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  • 1
    Electronic Resource
    Electronic Resource
    Subduction and collision processes in the Central Andes constrained by converted seismic phases (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 958-961 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Central Andes are the Earth's highest mountain belt formed by ocean–continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35050073
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    Paper (German National Licenses)
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  • 2
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    A Stochastic Earthquake Ground-Motion Prediction Model for the United Kingdom (2013)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2013-02-07
    Description: Low-seismicity regions such as the United Kingdom (UK) pose a challenge for seismic hazard analysis in view of the limited amount of locally recorded data available. In particular, ground-motion prediction is faced with the problem that most of the instrumental observations available have been recorded at large distances from small earthquakes. Direct extrapolation of the results of regression on these data to the range of magnitudes and distances relevant for the seismic hazard analysis of engineered structures generally leads to unsatisfactory predictions. The present study presents a new ground-motion prediction equation (GMPE) for the UK in terms of peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped pseudospectral acceleration (PSA), based on the results of numerical simulations using a stochastic point-source model calibrated with parameters derived from local weak-motion data. The predictions from this model are compared with those of previous GMPEs based on UK data, other GMPEs derived for stable continental regions (SCRs), as well as recent GMPEs developed for the wider European area.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 3
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    Convolutional Neural Network for Seismic Phase Classification, Performance Demonstration over a Local Seismic Network (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉Over the past two decades, the amount of available seismic data has increased significantly, fueling the need for automatic processing to use the vast amount of information contained in such data sets. Detecting seismicity in temporary aftershock networks is one important example that has become a huge challenge because of the high seismicity rate and dense station coverage. Additionally, the need for highly accurate earthquake locations to distinguish between different competing physical processes during the postseismic period demands even more accurate arrival‐time estimates of seismic phase. Here, we present a convolutional neural network (CNN) for classifying seismic phase onsets for local seismic networks. The CNN is trained on a small dataset for deep‐learning purposes (411 events) detected throughout northern Chile, typical for a temporary aftershock network. In the absence of extensive training data, we demonstrate that a CNN‐based automatic phase picker can still improve performance in classifying seismic phases, which matches or exceeds that of historic methods. The trained network is tested against an optimized short‐term average/long‐term average (STA/LTA) based method (〈a href="https://pubs.geoscienceworld.org/srl#rf25"〉Rietbrock 〈span〉et al.〈/span〉, 2012〈/a〉) in classifying phase onsets for a separate dataset of 3878 events throughout the same region. Based on station travel‐time residuals, the CNN outperforms the STA/LTA approach and achieves location residual distribution close to the ones obtained by manual inspection.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 4
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    Order of magnitude increase in subducted H2O due to hydrated normal faults within the Wadati-Benioff zone (2014)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2014-02-28
    Description: It is widely proposed that the oceanic mantle is hydrated by outer rise normal faults, and carries large amounts of water to the deep mantle. However, the extent of oceanic mantle hydration is poorly constrained by existing observations, and is a major source of uncertainty in determining the total water delivered to the mantle. Full waveform modeling of dispersed P-wave arrivals from events deep within the Wadati-Benioff zone of northern Japan shows that hydrated fault zone structures are present at intermediate depths. Analysis of the P-wave coda associated with events 5–35 km below the top of the slab gives an overall indication of the bulk hydration of the subducting oceanic mantle, and can be explained by a 40-km-thick layer that is 17%–31% serpentinized. This suggests that the top of the oceanic mantle is 2.0–3.5 wt% hydrated, subducting 170–318 Tg/m.y. of water per meter of arc beneath northern Japan. This order-of-magnitude increase in the estimated H 2 O flux in this arc implies that over the age of the Earth, the equivalent of as many as 3.5 present-day oceans of water could be subducted along the Kuril and Izu-Bonin arcs alone. These results offer the first direct measure of the lower lithosphere hydration at intermediate depths, and suggest that regassing of the mantle is more vigorous than has previously been proposed.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 5
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    Downdip velocity changes in subducted oceanic crust beneath Northern Japan--insights from guided waves (2014)
    Oxford University Press
    Details
    Publication Date: 2014-07-04
    Description: Dispersed P -wave arrivals observed in the subduction zone forearc of Northern Japan suggest that low velocity subducted oceanic crustal waveguide persists to depths of at least 220 km. First arrivals from events at 150–220 km depth show that the velocity contrast of the waveguide reduces with depth. High frequency energy (〉2 Hz) is retained and delayed by the low velocity crustal waveguide while the lower frequency energy (〈0.5 Hz) travels at faster velocities of the surrounding mantle material. The guided wave energy then decouples from the low velocity crustal waveguide due to the bend of the slab and is seen at the surface 1–2 s after the low frequency arrival. Dispersive P -wave arrivals from WBZ earthquakes at 150–220 km depth are directly compared to synthetic waveforms produced by 2-D and 3-D full waveform finite difference simulations. By comparing both the spectrogram and the velocity spectra of the observed and synthetic waveforms we are able to fully constrain the dispersive waveform, and so directly compare the observed and synthetic waveforms. Using this full waveform modelling approach we are able to tightly constrain the velocity structures that cause the observed guided wave dispersion. Resolution tests using 2-D elastic waveform simulations show that the dispersion can be accounted for by a 6–8 km thick low velocity oceanic crust, with a velocity contrast that varies with depth. The velocities inferred for this variable low velocity oceanic crust can be explained by lawsonite bearing assemblages, and suggest that low velocity minerals may persist to greater depth than previously thought. 2-D simulations are benchmarked to 3-D full waveform simulations and show that the structures inferred by the 2-D approximation produce similar dispersion in 3-D. 2-D viscoelastic simulations show that including elevated attenuation in the mantle wedge can improve the fit of the dispersed waveform. Elevated attenuation in the low velocity layers can however be ruled out.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Convolutional Neural Network for Seismic Phase Classification, Performance Demonstration over a Local Seismic Network (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉Over the past two decades, the amount of available seismic data has increased significantly, fueling the need for automatic processing to use the vast amount of information contained in such data sets. Detecting seismicity in temporary aftershock networks is one important example that has become a huge challenge because of the high seismicity rate and dense station coverage. Additionally, the need for highly accurate earthquake locations to distinguish between different competing physical processes during the postseismic period demands even more accurate arrival‐time estimates of seismic phase. Here, we present a convolutional neural network (CNN) for classifying seismic phase onsets for local seismic networks. The CNN is trained on a small dataset for deep‐learning purposes (411 events) detected throughout northern Chile, typical for a temporary aftershock network. In the absence of extensive training data, we demonstrate that a CNN‐based automatic phase picker can still improve performance in classifying seismic phases, which matches or exceeds that of historic methods. The trained network is tested against an optimized short‐term average/long‐term average (STA/LTA) based method (〈a href="https://pubs.geoscienceworld.org/srl#rf25"〉Rietbrock 〈span〉et al.〈/span〉, 2012〈/a〉) in classifying phase onsets for a separate dataset of 3878 events throughout the same region. Based on station travel‐time residuals, the CNN outperforms the STA/LTA approach and achieves location residual distribution close to the ones obtained by manual inspection.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 7
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    Along‐Arc Heterogeneity in Local Seismicity across the Lesser Antilles Subduction Zone from a Dense Ocean‐Bottom Seismometer Network (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The Lesser Antilles arc is only one of two subduction zones where slow‐spreading Atlantic lithosphere is consumed. Slow‐spreading may result in the Atlantic lithosphere being more pervasively and heterogeneously hydrated than fast‐spreading Pacific lithosphere, thus affecting the flux of fluids into the deep mantle. Understanding the distribution of seismicity can help unravel the effect of fluids on geodynamic and seismogenic processes. However, a detailed view of local seismicity across the whole Lesser Antilles subduction zone is lacking. Using a temporary ocean‐bottom seismic network we invert for hypocenters and 1D velocity model. A systematic search yields a 27 km thick crust, reflecting average arc and back‐arc structures. We find abundant intraslab seismicity beneath Martinique and Dominica, which may relate to the subducted Marathon and/or Mercurius Fracture Zones. Pervasive seismicity in the cold mantle wedge corner and thrust seismicity deep on the subducting plate interface suggest an unusually wide megathrust seismogenic zone reaching ∼65  km depth. Our results provide an excellent framework for future understanding of regional seismic hazard in eastern Caribbean and the volatile cycling beneath the Lesser Antilles arc.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 8
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    Velocity Structure of the Subducted Yakutat Terrane, Alaska: Insights From Guided Waves (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-04-16
    Description: Dispersed P wave arrivals from intermediate-depth earthquakes in the Alaskan subduction zone provide insight into the low-velocity structure of the subducting oceanic crust. P wave arrivals from 41 earthquakes in the eastern section of the arc show significant guided wave dispersion, with high-frequency (〉1 Hz) energy delayed by up to 2–3 s. We simulate this dispersion using a 2-D finite difference waveform propagation model, systematically varying both P wave velocity and low-velocity layer thickness parameters to find the lowest misfit between the observed and synthetic waveforms. We infer a 6 to 10 km thick low-velocity layer with a P wave velocity contrast of 7–15% with the overriding mantle, velocities which cannot be entirely accounted for by metamorphosed mid-ocean ridge basalt compositions. We postulate that this structure is the remnant of the subducted Yakutat terrane, significantly thinned at depth by metamorphism or delamination of material during subduction. ©2018. The Authors.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 9
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    30 Years in the Life of an Active Submarine Volcano: A Time-Lapse Bathymetry Study of the Kick-'em-Jenny Volcano, Lesser Antilles (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-03-01
    Description: Effective monitoring is an essential part of identifying and mitigating volcanic hazards. In the submarine environment this is more difficult than onshore because observations are typically limited to land-based seismic networks and infrequent shipboard surveys. Since the first recorded eruption in 1939, the Kick-'em-Jenny (KeJ) volcano, located 8 km off northern Grenada, has been the source of 13 episodes of T-phase signals. These distinctive seismic signals, often coincident with heightened body-wave seismicity, are interpreted as extrusive eruptions. They have occurred with a recurrence interval of around a decade, yet direct confirmation of volcanism has been rare. By conducting new bathymetric surveys in 2016 and 2017 and reprocessing 4 legacy data sets spanning 30 years we present a clearer picture of the development of KeJ through time. Processed grids with a cell size of 5 m and vertical precision on the order of 1–4 m allow us to correlate T-phase episodes with morphological changes at the volcano's edifice. In the time-period of observation 7.09 × 106 m3 of material has been added through constructive volcanism – yet 5 times this amount has been lost through landslides. Limited recent magma production suggests that KeJ may be susceptible to larger eruptions with longer repeat times than have occurred during the study interval, behavior more similar to sub-aerial volcanism in the arc than previously thought. T-phase signals at KeJ have a varied origin and are unlikely to be solely the result of extrusive submarine eruptions. Our results confirm the value of repeat swath bathymetry surveys in assessing submarine volcanic hazards. © 2018. The Authors.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    Along‐Arc Heterogeneity in Local Seismicity across the Lesser Antilles Subduction Zone from a Dense Ocean‐Bottom Seismometer Network (2019)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉ABSTRACT〈/div〉The Lesser Antilles arc is only one of two subduction zones where slow‐spreading Atlantic lithosphere is consumed. Slow‐spreading may result in the Atlantic lithosphere being more pervasively and heterogeneously hydrated than fast‐spreading Pacific lithosphere, thus affecting the flux of fluids into the deep mantle. Understanding the distribution of seismicity can help unravel the effect of fluids on geodynamic and seismogenic processes. However, a detailed view of local seismicity across the whole Lesser Antilles subduction zone is lacking. Using a temporary ocean‐bottom seismic network we invert for hypocenters and 1D velocity model. A systematic search yields a 27 km thick crust, reflecting average arc and back‐arc structures. We find abundant intraslab seismicity beneath Martinique and Dominica, which may relate to the subducted Marathon and/or Mercurius Fracture Zones. Pervasive seismicity in the cold mantle wedge corner and thrust seismicity deep on the subducting plate interface suggest an unusually wide megathrust seismogenic zone reaching ∼65  km depth. Our results provide an excellent framework for future understanding of regional seismic hazard in eastern Caribbean and the volatile cycling beneath the Lesser Antilles arc.〈/span〉
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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