Core Concept: Seismic tomography uses earthquake waves to probe the inner Earth

Abstract

Computerized tomography (CT) scans revolutionized medicine by giving doctors and diagnosticians the ability to visualize tissues deep within the body in three dimensions. In recent years, a different sort of imaging technique has done the same for geophysicists. Seismic tomography allows them to detect and depict subterranean features.\n\n\n\nData gathered by a network of seismic instruments (red) have enabled researchers to discern a region of relatively cold, stiff rock (shades of green and blue) beneath eastern North America. This is likely to be the remnants of an ancient tectonic plate. Image credit: Suzan van der Lee (Northwestern University, Evanston, IL).\n\n\n\nThe advent of the approach has proven to be a boon for researchers looking to better understand what’s going on beneath our feet. Results have offered myriad insights into environmental conditions within the Earth, sometimes hundreds or even thousands of kilometers below the surface. And in some cases, the technique offers evidence that bolsters models of geophysical processes long suspected but previously only theorized, researchers say.\n\nSeismic tomography “lets us image Earth’s structures at all sorts of scales,” says Jeffrey Freymueller, a geophysicist at Michigan State University in East Lansing and director of the national office of the National Science Foundation’s EarthScope. That 15-year program, among other things, operates an array of seismometers—some permanent, some temporary—that has collected data across North America. Among its more impressive finds: the remnants of an ancient tectonic plate sitting deep below North America and a plume of buoyant material fueling a well-known geothermal hot spot.\n\nTomography, roughly translated from Greek, means “writing by slices.” Researchers relish this ability to take digital models of three-dimensional (3D) objects and slice through them to create cross-sections—to virtually dissect them from any angle. Both medical tomography and seismic tomography use large arrays of sensors to collect energy that …