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August 10, 2018

Sub-sea rift spills secrets to seismic probe (Image 1)

The Galicia group -- from left, Rice University graduate student Nur Schuba, alumnus Ara Alexanian and graduate research assistant Mari Tesi Sanjurjo -- discuss the northwest portion of the 3D seismic volume at Rice University’s Visualization Lab. [See related image Here.]

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The first study from a Rice University-led 2013 international expedition to map the seafloor off the coast of Spain has revealed details about the evolution of the fault that separates the continental and oceanic plates.

The study describes the internal structure of a large, 3D section of the Galicia, a non-volcanic passive margin between Europe and the Atlantic basin that shows no signs of past volcanic activity and where the crust is remarkably thin. This thinness made it easier to capture 3D data for about 525 square miles of the Galicia, the first transition zone in the world to be analyzed in this manner.

Researchers used sophisticated seismic reflection tools to model the Galicia. The rift is buried under several hundreds of meters of powdered rock and invisible to optical instruments, but seismic tools fire sound into the formation, which bounce back, telling researchers what kind of rock lies underneath and how it’s configured.

The study produced the first seismic images of the S-reflector, a prominent detachment fault within the continent-ocean transition zone. Researchers believe this fault accommodated slipping along the zone in a way that helped keep the crust thin.

"The S-reflector, which has been studied since the ’70s, is a very low-angle, normal fault, which means the slip happens due to extension," said Rice graduate student Nur Schuba. "What’s interesting is that because it’s at a low angle, it shouldn’t be able to slip. But it did. One mechanism people have postulated is called the rolling hinge," she said. "The assumption is that an initially steep fault slipped over millions of years. Because the continental crust there is so thin, the material underneath it is hot and domed up in the middle. The initially steep fault started rolling and became almost horizontal.

"So with the help of the doming of the material coming from below and also the continuous slip, that’s how it is likely to have happened," she adds.

The research was supported in part by the National Science Foundation (NSF).

Read more in the NSF News From the Field story Sub-sea rift spills secrets to seismic probe. (Date image taken: 2018; date originally posted to NSF Multimedia Gallery: Aug. 10, 2018)

Credit: Photo by Gary Linkevich

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