Posted on 01/01/2005 5:12:53 PM PST by Exton1
Measuring the Big One These days, an earthquake happens and right away you hear about it on the news, including its magnitude. Instant magnitudes seem like a routine achievement, like reporting the temperature. But that feat is the result of generations of scientific work.
Earthquakes, in fact, are very hard to measure. The problem is like coming up with one number to indicate the quality of a baseball pitcher. You can start with the pitcher's win-loss record, but the more you study the problem the more things you want to consider, like earned-run average, defensive range, strikeouts and walks, career longevity, and so on. Baseball statisticians love to tinker with indexes that weigh as many of these factors as possible. (And if you want to know more, visit the About Baseball Guide.)
Earthquakes are easily as complicated as pitchers. They are fast or slow. Some are gentle, others are violent. They are deep or shallow. They're even right-handed or left-handed. They are oriented different ways—horizontal, vertical, or in between. (For more, see The Three Types of Faults.) They occur in different geologic settings, deep within continents or out in the ocean. Yet somehow we want to get a single meaningful number we can use to rank the world's earthquakes. The goal has always been to figure out the amount of energy an earthquake releases, because that tells us profound things about the dynamics of the Earth's interior.
(Excerpt) Read more at geology.about.com ...
I for one have always found the QB Rating system a bit suspect.
Where's Slick? (sorry, couldn't resist).
I have watched a seismometer in Utah for 5 years now. The EQ Christmas day, within an hour I knew that it was big. I think I said around post 45 that I had never seen one this big. Little did I know just how big it was.
There was a couple interviewed on FoxNews on the 28th who were in Burma at the time of the earthquake. They were from CA, so were familiar with the feel and length of quakes. They knew it must have been a monster because they were near the top floor of a large hotel and they said their room swayed violently for over 3 minutes. That's a LONG time in earthquake time!!
yes, here is the link to the seismograph. You can see that it wasn't a sharp jolt, but lasted for a couple of mins. the thing that tipped me off were the waves that come in afterword. Most of the time, they are fairly small and last a much shorter time.
http://www.seis.utah.edu/helicorder/heli/utah/Uuss.BMUT_EHZ_UU.2004122500.gif
That one was located off the coast of Anchorage, Alaska and it produced gigantic tsumamis that produced waves as high as 300 feet in some places. The only reason the death toll wasn't higher was because of how sparsely populated Alaska was at the time (and still is for the most part).
If I remember correctly it was a 9.4.
I read that one wave went up into a bay to a height of 1700'! They know this because it scoured a hillside up into the forest at that height! I guess when the tsunami got into the bay, the only place the water was able to go was UP!
Thanks for posting this article. Knowledge saves more lives than all the world's money.
From:
http://www.drgeorgepc.com/Tsunami1964PrWilliam.html
"There was no time for warning. Within minutes, huge tsunami waves generated by the earthquake and the landslides destroyed local towns and fishing villages, killing 82 people. The maximum wave height recorded within the Prince William Sound was 67 meters at Valdez Inlet."
67 meters is close to 200 feet.
The tsunami started in the bay from a massive landslide into the bay; the reason it went so high is it occured in an almost fully-enclosed space.
It's reported that some buildings in SF swayed for 30 minutes after the World Series quake. But then, those buildings are built on tumblers and made to roll!
Different types of waves travel at different speeds, and you can use their time separation to measure the distance to the quake, much like counting the time between lightning and thunder. The fact the slower waves took so long to finally appear meant the quake was very far away. And the fact that it registered so big despite the distance, meant that it was really, really huge.
and because the secondary waves lasted so long (2.5 hours) it was, as somebody said, ringing the earth like a bell.
As I said, I knew it was a monster EQ as soon as I saw the seismograph. or at least I suspected it was because I had never seen one like this before.
Oh, that's right! My husband had said that a landslide started that particular one.
Thanks for that link! I'll show it to Sir SuziQ later in the morning. He was telling me about this particular incident, but didn't have a whole lot of info about it.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.
