Saturday, March 12, 2011

Alaska Earthquakes and Tsunamies

I had planned to put in a blog about more effects form recent local storms. Well, maybe another day.

The earthquake in Japan has reminded everyone of how vulnerable we are to sudden changes in the Pacific. We in Kodiak live along the Aleutian Trench. So earthquakes are of real interest to us.

The 1964 Good Friday earthquake outside of Anchorage was 9.2 on the moment scale. That was the second strongest quake in recorded history (after Chile's 9.5 in 1960). The recent 2011 Japan one was 8.9.

In our 1964 quake over 10,000 aftershocks were recorded following the main shock. In the first day alone, eleven major aftershocks were recorded with a magnitude greater than 6.0. Nine more occurred over the next three weeks. It was not until more than a year later that the aftershocks were no longer noticed

Fortunately we have lots less people and no nuclear power plants here to worry about than Japan. We only lost 13 people locally and 119-131 total in the 1964 Good Friday quake. Here, people felt the quake, noticed the sea level retract, so the police went out with magaphones telling enough to head for higher ground. As you have see form our pics, we have a lot of mountains at the edge of the water to climb out of harm's way.

The 2004 quake in the Indian Ocean took 230,000 lives. Dense concentration of population and flat ground caused that problem.

Anyway, we do worry about the quakes and the water. We have tsunami warning sirens that are tested every Wednesday at 2 PM. If they sound and it is not that time, get to high ground quickly......because the arrival time of a tsunami is quite fast....faster than he warning systems can detect them, perhaps.

The 1964 tsunami waves reached Kodiak only 30 minutes after the quake started. It was about 280 miles away. That means the waves travelled at over 500 miles per hour! From what I read, tsunami waves travel at up to 670 miles per hour.

Till improvements were made after the 2004 quake, it took about 1 hour for sensors to detect a tsunami....that meant it had already travelled and perhaps destroyed cities 670 miles away. Now they say they can detect it in 30 minutes. So if you are 300 mile form the epicenter, you might get a warning.

In Kodiak the 1964 first of 3 waves arrived within 30 minutes; 2 more came in in the next 30 min to 1 hour. They were 30 feet high. Downtown was gone. All the fishing fleet was gone.

And apparently, this wasn't particularly high waves. I read that the 1755 Lisbon tsunami waves reached 10 stories. The highest expected theoretically are 60 meter, over 180 feet. I didn't know they were that high. And I had felt safe with a house at 119 feet above mean sea level!

Anyway, Friday we got calls form people at 6:30 AM to warn us that at 9-10 PM Pacific time a big quake had occurred in Japan. But form what I read, we were just lucky. If a bad tsunami was coming our way, it would have hit us between 3 and 4 AM.

But, as you can see, quake activity around Kodiak has been quite calm over the last 24 hrs.

So, no need to worry. In the end, though, if it is not the big "C", it might be a speeding car; or being at the wrong place, like a hold up in the lower 48; or maybe just "The Big Infarct".

Someday maybe we'll worry about those things, until then, enjoy what you have around you! The sun is shinning, water's warming...up to 36.5 F !!!! Time to put the kayak in the water???? Any time now!!

1 comment:

Carlos said...

I looked further into the time between the quake and the arrival of the first tidal wave. I was "way off". It was about one hour (not half an hour) after the quake.

But times get dificult to determine if you just listen to what some people recall. Even the Academy of Science 1972 report on this event alluded to this. When equipment fails it is hard to tell what is real. In fact, there is even discussions about the heigth and explanations of why their estimates of the wave's arrival were off by one whole hour.

I know, with daylights savings time and longer days, there are better things to do. But if you are laid up with an injury or something, just for "fun" check out pages 230 to 233 of the report at