![]() Also, the rougher areas indicate where the megathrust jumped to form a new fault, and hasn’t had enough time to smooth the surface. Small changes in groove direction record a history of shifts in plate movement. This unique, highly-detailed image revealed other buried secrets. “Corrugations are a great record of how blocks are sliding past each other along a fault.” Scientists have found similar grooves at the base of fast moving glaciers and other faults, but not on megathrust faults. “Gently rolling hills and valleys that are parallel and stretch for miles.” That’s how Edwards described the scene if you could stand on the fault surface looking across the grooves. They are more likely to generate tsunamis, which as we saw from Japan and Sumatra, can be a bigger hazard than earthquake shaking.” In the United States, subduction zones with megathrust faults exist offshore of Alaska, Washington, Oregon, Northern California, Puerto Rico, the US Virgin Islands, Guam, and the Northern Mariana Islands. “And megathrust faults, within subduction zones, host the largest earthquakes on the planet. “Subduction zones are hugely important, both because of the hazards they pose and because it’s where the earth destroys crust,” said lead author Joel Edwards, a USGS student contractor pursuing a Ph.D. The study area is in the Pacific Ocean southwest of Costa Rica. ![]() Visit Media to see details.Ī yellow star marks the spot where researchers reported finding corrugations, or giant grooves, kilometers long, hundreds of meters wide, and tens of meters high, between the Cocos and Caribbean tectonic plates that form part of the Costa Rica subduction zone.
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