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Earth Matters

Seismic Surveying (Not Nazca) Lines

July 1st, 2015 by Adam Voiland

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Many readers were convinced that our June Puzzler (image above) showed Nazca lines in southern Peru. There certainly were lines in the image, but they were located about 10,000 kilometers (6,000 miles) away from Peru on a plateau in southern Libya. While the Nazca lines were probably created for religious purposes, the grid lines in Libya had a very different raison d’être: oil exploration.

As Stefano correctly noted at 12:26 p.m. on June 23, the lines were tracks left over from a seismic survey. While a layer of rocks, gravel, and ancient stone tools carpet most of the plateau, lines of large “thumper” trucks that use a vibrating metal plate to press down against the ground likely created the grid pattern. When they drove around prospecting the area with seismic sensors, the trucks kicked up a very fine layer of dust that was lighter brown than the rest of the surface. Less than two hours after Stefano weighed in, Miles Saunders explained much of this.

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Nazca lines in southern Peru. Read more about them here.

Twenty minutes later, Franco B. weighed in with some more key details. “This looks like geophysical prospection lines in some oil field in an arid zone, each line would be a succession of geophones placed in order to make seismic sections. The scattered dots are probably oil wells. The combination of lines at 90º allows to make very detailed 3D maps of the geological structures in depth, in order to improve the oil and gas exploration. All this overlays on what looks like an intermittent dendritic drainage pattern, evidence of the arid climate,” he said.

To get a sense of how the “thumper” trucks work, check out the video below from Maurin Media.

Here is a view of what the tracks look like on the ground.

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Photograph courtesy of Marta Lahr, University of Cambridge.

Meanwhile, twelve minutes before Stefano mentioned seismic lines on our blog, Kaye Simonson noted on our Facebook page that the grid was related to seismographs. About ten minutes later, Chris Leonard posted the exact coordinates on Facebook. By that afternoon, Leonard had figured out that the image featured seismic grid lines related to oil exploration. He worked it out by locating an archaeological study published in PLOS One that included the telling figure shown below. As the authors of that paper explain, the top part of the figure (a) shows the location of the grid lines that were laid out for oil exploration. The middle part (b) shows where archaeologists discovered stone tools (lithics) during a sweep before the seismic survey. A white circle indicates the presence of tools; larger circles indicate a higher density of stone tools. The bottom part (c) shows a more detailed view of a small portion of the plateau.

To learn more about the area, read our June 27, 2015, Image of the Day. Thanks to all of you who participated, and a big congratulations to the winners!

 

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