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Anne Valovcin - One of the best experts on this subject based on the ideXlab platform.
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Stochastic excitation of Seismic Waves by a hurricane
Journal of Geophysical Research, 2015Co-Authors: Toshiro Tanimoto, Anne ValovcinAbstract:Stochastic excitation of Seismic Waves by a hurricane Toshiro Tanimoto* and Anne Valovcin Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, California 93106, USA. *Corresponding author: Email toshiro@geol.ucsb.edu Abstract We investigate how a tropical cyclone (Hurricane Isaac in 2012) generated Seismic ground motions using Seismic and barometric data from the Earthscope network. In the frequency band 0.01-0.02 Hz, Seismic and surface-pressure amplitudes show a systematic decreasing trend with distance from the center of the hurricane. However, the decreasing rate is much higher for Seismic Waves than for pressure. We develop a stochastic theory of Seismic-wave excitation by surface pressure that connects these two observed data sets; surface pressure is the excitation source and Seismic data are the resulting Seismic- wave field. This theory contains two parameters: (i) the pressure power spectral density (pressure PSD, S p ) and (ii) the correlation length in the pressure field ( L ). Using the formula, we solve for the spatial variation of correlation lengths. The solution shows that longer correlation lengths in pressure are near the hurricane center. Because Seismic- wave excitation is proportional to L 2 S p , the excitation for Seismic Waves becomes effectively more localized closer to the center. Also the scaling relation between L and S p leads to an excitation source which is approximately proportional to the third power of surface pressure. This centralized source for Seismic-wave excitation explains why the
Toshiro Tanimoto - One of the best experts on this subject based on the ideXlab platform.
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Stochastic excitation of Seismic Waves by a hurricane
Journal of Geophysical Research, 2015Co-Authors: Toshiro Tanimoto, Anne ValovcinAbstract:Stochastic excitation of Seismic Waves by a hurricane Toshiro Tanimoto* and Anne Valovcin Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, California 93106, USA. *Corresponding author: Email toshiro@geol.ucsb.edu Abstract We investigate how a tropical cyclone (Hurricane Isaac in 2012) generated Seismic ground motions using Seismic and barometric data from the Earthscope network. In the frequency band 0.01-0.02 Hz, Seismic and surface-pressure amplitudes show a systematic decreasing trend with distance from the center of the hurricane. However, the decreasing rate is much higher for Seismic Waves than for pressure. We develop a stochastic theory of Seismic-wave excitation by surface pressure that connects these two observed data sets; surface pressure is the excitation source and Seismic data are the resulting Seismic- wave field. This theory contains two parameters: (i) the pressure power spectral density (pressure PSD, S p ) and (ii) the correlation length in the pressure field ( L ). Using the formula, we solve for the spatial variation of correlation lengths. The solution shows that longer correlation lengths in pressure are near the hurricane center. Because Seismic- wave excitation is proportional to L 2 S p , the excitation for Seismic Waves becomes effectively more localized closer to the center. Also the scaling relation between L and S p leads to an excitation source which is approximately proportional to the third power of surface pressure. This centralized source for Seismic-wave excitation explains why the
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Stochastic excitation of Seismic Waves by a hurricane - eScholarship
2015Co-Authors: Toshiro TanimotoAbstract:Stochastic excitation of Seismic Waves by a hurricane Toshiro Tanimoto* and Anne Valovcin Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, California 93106, USA. *Corresponding author: Email toshiro@geol.ucsb.edu Abstract We investigate how a tropical cyclone (Hurricane Isaac in 2012) generated Seismic ground motions using Seismic and barometric data from the Earthscope network. In the frequency band 0.01-0.02 Hz, Seismic and surface-pressure amplitudes show a systematic decreasing trend with distance from the center of the hurricane. However, the decreasing rate is much higher for Seismic Waves than for pressure. We develop a stochastic theory of Seismic-wave excitation by surface pressure that connects these two observed data sets; surface pressure is the excitation source and Seismic data are the resulting Seismic- wave field. This theory contains two parameters: (i) the pressure power spectral density (pressure PSD, S p ) and (ii) the correlation length in the pressure field ( L ). Using the formula, we solve for the spatial variation of correlation lengths. The solution shows that longer correlation lengths in pressure are near the hurricane center. Because Seismic- wave excitation is proportional to L 2 S p , the excitation for Seismic Waves becomes effectively more localized closer to the center. Also the scaling relation between L and S p leads to an excitation source which is approximately proportional to the third power of surface pressure. This centralized source for Seismic-wave excitation explains why the
Andrew L. Kurkjian - One of the best experts on this subject based on the ideXlab platform.
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Tube Waves, Seismic Waves And Effective Sources
Journal of the Acoustical Society of America, 1993Co-Authors: Robert Burridge, Sergio Kostek, Andrew L. KurkjianAbstract:The radiation of Waves from a monopole source in a fluid‐filled borehole into an elastic medium is considered. A simple asymptotic analysis, based on the smallness of the ratio of the borehole radius to the wavelength, reveals the interaction between tube Waves and Seismic Waves. The pressure field in a tube wave acts as a secondary source of Seismic Waves and conversely an incoming Seismic wave excites a tube wave. The asymptotic analysis leads to a characterization of these sources in terms of the solution to two‐dimensional elastostatic problems. These may be solved exactly when the borehole has an elliptical cross section even in an anisotropic formation. Also the borehole need not be straight provided that its radius of curvature is large compared with a wavelength. The problem of two boreholes, one containing a source and the other a receiver (crosswell tomography geometry) is analyzed and an explicit expression for the received signal is derived.
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Tube Waves, Seismic Waves and effective sources
Wave Motion, 1993Co-Authors: Robert Burridge, Sergio Kostek, Andrew L. KurkjianAbstract:Abstract A simple asymptotic analysis, based on the smallness of the ratio of the borehole radius to the wavelength, reveals the interaction between tube Waves and Seismic Waves. The pressure field in a tube wave acts as a secondary source of Seismic Waves and conversely an incoming Seismic wave excites a tube wave. The asymptotic analysis leads to a characterization of these sources in terms of the solutions to one-dimensional acoustic and two-dimensional elastostatic problems. These may be solved exactly when the borehole has an elliptical cross-section even in an anisotropic formation. Also the borehole need not be straight provided that its radius of curvature is large compared with a wavelength.
Salvatore Martino - One of the best experts on this subject based on the ideXlab platform.
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A Parametric Numerical Study of the Interaction between Seismic Waves and Landslides for the Evaluation of the Susceptibility to Seismically Induced Displacements
Bulletin of the Seismological Society of America, 2013Co-Authors: Luca Lenti, Salvatore MartinoAbstract:This study presents the results of a numerical analysis investigating the influence of the interaction between Seismic Waves and slopes on Seismically induced displacements of existing landslides. Three step-like slope geometries with dip angles varying from 10° to 45° and two landslide mechanisms were considered; 54 multifrequential dynamic equivalent signals were applied to the models and were derived according to the LEMA_DES approach based on the accelerometric records of the European Strong Motion and COSMOS databases. The simulations were performed using a finite-difference approach that assumed different viscous rheologies and considered different values for both the dynamic properties and the mechanical parameters. The interaction between Seismic Waves and landslides was analyzed using frequency ratios defined for characteristic periods associated with the landslide dimensions (i.e., thickness and length) and the Seismic input. A regression analysis was also performed to derive correlations between Seismically induced displacements and the frequency ratios, the values of the Arias intensity, and the critical accelerations. The obtained results reveal that (a) the Seismically induced displacements increase with the Seismic amplification induced by the landslide mass; (b) the coupling of a 2D interaction between Seismic Waves and slope with the 1D resonance of the landslide mass, which is strictly related to the high-impedance contrasts between the landslide mass and the substratum, significantly affects the Seismically induced displacements; and (c) the Seismically induced displacements increase more intensely with increasing slope angle for a rototranslational mechanism with respect to a translational one. Moreover, the Seismically induced displacements that can be expected from the hereobtained results can significantly differ from those computed by the sliding-block stability analyses based on Newmark's method.
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The role of near-field interaction between Seismic Waves and slope on the triggering of a rockslide at Lorca (SE Spain)
Natural Hazards and Earth System Sciences, 2012Co-Authors: P Alfaro, José Delgado, Fj Garcia Tortosa, Jj Giner, Luca Lenti, C Lopez Casado, Salvatore Martino, Gabriele Scarascia MugnozzaAbstract:A 1000m3 rockslide occurred close to Lorca (SE Spain) during the main shock (Mw = 5.1) of the May 2011 Seismic sequence. The location of the rockslide, within 10 km of the earthquake epicenter and along the southern slope of a valley in which similar geological conditions occur on both slopes of the valley, suggests a significant near-field effect due to local Seismic response. This could be related to the specific interaction between the topography and the obliquely propagating Seismic Waves. A dynamic stress strain numerical model was constructed using the FLAC 7.0 finite difference code to back analyze the Lorca rockslide event and relate its occurrence to both the local Seismic amplification and the interaction between Seismic Waves and local topography. The results indicate that only for Seismic Waves with incidence angles in the range 0deg-50deg are the occurred slope instabilities expected. These results do not significantly change when varying the values for either stiffness or strength parameters within the range of the experimental data.
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The interaction of Seismic Waves with step-like slopes and its influence on landslide movements
Engineering geology, 2012Co-Authors: Luca Lenti, Salvatore MartinoAbstract:The interaction of Seismic Waves with slopes is a major factor influencing landslide movements that involve slope stability, local site Seismic amplification and topographic effects affecting ground motion. The results of a numerical study of landslide movements induced by the interaction of Seismic Waves with step-like slopes are presented here. To investigate this input-slope interaction, a dynamic analysis was performed using the finite difference stress-strain numerical code FLAC 6.0 under visco-plastic conditions. The dynamic signals were selected to be representative of different peak ground accelerations (PGAs), Arias intensities and frequency contents, and they were used in a parametric study of different step-like slopes with different geometrical configurations in terms of dip, height and thickness of geological strata. The derived outputs were processed for a Seismic amplification analysis and to evaluate the induced stress-strain effects in terms of progressive failure and resulting displacements. The obtained results: i) describe a fundamental role of topography in amplifying or de-amplifying the Seismic ground motion; ii) demonstrate that the progressive failure of unsheared slopes influences the Seismic amplification; iii) show that the strain effects on unsheared slopes, in terms of progressive failure, are more intense with increasing Arias intensity and slope dip; iv) prove that amplification or de-amplification processes can justify the values of displacements involving pre-existing landslide masses,which are significantly differentwith respect to those expected on the basis of sliding block approaches (i.e., Newmark's and flexible sliding block methods); v) highlight that, in the geological setting considered here, the Seismically induced displacements arising from the reactivation of pre-existing landslide masses can be significantly underestimated by sliding block approaches in the case of low-angle slopes characterised by high K values, i.e. the ratios between the critical pseudostatic threshold (ky) of the landslide and PGAs of the applied Seismic input.
A G Kosovichev - One of the best experts on this subject based on the ideXlab platform.
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Properties of Flares-Generated Seismic Waves on the Sun
Solar Physics, 2006Co-Authors: A G KosovichevAbstract:The helioSeismic Waves excited by solar flares (“sunquakes”) are observed as circular, expanding Waves on the Sun’s surface. The first sunquake was observed for a flare on July 9, 1996, by the Solar and Heliospheric Observatory (SOHO) space mission. This paper presents results of new observations and a detailed qualitative analysis of the basic properties of the helioSeismic Waves generated by four solar flares in 2003 – 2005. For two of these flares, the X17 flare of October 28, 2003, and the X1.2 flare of January 15, 2005, the helioseismology observations are compared with simultaneous observations of flare X-ray fluxes measured from the RHESSI satellite. These observations show a close association between the flare Seismic Waves and the hard X-ray source, indicating that high-energy electrons accelerated during the flare impulsive phase produced strong compression Waves in the photosphere, causing the sunquake. The results also reveal new physical properties such as strong anisotropy of the Seismic Waves, the amplitude of which varies significantly with the direction of propagation. The Waves travel through surrounding sunspot regions to large distances, up to 120 Mm, without significant distortion. These observations open new perspectives for helioSeismic diagnostics of flaring active regions on the Sun and for understanding the mechanisms of the energy release and transport in solar flares.
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properties of flares generated Seismic Waves on the sun
arXiv: Astrophysics, 2005Co-Authors: A G KosovichevAbstract:The solar Seismic Waves excited by solar flares (``sunquakes'') are observed as circular expanding Waves on the Sun's surface. The first sunquake was observed for a flare of July 9, 1996, from the Solar and Heliospheric Observatory (SOHO) space mission. However, when the new solar cycle started in 1997, the observations of solar flares from SOHO did not show the Seismic Waves, similar to the 1996 event, even for large X-class flares during the solar maximum in 2000-2002. The first evidence of the Seismic flare signal in this solar cycle was obtained for the 2003 ``Halloween'' events, through acoustic ``egression power'' by Donea and Lindsey. After these several other strong sunquakes have been observed. Here, I present a detailed analysis of the basic properties of the helioSeismic Waves generated by three solar flares in 2003-2005. For two of these flares, X17 flare of October 28, 2003, and X1.2 flare of January 15, 2005, the helioseismology observations are compared with simultaneous observations of flare X-ray fluxes measured from the RHESSI satellite. These observations show a close association between the flare Seismic Waves and the hard X-ray source, indicating that high-energy electrons accelerated during the flare impulsive phase produced strong compression Waves in the photosphere, causing the sunquake. The results also reveal new physical properties such as strong anisotropy of the Seismic Waves, the amplitude of which varies significantly with the direction of propagation. The Waves travel through surrounding sunspot regions to large distances, up to 120 Mm, without significant decay. These observations open new perspectives for helioSeismic diagnostics of flaring active regions on the Sun and for understanding the mechanisms of the energy release and transport in solar flares.
