Newsgroups: alt.activism,alt.censorship,alt.conspiracy,alt.current-events.clinton.whitewater, alt.journalism,alt.politics.libertarian,alt.politics.media,alt.politics.org.batf, alt.politics.perot,alt.privacy,alt.radio.talk,alt.wired,talk.politics.guns Subject: OKC Seismic Data UPDATE 15 Sept. Date: 15 Sep 1995 12:09:08 -0500 Organization: UTexas Mail-to-News Gateway Lines: 182 Sender: nobody@cs.utexas.edu Message-ID: <9509151708.AA10740@icis.on.ca> NNTP-Posting-Host: news.cs.utexas.edu Xref: ix.netcom.com alt.activism:121554 alt.censorship:64479 alt.conspiracy:130221 alt.current-events.clinton.whitewater:15736 alt.journalism:27121 alt.politics.libertarian:125070 alt.politics.media:6985 alt.politics.org.batf:15638 alt.politics.perot:29195 alt.privacy:28818 alt.radio.talk:5125 alt.wired:23331 talk.politics.guns:265012 Date: Friday, Sept. 15, 1995 FROM:David Deming (UofOklahoma):FWD:by czeps@icis.on.ca Here is the latest information on analysis of the seismic data associated with the Oklahoma bombing. This posting may be copied, distributed, and cross-posted. I am an assistant professor of geology & geophysics at the University of Oklahoma in Norman, Oklahoma. I have a Ph.D in geophysics and work in the same building as Ray Brown. Ray is a seismologist who works for the Oklahoma Geological Survey and is the person who has been done most of the work on interpreting seismic data associated with the Oklahoma City bombing. Ray has a Ph.D in geophysics from MIT; his phone number is 405-325-3031. This is a succinct summary of what we know at the present time regarding seismic data associated with the Oklahoma City bombing. First, a brief historical summary. Two seismographs recorded ground motion signals related to the bombing of the Murrah Building last April 19. One seismograph was located at the OmniplexMuseum 4.21 miles northeast of the Murrah Building. The other (station FNO) was located 16.23 miles south-southeast of the Murrah Building near the city ofNorman. Both the Omniplex and FNO seismographs showed two distinct arrivals. The arrivals at the Omniplex were separated by 16 seconds, the arrivals at FNO were separated by about 10 seconds. These data led to the immediate speculation that there were two explosions. It is not possible to automatically conclude that 2 distinct arrivals on a seismogram represent 2 distinct source events because sound waves propagating through the solid Earth are subject to dispersion, refraction and reflection. In other words, the 2 arrivals could be a wave propagation phenomenon. It is most useful to define 3 classes of hypotheses: 1. Hypothesis (1): the seismic data are consistent with 2 separate explosions separated by several seconds. 2. Hypothesis (2): the seismic data are consistent with an extended period of explosive activity at the Murrah Building, as opposed to a single explosion. 3. Hypothesis (3): the seismic data are consistent with a single explosion. Hypothesis (1) has now been discredited. Consider, for example, that if the two arrivals at the FNO station 16.23 miles from the blast site were separated by 10 seconds, then the 2 arrivals at the Omniplex seismograph, 4.21 miles from the blast site, should have been separated by 10 seconds or less - yet they were separated by 16 seconds. We now believe that the second arrival at the Omniplex represents a slower-traveling air blast which excited ground motion at the seismograph station. On May 23, the remains of the Murrah Building were destroyed. The demolition was recorded on several seismographs set up at the Omniplex, station FNO, and intermediate sites by a team from the US Geological Survey (USGS) led by Tom Holzer (415-329-5637). The USGS is holding these data confidential, but they have been published in the August 7 issue of the New American Magazine. Only a week after the demolition (June 1) the USGS issued a press release stating (this is a verbatim quote): "Seismic recordings from the building's implosion indicate that there was only one bomb explosion on April 19". Following this press release I called Dr. Holzer and asked if he had a written report I could review. He said "no". It was approximately 1.5 months before the USGS produced a written report containing their data and analysis. This report is still being held confidential. However, Ray Brown reviewed the report and said that the USGS conclusions were "unsupported by the data or analysis", and asked that his name be taken off of it. I don't know of any seismologist who agrees with the USGS conclusion. For example, Jim Pechmann, director of the seismograph station at the Univ. of Utah in Salt Lake City has written me: " I see no convincing evidence in these records to support the multiple blast hypothesis, although they can't be used to rule it out either". This is a conservative and reasonable conclusion. However, Ray Brown believes the seismic data are more supportive of what might be called an extended period of explosive activity. Here is the reason. During the May 23 demolition a seismograph was set up only 74 meters from the Murrah Building and recorded about 10 seconds of ground motion. At the Omniplex 4.21 miles away, the ground motion was of the same duration, augmented perhaps by a second. In contrast, by the time the seismic signals from the Murrah Building demolition had traveled to station FNO 16.23 miles away, they had doubled in duration (to 20 seconds) due to dispersion. In other words, the demolition showed that the Omniplex seismogram is an accurate measure of thelength of time the ground was moving during the April 19 bombing. Both the demolition andthe bombing coincidentally produced about 10 seconds of ground motion. The demolition consisted of a series of staggered explosions lasting 4-5 seconds followed by another 4-5 seconds of the building falling down, producing a total disturbance lasting 10 seconds. What we don't understand is how a single truck bomb could produce the same period of ground motion. The most popular hypothesis is that the "extra ground motion" simply represents the building falling down. The problem with this hypothesis is that the amplitude of the bombing signal is greater than the demolition when 2/3 to 3/4 of the building collapsed. Jim Pechmann of the Univ. of Utah seismographic station has suggested the possibility that the air blast excited buildings in the neighborhood to move for several seconds. A similar phenomenon has been seen in Los Angeles where sonic booms from the Space Shuttle create seismic events. I believe this is a plausible hypothesis. Ray Brown also believes that the second arrival on the April 19 Omniplex seismogram representing the air blast is a measure of the period of time the truck bomb was active. This is about 1/2 the length of time the ground was moving; thus, an apparent inconsistency. In the past few days Ray Brown has obtained a higher-quality copy of the Omniplex seismogram from April 19 and now believes he can see 3 distinct events in the April 19 bombing. He believes he could learn even more from an inspection of the original seismogram which is being held by the FBI. Ray has asked to see it, but I do not believe the FBI has responded to his request. Ray has also told me that Sandia and Los Alamos national laboratories had planned a test ANFO explosion that would have been very helpful in discriminating between hypotheses. However, John Derr at the US Geological Survey in Albuquerque reportedly told Ray that the test had been postponed until after the bombing trial due to a request by an "Oklahoma District Attorney". Ray has Mr. Derr's phone number for anyone who wants to check this out. Summary: 1. The June 1 press release by the US Geological Survey stating that "Seismic recordings from the building's implosion indicate that there was only one bomb explosion on April 19" is simply wrong. 2. More conservative seismologists have concluded that the data are inconclusive with regard to single or multiple blasts. 3. The seismic data indicate about 10 seconds of ground motion at the blast site on April 19, apparently inconsistent with a single explosion. The seismologist who has worked the most on these data, Ray Brown, favors hypotheses related to "extra" explosive activity. 4. There are plausible alternative hypotheses such as the air blast exciting ground motion that could explain the "extra" ground motion at the Murrah Building. Addendum: An unidentified gentleman sitting in the back of the room during a presentation by Ray Brown last Wednesday, Sept. 13, said that a friend of his spotted 3 unexploded ANFO barrels inside the building shortly after the blast. He went on to speculate that the truck bomb had been shaped in such a fashion so as to blow some of the barrels into the interior of the building. He explained how this could have been done by arranging the barrels in a certain geometric form (he described what form, I'm not going to). This formation presumably would have created a focused pressure wave that would be much more damaging than that created by a random arrangement. The technique presumably would also allow some of the barrels to actually detonate inside the building so as to be much more destructive. I don't know how this would be done. The gentleman went on to say that this technique had first been developed by Gen. Patton to penetrate tank armor and it would have been taught to McVeigh as part of his training as a tank crewman. If true, this hypothesis would answer some of the more puzzling aspects of the bombing such as the fact that the largest indentation was not directly in front of the bomb crater. It would also possibly answer objections (i.e., General Partin) that the ANFO blast was not powerful enough to bring down the reinforced concrete columns. -30- ---- End Forwarded Message -- John Hammell, Political Coordinator, The Life Extension Foundation 800-333-2553, 305-929-2905, 305-929-0507 FAX jhammell@netcom.com http://www.webcom.com/~lef/index.html **Complimentary Copy Life Extension Magazine: Send Street Address*