East coast earth quake

[bntii]

Weird- I was in Annapolis Md & this if the first true quake I have been in.

I was walking out a long dock the almost got thrown off the thing.
I had a view down the dock and the whole length was whipping back a forth like a snake- maybe the piles were going over two feet to each side.
I suppose the soft mud in this creek has something to do with how lively the dock was.

[hoytedow]

I'm glad you are ok. How did the house fare? I know you had quite a problem with it last year.

[Submarine Tom]

Yes, soft, unconsolidated river bed sediment can magnify secondary waves up to ten times, but it really just depends on where you are and how the topography is reacting to the given input energy (which is largely unpredictable).

What a great first quake experience for you! Everyone okay?

-Tom

[bntii]

I don't think that I heard of a single injury.
The small quake was felt over a broad area though- most of the east coast.

Hoyte- there was some small worry/hope that the house would have fallen down & I would have one less project on my plate,,,

[Submarine Tom]

Magnitude 5.8 at 4 miles depth could certainly rock your world if you were close to the epicenter.

bntii, was it a good experience for you or bad?

-Tom

[bntii]

Oh this was a great conversation starter and filled a day with a bit of hubub.
The DC area has a relatively low threshold for upset and we all pride our selves as not being one of those who panic during the minor events which rock the boat in these parts: 4" snow falls or a bit of heavy rain & now this earthquake..

DC earthquake damage was extensive:



A good time.

[Submarine Tom]

Soooo, you're saying for you, on the dock, it was a "good time"?

-Tom

[bntii]

Originally Posted by Submarine Tom

Soooo, you're saying for you, on the dock, it was a "good time"?

-Tom

Ah a specific query.

I am of the type which looks towards the report to see the source before ducking..

So yes- a interesting moment distilled in time.

It's odd to have the flood of sensory input which is far outside of immediate obvious explanation.
I just have this image of a very substantial dock with a sinusoidal wave whipping down its length. I was scanning for the big boat which hit the dock as I was trying to keep my feet under me.
So yes a good time which I would repeat tomorrow if I could so I could take better notes...

[Submarine Tom]

I've experienced close to a dozen now, all minor, but having spent five years in earthquake research it's always interesting to hear others experience.

Thanks,

-Tom

[Brian@BNE]

Tom
When you mentioned 5 years of research I've got to ask: what's the latest thinking and work for the Cascadia 'seismic gap'? I've heard a wide range of estimates on their frequency, but realise it could also be +9 in magnitude, sometime within about 100 years.
- Brian

[Submarine Tom]

Well, I don't have the latest as I left about five years ago, but my understanding is that it hasn't changed much. It boils down to statistics: the Cascadia fault has released every 300-500 years for the last 5000 years (known) with Magnitude 9 (+/- 0.5) energy. It is known that the last release was in the year 1700. So, sometime between 2000 and 2200 it will very likely release again. It could happen in two minutes, two hours, two days, two weeks, two months, two years, two decades or two centuries... but, it will release again.

Episodic Tremor and Slip (ETS) was discovered here about eight years ago. It is now believed that the likely-hood of Cascadia rupturing during one of these episodes to be 30 to 50 times normal. ETS occurs about every seven months and lasts about two weeks.

Google some of the key words above for more information.

-Tom

[Brian@BNE]

Thanks Tom
I pretty much had most of that. What I cant figure out is why a place like Ocean Shores is still there. OK, no-one knows when the quake will happen. BUT you are absolutely right: it will happen, that's for sure. And when it does, almost certainly there'll be a tsunami that will completely obliterate Ocean Shores, and no doubt impact a bunch of other urban areas as well. Is there much publicity about this or is it all 'secret' so as not to affect real estate prices?

[Submarine Tom]

You are most welcome Brian, I could go on all day.

Afraid I don't know where Ocean Shores is.

Funny thing is, the Cascadia subduction zone has only been known to exist for about 25 years now. There is major denial by most inhabitants that it will happen in their lifetimes and there is very little seismic activity felt to remind them that they/we live in earthquake country. Another spin-off is there is little to no culling of old, poorly constructed buildings so that when the big one hits, they will collapse. Retrofitting is expensive and, of course, no one wants to pay for it.

The mechanism we're talking about here is identical to what happened in Sumatra and Haiti. They are called megathrust earthquakes and cause catastrophic damage.

Knowledge is power. There is no conspiracy around these things. There is a lack of funding and more knowledge than most realize BUT, the more they learn, the more they realize they don't know...

-Tom

[hoytedow]

It's easier to say US caused it.

[Brian@BNE]

Tom
Ocean Shores is on the west coast of Washington State, due west of Olympia, basically on a sandspit that separates Grays Harbor from the ocean.

It worries me that even though the USGS has published some good information about the hazard, more is not done. I'd be reluctant to visit Ocean Shores even briefly in daylight, and would never spend a night (sleep) there. The problem with earthquakes is that there is never any warning - the big one is the first one. So, knowing the hazard - avoid the place!