Saturday, March 6, 2010

What Would Another Great Alaska Earthquake do to Southcentral Alaska?

Chile tsunami timelapse in Seldovia, Alaska from Bretwood Higman on Vimeo.

That's the Chilean earthquake's tsunami, as it mildly hit Seldovia Harbor. Here's Bretwood Higman's description:

All I can say is that I may have seen a tsunami, albeit a really small one. On a beach here in Seldovia I watched the dropping tide. Did it drop a little faster during the last 5 minutes? Has it slowed now? The tide gauge in town definitely saw something… a wave several inches tall with a period of 10 minutes or so (link here, many gauges on this page, including a more easily seen example of a tsunami recorded by a tide gauge in King Cove a few hundred miles southwest of Seldovia).

I also set up my camera. I took a timelapse video, accelerating reality by 300x. I’ve watched this video many times now, and I think I can see slight variations in how fast the tide drops down the beach near the center of the image. Then again, maybe not… you can judge for
yourself. (The boat in the distance probably isn’t being moved by the tsunami, as the period of its motion is only 1-2 minutes, as opposed to about 10 minutes.)

Hig is observing the probable effects of something that happened 8,000 miles away. The most dramatic North American effect from the Chilean quake was in California's Santa Cruz Harbor. My son, Alex, was working on a barge in Humboldt Bay California, and noticed nothing.

The 1964 Good Friday earthquake in Alaska was the 3rd strongest in recent human history, at 9.2. The Chilean event was pegged at 8.8. The 2004 Sumatran undersea quake that caused the enormous losses of life from tsunamis, was 9.3.

The Alaska quake's effects on Prince William Sound, Seward, Kodiak and Anchorage were profound. Buildings were destroyed as the earth moved, and - in some places - reshaped the terrain markedly.

What would happen if we had another 9.2 quake centered somewhere in southcentral Alaska? A lot more people live here now than in 1964. Although places like Anchorage have attempted to assure most structures are built far better than those in Haiti or Wasilla, for instance - more like Santiago Chile - there is no doubt that in a 9.2 event there would be a lot of damage to Anchorage, for instance. And nobody can proof coastal areas against tsunamis like the one reported to have been around 70 meters high in southern Valdez Arm, or over 30 meters, near the junctions of Blackstone Bay and Passage Canal.

The building above is the Cordova Center (at 130 Cordova Street in Anchorage), Alaska's biggest halfway house. I worked there for seven years. I'm convinced it would not survive an event approaching the magnitude of last week's Chilean quake. Built by Pete Zamarello as a condo unit structure in the early 1980s, not only is it in an unstable area - the east slippage bank of lower Ship Creek - its 1991-92 foundation modifications, performed as part of an expansion of the correctional facility, are questionable at best.

The Cordova Center isn't the only Anchorage structure that was built after 1964 that makes one wonder, though.

What are some other local prime suspects for total failure or collapse, should we experience another catastrophic seismic event here?


Anonymous said...

I always think about earthquakes while in the Inlet Towers and the JC Penneys parking garage. I think they were both damaged in 64 and I don't really trust the "repairs".

And you couldn't pay me to live in Turnagain. I was in a five or six point earthquake in an attorney's office down around 9th & N once, and the building was shaking in a way that made me Very Nervous. You could tell the ground underneath was "different". akbat

Anonymous said...

tsunami, tsunami, bologni.

Anonymous said...

It's all Palin's fault !!!

Anonymous said...

I think the people who built their big houses right to the east of Earthquake Park along the Coastal Trail probably should have thought twice. More dollars than sense, those people.


Anonymous said...

I have been wondering the same thing, Phil. I do think Seward would be destroyed by a tidal wave again. And Anchorage would be one huge mess and mass of rubble (wouldn't want to be in the Hotel Captain Cook or the 5th Avenue Mall). I also wonder about all of the development on the Hillside and south of town these days.

Anonymous said...

i know im only thirteen but i went on this website to find information about what happened in the following week of the alaskan earthquake in 1964. but i found none of use. but i liked reading it!