I am hoping to get the opportunity to hike out to the 1964 Alaskan Tsunami line on the island if I get some time. I've heard that it is accessible in a few locations on the island. If you've never heard of the 1964 earthquake, I'll give you a quick rundown. Armed with this information, you will now be able to hold your own in style at any cocktail party thrown by members of the US Geological Survey, should you ever find yourself there. One can never be too prepared.
On Good Friday (of all days) in 1964, a large (9.2) earthquake struck the area of Prince William Sound. To date, this is the largest recorded earthquake in the United States. Let's keep it that way.
All of my Earth Science Honors students know to practice caution when throwing around magnitude numbers, especially with very old and very large earthquakes. (In this case, it's a double whammy.) The moment magnitude scale was not introduced until a few years after this particular earthquake. If you recall, seismologists use Moment Magnitude to measure very large earthquakes, so when you see a number like 9.2, the automatic assumption would be that this particular scale was used. Not so, in this case, as it wasn't invented yet. It's like assuming that World War II fighter pilots used GPS to land planes. The technology didn't exactly exist. Now, I will say this with a caveat - the numbers may have been back-measured with this particular scale after the fact and the 9.2 is a revised (and legitimate) number. I'm having a hard time finding any information on what type of scale they used to arrive at this number. Any smart people out there who can help me with this?
*I took this photo from: http://earthquake.usgs.gov/earthquakes/states/events/1964_03_28_seismogram.php
This is the long-period seismogram, the vertical component.
According to the USGS website, the quake was so bad that the seismograms couldn't even keep up with the darn thing and they had to reset the machines the following day because even the seismographs gave up after about 1 minute of recording. Either way, it was quite ugly. Until the Sendai quake (Japan Quake this year), this was the Cloverfield of Earthquakes - particularly because it was a giant monster, and no one really knew any details - just that they were getting attacked, and get they needed to get out. Run first, ask questions later. Stay out of tunnels.
As if the quake wasn't a nasty enough beast, the fault that it occured on was a thrust fault at the bottom of the ocean. (Earth Sci kids: If the bells and warning whistles are not going off in your Earthly-adept heads right now, I've failed you as a trainer of natural hazards.) When the Earth moves (as in a quake) along a thrust fault (as in Alaska) at the bottom of the Ocean (as in the Pacific), our planet gets the added bonus of a tsunami threat. This particular threat was carried out in true planet fashion shortly after the quake struck. A thirty foot wall of water overtook little Kodiak island. Fortunately, most people knew to get to higher ground, and few lives were lost.
Now, you may ask: "What did our lovely Earth accomplish in performing such a show?" According to the USGS, maximum displacement in some locations was a much as 14 feet. Let me help you put this in perspective. If you built a house along this displacement line, and your house managed to survive the ride (probably not), you would need to stand on your own shoulders almost THREE TIMES to get from your mailbox to your house. Armed with this information, you should never complain about bringing in groceries again. At least you don't need a ladder. Keep in mind also, that displacement is a vector quantity and goes in three dimensions, so your house could be moved 14 feet down, right, or left (or some combination of the four), depending on where it was located. In Kodiak, the ground subsided (sank) about 5 feet in some places. One might say that Mother Earth "rearranged the furniture" that day, and by furniture I mean coastlines.
*I took this photo from: http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID. This is the area of maximum displacement, which doesn't occur where the man is standing, it's actually closer to the trees.
This historic earthquake almost always gets an honorable mention in the question "What was the largest quake ever recorded?" As you know, (or may not know) that question doesn't really have an answer, and anyone who gives you one is just giving you their opinion. He or she should, however, make mention of a few noteworthy quakes, this being one of them.
Did I say that I would give a quick explanation? I lied.
Either way, some of the scientists have graciously offered to give me a lift from the hotel to the ship (hallelujah!), so depending on if I have time or not, I would like to make the hike up to the uppermost wave line on the island. What can I say? Some people like to look at animals, I like to look at rocks. Nerd alert!
Ladies and gentlemen, I have stalled long enough for today. It is time to return to school prep work for next year. Until next time...
No comments:
Post a Comment