32 Volcanoes of the Pacific Basin and Rim: Geological and Geophysical Observations (Posters)
MAGNETOTELLURIC STUDY OF MT ST HELENS WASHINGTON, USA: PHASE TENSOR ANALYSIS PRELIMINARY RESULTS
Paper number: 32-4
Program: THEME SESSIONS
Time: 8:00 AM – 6:00 PM
Authors
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G.J. HillMonash University, Victoria, N/A
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R.A.F. CasMonash University, Victoria, N/A
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J.P. CullMonash University, Victoria, N/A
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T.G. CaldwellInstitute of Geologic and Nuclear Sciences, Lower Hutt, N/A
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H.M. BibbyInstitute of Geologic and Nuclear Sciences, Lower Hutt, N/A
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W. HeiseInstitute of Geologic and Nuclear Sciences, Lower Hutt, N/A
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L.G. MastinUnited States Geological Survey, Vancouver, WA
Abstract
Mount St. Helens is a quaternary stratovolcano located in south-western Washington, USA, lying along the western front of the Cascade Range between Mt. Hood to the south and Mt. Rainier to the north, Mt. St. Helens is located in a region of transition both geologically and geophysically. Phase tensor and induction arrow analysis from 37 broadband magnetotelluric (~0.01 – 2000 s) sounding sites show the regional conductivity structure in a ~1000 km2 area around the volcano is 3-D at all period scales. Phase tensor analysis indicates that Mount St. Helens lies on the boundary of a large regional conductor to the north east of the volcano which begins at a depth of ~25 km and extends into the lower crust.