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  • 1
    Electronic Resource
    Electronic Resource
    A model for the magmatic–hydrothermal system at Mount Rainier, Washington, from seismic and geochemical observations (2000)
    Springer
    Bulletin of volcanology 61 (2000), S. 425-436 
    Details
    ISSN: 1432-0819
    Keywords: Key words Mount Rainier ; Seismicity ; Geochemistry ; Magmatic–hydrothermal system model ; Volcano monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Mount Rainier is one of the most seismically active volcanoes in the Cascade Range, with an average of one to two high-frequency volcano-tectonic (or VT) earthquakes occurring directly beneath the summit in a given month. Despite this level of seismicity, little is known about its cause. The VT earthquakes occur at a steady rate in several clusters below the inferred base of the Quaternary volcanic edifice. More than half of 18 focal mechanisms determined for these events are normal, and most stress axes deviate significantly from the regional stress field. We argue that these characteristics are most consistent with earthquakes in response to processes associated with circulation of fluids and magmatic gases within and below the base of the edifice.Circulation of these fluids and gases has weakened rock and reduced effective stress to the point that gravity-induced brittle fracture, due to the weight of the overlying edifice, can occur. Results from seismic tomography and rock, water, and gas geochemistry studies support this interpretation. We combine constraints from these studies into a model for the magmatic system that includes a large volume of hot rock (temperatures greater than the brittle–ductile transition) with small pockets of melt and/or hot fluids at depths of 8–18 km below the summit. We infer that fluids and heat from this volume reach the edifice via a narrow conduit, resulting in fumarolic activity at the summit, hydrothermal alteration of the edifice, and seismicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008909
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  • 2
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    Short‐term and long‐term tremor migration patterns of the Cascadia 2004 tremor and slow slip episode using small aperture seismic arrays (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Tectonic tremor has been recorded at many subduction zones, including the Nankai, Cascadia, Mexican, and Alaskan subduction zones. This study, the first to use small aperture seismic arrays to track tremor, deployed three small aperture seismic arrays along the Cascadia subduction zone during a tremor and slow slip episode in July 2004. The tremor was active during virtually all (up to 99%) minutes of the analyzed tremor episode using 5 min sample windows. Individual wave phases were tracked across the arrays and used to derive slowness vectors. These were compared with slowness vectors computed from a standard layered Earth model to derive tremor locations. Locations were stable within a volume roughly 250 km2 in epicenter and 20 km in depth for hours to days before moving to a new volume. The migration between volumes was not smooth, and the movement of the sources within the volume followed no specific pattern. Overall migration speeds along the strike of the subduction zone were between 5 and 15 km/d; smaller scale migration speeds between volumes reached speeds up to 2 km/min. Uncertainties in the best locations were 5 km in epicenter and 10 km in depth. For this data set and processing methodology, tremor does not locate predominately on the primary subduction interface. Our favored model for the generation of tectonic tremor signals is that the tremor is triggered by stress and fluid pressure changes caused by slow slip and is composed, at least in part, of low‐frequency earthquakes broadly distributed in location
    Description: Published
    Description: B00A24
    Description: 3.2. Tettonica attiva
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: tremor migration ; Cascadia 2004 ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Stress tensor computations at Mount St. Helens (1995-1998) (2006)
    Details
    Publication Date: 2019-11-04
    Description: Fault plane solutions of 459 events occurring between 1995 and 1998 at Mount St. Helens (State of Washington, Northwest U.S.A.) were considered in order to infer the state of stress beneath the volcano. These events occurred in two distinct depth zones. The shallower zone is between 2 and 5.5 km, with shocks clustering in a tight cylindrical distribution about 1 km in radius directly beneath the crater. The deeper events are spread over a larger volume from 5.5 to 10 km depth and surround an aseismic zone below and slightly west of the lava dome. Faulting is characterized by a mixture of strike-slip, reverse and normal faults with maximum compression axes which do not cluster around a single direction. In the deep zone, between 5.5 and 10 km, P axes define a wheel-spoke pattern pointing radially away from the center of the aseismic zone. The 459 fault plane solutions were inverted for stress tensor parameters using the algorithm of Gephart and Forsyth. The inversion of the whole data set revealed that faulting was not produced by a uniform stress distribution. The subdivision of the zone into smaller volumes significantly reduced misfit and confidence areas of the solutions, whereas temporal subdivision of the sample did not lead to significant improvements in terms of stress uniformity. We suggest that the inhomogeneous stress field is consistent with a varying pressure source originating from the inferred crustal magma chamber and a thin conduit extending above it.
    Description: JCR Journal
    Description: open
    Keywords: Mount St. Helens (USA) ; fault-plane solutions ; inversion ; stress field ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 6578807 bytes
    Format: application/pdf
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  • 4
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    Earthquake Early Warning: ShakeAlert in the Pacific Northwest (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-07-26
    Description: We evaluate the performance of earthquake early warning algorithm ElarmS-2 (earthquake alarm system v. 2) in the Pacific Northwest. Real-time and prerecorded seismic data from Oregon, California, and Washington in the United States and British Columbia in Canada are used. The earthquakes tested range up to moment magnitude 7.2, the limit for which the ElarmS-2 magnitude method is accurate. ElarmS-2 reliably detects catalog magnitude 3 and larger earthquakes within the network, but the cut-off magnitude for accurate event recognition is higher for events offshore and on the edges of the network. We have made several adjustments that make the ElarmS-2 algorithm less likely to falsely report multiple alerts for earthquakes. Replaying of past earthquakes shows that the new settings improve the algorithm’s behavior for edge cases while not degrading previously well-constrained solutions within the dense part of the network. We expect few false alerts, none that would predict significant shaking anywhere in our region. Even though ElarmS-2 assumes a fixed earthquake depth, the epicenter and magnitude estimates are accurate enough to provide good predictions of shaking intensities. Online Material: Tables listing parameters of 31 calibration earthquakes, ElarmS-2 real-time detections, and comparison of ElarmS-2 performance for calibration events before and after adjusting configuration.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 5
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    Observations of seasonal and diurnal glacier velocities at Mount Rainier, Washington, using terrestrial radar interferometry (2015)
    Copernicus
    Details
    Publication Date: 2015-12-01
    Description: We present surface velocity maps derived from repeat terrestrial radar interferometry (TRI) measurements and use these time series to examine seasonal and diurnal dynamics of alpine glaciers at Mount Rainier, Washington. We show that the Nisqually and Emmons glaciers have small slope-parallel velocities near the summit (〈 0.2 m day−1), high velocities over their upper and central regions (1.0–1.5 m day−1), and stagnant debris-covered regions near the terminus (〈 0.05 m day−1). Velocity uncertainties are as low as ±0.02–0.08 m day−1. We document a large seasonal velocity decrease of 0.2–0.7 m day−1 (−25 to −50 %) from July to November for most of the Nisqually Glacier, excluding the icefall, suggesting significant seasonal subglacial water storage under most of the glacier. We did not detect diurnal variability above the noise level. Simple 2-D ice flow modeling using TRI velocities suggests that sliding accounts for 91 and 99 % of the July velocity field for the Emmons and Nisqually glaciers with possible ranges of 60–97 and 93–99.5 %, respectively, when considering model uncertainty. We validate our observations against recent in situ velocity measurements and examine the long-term evolution of Nisqually Glacier dynamics through comparisons with historical velocity data. This study shows that repeat TRI measurements with 〉 10 km range can be used to investigate spatial and temporal variability of alpine glacier dynamics over large areas, including hazardous and inaccessible areas.
    Print ISSN: 1994-0416
    Electronic ISSN: 1994-0424
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 6
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    Observations of seasonal and diurnal glacier velocities at Mount Rainier, Washington using terrestrial radar interferometry (2015)
    Copernicus
    Details
    Publication Date: 2015-07-31
    Description: We present spatially continuous velocity maps using repeat terrestrial radar interferometry (TRI) measurements to examine seasonal and diurnal dynamics of alpine glaciers at Mount Rainier, Washington. We show that the Nisqually and Emmons glaciers have small slope-parallel velocities near the summit (〈 0.2 m day−1), high velocities over their upper and central regions (1.0–1.5 m day−1), and stagnant debris-covered regions near the terminus (〈 0.05 m day−1). Velocity uncertainties are as low as ±0.02–0.08 m day−1. We document a large seasonal velocity decrease of 0.2–0.7 m day−1 (−25 to −50 %) from July to November for most of the Nisqually glacier, excluding the icefall, suggesting significant seasonal subglacial water storage under most of the glacier. We did not detect diurnal variability above the noise level. Preliminary 2-D ice flow modeling using TRI velocities suggests that sliding accounts for roughly 91 and 99 % of the July velocity field for the Emmons and Nisqually glaciers, respectively. We validate our observations against recent in situ velocity measurements and examine the long-term evolution of Nisqually glacier dynamics through comparisons with historical velocity data. This study shows that repeat TRI measurements with 〉 10 km range can be used to investigate spatial and temporal variability of alpine glacier dynamics over large areas, including hazardous and inaccessible areas.
    Print ISSN: 1994-0432
    Electronic ISSN: 1994-0440
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
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    Focal Determination of Microearthquakes Using a Tripartite Seismic Array (1969)
    Seismological Society of America
    Details
    Publication Date: 1969-09-01
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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  • 8
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    Dr. Anthony "Tony" Qamar (2006)
    Seismological Society of America
    Details
    Publication Date: 2006-01-01
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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  • 9
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    SSA 2005 Annual Meeting Presidential Address (2005)
    Seismological Society of America
    Details
    Publication Date: 2005-11-01
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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  • 10
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    Identifying the Rupture Plane of the 2001 Nisqually, Washington, Earthquake (2008)
    Seismological Society of America
    Details
    Publication Date: 2008-06-01
    Description: The 2001 Nisqually earthquake occurred within the subducting Juan de Fuca plate. Previous seismic and geodetic studies could not confidently identify its actual fault plane from the two nodal planes. In this study, we apply the recently developed source-scanning algorithm to local seismic waveforms and show unambiguously that the steeply east-dipping plane is the rupture plane. The rupture began near the bottom of the subducting crust and propagated downward into the subducting uppermost mantle. If intraslab earthquakes are assumed to be due to dehydration embrittlement, the source dimension is unlikely to grow any larger because the warm thermal state of the subducting Juan de Fuca plate limits dehydration to a shallow depth below the slab surface. Numerical modeling of the thermal structure indicates that dehydration embrittlement can only take place in the top 10 km of the subducting mantle, implying that the maximum size of an intraslab earthquake in northern Cascadia would be M (sub w) approximately 7 or less.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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