Two Searches for Observational Evidence of Inner Core Rotation

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RichardsEAR-0125691This project will develop and apply two seismological methods for improving estimates of the inner core's rate of rotation with respect to the rest of the solid Earth. First, the investigators shall search for doublets in pertinent source regions, to enable very precise measurement of differential travel times that are indicative of inner core rotation. (A doublet, is a pair of earthquakes occurring at different times but in almost exactly the same location. A differential travel time is the time between two signals on the same seismogram.) Second, they shall search for indications of travel time change in seismic waves that have traveled almost vertically in the Earth, from a seismic source (an earthquake, or a nuclear explosion) to its antipode. By working with examples of seismic waves that have passed very deeply into the inner core, and are thus more sensitive to effects of anisotropy and inhomogeneity in the inner core, the investigators will be better able to understand the basic mechanism causing travel time changes.