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Re: [OM] You don't get these in Iowa

Subject: Re: [OM] You don't get these in Iowa
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Wed, 24 Jan 2018 12:06:40 -0900
> Here in SW BC, numerous communities had tsunami warnings and sirens. The 
> biggest wave was only 3cm, in Tofino, I think. There’s a lot of criticism 
> about how much warning was warranted, and about how few people were alerted. 
> Most people slept right through automagically-delivered cell phone texts, and 
> only a few communities blew sirens.


It took a while before they determined it was a strike-slip
earthquake. The problem is that this particular fault is more prone to
Reverse-Fault style earthquakes which can result in tsunamis. Within
seconds, they knew the size, location and depth, which wasn't deep at
all, and rightfully issued the tsunami alert. Within an hour the data
analysis indicated that it was strike-slip, but with the curving
fault-line in that location, subduction could still occur. It wasn't
until Kodiak got the wavelets that they were able to confirm the
nature of the quake. But the most vulnerable communities in Alaska had
already evacuated and once Homer and Seward got their wavelets that
they changed the warnings to just an advisory.

I certainly do not fault (no pun intended) them at all for the
warnings. People along those coastal communities were already getting
their pants on before the sirens sounded. Which was only six minutes
after the quake started. When your house is 10 feet above sea level
and past tsunamis reached 100+ feet, you don't mess around when the
ground shakes like that and the sirens go off. When you consider that
1964 is pretty recent history and you can still find evidence of past
tsunamis, people tend to take it a little more seriously.

Timeline (AKST):

12:32AM - Earthquake. Lasted about two minutes. Preliminary magnitude
of 8.0, then upgraded to 8.2 within minutes then downgraded to 7.9 an
hour later. Located about 175 miles from Kodiak, Alaska.
12:38AM - Tsunami Warning issued.
01:45AM - Kodiak had first wavelets hit. No rushout of water along the
shoreline. Confirmed that the westward direction is safe.
01:55AM - Elfin Cove and Seward had their wavelets hit. No rushout of
water along the shoreline. Confirmed that the northward direction is
safe.
02:00AM - Sitka had their wavelets hit. No rushout of water along the
shoreline. Confirmed that he eastward direction is safe.

After this, the style of earthquake was confirmed and the tsunami
warning was downgraded for Alaska, but the decision to change the
alert level for southerly directions was held off until confirmation
of the wave characteristics could be determined to the south. This
didn't happen for a while as the buoy sensors are spaced out quite a
bit. Actually, there were two warning levels initially issued with
Alaska and BC having the highest and the rest of the PAC-NW at a lower
level. Alaska's downgraded to the lower level and the rest didn't
change.

So, the early postmortem up here is that there is little criticism of
the warnings and people took it seriously.  Nobody was upset that the
waves were small, because they felt the quake and knew that anything
could happen. You really don't know what will happen until the first
communities actually get hit.

I'm quite intrigued with the nature of the Cook Inlet. Logic would say
that the Anchorage harbor should be vulnerable, but it isn't We get
massive tides here (30-40 feet), but it's very shallow and has weird
topography that creates an out-of-phase arrangement that attenuates
tsunamis.


> Personally, I’ll take the possibility of an earthquake to the possibility of 
> a tornado any day.

Bingo.

AG
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