earthquake-shattered cliffs, valleys, lava formations of every conceivable shape – that is the Mid-Ocean Ridge.” Joe Worzel remembered his collaboration with Ewing (Worzel, 1996): “In one of the contracts, probably it would be in ’42 or ’43, they had what we called the ‘fine print clause’ which was a statement that Woods Hole will find out all there is to know about underwater sound and tell the navy. Well, that still hadn’t been done by thousands of researchers. And Ewing and I were put on the project and we tried to find out what the problem was. What they were trying to solve. And they wouldn’t tell us. It was too classified to tell the people who were going to do the work… But anyhow we talked to them about what it was they wanted us to measure. After all you got to know what in heck you’re trying to do. And they wanted us to find four grossly different geological situations and to see what the sound did in those grossly different situations. And we kind of guessed what the problem was from little things, little bits of things we heard here and there and one thing and another… We were thinking that the Germans were blowing up our mine fields, our acoustic mine fields, using explosive sounds and our people couldn’t figure out how they were doing it. And this was in fact what was happening. And so we said we would go to Solomons, Maryland, which was a thick layer of mud, soft sediment. We’d go down and we’d do these measurements in ten fathoms and twenty fathoms, that was the range of depths that we were supposed to understand for them… We went off and we started making these measurements and we found what they wanted to know. What these acoustic mines did is they had a device on the mine so that a water wave from an explosion wouldn’t set it off. And so we figured immediately, well that was obvious, the low frequency acoustic waves that travelled through the bottom travelled faster, they’d get there before the water wave could shut the mine off and boom it goes. And they would set off a whole mine field by setting off one explosion. Te whole mine field would go up that our people spent days laying. But at any rate we made these measurements and we found the dispersion in the water wave and we turned that over to Pekeris for his analysis, his theoretical reasoning for, which he as I told you had already figured out. And we gave them the answer that they wanted and they adjusted their acoustic mines accordingly and the problem was solved.”
Anton Ziolkowski (1946–) was the first scientist to model the output pressure waveform from an airgun in 1970. He understood early on that measurements of underwater sound should be done in conjunction with development of physical theories explaining the observations to us. Anton modified the old saying of “Measuring is knowing” into “Measuring is the way to knowing”. According to his colleague Jacob Fokkema, this is a good way to characterise Anton’s approach to science as well as his significant contributions to the geophysical science. Anton has worked both for the industry and for academia
Figure 3.59: Anton Ziolkowski.
through his career. From 1982 to 1992 he was Professor of Applied Geophysics at Delft University of Technology, and in 1992 he became Professor of Petroleum Geoscience at the University
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of Edinburgh. During his time in Delft Anton contributed significantly within the field of convolution and especially de- convolution (how to separate the source signal from the seismic signal, so that we get closer to the true earth response). As an enabling technique for this he suggested (together with his co- authors) to estimate the source signature of an airgun array by mounting near-field hydrophones close to each individual gun. For his contributions within geophysics, he has received
several awards and honours, the latest one being the Desiderius Erasmus award of EAGE (European Association of Geoscientists and Engineers) in 2016.
Svein Vaage (1948–2008) graduated from the University of Bergen in 1978 with an
M.Sc. in solid-earth physics. During his first year of research he worked on earthquakes and classical seismology, before embarking on seismic exploration. Svein Vaage was instrumental in measuring signals from marine seismic sources. In the mid 1980s he established a comprehensive measurement programme where the seismic signatures of airguns were measured at various depths, various firing pressure and in numerous configurations. Tis huge experimental database established the foundation for a comprehensive tool for modelling the source signal generated by airguns and water-guns used for seismic exploration. One of the authors (ML) of this book actually worked under Svein’s guidance in the late 1980s. During intensive working periods Svein often used the typical Norwegian quote: “Te winter is long but not eternal” to encourage his co-workers. He had a strong belief in the value of accurate measurements, and also in repeating measurements if possible. Svein was also a pioneering force behind many innovations
Figure 3.60: Svein Vaage.
in seismic streamer acquisition, including the Continuous Long Offset (CLO) method and Simultaneous Shooting. He was a significant contributor to the development of the GeoStreamer, a marine seismic streamer measuring both pressure and vertical particle velocity simultaneously. Tis streamer was patented by PGS, and this led to the development of the concept of broadband seismic.
Eivind W Berg (1955–), a Norwegian geophysicist who, together with James Martin and Bjørnar Svenning, was honoured in 1999 with the SEG’s Kauffman Gold Medal for demonstrating that high-quality, high-density marine shear-wave data can be acquired by recording converted waves at the seabed. Berg presented their work at the 1994 EAEG (now EAGE) Annual Meeting and this sparked an explosion of activity and advancement in marine shear-wave seismic technology.
Figure 3.61: Eivind Berg, 1999 recipient of the SEG’s Kauffman Gold Medal.
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