What can GPS tell us about future earthquakes?

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Anchorage, Alaska earthquake and landslide

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How does the land over a subduction zone move before, during, and after a great earthquake? This animation compares the subduction zone east of Japan with a mirror-image subduction zone across the Pacific--the Cascadia subduction zone off the coast of the Pacific Northwest. Using GPS, we can watch the surface of the Earth deform in response to the drag of one tectonic plate going under another. GPS stations along the coast of Japan had been moving to the west before the March 11, 2011 earthquake, and rebounded back to the east following the earthquake. Across the Pacific ocean, the shallow portion of the Cascadia plate boundary is similarly locked by friction, compressing the overlying North American Plate in a northeast direction during subduction of the Juan de Fuca Plate. We see this in data from EarthScope's Plate Boundary Observatory, a network including more than 1000 continuous GPS sites managed by UNAVCO. Ultimately, the continental margin will rebound suddenly to the southwest as the stored elastic energy is released for the first time since the last great Cascadia earthquake on January 26, 1700.

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