'Oftentimes - doing something simply because it's right - not expecting it to instantly pay off, turns out to be the economical thing to do.'

     By DOLORES PROUBASTA
     Staff Writer

     "He is in his studio" is Tonnie's likely answer if someone is looking for her husband. John Marion Crawford's sanctum in their garage is cluttered and kaleidoscopic. A visitor, dodging easels, lightstands and buckets, and focusing through the polychromic confusion, finds the beauty of his paintings astounding. It is even more improbable as the artist, almost by way of apology, admits he first brandished a brush at age 53.
     The medium is watercolor - not his first choice but as a result of an allergy to oil bases and no interest in acrylics. And the style? Well, the measure of realism - the jaded blade of grass - has been surpassed. The minute, circular ripple left in the wake of a trout's dive is not forgotten in one of Crawford's immortalized fishing ponds. Perhaps this is a clue to the scientist/artist's meticulous mind.

     Crawford's belated embrace of the arts was not at first passionate. He reluctantly attended some classes because of a childhood memory - his father, a happy, active Irishman, suffered a stroke which impaired his mobility. The father, having no sedentary interests, turned inward - and John never forgot it. Thus, later, anticipating his own old age, he determined he would have something to foil the fate of inactivity.
     As it is, at 73 the search for inspiration may take the Crawfords as far away as the Swiss Alps. Numerous juried show awards, exhibits, and some 200 originals plus uncounted prints sold, bespeak his work - and his drive.
     "My idea of hell," Crawford says, "is a place with nothing to do."

     Even as a boy, in Madison, Kansas, he'd rush to his father's hardware store after school to lend a hand. Merchandising was only a part of the business. "We overhauled tractors, repaired farm implements, built windmills, fixed faulty plumbing, and much more. Years later, as a doodlebugger, those skills came in handy. As far as field work, what I learned from dad was probably more valuable than my college education."
     However, in 1932 he obtained his Bachelor's at Phillips University in Enid, Oklahoma, and in 1934 a Master's in physics from the University of Oklahoma. He worked his way through both. While at Phillips he waited tables until the restaurateur realized that John's curtness with patrons made a transfer to fry cook in the kitchen advisable.

     Because of his undergraduate performance and the recommendation of his physics professor, Dean Knowles, he got the only assistantship available at OU that year - with a $700 a year stipend. (In a depressed economy, Crawford was the rich man on campus. With money to spare, he even contributed toward one of his sisters' college expenses.)
     Upon graduation he joined Continental Oil as assistant operator on a seismograph crew. But his introduction to the work had occurred, ironically - almost mystically - via a seismic event itself a few days before. Crawford says:
     "My brother and I were walking into his house. Suddenly, we both felt as though someone, or something, had struck us in the small of the back. And sure enough, later that day we got word of a tragic dynamite accident on a Petty geophysical party which had been working miles away [TLE, December 1982].
     "The impression that made on me was revived my first day on the job at Conoco. I rode out to the magazine with the shooter. He got into it, lifted a 50-pound case of dynamite, and threw it to me. If I could have fainted without dropping the dynamite, I would have."

     That first assignment was in the verminous Gulf Coast - US doodlebuggers' boot camp. Crawford's wife of only one month, Alice, his former laboratory partner at Phillips, had traded a promising career of her own in physics for life in the marshes. But with is promotion in 1935 to development engineer, they moved back to headquarters in Ponca City. Those 18 months in the field, he thinks, added an important dimension to his forthcoming years of office and lab work.
     "What field work teaches you is never to ask a man to do something that you couldn't or wouldn't do."
     Further promotions arrived at regular intervals. Then, in 1951, his boss, Dr. L. F. Athy, asked Crawford if he would be interested in organizing and directing a geophysical research group.
     "I was elated," says Crawford. "They probably chose me because the gravity work I was supervising was winding down and they didn't know what else to do with me. Be that as it may, they told me I could have four men. Some names were suggested by management and I was pleased with their qualifications. But I had a special request. I wanted William Doty to join my group. Understandably, the operations group where he was working wouldn't give him up. But I fought until they changed their minds - the smartest thing I ever did."

     And so, the geophysical development and research department came to life with Conocoans Crawford, Doty, Adrian Becker, Hugh Evans, and James Gaebe. Others would soon join. At the outset, however, the cabalistic question was - what to research? While awaiting the muse, they made themselves available to any explorationist in a quandary. Crawford recalls his team's first contribution:
     "A division geophysicist told us of an area where he believed there was a structure - but it wasn't showing. The problem, he thought, was that the velocities were changing fast as they went across the structure. That was before the days of velocity control.
     "Becker was put in charge of making a statistical study of the area records we had, in order to see how the velocity changed in going from east to west. We came up with a pretty good notion. We made a velocity correction on the map - a wiggle in the contour turned up to be a closed contour. Well, wiggles don't mean much, but closures do. So Conoco drilled a well, and found an oil field."

     For a year things continued to be interesting in the research department but not exciting. At least not until August of 1952, after Doty returned from a symposium in Boston. Soon, in Doty's words, "It became electric." What followed - Vibroseis- made history.
     In February 1960 Crawford, Doty and another researcher, Milford Lee, published Continuous Signal Seismograph in Geophysics. The scientific and pragmatic caliber of their findings deserved that year's SEG Best Technical Paper award. The first license agreement had just been signed and others were looming.

     But the beginning and culmination of Vibroseis had both been paralleled by tragedy in the Crawford family. At the early stages of the project's success in 1955, his wife, Alice, died of cancer. Then, as the first license was being issued, his daughter Ann lost a long battle with heart disease.
     In both cases, Crawford's grief was eventually assuaged - but not without providential help; his two sons were great sources of comfort and pride. John, the elder son, is now a director of Sandia Research Laboratories, and Jim is a physics professor and department head at Southwest Texas University.
     On the passing of his daughter, the senior John also found himself with his 18-month-old granddaughter, Debbie, to care for, but again, providentially with the help of Latane Tracy Crawford whom he had married in 1956. Tonnie, a science teacher in Ponca City for 15 years, was well acquainted with children, including Crawford's. And she switched roles from step-grandmother to mother with ease and grace. The Crawfords' long parenting was recently crowned with Alisha Ann - their first great-granddaughter.

     In 1960, Crawford was promoted to assistant manager of research and development. But the added prestige was not all-important to him.
     "While I was director of geophysical research I wouldn't have traded jobs with anyone in the country, including the President. But the new title involved complex labor relations and red tape. In other words - gone were the days of doing my job while enjoying good one-to-one relationships with colleagues.
     "Furthermore, the upcoming wave of management seemed too concerned with the short-term balance sheet. If ideas were not going to pay off immediately there was no use fooling with them. I, and so many colleagues, used to operate differently, because we knew that oftentimes doing something simply because it's right - not expecting it to instantly pay off - turns out to be the economical thing to do. So, after the excitement and the teamwork of early Vibroseis development, my new responsibilities were a big drab and cold."

     Pondering what to do next did not reduce Crawford to a meditative slumber. It seems to have had the opposite effect - triggering a whirlwind of professional activity without detriment to family, civic, and church activities. In 1963, while keeping up with his Conoco assignments, he toured the US and Canada as SEG's Distinguished Lecturer on the development of Vibroseis. Simultaneously he presided over the Geophysical Society of Tulsa. If this were not enough, he also attended his first painting lessons. In view of other people's amazement at his gift for making time, Crawford simply jokes: "I didn't waste any getting rich."
     He also was chairman of the geophysical research committee of the American Petroleum Institute, and seismic advisor for the US Defense Department's ad hoc advisory group on the detection of nuclear detonations. In this latter capacity he was with scientists such as Drs. W. Panofsky, Frank Press, Jack Oliver, Hugo Benioff, and F. G. Blake, with Richard Latter - the big-hole advocate - chairing the illustrious panel. Their recommendations are undoubtedly classified material.

     Then, early in 1964, Crawford became research fellow. As such, he administered all Vibroseis licenses and handled new negotiations worldwide. "It was pleasant work," comments Crawford, "but it became rather redundant." And again, hyperactivity was his answer to any shortcomings.
     In between licensing engagements in England, France, Germany or wherever his method was in demand, Crawford continued inventing. He already held several US patents, including the co-signed Method of and Apparatus For Determining the Travel Time of a Vibratory Signal Between Spaced Points (Vibroseis for short). But in the mid- to late '60s a flurry of new Crawford ideas were filed and patented - Automatic Positioning Device; Floating Support for Seismic Transducers; Chromatography Apparatus; and Process for Transporting Solids in Pipelines, are but a few.

     Naturally, a list of kudos had preceded this. In 1947 his old alma mater, Phillips University, elected him to the board of trustees, and in 1957 he was awarded an Honorary Doctor of Science Degree. In 1967, Crawford and the co-inventors of Vibroseis, Doty and Lee, became the third recipients of the SEG Medal Award (later the Reginald Fessenden) for their technical contribution to exploration.
     His most cherished award, however, was SEG's Honorary Membership. It came in 1978 - a stellar year with eight recipients, thus the largest group to date. Crawford was on stage in San Francisco's Civic Auditorium with Howard Breck, Milton Dobrin, Franklyn Levin, Harry Mayne, Vincent McKelvey, Turhan Taner, and Sam Worden. Offstage, at someone's suggestion, was a small display of some of Crawford's best work - paintings.
     "I had brought only four to show my friends what I had been doing in retirement. I had no intention of selling any of them because obviously they were my favorites. But since some were so insistent, I finally relented. And it paid my expenses to the convention."

     Crawford had chosen early retirement in 1971. After 37 years with the same employer - Conoco - it was a total divorce from industry except for reading the journals. Since then, he devotes his time to Tonnie, painting, some fishing with friends, Sunday School teaching, traveling and whatever time is left, to rest.
     While he indeed divorced himself from the industry, perhaps more conclusively than others, his name remains wedded to his work. Generally, he is considered the inventor - the father of Vibroseis, or Mr. Vibroseis (as some in Conoco called him). Ah - the human tendency to personify an invention, a major battle, a work of art.
     But as Crawford knows, only the latter can be a one-man show. Yet, talking about those early and exciting days of research, he drowns the facts in the credit he gives others.
     "I marvel at the caliber of the people I was associated with" - citing a long roster led by Bill Doty, the man he absolutely had to have in his department.
     The admiration is mutual. Per Doty: "Without the combination of talents that Crawford assembled, there might not be a Vibroseis as we know it today. Just as important as the science and the technology that go into a project, are the intangibles - and these are hard to assess. Crawford's leadership, his rapport with management, his knack for encouraging creativity and thinking, were just as necessary as all the ideas he contributed. And yet another intangible that made working with him very special, was the family atmosphere he encouraged - one in which we'd pour our first cup of coffee in the morning and ask each other: 'Well - what can we invent today?' In this sense, I don't think that the title of father of Vibroseis is misplaced at all."

     Now, setting his brushes aside for a moment, Crawford talks on the following pages about something which has no shape or color - a signal - one which shook the world.

     These signals were manually positioned with respect to each other at about three millisecond intervals. The correlation value was read out on a meter. Each of these values was plotted by hand and the final record was a hand tracing of the plotted points. Thus, a 10-channel, one-second record required over 3,000 individual signal positionings, meter readings, and point plots. All this may seem as arduous as the stacking of the Egyptian pyramids to 3D- and home-computer setters - not so to the Conoco research team.
     The excitement mounted. At last, their data points began to systematically match the dynamite profiles right down to the Viola sandstone.
     "It was one of those Eureka moments," says Doty. "We were shooting for the moon. We didn't know if the earth would cooperate. The big question was the ultimate penetration depth of our acoustic signal that we could recover back from the noise. Yet there it was - 5,000 feet, point by point. We knew from then on that our contribution to seismology was a sure thing."

     But the success was embryonic. Each component of the system had to perform vastly better. Vibrators needed greater coupling to the ground and they had to be mobile. The signal they put out had to be controllable. The recording system had to be tailored to the new seismic source. And the correlation process had to be streamlined - pre-compositing of sweeps before correlation, a pressing need. All of which boiled down to making the method cost-effective.
     A flatbed truck soon replaced the borrowed water vehicle. It also provided hold-down with its weight via two wedge-shaped attachments at either side of the vibrator assembly. After the vibrating period, the truck would drive forward, enough to release the wedges. The vibrator was then hoisted for transport to the next spot - a slow, awkward procedure.

     The following development was mounting the swinging weight vibrator on a trailer. Off-center weights inside the centrally located box provided a thrust proportional to the square of the instantaneous frequency and confined to the vertical direction.
     In vibrate position, the unit advanced on steel rollers, which also transferred amplitude and phase of the vibrator to the earth. Rubber-tired wheels were used to tow it short distances. For highway travel, the trailer was loaded on the flatbed.
     Vibrational output was obtained by causing the direct-coupled vibrator shaft to sweep through the desired frequency band. And in this model the gasoline engine was replaced by a shock-mounted DC motor. The generator was on the tow truck.

     Although the apparatus was meant to advance on its rollers while the sweep was in progress, this didn't produce the desired results. (The earth isn't sufficiently compacted for signal transmission until a few cycles of vibration occur.) So the unit did not vibrate while moving.
     In the summer of 1957 this prototype starred in Conoco's first serious attempt at exploration with Vibroseis. Steel rollers, however, left deep ruts - farmers equated the vibrators with locusts. And all prototypes had one thing in common - they were gargoylian. One Texas rancher described a later model as "a strange monster who raises his posterior in the air and then has a chill."

     Outside Conoco, seasoned geophysicists were similarly aghast. In the early '50s, Craig Ferris, then with E. V. McCollum & Co., of Tulsa (TLE, October 1982), was on his way to visit one of their gravity crews in the hinterlands of New Mexico. Something by the road made him stop.
     "I came upon a strange contraption. I took a good look at it, wondering what that thing could be doing near a geophone spread. Then I saw Bill Doty. I don't know who was more surprised, he or I. Later I learned he thought the secret was out, that I was scouting their Vibroseis crew. He had the crew pick up the gear and move out - to still another remote location. I have to admit, I had no idea what I was looking at."

     In April 1958, Conoco ended the hush. At a meeting of the Geophysical Society of Tulsa held in Ponca City, Crawford and Doty spoke about their work of the past five years. Despite their confidence that someday the method would replace totally, or partially, dynamite in exploration, they admitted it was "u difficult and expensive and still in the experimental stages."
     One of the problems was the apparatus's non-synchronicity, Crawford comments:
     "Swinging weights rotated in opposite directions. They were off-balance and made a hell of a vibration. We could run them fast or slow, but we didn't know exactly when they'd vibrate. The sweep signal was generated by opening the throttle on the engine to increase the vibrator mechanism to the highest desired frequency. Then, we'd shut off the power to allow the speed - and the frequency - to decrease.
     "While this was being done we never stopped recording. And since no two sweeps were ever alike, every time one was generated we had to transmit a separate correlation signal to the recording truck. The amount of record processing was tremendous."

     Obviously, the variables were equally awesome. Relatively small weights and practical speeds of the engine could produce seismic signals in the 20-80 cycle frequency range. But since the mechanical displacement of the swinging weights was constant, the generated force was nonlinear. Thus, output at 20 cycles per second would be only one fourth of that at 40 cycles. And so the impossibility of producing two identical sweeps brought home the need to develop vibrators which could be driven synchronously from a pre-recorded sweep signal.
     By the mid-'50s a concerted research effort began in that direction. Says Crawford:
     "We experimented with an electromagnetic transducer, but we didn't get the necessary output. Then, once more, we resorted to something originally designed for other purposes - missile guidance, of all things. It was a hydraulic valve which could take an electrical signal and move high-pressure hydraulic fluid into a cylinder, thus moving it very fast but in a controlled way. Therefore, the cylinder could be positioned in perfect harmony with the electrical signal. Adapting this valve to our requirements, we were eventually able to devise a system by which several vibrators would generate precisely the same signal in unison, and do so in successive sweeps."

     The first operational servo-hydraulic vibrator was tested in 1957. And - like the latter swinging weight models - it was truck-mounted. (Why pull a 15,000-lb steel trailer when the tow truck itself is heavy enough to hold down the vibrator?)
     It had not been done before for good reasons. Frank Clynch explains: "The big problem was isolating the energy source from the vehicle carrying it. Without proper isolation the force of the vibrator would literally shake the truck apart."

     In 1958 four servo-hydraulic units were tested synchronously. The following year, the system of multiple vibrators working in unison became part of routine operations. Most of the consecutive servo-hydraulic, rear-mounted models built had an output of about five tons and a usable frequency range of 8-50 cycles per second.
     By the 1960s, Vibroseis was out of its infancy - much of the pioneering improvisation behind and licensing underway. Nonetheless, there were major alterations to come before it looked modern (a fleeting attribute) by today's standards.
     Improving baseplate-to-ground coupling had been a continued concern. In 1961 a feedback system was developed which minimized the effect of variations in ground contact, reducing distortion in phase of the signal delivered downwards. But for years coupling would remain a problem on hard surfaces - highways and limestone outcrops - which cannot be sufficiently displaced by conventional baseplates, and also in areas requiring a very low frequency energy source.

     Then, by the mid-'60s, the vibrator assembly was moved to the center of the vehicle. As a larger percentage of gross weight was placed on the baseplate, a lighter vibrator could be used without diminishing hold-down weight. Center-mounted models were known as "stilt" vibrators because the reaction mass - located above the truck frame - was connected to the baseplate, carried below the drive shaft by long vertical columns.
     The stilt structure, however, presented obvious inconveniences. Soon, the pressure fluid system which operated the vibrators provided a solution. Hydraulic hoses replaced the cumbersome drive shaft, and hydraulic motors turned the truck wheels. This improved bottom clearance since the baseplate could be further elevated for travel.

     In 1967 Conoco's equipment division began construction of Model 8 - the first of a new generation of vibrators. This center-mounted servo-hydraulic unit incorporated extended low frequencies and a nominal output rating of 6.5 tons - 9.5 at peak force. The 4,500-lb actuator was a three-section unit. Model 8 was mounted on an International Harvester M623 6x4 diesel truck with a gross weight of 36,000 lbs. And by 1971 it was in routine use on Conoco and licensee crews requiring high output. Vast scale manufacture of Vibroseis was underway - a lucrative business outside of Conoco, too.
     Since the very first prototype, the company's shop had been unable to produce each of the components - often entire units - needed. To list their many contractors would be tedious. Suffice to say that at least two Oklahoma firms of early association became, with Crawford and Doty, and Conoco, namesakes of the vibrator - i.e., George E. Failing Co., of Enid, and Mertz Inc., of Ponca City. Both remain major manufacturers for Vibroseis licensees worldwide. The Pelton Company, also of Ponca City, became a steady supplier of electronic components.

     Vibroseis had thus won an enthusiastic market. Perhaps its most singular feature was - and is - that it opened an exploration frontier in areas implicitly closed to dynamite. As early as 1956 the first attempt at city street operation took place - a steel roller swinging weight vibrator in Los Angeles. Spectator curiosity was more than casual. Early experimental crew members could be quite creative at producing logical - though not necessarily complete - explanations. Appeasing home-owners and shopkeepers at whose door strange trucks were causing earthquakes was part of the job. But Vibroseis made it possible to survey densely populated areas such as the Los Angeles Basin.
     By 1967 the Department of the Interior recognized Vibroseis as an environmentally safe tool. And some wilderness areas also became open to exploration. Entering swamps, thick forests, packed ice, and other difficult terrains prompted further development of special prototypes. Features of these, in turn, were adapted to standard vehicles and vibrators to improve maneuverability, coupling, etc.

     A logical spin-off was the marine Vibroseis. However, this application had received consideration almost from the beginning. Tests conducted in 1955 proved that the marine version had definite possibilities, culminating in a full-scale program off Cook Inlet, Alaska in 1965. A detailed recount of its evolution is found in Conoco's The First 50 Years - an excellent pictorial collection of the complete Vibroseis saga up to 1975.
     As the seismic source evolved, so did the recording gear and data processing. It has been already noted that compositing of sweeps was possible only after correlation. At the momentous 1953 Orlando field test, the nerve center of both the recording and correlating systems was the Western Electric Optical Mirragraph - a variable density film recorder first used in 1949 in frequency analysis studies and then adapted for Conoco's research purposes.

     Crawford says: "The film record it produced was played back by means of a photocell arrangement. It was quite accurate, but terribly time-consuming. So as we began experimenting with the servo-hydraulic vibrator, we also were trying to come up with a recorder which would composite sweeps ahead of correlation. A special magnetic recorder invented for this specific purpose by Doty became the answer.
     "It was called a narrow track recorder because it used magnetic record heads which were only a fraction of the width of standard heads. In the same drum assembly there was a set of standard width reproduce heads. In operation, the narrow track heads were indexed on successive drum rotations so that a series of parallel, time-aligned tracks was laid down in the lateral distance covered by one reproduce head.
     "The number of tracks was dependent on width of the heads and indexing dimension. But normally it was 10-15. After recording the sweeps of one vibrator pattern, a composite playback was made which could be used by the correlator."

     The narrow track recorder - Decatrack - became the heart of the Vibroseis field unit. Because of its other many applications in seismic work, it was patented by Conoco and marketed under license agreements. This analogue recording system remained in field service until the early '70s even though Conoco had begun conversion to digital processing in 1965.
     In this, the digital era, the capabilities of slow and bulky - yet only recently discarded - analogue hardware are sometimes underestimated. Analogue correlators, for example, were used well into the '60s because they provided more economical processes then the early, massive and very expensive digital units. Analogue data interpretations led to discoveries in plays as dissimilar as Saudi Arabia and Alaska's North Slope. With due respect for the quantum leap which continuous signal vibrators and magnetic recorders afforded geophysical prospecting, their roles were no different from their counterparts in dynamite shooting - one sends a signal, and one receives it.

     The correlator was the real brainchild. The mathematical principles it served were discussed in Continuous Signal Seismograph by Crawford, Doty and Lee (Geophysics, February 1960) - imperative reading for the student of Vibroseis evolution, past, present, or future. To apply the theory - before software became a household word - only analogue hardware was on hand. Of course, it wasn't quite ready for the formidable computing step that correlation was adding to conventional record processing. And the search for individual components was coast to coast.
     Crawford comments: "We needed an electronic circuit which would multiply two signals and integrate them. MIT had developed an instrument that would suit our purpose and we bought a unit from a company which had taken over its development. That was the correlator's multiplier-integrator circuit. We also needed something which would give us a variable time delay for a signal. A company in Minnesota manufactured a device which recorded and played back electrical signals on a magnetic drum which did not require that the magnetic material be rubbed against the head. It was an out-of-contact recording and playback device which could apply nearly any amount of time delay without otherwise altering the signal, simply by changing the spacing between the recording and playback heads as the drum rotated at constant speed. The fact that the heads did not contact the abrasive magnetic recording material eliminated headwear which would otherwise have been prohibitive.
     "As research went on, we added elements, modified, adapted - and we ended up with an electronic system which made the operation multichannel and photographically recorded the correlation values. Still, the final record required hand tracing of the plotted points."

     Further evolution at the processing end blossomed into an electronic system nicknamed "the monster" - a cyclopean grouping of nine consoles. Its maintenance needs and immobility caused a lag of several days between field recording and data read-out - an expensive bottleneck once Vibroseis crews began routine operations. A research effort (simultaneous to those of the servo-hydraulic vibrator and the Decatrack) produced an interesting optical system which, using light, proved that a unique signal overlays itself in one position only.
     Says Doty: "John and I were on a plane en route to demonstrating this to management. Suddenly it hit me that precisely that feature meant the apparatus could do the correlation. I ran down the aisle to tell John, beside myself with excitement. But John was a bit skeptical. However, we tried it and it worked."

     Processing was thus dramatically streamlined since the analogue light correlator could process a 10-trace record in about five seconds - vs. 30 minutes required by the electronic monster.
     Crawford comments: "It worked on the same principle that the original film recorder did. It held two pieces of film in close contact but allowed one to slide over the other. One was a variable area record of the control signal put out by the vibrator - the other a recording of the field traces. These pieces of film were superimposed, and light passed through them and subsequently to a photocell.
     "Then, as we pulled one of them with reference to the other, the photocell assembly would give the read-out of the total transmitted light. Lo and behold, with this little invention of ours we could do the correlation process in seconds!" (And it was compact enough that optical correlators could be moved to field headquarters.)

     In the early '60s, Seismograph Service Ltd., the English subsidiary of SSC - the first Vibroseis licensee - devised yet another correlator. As explained in Conoco's book:
     "This unit employed a magnetic head which basically was a wire, shaped in the form of a frequency sweep. The signal to be correlated was recorded on a magnetic tape in such a manner that it matched the physical dimensions of the magnetic head which was referred to as the 'Copperhead.' Adaptations of this correlator could be conducted for special purpose filtering and frequency analysis. A major advantage of the magnetic correlator over the optical system was elimination of the large quantity of photographic processing which it entailed."

     With the advent of digital systems, the magnetic correlator - like a multitude of other early Vibroseis relatives - went to the museum. But the outcome of the first two decades of individual ingenuity in a team effort was a system without which the geophysical industry would be at a loss on many fronts. As Frank Searcy observed as an "operations" man: "We lived and breathed Vibroseis for several years. It's all we'd talk about - except maybe when we went fishing. It was exciting then, as it is now, to see what a high-powered exploration tool was developing."
     All expectations have been surpassed. Vibroseis crews have found deeper horizons beneath older, depleting fields. Approximately 50% of the seismic crews worldwide, through some 70 licensed operators, use the method. Its versatility was established early by extracurricular applications - a deep drainage tunnel project in Chicago; studies of the Mohorovicic discontinuity and of shear wave propagation; and classified work with the Department of Defense. And its cost-effectiveness - such as CDP shooting - is yet another bonus.

     Indeed, the success is enhanced by the inventors' sober outlook when in 1960 they unveiled their work to the geophysical community. While acknowledging that a completely controllable surface source warranted continued research and development, they were aware of "u the practical as well as technical problems which are likely to beset any competing approach which differs markedly from a well established, successful method." And dynamite, of course, is still successful. But Vibroseis became a much-needed alternative - the notable legacy of Crawford, Doty, and their invaluable colleagues.

     About 20 years ago, two Continental Oil men left their Ponca City offices and took to the road. John Crawford, director of the exploration research department (geophysics), and Frank Searcy, assistant manager of geophysics of the firm's operating group, were to meet with major geophysical contractors regarding Conoco's newest development - the Vibroseis.
     Crawford recalls: "Our crews had been using the method successfully since 1956. By 1960, management decided to make it available to industry through licensing. Frank and I found much interest on the part of all the companies we visited, but there was a problem. The mathematical principle involved was hard to understand. Even people familiar with seismic methods had difficulty visualizing it."
     The uniqueness of Vibroseis - and dynamite's enduring reign as a seismic source - is best exemplified by an event of February 1953 at the US Patent Office. The patent examiner was having trouble grasping the purpose and mechanics of:

     Method of and Apparatus for Determining Travel Time of Signals
     
     So the inventors brought in some key technical people for a detailed presentation. When it was over, every Conoco representative was sure they had made a crystal clear case for the method's workability. But there was a pregnant silence. Finally, the patent examiner asked: "Well - where does the dynamite come in?"
     Although industry had dabbled with air shooting as early as 1922 and McCollum Laboratories' Thumper was commercially available in 1955, the mechanical vibrator seemed too astounding - definitely not a thing to rush into for an expensive licensing agreement. But after several noncommittal meetings, the inventors talked to a man who needed no convincing, Gerald Westby (The Leading Edge, June 1982). Westby, president of Tulsa's Seismograph Service Company, couldn't wait to become the first licensee. In Crawford's words, "He went for it like a fish for a fly."

     SSC's first foreign Vibroseis crew went to Libya in August 1961. By 1975, of some 560 seismic crews operating in the Western world, 155 were employing the method under Conoco license. And today, over half the crews worldwide use it. In fact, the method is considered the most important contribution to seismic exploration since the reflection seismograph.
     But the invention itself was serendipitous. The basic concepts were born in a couple of hours, parented by John Crawford and Bill Doty - who claim that without each other, neither might have followed the lead toward the invention.
     Says Crawford: "In the summer of '52, Bill Doty had just come back from a seminar where new math concepts on information theory had been presented. He laid a magazine on my desk - Electronics, June 1950. In it, a paper by Lee and Wiesner of the Massachusetts Institute of Technology discussed autocorrelation and cross-correlation. Bill thought some of the principles discussed could be applied in our business. Just how wasn't clear yet.
     "But we agreed that the mathematical process of correlation would allow accurate measure of the travel time of a seismic wave through acoustic material. That is, if we could produce a nonrepetitive, long-duration signal, and if we could get an accurate copy of the signal as transmitted."

     Doty had served on a US Navy mine sweeper during World War II. He and Crawford had had at least one discussion about the practice of detonating acoustical mines with a "sweep" vibration - which uniformly varies frequency to hopefully hit the one that triggers the mine.
     "It occurred to Crawford," Doty says, "that a sweep was the type of unique signal we needed - it would match itself only at one time-phase relationship during a single frequency trip."
     That was the first breakthrough. But no equipment existed to generate such a signal with sufficient power. Then Crawford remembered having read about an old principle for making a mechanical vibrator.
     "Counter-rotating, off-center weights were geared together in such a way that their vibrations added in the vertical direction and cancelled in the horizontal. To make a sweep signal, all we needed to do was to continually speed up and slow down the driving engine."
     Doty and Crawford knew they were onto something. In fact, 20 years earlier, as assistant operator in a seismograph crew, Crawford had wondered why, instead of an impulse, couldn't a steady state signal be used? Probably others wondered too. But admittedly, Crawford never gave it a second thought until Doty tossed that article on his desk.
     "I'd be the last to claim that we had as a clear aim the development of a routine, high-power exploration tool. What we were after was a scientific method of measuring velocity in earth materials with a continuous signal instead of an impulse - that's all. It seemed like a good idea for a highly specialized research tool."

     But Conoco's president, Leonard McCollum, took an immediate interest in the project. He suggested a visit with the directors in New York. Crawford recalls: "McCollum, grinning, told them: 'I'm not sure I understand much of this but it sounds interesting and I think we ought to go ahead.' He was our friend at the top and we couldn't have made it otherwise. There were some in management who should have gladly abandoned the project."
     In fairness to the more conservative executive, It should be noted that $1 million was spent without definite results. However, Doty emphasizes: "By the time those initial funds were running alarmingly low, the Vibroseis had been essentially developed."

     And as it turned out, McCollum's endorsement in New York had secured the financing. By January 1953, equipment fabrication started and the Vibroseis task force went into high gear. The inventors were the overall orchestrators of the idea sessions. Doty, the research group leader, was in charge of testing and evaluation. Crawford selected and procured equipment. He also had the tenuous task of ensuring that some of Conoco's money (then a $448-million annual gross) would be apportioned to research.
     Other key members of the task force included Milford Lee, Frank Clynch, and Steve Moxley. Lee, who had just received a PhD in physics, handled design and procurement of the recording equipment. He also directed field operations and laboratory correlation. Clynch was in charge of design and construction of the vibrator. And Moxley, the last to join the team, was to devise a correlation system.
     "We had a magical combination of talents," says Doty. "Thanks to Clynch, for instance, we could test something almost as soon as we thought of it. Moxley, on his part, helped us move rapidly into the precision era. Until he arrived, he had operated a lot on trial and error. Masterfully, he understood what we wanted to do - his feeling for the servomechanism produced quick results. And overall, the efforts of each of the men were limitless."

     It had to be so - the available technology needed a big push. The required hardware had to be either invented or adapted from something unrelated. Often, equipment was borrowed from other departments. With such resilience and imagination, the prototype was assembled. The 25 hp gasoline engine for instance, was lent by Conoco's pipeline department, and to couple the vibrator to the ground they applied the weight of a water truck - courtesy of geophysical operations.
     But the precarious research team had to resolve bearing failures, surface noise problems, weathering depth determination puzzles, and much, much more. However, by April 1953, in a rock quarry near Ponca City, the first vibrator was tested. After several adjustments, they took it to Orlando, Oklahoma - a site carefully chosen. There, the Viola sandstone formation had been distinctly recorded at 5,000 feet by means of the ever-reliable explosives. The crew gathered 10 vibration traces. Then they drove back to the lab at full throttle.