seismic – Alex Acks: Sound and Nerdery

Lunch today was quite fun; we had a “lunch and learn” that involved a lot of really tasty brownies and an hour-long talk by John M Holbrook. It was for the most part a general overview of the surface process quirks of meandering rivers and how those affect their usefulness as reservoirs. Most basically, oil companies like drilling in point bars since that’s where the best sand packages are to be found. Understanding the complex ways that rivers meander and stack up point bars over time (and that coarse channel fill can act as a fluid transmitter between sets of point bars at times) is a way to try to maximize drilling effectiveness.

Not that mapping out historical meanders is an easy task even for a river that’s still active and not buried hundreds of feet down and only visible via cores or seismic. Dr. Holbrook used a particular section of the Mississippi River (where it crosses the New Madrid seismic zone) to illustrate these concepts, and said that when they were trying to map out the old meanders by taking sediment cores, they were wrong about 30% of the time.

I thought the most interesting part of his talk was a brief look at fluvial response to tectonic activity, particularly how a river reacts to displacement on a fault that it crosses, since that normally means a change in grade on both sides of the fault. Looking at the Mississippi’s reaction to the displacement on the faults it crossed, the basic response was for the river to straighten out (cutting off meanders) on the downdropped side of the fault (where the gradient decreases) and resume meandering on the uplifted side. Which makes a lot of sense, really, though the other interesting thing was how quickly this response occurs. (Answer: very quickly.)

He’s got a paper in the pipe¹ about using the Mississippi to examine tectonic activity on the New Madrid fault, which is currently in review for Tectonophysics. Apparently it’s a bit controversial since what the river seems to show is that earthquakes along the fault system are temporally clustered, which doesn’t necessarily fit with the current consensus on the seismic zone. So I hope that it does get published and I can find a way to get my hands on the paper, since it sounds like an interesting read.

1 – If it gets published, here’s the title: Restored river courses reveal millennial-scale temporal clustering on a midplate fault

Monkeywrenching the Batholiths

I saw this item on Pharyngula, and it just kind of blew me away. I mean, you hear about animal rights groups going after biologists all the time, but I’d always thought at least academic geologists were safe from this kind of interference with their experiments.

There were several things about the exchange that really struck me.

First of all, Dr. Hole is incredibly patient in his replies. Far calmer and more patient than I could ever manage, though admittedly I also tend to have an explosive temper.

I’m very surprised that Ingmar Lee didn’t get himself hurt, or blow up a significant chunk of the landscape he so loves. Seismic shots are explosives, pure and simple. Messing with them is pretty risky business.

I was also struck by the apparent misunderstanding of how seismic shots work. Now, I wouldn’t want to be standing on top of a big one when it goes, but the point of them is to direct the explosive force downward into the ground, in order to create seismic waves. If seismic shots set off classic surface explosions like you see in the movies, they’d be worthless, they’d cause a lot of destruction, and they’d probably cause damage to the receiver arrays. If seismic shots are set properly (and not messed with by people who don’t know what they’re doing) then there’s no surface damage and no surface danger.

From what I’ve been able to come up with, research-wise, the biggest environmental concern caused by seismic surveys is actually in the wear and tear on the plant life that all the necessary vehicles cause – and the potential of scaring animals away. You do have to be able to get all the equipment out there and back, and that’s going to take vehicles. A survey done with explosives is actually far less disturbing to the environment than one using seismic trucks. One thump from the explosives, and it’s done. Considering the area is often subject to lightning strikes and its own natural earth quakes, the seismic shots are negligible in comparison to those.

I’m sure the mental image of hapless residents (and cranes) being cartoonishly thrown from the ground by enormous explosions is very dramatic, but in this case, it’s just silly.

I think the crux of this is Mr. Lee’s accusation that the data from this project will somehow be given to Big Oil, or that Big Oil has its evil little fingers in this scientific pie. Since most seismic surveys are probably done by oil companies (they have more money to do expensive things like that, after all), I can’t really blame him for the initial suspicion. However, basic knowledge of geology would prove that notion wrong, considering the area that the seismic is being shot for is chock full of igneous rocks. It’s a project looking at batholiths (giant intrusive structures – mountains, basically) which are not known for their rich oil reserves. Oil is found only in sedimentary rocks.

Hating oil companies doesn’t make this sort of dangerous vandalism at all okay, though. It also doesn’t help the efforts of environmentalists who are fighting oil companies, when someone associated with them goes after a permitted scientific research project while sounding like a self-righteous jerk – and one that could use a little extra geology education, at that. I certainly don’t advocate blowing up the landscape. I like the landscape. It’s where I keep my stuff. And it has surface processes! But that was never a danger here, at least not until Mr. Lee broke the top off the charge tube.

It really makes me wonder how people like Mr. Lee would have reacted to this very cool project, which determined the age of the Amazon River by drilling into its sediment fans. Well, it involves drills, so it must be evil and associated with the oil companies, right?