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Colloquia

Journey to the Center of the Earth

Gunther Uhlmann (U. of Washington)

Location:  Join Zoom Meeting, https://rutgers.zoom.us/j/93327481850?pwd=WFEzck1lL09vTjhkcFp1eWcwS3J6QT09
Date & time: Wednesday, 23 September 2020 at 3:30PM - 4:30PM

We will consider the inverse problem of determining the sound speed or index of refraction of a medium by measuring the travel times of waves going through the medium. This problem arises in global seismology in an attempt to determine the inner structure of the Earth by measuring travel times of earthquakes. It has also several applications in optics and medical imaging among others.

The problem can be recast as a geometric problem: Can one determine the Riemannian metric of a Riemannian manifold with boundary by measuring the distance function between boundary points? This is the boundary rigidity problem. The linearization of this problems involves the integration of a tensor along geodesics, similar to the X-ray transform.

We will also describe some recent results, joint with Plamen Stefanov and Andras Vasy, on the partial data case, where you are making measurements on a subset of the boundary.

No previous knowledge of Riemannian geometry will be assumed.