eprintid: 1738 rev_number: 10 eprint_status: archive userid: 6 dir: disk0/00/00/17/38 datestamp: 2016-09-15 11:52:41 lastmod: 2017-02-08 12:21:43 status_changed: 2016-09-15 11:52:41 type: article metadata_visibility: show creators_name: Waite, Gregory P. creators_name: Chouet, Bernard A. creators_name: Dawson, Phillip B. corp_creators: U.S. Geological Survey, Volcano Hazards, Menlo Park, California, USA Now at Geol. & Mining Eng. & Sci., Michigan Technological University, Houghton, Michigan, USA. corp_creators: U.S. Geological Survey, Volcano Hazards, Menlo Park, California, USA corp_creators: U.S. Geological Survey, Volcano Hazards, Menlo Park, California, USA title: Eruption dynamics at Mount St. Helens imaged from broadband seismic waveforms: Interaction of the shallow magmatic and hydrothermal systems subjects: O subjects: RU subjects: SS full_text_status: none abstract: The current eruption at Mount St. Helens is characterized by dome building and shallow, repetitive, long-period (LP) earthquakes. Waveform cross-correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks. Stacked spectra of these events display multiple peaks between 0.5 and 2 Hz that are common to most stations. Lower-amplitude very-long-period (VLP) events commonly accompany the LP events. We model the source mechanisms of LP and VLP events in the 0.5–4 s and 8–40 s bands, respectively, using data recorded in July 2005 with a 19-station temporary broadband network. The source mechanism of the LP events includes: 1) a volumetric component modeled as resonance of a gently NNW-dipping, steam-filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2) a vertical single force attributed to movement of the overlying dome. The VLP source, which also includes volumetric and single-force components, is 250 m deeper and NNW of the LP source, at the SW edge of the 1980s lava dome. The volumetric component points to the compression and expansion of a shallow, magma-filled sill, which is subparallel to the hydrothermal crack imaged at the LP source, coupled with a smaller component of expansion and compression of a dike. The single-force components are due to mass advection in the magma conduit. The location, geometry and timing of the sources suggest the VLP and LP events are caused by perturbations of a common crack system. date: 2008-02 date_type: published publication: Journal of Geophysical Research volume: 113 number: B2 publisher: American Geophysical Union id_number: doi:10.1029/2007JB005259 issn: 0148-0227 official_url: http://doi.org/10.1029/2007JB005259 access_IS-EPOS: limited owner: Publisher citation: Waite, Gregory P. and Chouet, Bernard A. and Dawson, Phillip B. (2008) Eruption dynamics at Mount St. Helens imaged from broadband seismic waveforms: Interaction of the shallow magmatic and hydrothermal systems. Journal of Geophysical Research, 113 (B2). DOI: https://doi.org/10.1029/2007JB005259