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  • Articles  (228)
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  • 1
    Publication Date: 2011-06-29
    Description: Inverted models of the deep mantle show a decorrelation between maps of shear VS and compressional VP wave velocities, an anti-correlation between the bulk sound velocity V$\phi$ and VS and a much larger variability of VS with respect to VP, expressed by large values of the ratio of their relative lateral variations. We carried out synthetic tests to verify if these features could be artifacts, explained by limits in tomographic resolution: synthetic data are calculated for an “input” model, and linearly inverted, as in tomography, to find an “output” model. Comparing the values of the aforementioned parameters for two different chemically homogeneous input models with the associated reconstructed output ones, we found that artifacts caused by realistic data noise and the nonuniform distribution of seismic sources and stations over the globe are not sufficient to introduce the features previously described. We confirm that compositional effects are required to explain them.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2001-09-15
    Description: We have identified an active normal fault in the epicentral area of the Basel (Switzerland) earthquake of 18 October 1356, the largest historical seismic event in central Europe. The event of 1356 and two prehistoric events have been characterized on the fault with geomorphological analysis, geophysical prospecting, and trenching. Carbon-14 dating indicates that the youngest event occurred in the interval 610 to 1475 A.D. and may correspond to the 1356 Basel earthquake. The occurrence of the three earthquakes induced a total of 1.8 meters of vertical displacement in the past 8500 years for a mean uplift rate of 0.21 millimeters per year. These successive ruptures on the normal fault indicate the potential for strong ground movements in the Basel region and should be taken into account to refine the seismic hazard estimates along the Rhine graben.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Meghraoui, M -- Delouis, B -- Ferry, M -- Giardini, D -- Huggenberger, P -- Spottke, I -- Granet, M -- New York, N.Y. -- Science. 2001 Sep 14;293(5537):2070-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ecole et Observatoire des Sciences de la Terre-Institut de Physique de Globe (EOST-IPAS), 5 rue Rene Descartes, 67084 Strasbourg, France. mustapha@eost.u-strasbg.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11557888" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2001-09-15
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Romanowicz, B -- Giardini, D -- New York, N.Y. -- Science. 2001 Sep 14;293(5537):2000-1.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Berkeley Seismological Laboratory, Berkeley, CA 94720-4760, USA. barbara@seismo.berkeley.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11557863" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
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    Nature Publishing Group (NPG)
    Publication Date: 2009-12-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Giardini, Domenico -- England -- Nature. 2009 Dec 17;462(7275):848-9. doi: 10.1038/462848a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Swiss Seismological Service, ETH Zurich, Sonneggstrasse 5, CH-8092 Zurich, Switzerland. giardini@sed.ethz.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20016577" target="_blank"〉PubMed〈/a〉
    Keywords: *Earthquakes ; *Energy-Generating Resources/standards ; *Hot Springs ; Public Opinion ; *Risk Management
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 2019
    Description: Abstract We present a new methodology for inverting P‐to‐S receiver function (RF) waveforms directly for mantle temperature and composition. This is achieved by interfacing the geophysical inversion with self‐consistent mineral phase equilibria calculations from which rock mineralogy and its elastic properties are predicted as a function of pressure, temperature, and bulk composition. This approach anchors temperatures, composition, seismic properties, and discontinuities that are in mineral physics data, while permitting the simultaneous use of geophysical inverse methods to optimize models of seismic properties to match RF waveforms. Resultant estimates of transition zone (TZ) topography and volumetric seismic velocities are independent of tomographic models usually required for correcting for upper mantle structure. We considered two end‐member compositional models: the equilibrated equilibrium assemblage (EA) and the disequilibrated mechanical mixture (MM) models. Thermal variations were found to influence arrival times of computed RF waveforms, whereas compositional variations affected amplitudes of waves converted at the TZ discontinuities. The robustness of the inversion strategy was tested by performing a set of synthetic inversions in which crustal structure was assumed both fixed and variable. These tests indicate that unaccounted‐for crustal structure strongly affects the retrieval of mantle properties, calling for a two‐step strategy presented herein to simultaneously recover both crustal and mantle parameters. As a proof of concept, the methodology is applied to data from two stations located in the Siberian and East European continental platforms.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2003-06-07
    Description: Water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone. Observations of converted seismic waves provide evidence of a 20- to 35-kilometer-thick discontinuity near a depth of 410 kilometers, most likely explained by as much as 700 parts per million of water by weight.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉van der Meijde, Mark -- Marone, Federica -- Giardini, Domenico -- van der Lee, Suzan -- New York, N.Y. -- Science. 2003 Jun 6;300(5625):1556-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Geophysics, Eidgenossische Technische Hochschule-Honggerberg (HPP)/Swiss Federal Institute of Technology CH-8093 Zurich, Switzerland. mark@tomo.ig.erdw.ethz.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12791988" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
    Publication Date: 2013-11-16
    Description: [1]  The underestimation of the size of recent megathrust earthquakes illustrates our limited understanding of their spatiotemporal occurrence and governing physics. To unravel their relation to associated subduction dynamics and long-term deformation, we developed a 2D continuum viscoelastoplastic model that uses an Eulerian-Lagrangian finite difference framework with similar on- and off-fault physics. We extend the validation of this numerical tool to a realistic subduction zone setting that resembles Southern Chile. The resulting quasi-periodic pattern of quasi-characteristic M8-M9 megathrust events compares quantitatively with observed recurrence and earthquake source parameters, albeit at very slow coseismic speeds. Without any data fitting, surface displacements agree with GPS data recorded before and during the 2010 M8.8 Maule earthquake, including the presence of a second-order flexural bulge. These surface displacements show cycle-to-cycle variations of slip deficits, which overall accommodate ~5% of permanent internal shortening. We find that thermally (and stress) driven creep governs a spontaneous conditionally stable downdip transition zone between temperatures of ~350 °C and ~450 °C. Ruptures initiate above it (and below the fore-arc Moho), propagate within it, interspersed by small intermittent events, and arrest below it as ductile shearing relaxes stresses. Ruptures typically propagate upward along lithological boundaries and widen as pressures drop. The main thrust is constrained to be weak due to fluid-induced weakening required to sustain regular subduction and to generate events with natural characteristics (fluid pressures of ~75-99% of solid pressures). The agreement with a range of seismological, geodetic and geological observations demonstrates the validity and strength of this physically consistent seismo-thermo-mechanical approach.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2017-11-15
    Description: We invert the Martian tidal response and mean mass and moment of inertia for chemical composition, thermal state, and interior structure. The inversion combines phase equilibrium computations with a laboratory-based viscoelastic dissipation model. The rheological model, which is based on measurements of anhydrous and melt-free olivine, is both temperature and grain size sensitive and imposes strong constraints on interior structure. The bottom of the lithosphere, defined as the location where the conductive geotherm meets the mantle adiabat, occurs deep within the upper mantle (∼250–500 km depth) resulting in apparent upper mantle low-velocity zones. Assuming an Fe-FeS core, our results indicate: 1) a Mantle with a Mg# (molar Mg/Mg+Fe) of ∼0.75 in agreement with earlier geochemical estimates based on analysis of Martian meteorites; 2) absence of bridgmanite- and ferropericlase-dominated basal layer; 3) core compositions (13.5–16 wt% S), core radii (1640–1740 km), and core-mantle-boundary temperatures (1560–1660 ∘ C) that, together with the eutectic-like core compositions, suggest the core is liquid; and 4) bulk Martian compositions that are overall chondritic with a Fe/Si (wt ratio) of 1.63–1.68. We show that the inversion results can be used in tandem with geodynamic simulations to identify plausible geodynamic scenarios and parameters. Specifically, we find that the inversion results are reproduced by stagnant lid convection models for a range of initial viscosities (∼10 19 –10 20 Pa·s) and radioactive element partitioning between crust and mantle around 0.001. The geodynamic models predict a mean surface heat flow between 15–25 mW/m 2 .
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2017-11-02
    Description: In this study, we present a Bayesian hierarchical framework to model fluid-induced seismicity. The framework is based on a non-homogeneous Poisson process (NHPP) with a fluid-induced seismicity rate proportional to the rate of injected fluid. The fluid-induced seismicity rate model depends upon a set of physically meaningful parameters, and has been validated for six fluid-induced case studies. In line with the vision of hierarchical Bayesian modeling, the rate parameters are considered as random variables. We develop both the Bayesian inference and updating rules, which are used to develop a probabilistic forecasting model. We tested the Basel 2006 fluid-induced seismic case study to prove that the hierarchical Bayesian model offers a suitable framework to coherently encode both epistemic uncertainty and aleatory variability. Moreover, it provides a robust and consistent short-term seismic forecasting model suitable for online risk quantification and mitigation.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2013-03-02
    Description: [1]  Ambient-noise seismology is of great relevance to high-resolution crustal imaging, thanks to the unprecedented dense data coverage it affords in regions of little seismicity. Under the assumption of uniformly distributed noise sources, it has been used to extract the Green’s function between two receivers. We determine the imprint of this assumption by means of wave propagation and adjoint methods in realistic 3D Earth models. In this context, we quantify the sensitivity of ambient-noise cross correlations from central Europe with respect to noise-source locations and shear wavespeed structure. We use ambient noise recorded over one year at 196 stations, resulting in a database of 864 cross-correlations. Our mesh is built upon a combined crustal and 3D tomographic model. We simulate synthetic ambient-noise cross-correlations in different frequency bands using a 3D spectral-element method. Traveltime cross-correlation measurements in these different frequency bands define the misfit between synthetics and observations as a basis to compute sensitivity kernels using the adjoint method. We perform a comprehensive analysis varying geographic station and noise-source distributions around the European seas. The deterministic sensitivity analysis allows for estimating where the starting crustal model shows better accordance with our dataset and gain insight into the distribution of noise sources in the European region. This highlights the potential importance to consider localized noise distributions for tomographic imaging and forms the basis of a tomographic inversion in which the distribution of noise sources may be treated as a free parameter similar to earthquake tomography.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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