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Seismic Structure of Cascade Volcanoes: Gregory Waite
Project Title: Seismic Structure of Cascade Volcanoes
Mendenhall Fellow: Gregory Waite, (650)329-5237,
Duty Station: Menlo Park, CA
Start Date: May 17, 2004
Education: Ph.D. (Geophysics), University of Utah, 2004
Research Advisors: David Hill, (650) 329-4795,; Seth Moran, (360) 993-8934,; Daniel Dzurisin, (360) 993-8909,; Wayne R. Thatcher, (650) 329-4810,; Steven E. Ingebritsen, (650) 329-4422,

Project Description: Seismic velocity tomography is an important tool for investigating processes and structures beneath volcanoes.  Comparisons of P and S wave velocities are especially important for determining the compositions of low-velocity anomalies that may represent bodies of hot, partially-molten rock, cracks filled with aqueous fluid, or gas-filled pore spaces.  More detail about the structure of fluid-rich bodies can be inferred from velocity anisotropy.  For example, fluid-filled cracks in the crust are oriented by the regional stress field.  Measurements of anisotropy can characterize the preferred orientation of fluid-filled cracks, which is important for understanding fluid transport in the crust.  

The objective of this project is to investigate active volcanic systems using isotropic seismic velocity tomography and anisotropic shear-wave velocity modeling.  The USGS and cooperating organizations have been monitoring earthquakes at Cascade volcanoes for more than 25 years.  This rich dataset of earthquake records will be supplemented with recordings from a temporary array of three-component seismographs deployed around Mount St. Helens.  The combined data set will be used to compute models of P and S wave velocities of the upper crust.  Observations of crustal shear-wave splitting will be used to characterize the extent of anisotropic structures expected to be related to hydrothermal and magmatic systems.  The structures revealed by the seismic velocity modeling will be incorporated into existing models for the magmatic and hydrothermal systems to elicit a more accurate picture of the physical state of the volcano. 

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Last modified: 16:08:33 Thu 13 Dec 2012