DISC by the numbers

Dean Clark, TLE editor

SEG's 82^nd Annual Meeting doesn't officially start until Sunday, 4 November 2012, but for some the "fun" started as early as Friday with  the 25^th incarnation of the 2012 Distinguished Instructor Short Course taught by Chris Liner.

This program, almost universally known as DISC, began in 1999 and instantly blossomed into one of SEG's most popular offerings. It is annually requested by many more Sections than even the most indefatigable instructor can possibly visit, even if faster than light travel were possible. By the time Liner completes his tour in December, he will have presented the eight-hour course "Elements of Seismic Dispersion: A somewhat practical guide to frequency-dependent phenomena" 30 times (not counting a "practice" session given to University of Houston students in January) or 2.5 times per month. He will have visited five of the seven continents (no Africa or Antarctica) and 22 countries. Attendance prior to the Las Vegas course was 1058.  Advance registration in Las Vegas was 37, although the final attendance was probably a bit higher due to on-site registration.

The mileage Liner has traveled is a bit fuzzier. He has booked 113,000 miles on just one airline. That is 4.5 times the equatorial circumference of the Earth or just a bit more than the diameter of Jupiter. Somewhat amazingly, while traveling all over the world, Liner managed to interview for a new job and relocate from the University of Houston to the University of Arkansas where he became the first Maurice F. Storm Professor of Petroleum Geology.

Although DISC's obvious purpose is to teach the students, Liner has joined several other SEG lecturers on a list of those whose tours, and resulting interaction with a largely professional audience, have caused him to "re-think" the subject matter. Liner says, "Seismic attenuation has been intensely studied for nearly a century and is the subject of many hundreds of scientific papers, dozens of books, and endless discussion. Making enough sense of this to present a coherent, meaningful overview was the greatest challenge of writing the text which complements the course.

"It slowly became clear that the vast amount of scientific data supported a dual-attenuation model. At the small scale, intrinsic viscous attenuation is in accord with laboratory experiments and the best poro-elastic theory that we have. But field data field data clearly support the existence of an apparent attenuation mechanism, constant-Q in nature, that is due to layering effects.

"I developed some evidence to support the argument of constant-Q behavior due to layering. But the evidence was complicated, rather ambiguous, and hardly convincing. As I presented this evidence around the world, I became increasingly dissatisfied with it. Then it occurred to me that a simple argument was possible.'

That "simple" argument, and some clarifying diagrams, can be found on Seismos, Liner's blog (http://seismosblog.blogspot.com/) that has transitioned to the Web from its beginnings two decades ago as one of the most popular features in TLE.   

"Serving as the 2012 DISC instructor has been exhausting, exhilarating, and a rewarding honor," Liner says. "But when the tour ends, I play to spend a lot of time in my new home and let somebody else (David Johnston of ExxonMobil in this case) book all those miles back and forth through Jupiter next year."