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Research Areas: Seismology

1. Aqueous Geochemistry
2. Environmental and Theoretical Geochemistry
3. Mineral Physics and Petrology
4. Paleoecology
5. Paleoclimatology and Paleoceanography
6. Planetary Science    
7. Sedimentology and Stratigraphy
8. Seismology
9. Space Geodesy
10. Tectonics and Structural Geology

Seth Stein uses global earthquake seismology for tectonic studies of plate boundary processes, intraplate deformation, present-day plate kinematics and the rheology of the lithosphere. His goal is to obtain constraints on the nature and characteristics of dynamic processes in the Earth. He has recently focused on the mechanics of subduction zones and the relation between seismic and aseismic deformation in different tectonic environments including the boundary between the Nazca and South American plates and the central U.S. (New Madrid) seismic zone. 

Suzan van der Lee uses the shapes and arrival times of the various seismic waves that make up a seismogram to create images of the Earth's upper mantle.  These images provide major clues to the spatially varying thermal and compositional conditions within the upper mantle, which are causes and consequences of mantle convection and lithospheric deformation. She collects the seismograms during field experiments (see picture) in locations that are particularly suitable for answering specific questions about the upper mantle, e.g., "How thick is the lithosphere?" The techniques used by Van der Lee for the creation of these images include state-of-the-art computer tomography.

Emile Okal's research in hydroacoustics involves the nature and origin of sound propagating directly in the water mass of the ocean, after generation by both man-made explosions and natural phenomena such as earthquakes, landslides, volcanic eruptions, and undetermined sources within large icebergs. In this context, he presently directs a 3-year deployment of seismic stations on mega-icebergs recently detached from the Antarctic ice shelf. He has also studied the characteristics and origin of intraplate island volcanism, in particular at Polynesian edifices discovered through volcanoseismic swarms.

In addition, Okal studies the generation and propagation of tsunamis by large earthquake sources, and in particular the contribution of landslides to their genesis. These studies are carried out both theoretically, and from field work taking place either in the aftermath of large tsunamis, or through the interview of elderly witnesses of large, historical events. Okal is also contributing to the development of algorithms for real-time tsunami warning, presently implemented at several observatories.

Seismological studies of the deep mantle are carried out by Craig Bina, who investigates the D" region at the core-mantle interface, using low-frequency modal summation and high-frequency reflectivity and full-wave techniques; and by Bina, Okal and Stein, who study the source characteristics of deep and intermediate earthquakes inside the descending Benioff slabs, with the goal of unraveling the mineralogical and/or thermal transformations which may accompany these events, as well as the exact seismic energy budget at these depths.

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