One thing to keep in mind, is that the more technology we have deployed, the more earthquakes we are actually detecting. 20 to 30 years ago, the technology improved dramatically. Prior to that many of the earthquakes never made it to our data banks, because they were not big enough, or close enough to a population center, or deadly enough, to be reported. I recommend this blog http://www.science20.com/florilegium/blog/why_so_many_earthquakes_decade for an explanation, and then following to this link http://earthquake.usgs.gov/earthquakes/eqarchives/year/graphs.php to see the real data for the last 30 years. Keep in mind, the USGS has not put together a complete list going back farther than 30 years, just the ones of "General Historic Interest", a point forgotten by the creators of the charts based on the USGS data. Jo Quoting Kim Hyatt <kimharch@cut.net>:
As y'all may know, the Richter Scale (and similar Moment Magnitude scale) is simply a measure of the total energy output of an earthquake. Structures are not designed for a given magnitude quake but are designed based on a theoretical ground acceleration caused by earth shaking. Every large earthquake will cause codes to be re-written, but they seem to be coming much faster now than a few decades ago, and even faster than new data can be incorporated into building codes. Check out this page: http://www.infoplease.com/ipa/A0001439.html. Notice the number of significant events in recent years. Frequency of events appears to be increasing, but I don't know enough about the data or statistics to know if it is actual or merely perceived.
Kim
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of erikhansen@thebluezone.net Sent: Friday, March 18, 2011 4:19 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Japan Earthquake Discussion
The most telling comparison I saw was damage done in S. California from a 7th or 8th mag quake that lasted for seconds. Interstate Bridges collapsed along with other extensive damage in an area "prepared" for quakes. The shaking in Japan lasted several minutes, this type of quake would devastate S. California, or any urban area for that matter. They also mentioned that the Nuclear Power plants were not designed to withstand an earthquake of this magnitude. How confident are you that S California N Plants are built to withstand any magnitude of earthquake that is possible? The one proposed for Green River? Cost evidently trumps safety.
This is mildly off topic but does talk about crustal tides and earthquake
predictions.
I don't know much about this guy but what he is saying may provide for an interesting discussion.
Time will Tell.
Follow this link:
http://www.youtube.com/watch?v=xQXDt4VdS0E
Rodger Fry
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