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Re: Shift in the seismic paradigm?[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: Shift in the seismic paradigm?
- From: John Nichols <cejn(--nospam--at)engmail.newcastle.edu.au>
- Date: Wed, 18 Mar 1998 10:38:08 +1100
Dear Frank, Earlier this week I completed a literature review for my PhD. In it I had to look at the data for earthquakes in a lot of places. If you look at teh really excellent work of the USGS at Menlo PArk one can gain an appreciation for how many earthquakes occur in the world and how regular is there rate of occurence. I just plotted teh last 9 months of data from MenloPark on big quakes and it matched Gutenbergs data at least well enough for me. M QED List Big Quake list ' ' ' combined 5.5 36 18 36 5.6 19 10 19 5.7 15 21 21 5.8 15 12 12 5.9 6 12 12 6 0 4 4 6.1 3 4 4 6.2 1 3 3 6.3 2 2 2 6.4 6 4 4 6.5 1 8 8 6.6 1 3 4 6.7 1 3 3 6.8 2 2 6.9 1 1 1 7 1 1 7.1 7.2 7.3 7.4 7.5 7.6 7.7 1 1 7.8 7.9 1 1 8 8.1 8.2 8.3 8.4 8.5 Remeber this is over 9 months or there abouts. The problem as Alison Bent points out so well in her work is not the places like PArkfield that have a known earthquake problem and a unknown probability of return. (In this instance refer to my quotes last week from Richter he certainly said a lot more succiently than the message below. The world problem is teh ones above 6.5 that occur outside interplate areas in intraplate areas. CA is lucky you know about your earthquakes, your ground is well broken so the waves attenuate east west quite quickly. It is the 7 in New Madrid in Mo that will be the big killer if and when it ever strikes again. Out of interest there were a few minot rumbles there in the last few weeks. Having lived in Mo for three years and being aware of the consequences of an intraplate earthquake of moderate size in this type of urban environmetn the work of Abrams at Urbana takes on an important emphasis. My humble opinion John Nichols At 14:00 17/03/98 -0500, you wrote: >The following item just came in via a news tracking service I subscribe to. >Interesting reading for all who follow earthquake policymaking in California, >and the impact that recurrence intervals have on such decisions. > >Frank Lew, SE >Orinda, CA >================================================ > >Tuesday March 17 10:43 AM EST > >Earthquake rules change >UPI Science News >PARKFIELD, Calif., March 17 (UPI) _ The long ``overdue'' shaker in the >earthquake capital of the world is not much more than a myth. > >Not only that, earthquakes follow a far less structured schedule than they're >given credit for and do not necessarily increase in likelihood with the >passage of time. > >Those unorthodox conclusions are drawn by a University of California, Los >Angeles, seismologist from data gathered by the myriad earthquake- monitoring >instruments set up in Parkfield, Calif., a decade ago. This tiny town's claim >to fame is its location on the notorious San Andreas fault and what has been >thought of as a pretty regular earth-shaking pattern. > >In fact, asserts David Jackson, professor of earth and space sciences at UCLA, >the treasure-trove of data coming out of Parkfield strongly indicates the >long-held belief that magnitude 6 shakers jolt the area just about every 22 >years is not much more than a myth. > >Says Jackson, also sciencie director of the Southern California Earthquake >Center: ``Earthquakes are not like comets that can be reliably predicted to >return. We have been warned for more than 10 years that an earthquake is >coming to Parkfield any time now. I'm not holding my breath. I would not be >surprised if Parkfield goes another 20 or 30 years _ or even longer _ without >another magnitude 6 earthquake.'' > >Jackson's view is bound to shake up the scientific community, which has a near >consensus that the probability of another quake measuring 6 on the Richter >scale in Parkfield is as high as 10 percent each year. Jackson puts the odds >at less than 1 percent. > >The view favored by the vast majority is based on data _ sketchy though some >of it may be _ that indicate Parkville has been jolted by magnitude 6 shakers >at pretty regular intervals over the past 140 years. Since the town last >rattled and rolled to that tune in 1966, it is commonly thought the time is >more than ripe for an encore. > >Jackson, however, points out the earthquake data prior to 1922 are sadly >lacking. In his scientific opinion, ``I think in Parkfield, people have found >an apparent pattern in random data. It's easy to imagine patterns in >retrospect.'' > >To him the ``pattern'' is nothing more than coincidence. > >He also questions the assumption that earthquake probability increases with >time. > >As he puts it, ``Scientists have not been able to establish that, and while >some earthquakes are said to be 'overdue,' many others occur where they are >'way underdue.''' > >Jackson disputes the notion that Parkfield, and the entire state of California >for that matter, face an ``earthquake deficit'' that must be made up in the >coming decades with more large shakers. > >The earth may decide to do just one big bang-up job with a magnitude 8 jolt in >place of more frequently scheduled magnitude 6 or 7 temblors. In Jackson's >view, it may be centuries before the really big one hits. > >The assumed Parkfield predicament of a magnitude 6 shaker every 22 years is >based on two assumptions _ both of them unproven, according to Jackson. One is >that a large fault such as the San Andreas can be divided into independent >segments, each with its own magnitude and interval between earthquakes. The >second is that those earthquakes will follow a relatively regular routine. > >Says Jackson: ``These ideas seem reasonable, but none has been validated by >any objective test. They just don't seem to work.'' > >He points out the next quake was already overdue in 1989 when the Parkfield >monitoring system was being instigated. > >Now, Jackson says, ``it's so far overdue that instead of saying it is >imminent, we should reflect on whether the whole idea of the Parkfield >earthquake is valid. There will certainly be earthquakes on the San Andreas >and some future earthquake will visit Parkfield, but it won't be a copy of the >last one. Furthermore, I don't believe Parkfield is the most likely place in >California to have an earthquake in the next decade or the next year.'' > >While Jackson advocates earthquake preparedness, he points out that more >Californians are killed in car accidents each year than all Americans who have >ever lost their lives to an earthquake. > >Jackson made his presentation at the annual meeting of the Seismological >Society of America in Boulder, Colo. > >(Written by UPI Science Writer Lidia Wasowicz in San Francisco) _- > >Copyright 1998 by United Press International. > >All rights reserved. > > > >
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