Rayleigh-Wave Multicomponent Crosscorrelation-Based Estimation of Phase Velocities and Ambient Seismic Source Distributions

2020 ◽  
Author(s):  
Zongbo Xu
Keyword(s):  
Rayleigh Waves ◽  
Field Data ◽  
Seismic Source ◽  
Coda Waves ◽  
Seismic Sources ◽  
Subsurface Structure ◽  
Phase Velocities ◽  
Wave Phase ◽  
Multicomponent Data ◽  
Seismic Wavefield

One uses seismic interferometry (SI) to recover Green's functions (i.e. impulse response) from ambient seismic recordings and estimate surface-wave phase velocities to investigate subsurface structure. This method has been commonly used in the last 20 years because this method only utilizes ambient seismic recordings from seismic stations/sensors and does not rely on traditional seismic sources (e.g. earthquakes or active sources). SI assumes that the ambient seismic wavefield is isotropic, but this assumption is rarely met in practice. We demonstrate that, with linear-array spatial sampling of an anisotropic ambient seismic wavefield, SI provides a better estimate of Rayleigh-wave phase velocities than another commonly used ambient seismic method, the refraction microtremor (ReMi) method. However, even SI does not work in some extreme cases, such as when the out-of-line sources are stronger than the inline sources. This is because the recovered Green's functions and surface-wave phase velocity estimations from SI are biased due to the anisotropic wavefield. Thus, we propose to use multicomponent data to mitigate this bias. The multicomponent data are vertical (Z) and radial (R) components, where the R direction is parallel to a line or great circle path between two sensors. The multicomponent data can deal with the extreme anisotropic source cases, because the R component is more sensitive to the in-line sources than the out-of-line sources, while the Z component possesses a constant sensitivity to sources in all directions. Estimation of source distributions (i.e. locations and strengths) can aid correction of the bias in SI results, as well as enable the study of natural ambient seismic sources (e.g. microseism). We use multicomponent seismic data to estimate ambient seismic source distributions using full-waveform inversion. We demonstrate that the multicomponent data can better constrain the inversion than only the Z component data, due to the different source sensitivities between the Z and R components. When applying the inversion to field data, we propose a general workflow which is applicable for different field scales and includes vertical and multicomponent data. We demonstrate the workflow with a field data example from the CO2 degassing in Harstouˇsov, Czech Republic. We also apply the workflow to the seismic recordings in Antarctica during February 2010 and estimate the primary microseism source distributions. The SI results include both direct and coda waves. While using the direct waves in investigating subsurface structure and estimating source distributions, one can utilize the coda waves to monitor small changes in the subsurface. The coda waves include multiply-scattered body and surface waves. The two types of waves possess different spatial sensitivities to subsurface changes and interact each other through scattering. We present a Monte Carlo simulation to demonstrate the interaction in an elastic homogeneous media. In the simulation, we incorporate the scattering process between body and Rayleigh waves and the eigenfunctions of Rayleigh waves. This is a first step towards a complete modelling of multiply-scattered body and surface waves in elastic media.

Measurements of Rayleigh-wave phase velocities in Nevada: Implications for explosion sources and the Massachusetts Mountain earthquake

1982 ◽  
Vol 72 (4) ◽  
pp. 1329-1349
Author(s):  
H. J. Patton
Keyword(s):  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Moment Tensor ◽  
Test Site ◽  
P Wave ◽  
Stress Axis ◽  
Phase Velocities ◽  
Wave Phase ◽  
Single Station ◽  
Source Phase

abstract Single-station measurements of Rayleigh-wave phase velocity are obtained for paths between the Nevada Test Site and the Livermore broadband regional stations. Nuclear underground explosions detonated in Yucca Valley were the sources of the Rayleigh waves. The source phase φs required by the single-station method is calculated for an explosion source by assuming a spherically symmetric point source with step-function time dependence. The phase velocities are used to analyze the Rayleigh waves of the Massachusetts Mountain earthquake of 5 August 1971. Measured values of source phase for this earthquake are consistent with the focal mechanism determined from P-wave first-motion data (Fischer et al., 1972). A moment-tensor inversion of the Rayleigh-wave spectra for a 3-km-deep source gives a horizontal, least-compressive stress axis oriented N63°W and a seismic moment of 5.5 × 1022 dyne-cm. The general agreement between the results of the P-wave study of Fischer et al. (1972) and this study supports the measurements of phase velocities and, in turn, the explosion source model used to calculate φs.

The Wolfspar experience with low-frequency seismic source field data: Motivation, processing, and implications

2022 ◽  
Vol 41 (1) ◽  
pp. 9-18
Author(s):  
Andrew Brenders ◽  
Joe Dellinger ◽  
Imtiaz Ahmed ◽  
Esteban Díaz ◽  
Mariana Gherasim ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Seismic Data ◽  
Field Data ◽  
Model Building ◽  
Low Frequency ◽  
Seismic Source ◽  
Velocity Model ◽  
Seismic Sources ◽  
Velocity Model Building ◽  
Air Gun

The promise of fully automatic full-waveform inversion (FWI) — a (seismic) data-driven velocity model building process — has proven elusive in complex geologic settings, with impactful examples using field data unavailable until recently. In 2015, success with FWI at the Atlantis Field in the U.S. Gulf of Mexico demonstrated that semiautomatic velocity model building is possible, but it also raised the question of what more might be possible if seismic data tailor-made for FWI were available (e.g., with increased source-receiver offsets and bespoke low-frequency seismic sources). Motivated by the initial value case for FWI in settings such as the Gulf of Mexico, beginning in 2007 and continuing into 2021 BP designed, built, and field tested Wolfspar, an ultralow-frequency seismic source designed to produce seismic data tailor-made for FWI. A 3D field trial of Wolfspar was conducted over the Mad Dog Field in the Gulf of Mexico in 2017–2018. Low-frequency source (LFS) data were shot on a sparse grid (280 m inline, 2 to 4 km crossline) and recorded into ocean-bottom nodes simultaneously with air gun sources shooting on a conventional dense grid (50 m inline, 50 m crossline). Using the LFS data with FWI to improve the velocity model for imaging produced only incremental uplift in the subsalt image of the reservoir, albeit with image improvements at depths greater than 25,000 ft (approximately 7620 m). To better understand this, reprocessing and further analyses were conducted. We found that (1) the LFS achieved its design signal-to-noise ratio (S/N) goals over its frequency range; (2) the wave-extrapolation and imaging operators built into FWI and migration are very effective at suppressing low-frequency noise, so that densely sampled air gun data with a low S/N can still produce useable model updates with low frequencies; and (3) data density becomes less important at wider offsets. These results may have significant implications for future acquisition designs with low-frequency seismic sources going forward.

Wave propagation and subsurface velocity structure at the Virgo gravitational wave detector (Italy)

2020 ◽  
Author(s):  
Gilberto Saccorotti ◽  
Sonja Gaviano ◽  
Carlo Giunchi ◽  
Irene Fiori ◽  
Soumen Koley ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Phase Velocity ◽  
Rayleigh Wave ◽  
Gravitational Wave ◽  
Rayleigh Waves ◽  
Velocity Structure ◽  
Band Frequency ◽  
Frequency Bands ◽  
Phase Velocities ◽  
Wave Phase

<p>The performances and sensitivity of gravitational wave (GW) detectors are significantly affected by the seismic environment. In particular, the seismic displacements and density fluctuations of the ground due to seismic-wave propagation introduce noise in the detector output signal; this noise is referred to as gravity-gradient noise, or Newtonian Noise (NN). The development of effective strategies for mitigating the effects of NN requires, therefore, a thorough assessment of seismic wavefields and medium properties at and around the GW detector. In this work, we investigate wave propagation and the subsurface velocity structure at the Virgo GW detector (Italy), using data from a temporary, 50-element array of vertical seismometers. In particular, we analyze the recordings from the catastrophic Mw=6.2 earthquake which struck Central Italy on August 24, 2016, and six of the following aftershocks.  The general kinematic properties of the earthquake wavefields are retrieved from the application of a broad-band, frequency-domain beam-forming technique. This method allows measuring the propagation direction and horizontal slowness of the incoming signal; it is applied to short time windows sliding along the array seismograms, using different subarrays whose aperture was selected in order to match different frequency bands. For the Rayleigh-wave arrivals, velocities range between 0.5 km/s and 5 km/s, suggesting the interference of different wave types and/or multiple propagation modes. For those same time intervals, the propagation directions are scattered throughout a wide angular range, indicating marked propagation effects associated with geological and topographical complexities. These results suggest that deterministic methods are not appropriate for estimating Rayleigh waves phase velocities. By assuming that the gradient of the displacement is constant throughout the array, we then attempt the estimation of ground rotations around an axis parallel to the surface (tilt), which is in turn linearly related to the phase velocity of Rayleigh waves. We calculate the ground tilt over subsequent, narrow frequency bands. Individual frequency intervals are investigated using sub-arrays with aperture specifically tailored to the frequency (wavelength) under examination. From the scaled average of the velocity-to-rotation ratios, we obtain estimates of the Rayleigh-wave phase velocities, which finally allow computing a dispersion relationship. Due to their diffusive nature, earthquake coda waves are ideally suited for the application of Aki’s autocorrelation method (SPAC). We use SPAC and a non-linear fitting of correlation functions to derive the dispersion properties of Rayleigh wave for all the 1225 independent inter-station paths. The array-averaged SPAC dispersion is consistent with that inferred from ground rotations, and with previous estimates from seismic noise analysis.  Using both a semi-analytical and perturbational approaches, this averaged dispersion is inverted to obtain a shear wave velocity profile down to ~1000m depth. Finally, we also perform an inversion of the frequency-dependent travel times associated with individual station pairs to obtain 2-D, Rayleigh wave phase velocity maps spanning the 0.5-3Hz frequency interval. </p>

On the use of a seismic sensor as a seismic source

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. A39-A43
Author(s):  
David F. Halliday ◽  
Taiwo Fawumi ◽  
Johan O. A. Robertsson ◽  
Ed Kragh
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Group Velocity ◽  
Seismic Source ◽  
Body Waves ◽  
Seismic Sources ◽  
Wave Group ◽  
Seismic Sensors ◽  
Voltage Signal ◽  
Seismic Wavefield

We investigated the use of seismic sensors as small seismic sources. A voltage signal is applied to a geophone that forces the mass within the geophone to move. The movement of the mass generates a seismic wavefield that was recorded with an array of geophones operating in the conventional sense. We observed higher-frequency (25 Hz and above) surface and body waves propagating from the geophone source at offsets of 10 s of meters. We further found that the surface waves emitted from geophone sources can be used to generate a surface-wave group velocity map. We discuss potential developments and future applications.

Love-Wave Phase-Velocity Estimation from Array-Based Rotational Motion Microtremor

2020 ◽  
Author(s):  
Kunikazu Yoshida ◽  
Hirotoshi Uebayashi
Keyword(s):  
Phase Velocity ◽  
Rayleigh Waves ◽  
Love Wave ◽  
Velocity Estimation ◽  
Love Waves ◽  
Phase Velocities ◽  
Wave Phase ◽  
Wave Phase Velocity ◽  
Spatial Derivatives ◽  
Rotational Motions

ABSTRACT The most popular array-based microtremor survey methods estimate velocity structures from the phase velocities of Rayleigh waves. Using the phase velocity of Love waves improves the resolution of inverted velocity models. In this study, we present a method to estimate the phase velocity of Love waves using rotational array data derived from the horizontal component of microtremors observed using an ordinal nested triangular array. We obtained discretized spatial derivatives from a first-order Taylor series expansion to calculate rotational motions from observed array seismograms. Rotational motions were obtained from a triangular subarray consisting of three receivers using discretized spatial derivatives. Four rotational-motion time histories were calculated from different triangular subarrays in the nested triangular arrays. Phase velocities were estimated from the array of the four rotational motions. We applied the proposed Love-wave phase-velocity estimation technique to observed array microtremor data obtained using a nested triangular array with radii of 25 and 50 m located at the Institute for Integrated Radiation and Nuclear Science, Kyoto University. The phase velocities of rotational and vertical motions were estimated from the observed data, and results showed that the former were smaller than those of the latter. The observed phase velocities obtained from vertical and rotational components agreed well with the theoretical Rayleigh- and Love-wave phase velocities calculated from the velocity structure model derived from nearby PS logs. To show the ability of the rotation to obtain Love wave, we estimated apparent phase velocities from north–south or east–west components. The apparent velocities resulted in between the theoretical velocities of Rayleigh and Love waves. This result indicates that the calculated rotation effectively derived the Love waves from a combination of Love and Rayleigh waves.

Geographical interpretation of measurements of average phase velocities of surface waves over great circular and great semi-circular paths

1964 ◽  
Vol 54 (2) ◽  
pp. 571-610
Author(s):  
George E. Backus
Keyword(s):  
Spherical Harmonics ◽  
Rayleigh Waves ◽  
Seismic Station ◽  
Great Circle ◽  
Explicit Formulas ◽  
Phase Velocities ◽  
Rapid Accumulation ◽  
Generalized Spherical Harmonics ◽  
Geographical Position ◽  
The Difference

ABSTRACT If the averages of the reciprocal phase velocity c−1 of a given Rayleigh or Love mode over various great circular or great semicircular paths are known, information can be extracted about how c−1 varies with geographical position. Assuming that geometrical optics is applicable, it is shown that if c−1 is isotropic its great circular averages determine only the sum of the values of c−1 at antipodal points and not their difference. The great semicircular averages determine the difference as well. If c−1 is anisotropic through any cause other than the earth's rotation, even great semicircular averages do not determine c−1 completely. Rotation has negligible effect on Love waves, and if it is the only anisotropy present its effect on Rayleigh waves can be measured and removed by comparing the averages of c−1 for the two directions of travel around any great circle not intersecting the poles of rotation. Only great circular and great semicircular paths are considered because every earthquake produces two averages of c−1 over such paths for each seismic station. No other paths permit such rapid accumulation of data when the azimuthal variations of the earthquakes' radiation patterns are unknown. Expansion of the data in generalized spherical harmonics circumvents the fact that the explicit formulas for c−1 in terms of its great circular or great semicircular integrals require differentiation of the data. Formulas are given for calculating the generalized spherical harmonics numerically.

Surface-Wave Simulation for the Continuously Moving Seismic Sources

2021 ◽  
Author(s):  
Yuefeng Yan ◽  
Chengyu Sun ◽  
Tengfei Lin ◽  
Jiao Wang ◽  
Jidong Yang ◽  
...  
Keyword(s):  
Rayleigh Waves ◽  
Frequency Dispersion ◽  
Dispersion Curves ◽  
Velocity Estimation ◽  
Surface Velocity ◽  
Seismic Sources ◽  
Near Surface ◽  
Moving Source ◽  
Source Data ◽  
Doppler Effects

Abstract In exploration and earthquake seismology, most sources used in subsurface structure imaging and rock property estimation are fixed in certain positions. Continuously moving seismic sources, such as vehicles and the metro, are one kind of important passive sources in ambient noise research. Commonly, seismic data acquisition and processing for moving sources are based on the assumption of simple point passive sources, and the dispersion curve inversion is applied to constrain near-surface velocity. This workflow neglects the Doppler effects. Considering the continuously moving properties of the sources, we first derive the analytical solution for the Rayleigh waves excited by heavy vehicles and then analyze their Doppler effects and dispersion curves. We observe that the moving source data have the Doppler effect when compared with the changes in the frequency of the source intensity, but this effect does not affect the frequency dispersion of Rayleigh waves. The dispersion curves computed for moving source records are consistent with the analytical dispersion solutions, which provide a theoretical foundation for velocity estimation using moving source data.

scholarly journals Detailed shallow structure seismic refraction investigation, with the application of different processing techniques

2001 ◽  
Vol 34 (4) ◽  
pp. 1309
Author(s):  
Τ. ΠΑΠΑΔΟΠΟΥΛΟΣ ◽  
Π. ΚΑΜΠΟΥΡΗΣ ◽  
Ι. ΑΛΕΞΟΠΟΥΛΟΣ
Keyword(s):  
Seismic Velocity ◽  
Seismic Refraction ◽  
Seismic Sources ◽  
Subsurface Structure ◽  
Seismic Refraction Data ◽  
Processing Techniques ◽  
National Road ◽  
Gradual Variation ◽  
Refraction Data ◽  
Shallow Structure

A comparative study of conventional and modern processing techniques of seismic refraction data is examined in this paper, for shallow structure investigation in the framework of a geotechnical research. The techniques used here were applied for the detection of narrow and low seismic velocity zones along the bedrock in the 10.5th Km of the new national road Igoumenitsa-Ioannina. The results were comparable and only slight deviations were observed due mainly to different algorithm procedures applied on data and the resolution provided by each technique. It is pointed out that the non linear tomography seismic refraction technique, overcomes the conventional ones since by increasing the number of seismic sources and considering the gradual variation of seismic velocity with depth, a better resolution and image reconstruction for the subsurface structure is obtained.

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