japan rather than the one that made the news everywhere.

Remember... the poster was wondering why (s)he never heard of such quakes. It's a better connection to say "you have" and point to the example.

But it's hardly a big deal. I was just wondering.

[OKIsItJustMe]

12. I didn’t see it as wondering what one was…

…

It's really frightening -- a 9.0 shake lasting anywhere from 4 to 10 minutes.

(I’d call that a definition.)

However, since the poster has, “lived in the Bay Area for over 33 years.” I assumed the interest was in the Cascadia megathrusts.

[CreekDog]

6. Megathrust is a risk to Northern California, FBaggins has a separate agenda, don't be mislead

A megathrust earthquake of the magnitude predicted would effect the Bay Area, less in terms of shaking, the subduction zone begins up by Mendocino

With a time line of 41 events the science team at OSU has now calculated that the California–Oregon end of Cascadia’s fault has a 37 percent chance of producing a major earthquake in the next 50 years. The odds are 10 percent that an even larger quake will strike the upper end, in a full-margin rupture, within 50 years. Given that the last big quake was 312 years ago, one might argue that a very bad day on the Cascadia Subduction Zone is ominously overdue. It appears that three centuries of silence along the fault has been entirely misleading. The monster is only sleeping.

http://discovermagazine.com/2012/extreme-earth/01-big-one-earthquake-could-devastate-pacific-northwest

[FBaggins]

8. You didn't read the thread

Try again.

Auggie just wanted to know why (s)he hadn't heard of them before.

"Possible some time in the next few centuries" isn't something that will rise to the attention for people who live with earthquakes all the time... and have never seen that type (and likely never will).

"Living in the Bay Area" doesn't provide any reason to hear about those types of quakes it isn't what they get.

[CreekDog]

13. so you're saying living in the Bay Area, she has not heard of the Fukushima earthquake

because we didn't have that in the Bay Area.

also, she did not hear nor see the tsunami we experienced in the Bay Area from that earthquake --because we didn't get that earthquake here AND because you rule our airwaves, we are prohibited from discussing and/or knowing that tsunamis travel great distances.



unfortunately, i've read both threads you've stunk up, carefully to see your handiwork.

[FBaggins]

14. So I point out that you didn't read the thread...

... and you then prove it?

so you're saying living in the Bay Area, she has not heard of the Fukushima earthquake

She said just the opposite and I used it as an example... she just didn't know that it was an example of the term.

also, she did not hear nor see the tsunami we experienced in the Bay Area from that earthquake

You mean the one foot tsunami?

we are prohibited from discussing and/or knowing that tsunamis travel great distances.

Nope... but you should recognize the impact that thousands of miles of distance had on it.

45-50 ft... vs. 1 ft. Yeah... that really supports your nonsense that because SONGS can see the sea... the sea wall isn't big enough.

[CreekDog]

15. I based my post on responding to the nonsense you posted in our 1st post to this thread

FBaggins (11,779 posts)
2. Where you live is why you haven't heard of them.

You live along another type of fault ... one that slips sideways rather than thrusting upwards.

But the 2011 quake in Japan was of that type.

[FBaggins]

16. Then you should revisit your post

Because what I said was correct. She does live along a different type of fault - and that's why she has never heard of that type of quake.

They have quakes all the time... but haven't had to worry about this.

And, of course, the one in Japan was a megthrust.

In short... you had no reason to reply at all except for your continued desperation to pretend that you didn't stick your foot in your mouth in your initial reply on the other thread.

[wtmusic]

17. It was a John Holmes film from the 70s. nt