I AM sorry for the technical talk, but it feels so good to reminisce about the old days when I actually felt useful (self-pity old age moment here!).

The principle is simple: Create sound waves and catch their reflections/refractions on sensors. The time it takes for the waves to return gives an indication of the density of the rock through which they passed. By some magical computer stuff, cross-sections are created--sorta like a layer cake, but much messier! It is much more complicated than that, but essentially we use sound waves rather than light waves to see things. (Chris---I had forgotten about the migration factor. Ugh.)

For the non-technicals here--imagine a multi layer cake that has been stretched, and then smashed together, and compacted. Then try to map the layer of raspberry jam as opposed to the chocolate cream filling. Crude, but effective analogy to the Santa Barbara area! Because there is oil there in the Miocene and Pliocene formations, the area has been fairly intensively mapped by oil companies over the past few years.

For a long time, it was difficult to actually get the oil company data--it was expensive to produce and you had to buy it from them in those days.

Actually the 2d seismics were pretty good---and fun to work with sometimes. The real fun was taking well logs, trying to locate exactly where the well was at some given depth(none of them are straight), and matching that rock to the data you had.

I remember thinking of it as a puzzle, and I loved doing it---even if my results didn't match somebody else's. Have fun with the Hosgri/San Gregorio system. Did a little bit of work there for the Diablo Canyon project many years ago. I do recall the apparent deep shallow thrust fault (old subduction zone?) that seemed to exist right beneath the Central Coast there in Mesozoic rock.