In the 1960s conspiracy theorists debated the ``one-bullet'' hypothesisof the Kennedy assassination.
Now they're debating the ``one bomb'' notion of the explosion of the OklahomaCity federal building on April 19, 1995.
The Justice Department says a single, 4,800-pound fuel-and-fertilizer bombdestroyed the building, killing 168 people.
In contrast, militia groups, right-wing activists and conspiracy theoristshave championed a theory worthy of TV's ``X-Files'': that two or more bombsexploded, bombs placed by unknown people with mysterious agendas. An MIT-trainedgeophysicist says they may be right.
But conspiracy enthusiasts face a new and surprising foe: the U.S. GeologicalSurvey, whose laid-back, nature-loving, John Muirish employees don't usuallyplay Sherlock Holmes.
The No. 1 piece of ``evidence'' for the two-bomb argument is a squigglyline on a piece of paper.
It's a seismogram, a record of seismic waves recorded by a seismograph 16miles from the blast. The seismograph's original purpose was to monitorOklahoma's occasional earthquakes: 167 in 1995, all pretty wimpy by Californiastandards.
Seconds after the federal building blast, the seismograph detected two seismicwaves rippling across the flat Oklahoma countryside.
The dual wave proves more than one bomb was involved, conspiracy theoristsclaim. They've promoted the idea relentlessly for more than a year via radiotalk shows, extremist newsletters and militia Internet sites.
But now, after intensive computer analysis, USGS scientists say they'vesnuffed the multiple-bomb theory. They say the puzzling dual seismic wavesare, in fact, a single wave that divided underground.
USGS researcher Thomas Holzer and five associates are scheduled to reportthe finding in a forthcoming issue of Eos, a publication of the AmericanGeophysical Union. The Examiner obtained an advance copy of the report,dated Aug. 23, from a source outside the agency.
``What we're really trying to say is the data are consistent with one explosion,''says one of the authors, Thomas M. Brocher of USGS. ``The different (seismicwave) arrival (times) ... are just the result of what you'd expect normalwave propagation to do.''
As the USGS sees it, the explosion triggered vibrations in the upper layerof the Oklahoma crust, perhaps around 1,000 feet deep. The speed with whichseismic waves travel through the Earth varies according to factors suchas ground density and composition. For example, seismic waves typicallymove more slowly through underground lava than solid rock, and faster throughsandstone than shale.
In this case, ``the seismic velocity increases significantly with depth,''the report says. For this and other reasons, the seismic pulse split intotwo main segments that reached the seismograph about 10 seconds apart.
Charles Mankin, the head of the Oklahoma Geological Survey, concurs withthe USGS conclusion and offers a down-to-Earth analogy.
``Imagine two cars leaving Oklahoma City at the same time, one on the interstatehighway and one on the service road beside it,'' he says. ``The one on thehighway could get to its destination sooner because the speed limit is higher.''
But the USGS explanation still doesn't eliminate the possibility of multiplebombs, argues Raymon Brown, a geophysicist for the Oklahoma Geological Survey.Brown has expressed his doubts about the single-bomb theory since mid-1995.Conspiracy buffs have relied heavily, although not exclusively, on Brown'sviews.
Brown agrees with the USGS theory that the two waves came from a singlewave that split underground. He believes multiple bombs might have exploded,however.
``I have to say that it's still an open question,'' Brown says. ``I havenot seen any information that can prove one side or another.''
For one thing, ``the degree of damage accomplished by a single bomb notplaced in the building was significantly higher than I would have personallyexpected,'' says Brown, who received his geophysics doctorate from MIT.
Brown also is puzzled that the seismic signal lasted eight seconds, muchlonger than the blast itself. How, he asks, could an explosion lasting afew seconds generate a seismic signal persisting for eight seconds? Additionalseismic energy may have been emitted by falling debris or car explosionstriggered by the original blast, but he isn't convinced they emitted enoughenergy to explain the eight-second signal.
Mankin acknowledges that the length of the signal puzzles him, too. He speculatesthe blast may have created ``harmonic vibrations'' in the building's concretecolumns that persisted a few seconds after the blast and protracted theground tremors.
Brown is ``a very competent person,'' stresses Mankin, a sedimentary geologist.``In fact, he knows a lot more about this subject than I do. I rely heavilyon him.''
For Brown, his lone stance has been ``an emotional drain.''
``It's not just a `science' thing,'' he says. ``I wish it were - it wouldbe a lot more fun. ... We've got neighbors that died. A lot of kids whogo to school with my kids have lost parents.
``When it's close to home (like that), you tend not be willing to just saythe two signals (received) in Norman (a community 16 miles southeast ofOklahoma City) are `consistent' with a single bomb. There's more there tobe done than make that statement.''
Still, Brown has no personal quarrel with the USGS scientists, who, he says,shared their data with him and treated him ``very respectfully.'' Holzeris ``a first-rate person, a nice guy to work with,'' he says, ``but I canonly push him so far.''
The USGS scientists acknowledge that they couldn't have distinguished ablast from two bombs if they occurred extremely close in time - say, a fewthousandths of a second apart. They add, however, that two such closelytimed explosions wouldn't have generated two seismic waves traveling atsuch different speeds that the first would traverse 16 miles 10 secondsfaster than the other.
Besides, witnesses ``heard one explosion,'' Brocher says. ``They certainlywould have heard two explosions 10 seconds apart.''
John Trochmann and his brother Randy of the Noxon, Mont.-based Militia ofMontana are lay advocates of the multiple-bomb theory.
Last week, Randy Trochmann issued a statement dismissing the USGS reportas ``nothing more than election year politics. ... The Aug. 23, 1996, reportconstantly uses terms such as `likely, probably, imply, prefer, assumes,'etc. and therefore is not a conclusive analysis.''
Randy Trochmann also claims that after the building blew up, ``rescuersand government agents found numerous explosive devices which had not detonated.''
The USGS report also draws fire from Ted Gunderson of Las Vegas, formerhead of the FBI office in Los Angeles. Now a stalwart conspiracy theoristand Nevada congressional candidate, Gunderson says: ``The next time I believea press release from the U.S. government will probably be the first timein years, regardless of whether they say it's scientific or not.
``There were definitely two explosions - one at 9:02 and 3 seconds, andone at 9:02 and 13 seconds,'' Gunderson says. In fact, he believes therewas a third explosion involving a weapon he calls an ``electrohydrodynamicgaseous fuel device - a `barometric' bomb.''
Gunderson, 67, says he interviewed two witnesses and asked them to re-enactthe sound of the disaster. ``Both of them said `Boom! ... Boom!' with thesecond explosion being louder than the first.''
He claims government figures - ``an evil element'' - deliberately destroyedthe building to spur passage of an anti-terrorist bill.
Look at what the major tv studios reported that really hasn't beenmentioned since, including the U.S. Army defusing bombs inside the buildingfor two hours before rescuing the victims could begin.
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