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THE NEW AMERICAN -- June 12, 1995
Copyright 1995 -- American Opinion Publishing, Incorporated
P.O. Box 8040, Appleton, WI  54913

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ARTICLE: Nation
TITLE: Were There Two Explosions?
AUTHOR: William F. Jasper

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Shortly after the Oklahoma City bombing The New American received
a fax of a seismogram purporting to be the seismic recording of the
blast as recorded on an Oklahoma Geological Survey seismometer. The
seismogram was of particular interest because it seemed to indicate
that there were two explosions of similar magnitude just seconds
apart on the morning of April 19th.

It did not take long before wild stories were streaking across the
Internet and various fax networks, citing the seismogram as proof
positive that the FBI, ATF, or some other government agency had
actually perpetrated the crime. Linda Thompson, Mark Koernke, and
other self-styled "patriot" leaders notorious for pumping out a
steady stream of sensationalistic propaganda combined the
seismogram with various hearsay "evidence" to advance their own pet
theories about the bombing.

"Official" Interpretation

As might be expected, the liberal media cartel responded with
disbelief and ridicule -- which is understandable with respect to
Thompson, Koernke, et al, who have amply proven themselves
unbelievable and ridiculous (or worse) with their past escapades
and false alarms. All of the media accounts that we have seen
concerning the seismic record for Oklahoma City on April 19th have
linked it to these disreputable sources, thus discrediting by
association both the evidence and any interpretation of the
evidence that may run counter to the official explanation.

The "official" interpretation of the seismogram most frequently
cited is that the two seismic events recorded on the morning of
April 19th are best explained not as two explosions, but as one
explosion followed by the collapse of the building. As we shall
see, there are serious problems posed by this scenario which
appears to have been accepted without question by the major media.

The expropriation of (and "tainting" of) the seismic evidence by
the "right wing loonies" on the one hand, and the complete
discounting of it by the official investigators and the
Establishment media on the other, is doubly unfortunate, since it
is one of the most troubling pieces of forensic evidence in the
case and deserves to be thoroughly examined on its own merits --
regardless of who may be wrongfully exploiting it.

There are actually two seismograms of the explosion(s) recorded by
two separate seismometers in the Oklahoma City area, and both
recordings show essentially the same thing for the time of the
blast. (See illustration below.) One of the seismometers is located
at the Omniplex Museum 4.34 miles northeast of the site of the
Alfred P. Murrah Federal Building, while the other is located 16.25
miles to the southeast of the blast site at the Oklahoma Geological
Survey on the campus of the University of Oklahoma-Norman.

The New American contacted the Oklahoma Geological Survey by
telephone and talked with OGS geophysicist Dr. Raymon L. Brown. Dr.
Brown was very helpful and patiently explained, in both scientific
and layman's terms, the technical and interpretive aspects of the
seismograms. However, as wonderful as the miracle of modern
telecommunications may be, there were too many details which did
not lend themselves to easy and clear understanding at a distance.
So, on our recent week-long investigation in Oklahoma City, we
journeyed to Norman, Oklahoma to visit Dr. Brown at the University
of Oklahoma campus for a thorough "hands-on" explication.

Examining the Data

In a conference room on the first floor of the impressive Sarkeys
Energy Center, Dr. Brown carefully went over the two seismograms,
explaining the various wave signals, and then illustrated on a
white board the problems inherent in the five explanations that he
and others have considered for the events. The seismogram from the
Norman station shows three signals between 9:02 and 9:03 a.m. on
April 19th. The first signal has a high-frequency character very
much like traffic noise (possibly a passing train). The second two
events have a low-frequency character much like the signals
associated with quarry blasts around the state. They begin with
low-frequency signals (the larger wavy lines) and then degrade into
high-frequency signals (the smaller waves). The first of these two
signals, called Rayleigh waves (or Lg surface waves), was recorded
shortly after 9:02 and lasts for about ten seconds. The second
event begins about 12 seconds after the onset of the first event
and after a quiescent interlude of about two seconds.

The seismogram from the Omniplex Museum looks significantly
different but points toward similar conclusions. First of all,
because it is located in a noisy city environment with a
considerable amount of traffic, the Omniplex seismometer is set at
a reduced "gain" to avoid picking up ambient signals. In spite of
this reduced gain, the signal amplitude of the April 19th event was
large enough to cause the loss of the high amplitude portions of
the signals. The heat-sensitive pens on the seismometer were moving
so fast that the details of the signal were lost during the highest
levels of ground movement. "The two large events on the Omniplex
recording," says Dr. Brown, "are represented by the white portions
of the record where the signal trace disappears because of the pen
movement." Because it was closer to the blast and in the
directional path that the main force of the explosion traveled, the
Omniplex seismometer also picked up much surface- and air-wave
energy that did not reach to the Norman station.

Five Theories

The first three of the five explanations Dr. Brown has considered
view the two Rayleigh signals captured on both seismograms as
caused by different types of energy wave phenomena associated with
the one blast. The fourth and fifth scenarios consider the
possibility of two separate events causing the signals:

1) SURFACE WAVE VELOCITY DISPERSION. This phenomenon that occurs
with surface waves is due to the fact that low-frequency energy
travels faster than higher frequency energy. Surface wave
propagation can therefore give the appearance of signaling two
events even though there has been only a single seismic source.
This phenomenon, says Dr. Brown, "is very much like a car race in
which a group of cars has one velocity and another group has a
different velocity. If you look at them early in the race they look
like one collection of cars, but if you look later in the race the
faster cars develop a separate group or package. And that same
phenomenon -- called velocity dispersion -- can result in the
appearance of two wave forms for a single event. That difference in
frequency I don't see here, so I don't feel that is a likely
explanation." The seismogram, says Brown, shows two separate
signals, each beginning with "a low frequency signal degrading into
a high frequency signal."

2) AIR WAVE. This might possibly explain the second event recorded
at the Omniplex Museum. "However," says Brown, "it is difficult to
describe the second event at the Norman station as an air wave
because the speed of travel would far exceed the speed of sound in
air [which is] 1,100 feet per second. Admittedly, the velocity of
the air wave must be supersonic for a certain distance away from
the explosion," but it would be impossible for the air wave to
reach the Norman seismometer in the ten seconds recorded between
the two signals.

3) AIR-COUPLED RAYLEIGH WAVE. This phenomenon, says Brown, occurs
when "the motion of the air induces a type of motion identical to
the Rayleigh wave that we observe in the subsurface and causes the
appearance of a second event. So you could have the first Rayleigh
wave from the seismic explosion and then an air wave pushing and
inducing a Rayleigh wave which would come trailing in behind." That
did not seem a plausible explanation in Brown's opinion, "because
most of the felt accounts of the air wave [from the explosion] are
out to the north, so most of the air wave was going from south
[from the federal building downtown] to the north, not to the
south" toward the Norman seismic station.

4) THE BUILDING COLLAPSE. This explanation holds that the seismic
signals portray two separate events, the first being the bomb
explosion and the second being caused by the collapse of a portion
of the federal building following the blast. "If you're trying to
explain the second event as a collapse," says Brown, "you're saying
the collapse of the building actually has a shorter duration than
the explosion itself," since the Omniplex seismogram shows a
shorter duration pulse for the second signal. This scenario also
suggests that the falling of the tons of building debris would send
the same kind of mix of high frequency and low frequency waves as
the explosion, which Dr. Brown also finds highly unlikely. Still
another problem with that version is the time involved between the
blast and the collapse under this scenario: ten seconds would seem
far too long a delay.

5) TWO EXPLOSIONS. His analysis of both seismograms, says Dr.
Brown, leads him to the logical conclusion that there were "two
separate seismic events" and that the simplest explanation is "two
separate explosions."

As befits a scientist, Dr. Brown is cautious and admits that his
conclusions are far from "conclusive" and require "more thorough
investigation." He states, for example, that it is not possible at
this time to say with "absolute" certainty that the seismograms in
question are related to the Oklahoma City explosion. However,
because of the timing at both locations and the absence of any
other known phenomenon to explain the seismic signals, it is
reasonable to identify the seismograms with the blast.

A Troubling Question

In order to evaluate Raymon Brown's analysis, we submitted the
seismograms and Dr. Brown's explanations to other experts in the
field. One of the most highly regarded authorities in the field of
observational seismology is Professor Keiiti Aki, a seismologist
and geophysicist at the University of Southern California-Los
Angeles. Dr. Aki agreed with Dr. Brown's analysis and conclusions.
However, he asked a question that also troubled us. "It certainly
looks like there were two explosions," he said, "but I have this
question: If there were two explosions that far apart, wouldn't
there have been many thousands of people in the area who would have
heard two explosions? But I have not heard of any."

We had heard of a number of witnesses who reported hearing more
than one explosion, but, as Dr. Aki noted, if there were two
explosions of similar magnitude one would expect many thousands to
report a double event. As we interviewed people in the Oklahoma
City area we found a variety of "ear witness" accounts. This was
not entirely surprising, considering the uniqueness and traumatic
magnitude of the event. Even with more "ordinary" traumatic
occurrences -- car accidents, homicides, robberies, etc. -- eye-
witness accounts of the same incident are notorious for widely
divergent and sometimes opposite descriptions.

Many of the people we interviewed preferred not to be identified.
Some were within a block of the blast, while others were several
miles away. Those we talked with who were closest to the blast
provided some of the most confusing and contradictory testimony.
This is understandable when one takes into consideration that the
sensory stimuli overload caused by the explosion was very
disorienting. Many people who worked within a few blocks of the
federal building were knocked from their chairs or from their feet,
or had ceilings, walls, furniture, and broken windows crashing into
them. Some could not even recall hearing a specific sound, but were
simply overwhelmed by the "impression" of a massive explosive
event. One young man who works as a parking garage attendant one
block north of the federal building told The New American that he
was test driving a new pickup truck in the street in front of the
parking structure when the bomb went off. "It seemed like one, big,
long explosion," he said, "but I can't say for sure. My ears were
ringing and glass and rocks and concrete were falling all over and
around me."

A manager of a loan company on Hudson Avenue two blocks west of the
Murrah building told us he was fairly sure he heard only one blast.
It blew out his office's plate glass windows just a few feet from
his desk and knocked down the false ceiling, but no one was
injured. Two secretaries who were at the office at the time of the
explosion also recalled hearing only one blast. At the corporate
offices of a department store two blocks northeast of the federal
building, the receptionist on the ground floor was thrown out of
her chair and against the wall by the force of the blast. She could
not recall actually hearing the explosion, but had more the
impression of feeling it.

Three construction workers who were on a job just south of the
federal building and who were among the first rescuers to arrive on
the scene recounted that they remembered hearing only one
explosion. However, they said, everything was in pandemonium, with
numerous car and building alarms set off by the blast, people
screaming and "an incredible amount of noise" from numerous
sources.

One reliable witness we interviewed who heard more than one
explosion is Lieutenant Colonel George Wallace, a retired Air Force
fighter pilot with 26 years experience in the service (1952-78). On
the morning of the explosion, Colonel Wallace was at his home nine
miles northwest of the federal building. It sounded to him like "a
sustained, loud, long rumble, like several explosions." "I was
pouring a cup of coffee and saw it jiggle and shake and immediately
ran outside" to see what might have caused it, he recounted to The
New American. To this combat pilot who has had much experience with
explosives it sounded very much like the familiar sound of a
succession of bombs being dropped in the distance by B-52s. It was
a sound he had heard often in Vietnam and one he didn't think he
would be likely to misread.

Another ear witness who is "positive" that he heard two explosions
was in his car five blocks north of the federal building. It
sounded to him, he said, like two distinct blasts several seconds
apart.

Another highly qualified military expert who questions the single-
explosion premise offers a possible explanation for the conflicting
testimony. Brigadier General Benton K. Partin (USAF, retired), one
of the world's foremost explosive experts and the guiding genius
behind the development of many of today's precision guided weapons
systems, suggests that if a second bomb or series of bombs were
detonated in the parking structure below the Murrah building, and
if smaller charges were used, the sound waves from the later
event(s) may have been much smaller than the original truck blast
and greatly muffled by the floor and the debris above it. In the
confusion and trauma of the moment they might not have been
discerned by many people as a separate event.

As stated earlier, no conclusive answers can be drawn from Dr.
Brown's research, the conjectures of other experts, or the
recollections of those who heard the blast(s). There is much still
to investigate, and The New American will continue to provide
updates on this and other aspects of the bombing.

END

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THE NEW AMERICAN -- June 12, 1995
Copyright 1995 -- American Opinion Publishing, Incorporated P.O.
Box 8040, Appleton, WI  54913

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