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  • 1
    Electronic Resource
    Electronic Resource
    The upper mantle discontinuities in western Canada fromPs conversions (1995)
    Springer
    Pure and applied geophysics 145 (1995), S. 219-233 
    Details
    ISSN: 1420-9136
    Keywords: Upper mantle ; discontinuity ; Ps conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We have investigated variations in the travel times ofPs converted phases from the upper mantle 410 and 660 km discontinuities recorded on the western stations of the Canadian National Seismograph Network using a variant of the technique introduced byVinnik (1977). Clear and unambiguous signals for both discontinuities are observed at 8 of the 11 stations considered and exhibit variations which correlate well with regional tectonic setting. Stations located in regions which are currently tectonically active are characterized by largerPs arrival times relative to directP than those situated on the North American craton. In addition the difference in arrival times between the 410 and 660Ps phases suggest that most of the variation is the result of structure above the transition zone but below the Moho. Stations located in the Cascadia subduction zone generally exhibit poorer signal quality than those elsewhere, a feature that may result from upper mantle velocity heterogeneity, discontinuity topography or a combination of both. A detailed investigation of possible lateral variations in discontinuity topography associated with subduction awaits the compilation of a more comprehensive data set which will permit the monitoring of an azimuthal dependence in signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00880268
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Platinum-containing polypyrrole coatings on stainless steel electrodes for oxygen reduction in aprotic media (1992)
    Springer
    Journal of applied electrochemistry 22 (1992), S. 678-680 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01092619
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  • 3
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    Onshore/Offshore Structure of the Juan de Fuca Plate in Northern Cascadia from Bayesian Receiver Function Inversion (2013)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2013-10-01
    Description: This study applies Bayesian inversion to receiver functions (RFs) to estimate local shear-wave velocity ( V S ) structure of the Juan de Fuca (JdF) plate beneath the northern Cascadia subduction zone (CSZ) offshore and onshore Vancouver Island, British Columbia, Canada. We use passive seismic data recorded on NEPTUNE (NorthEast Pacific Time-series Undersea Networked Experiments) Canada ocean-bottom seismometers (OBSs), on temporary autonomous KECK Foundation OBSs, and on two land-based seismometers on Vancouver Island that are part of the Canadian National Seismograph Network (CNSN). Three-component, broadband recordings of large ( ), distant (30°–100°) earthquakes are used to compute RFs dominated by locally generated P -to- S converted waves. These are subsequently inverted using a nonlinear Bayesian approach that yields optimal profiles of V S , V P (compressional-wave velocity), and strike and dip angles, as well as quantitative uncertainty estimates for these parameters. The introduction of NEPTUNE Canada helps fill a gap in offshore seismic monitoring. Results from OBS stations indicate a thin oceanic crust at the JdF Ridge which thickens to ~10 km at the continental slope where sediment thickness also increases to ~5 km. At OZB, a coastal station, a 6–8 km thick, two-part low-velocity zone (LVZ) is imaged at 19 km depth. An LVZ of similar thickness is also observed 34 km beneath PGC, a south-central Vancouver Island station. The thickness of the LVZ imaged at these two land-based stations indicates that the oceanic sediments are not subducted but are scraped off the JdF plate and accreted to the North American plate. Determining these V S models at various stages of the CSZ provides a more detailed image of the subducting plate, and therefore contributes valuable new information useful for seismic-hazard analysis.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 4
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    Introduction to the Special Issue on the 2012 Haida Gwaii and 2013 Craig Earthquakes at the Pacific-North America Plate Boundary (British Columbia and Alaska) (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-05-01
    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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    Shear-Wave Velocity Structure in the Vicinity of the 2012 Mw 7.8 Haida Gwaii Earthquake from Receiver Function Inversion (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-05-01
    Description: The thrust mechanism of the 2012 M w  7.8 Haida Gwaii earthquake suggests convergence across the transpressive Pacific–North America plate boundary in the region is accommodated by underthrusting, with important consequences for seismic- and tsunami-hazard analysis. This article investigates the crustal structure and extent of subduction beneath Haida Gwaii by nonlinear inversion of receiver function data processed from teleseismic recordings at five land-based seismograph stations. Three of these stations were deployed since the 2012 earthquake to extend coverage to the southeast and have not been analyzed previously. The inversions provide estimates of the shear-wave velocity structure beneath much of Moresby Island. Results indicate a positive velocity contrast at approximately 18–26 km depth, interpreted as a shallow continental Moho. A 12–17 km thick low shear-wave velocity zone is also identified, which increases in depth from ~25 to 42 km along the direction of plate convergence, which is interpreted as subducting oceanic material. These results provide the first evidence that the subducting oceanic plate extends beneath the entirety of Moresby Island.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    Rupture Process of the 2012 Mw 7.8 Haida Gwaii Earthquake from an Empirical Green's Function Method (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-05-01
    Description: This article examines rupture processes of the 28 October 2012 M w  7.8 Haida Gwaii earthquake off the coast of British Columbia, Canada, using an empirical Green’s function (EGF) technique. The Haida Gwaii earthquake was the largest event along the Canadian portion of the Pacific–North American plate boundary since the M s  8.1 Queen Charlotte earthquake of 1949. It occurred along a potentially blind thrust fault dipping gently to the northeast rather than the main, subvertical Queen Charlotte fault. Surface waveforms from a 2001 M w  6.3 event, located only 15 km from the 2012 epicenter and with similar mechanism, are used as an EGF and deconvolved from those of the 2012 mainshock. The resulting source time functions contain minimal path effects, focal mechanism effects, and instrument response, so the waveforms display only properties of the 2012 mainshock rupture itself. By examining azimuthal variations in these source time functions, we constrain parameters such as average rupture velocity, extent, and directivity. In addition, information is obtained about the possible existence of major subevents and their relative locations. Results indicate two subevents within this rupture, the first 12 km south and updip of the epicenter and the second approximately 28 km from the first along a heading parallel to the Queen Charlotte terrace (~323°). Overall, the rupture front propagated roughly 50 km at an azimuth of 308.5°. This evidence for directivity to the northwest is important, given that earthquakes with strong directivity, such as the 2002 M w  7.9 Denali earthquake, have been shown to be capable of triggering earthquakes thousands of kilometers away. In this case, we suggest that northwest directivity of this earthquake is responsible for amplification of surface waves observed at seismic stations in Alaska ( Gomberg, 2013 ) and may provide a potential link between this 2012 event and the 2013 Craig, Alaska, earthquake. Online Material: Figure of all relative source time functions used in directivity analysis.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 7
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    Coulomb Stress Changes Following the 2012 Mw 7.8 Haida Gwaii, Canada, Earthquake: Implications for Seismic Hazard (2015)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2015-05-01
    Description: This article examines spatial changes to the local stress field resulting from the 28 October 2012, M w  7.8 Haida Gwaii earthquake, off the west coast of Moresby Island, British Columbia. This event occurred on a northeast-dipping, potentially blind-thrust fault rather than on the subvertical Queen Charlotte fault (QCF) that represents the Pacific–North American plate boundary. This was the largest earthquake along the Canadian portion of this plate boundary since the 1949 M s  8.1 Queen Charlotte earthquake. The U.S. Geological Survey Coulomb software is used to quantitatively estimate the effect of the mainshock on the background stress field, the known aftershock nodal planes, and the nearby QCF. We use two different mainshock finite-fault models, both of which are seismologically derived (by Lay et al. , 2013 , and Hayes, 2013 , separately) and subsequently adapted by K. Wang to account for the motion detected at four nearby Global Positioning System stations (see Nykolaishen et al. , 2015 , for more information). We also use the best-located set of aftershocks with information provided by a temporary array of ocean-bottom seismometers. Results indicate an apparent clustering of aftershocks slightly seaward of the main thrust, which is consistent with the modeled zone of promoted normal failure, likely related to extension in the footwall. Using existing models, we found a high number of aftershocks to be consistent with triggering by the mainshock, suggesting that static stress is a dominant control in the months following a large earthquake in this area. Further, we find loading greater than the triggering threshold on the QCF in an area interpreted as a seismic gap. This work improves understanding of the evolving seismic hazard along the Queen Charlotte margin and tests the usefulness of Coulomb modeling in this complex tectonic environment. Online Material: Figures of focal mechanisms and maximum Coulomb stress change, and table of aftershock moment tensor parameters.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 8
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    How did hydraulic-fracturing operations in the Horn River Basin change seismicity patterns in northeastern British Columbia, Canada? (2015)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2015-06-03
    Description: An increase in regional seismicity has been documented for the Horn River Basin (HRB) since the development of shale gas began in late 2006. Operational parameters of all hydraulic-fracturing (HF) treatments in the HRB between November 2006 and December 2011 were compiled from completion reports collected by the British Columbia Oil and Gas Commission (BCOGC). This database was compared with regional earthquake catalogs to delineate a quantitative relationship between the observed variation of regional seismicity and local HF operations. Taking the HRB as a whole, results suggest that the total injected volume from hydraulic fracturing is a more significant factor in affecting the pattern of local seismicity than injection pressure is. However, no clear change in background seismicity can be observed when the total monthly injected volume is less than ~ 20,000 m 3 . The initial effect of increasing injected volume is an increase in earthquake frequency but not magnitude. Relatively large seismic- moment release (〉 10 14 N m) occurred only when the monthly injected volume exceeded ~ 150,000 m 3 . Variable time lags, from days to four months, are observed between intense HF and the occurrence of a significant local earthquake. The hydrologic properties of the source formations and local geologic conditions (such as distribution, geometry, and dimension of preexisting faults) also might play important roles in induced seismogenesis, in addition to the total volume of injection.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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  • 9
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    Earthquake Ground Motion and 3D Georgia Basin Amplification in Southwest British Columbia: Deep Juan de Fuca Plate Scenario Earthquakes (2014)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2014-02-04
    Description: Finite-difference modeling of 3D long-period (〉2 s) ground motions for large ( M w  6.8) scenario earthquakes is conducted to investigate effects of the Georgia basin structure on ground shaking in Greater Vancouver, British Columbia, Canada. Scenario earthquakes include deep (〉40 km) subducting Juan de Fuca (JdF) plate earthquakes, simulated in locations congruent with known seismicity. Two sets of simulations are performed for a given scenario earthquake using models with and without Georgia basin sediments. The chosen peak motion metric is the geometric mean of the two orthogonal horizontal components of motion. The ratio between predicted peak ground velocity (PGV) for the two simulations is applied here as a quantitative measure of amplification due to 3D basin structure. A total of 10 deep subducting JdF plate earthquakes are simulated within 100 km of Greater Vancouver. Simulations are calibrated using records from the 2001 M w  6.8 Nisqually earthquake. On average, the predicted level of average PGV at stiff soil sites across Greater Vancouver for an M w  6.8 JdF plate earthquake is 3.2 cm/s (modified Mercalli intensity IV–V). The average increase in PGV due to basin structure across Greater Vancouver is 3.1. Focusing of north-northeast-propagating surface waves by shallow (〈1 km) basin structure increases ground motion in a localized region of south Greater Vancouver; hence, scenario JdF plate earthquakes located ≥80 km south-southwest of Vancouver are potentially the most hazardous. Online Material: Depth slices of 3D velocity model, peak ground velocity maps, and snapshots and videos of wave propagation.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 10
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    Investigation of regional seismicity before and after hydraulic fracturing in the Horn River Basin, northeast British Columbia (2015)
    National Research Council Canada (NRC)
    Details
    Publication Date: 2015-03-14
    Description: We systematically re-analyzed historical seismograms to verify the existence of background seismicity in the Horn River Basin of northeast British Columbia before the start of regional shale gas development. We also carefully relocated local earthquakes that occurred between December 2006 and December 2011 to delineate their spatiotemporal relationship with hydraulic fracturing (HF) operations in the region. Scattered seismic events were detected in the Horn River Basin throughout the study periods. The located seismicity within 100 km of the Fort Nelson seismic station had a clearly increasing trend, specifically in the Etsho area where most local HF operations were performed. The number of events was increased from 24 in 2002–2003 (prior to HF operations) to 131 in 2011 (peak period of HF operations). In addition, maximum magnitude of the events was shifted from M L 2.9 to M L 3.6 as the scale of HF operation expanded from 2006–2007 to 2011. Based on our relocated earthquake catalog, the overall b value is estimated at 1.21, which is higher than the average of tectonic/natural earthquakes of ~1.0. Our observations highly support the likelihood of a physical relationship between HF operation and induced seismicity in the Horn River Basin. Unfortunately, due to the sparse station density in the region, depth resolution is poor for the vast majority of events in our study area. As new seismograph stations are established in northeast British Columbia, both epicentral mislocation and depth uncertainty for future events are expected to improve significantly.
    Print ISSN: 0008-4077
    Electronic ISSN: 1480-3313
    Topics: Geosciences
    Published by National Research Council Canada (NRC)
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