The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Takeshi Tsuji - One of the best experts on this subject based on the ideXlab platform.
-
temporal variation and frequency dependence of seismic Ambient Noise on mars from polarization analysis
Geophysical Research Letters, 2020Co-Authors: Yudai Suemoto, Tatsunori Ikeda, Takeshi TsujiAbstract:We applied a polarization analysis of InSight seismic data to estimate temporal variation and frequency dependence of the Martian Ambient Noise field. An autocorrelation analysis suggests that a li...
W A Kuperman - One of the best experts on this subject based on the ideXlab platform.
-
emergence rate of the time domain green s function from the Ambient Noise cross correlation function
Journal of the Acoustical Society of America, 2005Co-Authors: Karim G Sabra, Philippe Roux, W A KupermanAbstract:It has been demonstrated experimentally and theoretically that an estimate of the Green’s function between two receivers can be obtained from the time derivative of the long‐time average cross correlation of Ambient Noise between these two receivers. The emergence rate of these deterministic coherent arrival times of the cross‐correlation function (i.e., the Green’s function estimate) from the recordings of an isotropic distribution of random Noise sources is derived by evaluating the amplitude of the variance of the cross‐correlation function. The knowledge of the emergence rate of NCF is essential for practical applications. To the first order, the variance is equal to the ratio of the product of the recorded energy by both receivers and the time–bandwidth product of the recordings. The variance of the time derivative of the correlation function is shown to have a similar dependency. These simple analytic formulas show a good agreement with the variance determined experimentally for the correlation of ocean Ambient Noise recorded in shallow water at a depth of 21 m, in the frequency band [300–530 Hz] for receiver separation up to 28 m and averaging time from 1 to 33 min.
-
using ocean Ambient Noise for array self localization and self synchronization
IEEE Journal of Oceanic Engineering, 2005Co-Authors: Karim G Sabra, Philippe Roux, Aaron Thode, Gerald L Dspain, W S Hodgkiss, W A KupermanAbstract:Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged Ambient Noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of Ambient Noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source.
-
arrival time structure of the time averaged Ambient Noise cross correlation function in an oceanic waveguide
Journal of the Acoustical Society of America, 2005Co-Authors: Karim G Sabra, Philippe Roux, W A KupermanAbstract:Coherent deterministic arrival times can be extracted from the derivative of the time-averaged Ambient Noise cross-correlation function between two receivers. These coherent arrival times are related to those of the time-domain Green’s function between these two receivers and have been observed experimentally in various environments and frequency range of interest (e.g., in ultrasonics, seismology, or underwater acoustics). This nonintuitive result can be demonstrated based on a simple time-domain image formulation of the Noise cross-correlation function, for a uniform distribution of Noise sources in a Pekeris waveguide. This image formulation determines the influence of the Noise-source distribution (in range and depth) as well as the dependence on the receiver bandwidth for the arrival-time structure of the derivative of the cross-correlation function. These results are compared with previously derived formulations of the Ambient Noise cross-correlation function. Practical implications of these results...
-
arrival time structure of the time averaged Ambient Noise cross correlation function in an oceanic waveguide
Journal of the Acoustical Society of America, 2005Co-Authors: Karim G Sabra, Philippe Roux, W A KupermanAbstract:Coherent deterministic arrival times can be extracted from the derivative of the time-averaged Ambient Noise cross-correlation function between two receivers. These coherent arrival times are related to those of the time-domain Green’s function between these two receivers and have been observed experimentally in various environments and frequency range of interest (e.g., in ultrasonics, seismology, or underwater acoustics). This nonintuitive result can be demonstrated based on a simple time-domain image formulation of the Noise cross-correlation function, for a uniform distribution of Noise sources in a Pekeris waveguide. This image formulation determines the influence of the Noise-source distribution (in range and depth) as well as the dependence on the receiver bandwidth for the arrival-time structure of the derivative of the cross-correlation function. These results are compared with previously derived formulations of the Ambient Noise cross-correlation function. Practical implications of these results for sea experiments are also discussed.
-
Ambient Noise cross correlation in free space theoretical approach
Journal of the Acoustical Society of America, 2005Co-Authors: Philippe Roux, Karim G Sabra, W A Kuperman, Andre RouxAbstract:It has been experimentally demonstrated that the Green’s function between two points could be recovered using the cross-correlation function of the Ambient Noise measured at these two points. This paper investigates the theory behind this result in the simple case of a homogeneous medium with attenuation.
Karim G Sabra - One of the best experts on this subject based on the ideXlab platform.
-
emergence rate of the time domain green s function from the Ambient Noise cross correlation function
Journal of the Acoustical Society of America, 2005Co-Authors: Karim G Sabra, Philippe Roux, W A KupermanAbstract:It has been demonstrated experimentally and theoretically that an estimate of the Green’s function between two receivers can be obtained from the time derivative of the long‐time average cross correlation of Ambient Noise between these two receivers. The emergence rate of these deterministic coherent arrival times of the cross‐correlation function (i.e., the Green’s function estimate) from the recordings of an isotropic distribution of random Noise sources is derived by evaluating the amplitude of the variance of the cross‐correlation function. The knowledge of the emergence rate of NCF is essential for practical applications. To the first order, the variance is equal to the ratio of the product of the recorded energy by both receivers and the time–bandwidth product of the recordings. The variance of the time derivative of the correlation function is shown to have a similar dependency. These simple analytic formulas show a good agreement with the variance determined experimentally for the correlation of ocean Ambient Noise recorded in shallow water at a depth of 21 m, in the frequency band [300–530 Hz] for receiver separation up to 28 m and averaging time from 1 to 33 min.
-
using ocean Ambient Noise for array self localization and self synchronization
IEEE Journal of Oceanic Engineering, 2005Co-Authors: Karim G Sabra, Philippe Roux, Aaron Thode, Gerald L Dspain, W S Hodgkiss, W A KupermanAbstract:Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged Ambient Noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of Ambient Noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source.
-
arrival time structure of the time averaged Ambient Noise cross correlation function in an oceanic waveguide
Journal of the Acoustical Society of America, 2005Co-Authors: Karim G Sabra, Philippe Roux, W A KupermanAbstract:Coherent deterministic arrival times can be extracted from the derivative of the time-averaged Ambient Noise cross-correlation function between two receivers. These coherent arrival times are related to those of the time-domain Green’s function between these two receivers and have been observed experimentally in various environments and frequency range of interest (e.g., in ultrasonics, seismology, or underwater acoustics). This nonintuitive result can be demonstrated based on a simple time-domain image formulation of the Noise cross-correlation function, for a uniform distribution of Noise sources in a Pekeris waveguide. This image formulation determines the influence of the Noise-source distribution (in range and depth) as well as the dependence on the receiver bandwidth for the arrival-time structure of the derivative of the cross-correlation function. These results are compared with previously derived formulations of the Ambient Noise cross-correlation function. Practical implications of these results...
-
arrival time structure of the time averaged Ambient Noise cross correlation function in an oceanic waveguide
Journal of the Acoustical Society of America, 2005Co-Authors: Karim G Sabra, Philippe Roux, W A KupermanAbstract:Coherent deterministic arrival times can be extracted from the derivative of the time-averaged Ambient Noise cross-correlation function between two receivers. These coherent arrival times are related to those of the time-domain Green’s function between these two receivers and have been observed experimentally in various environments and frequency range of interest (e.g., in ultrasonics, seismology, or underwater acoustics). This nonintuitive result can be demonstrated based on a simple time-domain image formulation of the Noise cross-correlation function, for a uniform distribution of Noise sources in a Pekeris waveguide. This image formulation determines the influence of the Noise-source distribution (in range and depth) as well as the dependence on the receiver bandwidth for the arrival-time structure of the derivative of the cross-correlation function. These results are compared with previously derived formulations of the Ambient Noise cross-correlation function. Practical implications of these results for sea experiments are also discussed.
-
Ambient Noise cross correlation in free space theoretical approach
Journal of the Acoustical Society of America, 2005Co-Authors: Philippe Roux, Karim G Sabra, W A Kuperman, Andre RouxAbstract:It has been experimentally demonstrated that the Green’s function between two points could be recovered using the cross-correlation function of the Ambient Noise measured at these two points. This paper investigates the theory behind this result in the simple case of a homogeneous medium with attenuation.
Fan Chi Lin - One of the best experts on this subject based on the ideXlab platform.
-
amplification and attenuation across usarray using Ambient Noise wavefront tracking
Journal of Geophysical Research, 2017Co-Authors: D C Bowden, Victor C Tsai, Fan Chi LinAbstract:As seismic traveltime tomography continues to be refined using data from the vast USArray data set, it is advantageous to also exploit the amplitude information carried by seismic waves. We use Ambient Noise cross correlation to make observations of surface wave amplification and attenuation at shorter periods (8–32 s) than can be observed with only traditional teleseismic earthquake sources. We show that the wavefront tracking approach can be successfully applied to Ambient Noise correlations, yielding results quite similar to those from earthquake observations at periods of overlap. This consistency indicates that the wavefront tracking approach is viable for use with Ambient Noise correlations, despite concerns of the inhomogeneous and unknown distribution of Noise sources. The resulting amplification and attenuation maps correlate well with known tectonic and crustal structure; at the shortest periods, our amplification and attenuation maps correlate well with surface geology and known sedimentary basins, while our longest period amplitudes are controlled by crustal thickness and begin to probe upper mantle materials. These amplification and attenuation observations are sensitive to crustal materials in different ways than traveltime observations and may be used to better constrain temperature or density variations. We also value them as an independent means of describing the lateral variability of observed Rayleigh wave amplitudes without the need for 3-D tomographic inversions.
-
Ambient Noise tomography with a large seismic array
Comptes Rendus Geoscience, 2011Co-Authors: Michael H Ritzwoller, Fan Chi Lin, Weisen ShenAbstract:Abstract The emergence of large-scale arrays of seismometers across several continents presents the opportunity to image the Earth's structure at unprecedented resolution, but methods must be developed to exploit the capabilities of these deployments. The capabilities and limitations of a method called “eikonal tomography” applied to Ambient Noise data are discussed here. In this method, surface wave wavefronts are tracked across an array and the gradient of the travel time field produces estimates of phase slowness and propagation direction. Application data from more than 1000 stations from EarthScope USArray in the central and western US and new Rayleigh wave isotropic and anisotropic phase velocity maps are presented together with an isotropic and azimuthally anisotropic 3D Vs model of the crust and uppermost mantle. As a ray theoretic method, eikonal tomography models bent rays but not other wavefield complexities. We present evidence, based on the systematics of an observed 1ψ component of anisotropy that we interpret as anisotropic bias caused by backscattering near an observing station, that finite frequency phenomena can be ignored in Ambient Noise tomography at periods shorter than ∼ 40 to 50 s. At longer periods a higher order term based on wavefront amplitudes or finite frequency sensitivity kernels must be introduced if the amplitude of isotropic anomalies and the amplitude and fast-axis direction of azimuthal anisotropy are to be determined accurately.
-
on the reliability of attenuation measurements from Ambient Noise cross correlations
Geophysical Research Letters, 2011Co-Authors: Fan Chi Lin, Michael H Ritzwoller, Weisen ShenAbstract:[1] We compare spatially averaged Rayleigh wave attenuation between 10 and 18 sec period observed on the symmetric component of Ambient Noise cross-correlations with regional seismic event measurements observed by the USArray Transportable Array across the western US. The Ambient Noise attenuation measurements are shown to be consistent with attenuation observed following an earthquake in Nevada and a mining blast in Wyoming. We demonstrate that common Ambient Noise data processing procedures such as temporal normalization and spectral whitening can be retained as long as the amplitudes of the cross-correlations are corrected for (1) the duration of the Ambient Noise cross-correlation, (2) geometrical spreading, and (3) the azimuthal variation in the strength of Ambient Noise sources. Correction for time-series length can be achieved accurately by dividing the empirical Green's function by the squared root-mean-squared (rms) amplitude of the trailing Noise. These results provide strong justification for the ability to constrain seismic attenuation using Ambient Noise. However, further study of the expected asymmetry in attenuation for waves approaching (incoming) or receding from (outgoing) a central station is needed to understand the effect of uneven Noise source distribution prior to estimation of local variations in attenuation.
-
Ambient Noise rayleigh wave tomography of new zealand
AGUFM, 2007Co-Authors: Fan Chi Lin, Michael H Ritzwoller, John Townend, Stephen Bannister, Martha K SavageAbstract:SUMMARY We present the first New Zealand-wide study of surface wave dispersion, using Ambient Noise observed at 42 broad-band stations in the national seismic network (GeoNet) and the Global Seismic Network (GSN). Year-long vertical-component time-series recorded between 2005 April 1 and 2006 March 31 have been correlated with one another to yield estimated fundamental mode Rayleigh wave Green’s functions. We filter these Green’s functions to compute Rayleigh wave group dispersion curves at periods of 5‐50 s, using a phase-matched filter, frequency‐time analysis technique. The uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3-month stacks. After selecting the highest quality dispersion curve measurements, we compute group velocity maps from 7 to 25 s period. These maps, and 1-D shear wave velocity models at four selected locations, exhibit clear correlations with major geological structures, including the Taranaki and Canterbury Basins, the Hikurangi accretionary prism, and previously reported basement terrane boundaries.
Lapo Boschi - One of the best experts on this subject based on the ideXlab platform.
-
On seismic Ambient Noise cross-correlation and surface-wave attenuation
Geophysical Journal International, 2019Co-Authors: Lapo Boschi, Fabrizio Magrini, Fabio Cammarano, Mark Van Der MeijdeAbstract:We derive a theoretical relationship between the cross correlation of Ambient Rayleigh waves (seismic Ambient Noise) and the attenuation parameter α associated with Rayleigh-wave propagation. In particular, we derive a mathematical expression for the multiplicative factor relating normalized cross correlation to the Rayleigh-wave Green’s function. Based on this expression, we formulate an inverse problem to determine α from cross correlations of recorded Ambient signal. We conduct a preliminary application of our algorithm to a relatively small instrument array, conveniently deployed on an island. In our setup, the mentioned multiplicative factor has values of about 2.5–3, which, if neglected, could result in a significant underestimate of α. We find that our inferred values of α are reasonable, in comparison with independently obtained estimates found in the literature. Allowing α to vary with respect to frequency results in a reduction of misfit between observed and predicted cross correlations.
-
high resolution rayleigh wave velocity maps of central europe from a dense Ambient Noise data set
Geophysical Journal International, 2012Co-Authors: Julie Verbeke, Lapo Boschi, Laurent Stehly, E Kissling, Alberto MicheliniAbstract:SUMMARY We present a new database of surface wave group and phase-velocity dispersion curves derived from seismic Ambient Noise, cross-correlating continuous seismic recordings from the Swiss Network, the German Regional Seismological Network (GRSN), the Italian national broad-band network operated by the Istituto Nazionale di Geosica e Vulcanologia (INGV). To increase the aperture of the station array, additional measurements from the Mediterranean Very Broad-band Seismographic Network (MedNet), the Austrian Central Institute for Meteorology and Geodynamics (ZAMG), the French, Bulgarian, Hungarian, Romanian and Greek stations obtained through Orfeus are also included. The Ambient Noise, we are using to assemble our database, was recorded at the above-mentioned stations between 2006 January and 2006 December. Correlating continuous signal recorded at pairs of stations, allows to extract coherent surface wave signal travelling between the two stations. Usually the Ambient-Noise cross-correlation technique allows to have informations at periods of 30 s or shorter. By expanding the database of Noise correlations, we seek to increase the resolution of the central Europe crustal model. We invert the resulting data sets of group and phase velocities associated with 8–35 s Rayleigh waves, to determine 2-D group and phase-velocity maps of the European region. Inversions are conducted by means of a 2-D linearized tomographic inversion algorithm. The generally good agreement of our models with previous studies and good correlation of well-resolved velocity anomalies with geological features, such as sedimentary basins, crustal roots and mountain ranges, documents the effectiveness of our approach.