

Oregon: 9 months pregnant and overdue for an 8.n quake? - hsmyers
http://dotearth.blogs.nytimes.com/2011/03/13/a-postcard-to-the-pacific-northwest-prepare/?partner=rss&emc=rss

======
btilly
I've known about this one for years, and it is one of the reasons I don't want
to move back to the Pacific Northwest (I grew up in Victoria).

It was only in the last few decades that geologists realized the size of the
earthquakes that the area experiences. Building codes have not caught up. And
a lot of the population centers in the area, including Seattle, Vancouver and
Victoria, have important construction predating any useful building codes.

A few areas have notable risks.

The scariest is Victoria. It is on Vancouver Island, which typically drops 10
feet during a Cascadia earthquake. Most of the city is under 20 feet above sea
level. Add a tsunami, and a lot of that could be covered. (I've read the
projections for a tsunami from the Cascadia quake are about 30 meters. But I
have no idea how big the tsunami would be within the Straits of Juan de Fuca,
which is what Victoria would be exposed to.) Normally one would worry about
the fact that densely populated areas (like James Bay) are largely built on
landfill, which behaves poorly in earthquake. But that's incidental compared
to being unexpectedly under the new sea level. I don't know exactly how many
people would be under the new sea level, but I think it is about 100,000. (You
can see the distribution of people in
[http://www.victoria.ca/cityhall/pdfs/sustainability-
census-p...](http://www.victoria.ca/cityhall/pdfs/sustainability-census-
population.pdf). All of Oak Bay, most of Victoria, a significant portion of
Esquimalt, all of View Royal, some of Saanich, and a small part of Langford
would be under water.) Given the unavailability of higher ground and low water
temperature, I don't expect a lot of survivors.

Next look at the delta area of Vancouver. It is called the delta because it is
the river delta from the Fraser River. Which means dirt with a high water
level. Take dirt and water, and shake. What do you get? Mud! The delta area of
Vancouver is perfect for
<http://en.wikipedia.org/wiki/Earthquake_liquefaction>. There are about
100,000 people living there.

Now consider Mt Rainier.
<http://www.geotimes.org/apr04/feature_MountRainier.html> documents some of
the lahar risks that it faces. Odds are that a Cascadia earthquake wouldn't
trigger one of those lahars with 150,000 people in its path. That will happen
some day regardless. But if it did, and you had a lahar on top of a major
earthquake, well, nothing good would happen.

Japan lost perhaps 10,000 people in this earthquake and tsunami. I firmly
believe that a Cascadia quake would kill at least an order of magnitude more
people in Victoria alone. And, unlike Japan, there is no real disaster
preparedness ethic to mitigate the follow-up to the disaster.

------
harshpotatoes
Seattle is another area I would worry about as far as preparedness for a Major
earthquake. Most of the new skyrises are probably safe, but the Alaskan Way
Viaduct would most certainly collapse (it was nearly destroyed due to a
moderate eathquake 10 years ago, but due to local politics no suitable
replacement/repair has been made), as would most of the waterfront, whose
foundations have been eaten away by something I've heard called 'gribbles.'
Additionally I would worry about many of the much older buildings downtown,
which have also been damaged before by moderate earthquakes.

~~~
futuremint
<http://en.wikipedia.org/wiki/Gribble>

Apparently a gribble is a wood boring crustacean. Interesting.

------
akkartik
_"The average time between magnitude 8 and larger Cascadia earthquakes is
about 240 years."_

The outliers on that graph make me extremely skeptical of an average[1].
Eyeballing it[2], the most common delta seems to be close to 300 years.
Doesn't using the mode make the most sense here, from the perspective of
_highest-probability outcome_?

[1] Should we just outlaw the average? Perhaps a real statistician can advise.

[2] Earthquakes:

    
    
      -7800 -7200
      -7100 -7000
      -6750 -6500
      -6200 -5800
      -5500
      -5150 -4800
      -4450
      -3900 -3800 -3750 -3500 -3300 -3100
      -2800 -2500 -2400
      -2200 -1900 -1600
      -1500 -1200
      -1100 -900 -800
      -500 -300
      -100 200
      500 600
      700 900
      1200 1400
      1500
      1700
    

Deltas:

    
    
      600 100 100 250 250 300 400 300 350 350 350 550 100 50 250 200 200 300 300
      100 200 300 300 100 300 100 200 100 300 200 200 300 300 100 100 200 300 200
      300 200
    

Frequency distribution of deltas:

    
    
      50 1
      100 9
      200 9
      250 3
      300 12
      350 3
      400 1
      550 1
      600 1

~~~
kenjackson
I actually think the average makes sense here. The mode will give you '300',
but you have 18 that have occurred at 100/200.

~~~
akkartik
I see, makes sense.

There's outliers, but not that many and not that far off.

~~~
seancron
Using the 1.5 * IQR (Interquartile Range) rule of thumb, there don't appear to
be any significant outliers.

    
    
        Q3 = 400
        Q1 = 200
        IQR = 400-200 = 200
        1.5 * IQR = 300
        300 + 400 = 700
        200 - 300 = 0 (can't have negative years)
    

All of the data points fall within that 0-700 year range.

------
nickbp
Hello from the East Bay, home of the Hayward Fault Line:

 _The last five major events were in 1315, 1470, 1630, 1725, and 1868, which
have intervals of about 140 years (note that 2008 is 140 years from the major
1868 event).

If a major earthquake were to occur on the fault, damage would be
catastrophic. More than 1.5 trillion U.S. dollars in property exists in the
affected area, and more than 165 billion US dollars in damage would likely
result if the 1868 quake were to recur.

The estimated probability of a major earthquake on the Hayward within the next
thirty years was estimated at nearly 30 percent, compared to about 20 percent
for the San Andreas Fault, which can have larger earthquakes but farther away
from a significant portion of the urbanized parts of the Bay Area._

(various rips from Wikipedia)

~~~
reneherse
Yup, and one of the major concerns in the East Bay are so called "soft story"
buildings: homes and apartment buildings with ground floors largely open to
create garage and retail space and therefore lacking adequate shear structure
to resist earthquake forces.

It's a well documented problem, with huge loss of life and housing stock
predicted in the event of a large earthquake on the Hayward fault. Not sure
exactly what measures other cities are taking to improve the situation, but
you can learn more on the City of Berkeley site:

<http://www.ci.berkeley.ca.us/contentdisplay.aspx?id=622>

There's a list where you can look up whether your building is structurally
vulnerable or has been retrofit.

------
tlrobinson
In case it's not obvious, when people talk about faults being "N months
pregnant" it doesn't mean it's extremely likely there will be a large
earthquake in the next week/month/year, but rather on the order of magnitude
of 50 years. The San Andreas in California has been considered overdue for a
major earthquake for decades as well.

------
endtime
Sorry if this is a stupid question, but would an 8-9 Cascadia quake have
implications for the Yellowstone supervolcano?

~~~
Jach
That's something I sometimes (perhaps stupidly) worry about too. Some
earthquakes go off over in Asia and set off earthquakes in California and
Pacific Northwest and set off earthquakes in Utah and then the supervolcano in
Yellowstone goes off...

~~~
borism
<http://en.wikipedia.org/wiki/Yellowstone_Caldera> sits on top of
<http://en.wikipedia.org/wiki/Yellowstone_hotspot>

Hotspots seem to be unaffected by plate movements - plate moves but hotspot
remains in place. That's how Hawaiian island chain has formed, actually.

------
wtn
Sell short catastrophe reinsurance bonds?

~~~
jerf
Tectonic plates can remain irrational longer than you can stay solvent.

Or something like that.

