Improving computational methods for imaging Earth's interior

Seismology offers the most powerful tool for characterizing the subsurface structure of Earth. Earthquakes occurring near the surface and as deep as 700 km emit elastic waves that are recorded by seismometers on Earth's surface. The shapes and arrival times of the recorded waves can be compared with seismograms modeled in a relatively simple, starting description of Earth's inner structure. By quantifying seismogram differences, seismologists can formally improve the description of Earth's structure by performing an inverse problem known as tomography. Tomography, best known in the medical fields, is about characterizing variations in a 3D medium (human body, oil reservoir, Earth's mantle) without directly measuring the properties.

Over the past 20 years, advances in computational methods and high-performance computing have enabled a new, more accurate form of seismic tomography. Previously the tomographic problem began with a simple description of Earth, whereby analytical methods could be used to represent wave propagation and measurement sensitivities. Now, it is possible to begin with a more accurate and complex 3D description of Earth, while also using 3D numerical simulations to account for realistic complexities of wave propagation.

On paper, seismic tomography is a straightforward optimization problem: ...

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Contributed by Carl Tape, University of Alaska Fairbanks