Detection of interfering Rayleigh waves at LASA

1971 ◽  
Vol 61 (4) ◽  
pp. 807-849
Author(s):  
Jack Capon ◽  
Jack F. Evernden
Keyword(s):  
Rayleigh Wave ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Detection Method ◽  
Wave Number ◽  
Continental Margins ◽  
S Waves ◽  
Analysis Technique ◽  
Multiple Paths ◽  
Back Azimuth

abstract The problem of detecting one Rayleigh wave in the presence of the coda of another larger Rayleigh wave is considered. A detection method is proposed in which a high-resolution, wave number analysis technique is applied to prefiltered data from the Large Aperture Seismic Array (LASA) to determine the direction of arrival of the 40-sec-period Rayleigh-wave group at the appropriate arrival time. The performance of this detection method is considered in great detail. A necessary concomitant of the study of the detection method is the determination of the phases which comprise the coda. It is shown that one component of the coda consists of fundamental-mode Rayleigh waves which propagate along multiple paths and may be caused by either reflections at continental margins or diffraction effects. As has been demonstrated many times, the coda is shown to consist also of fundamental-mode Rayleigh waves which have propagated around the Earth in the direction of the back azimuth. Multiply reflected P and S waves, which propagate primarily in the upper mantle, are detected easily.

Analysis of Rayleigh-wave multipath propagation at LASA

1970 ◽  
Vol 60 (5) ◽  
pp. 1701-1731 ◽  
Author(s):  
Jack Capon
Keyword(s):  
Rayleigh Waves ◽  
Multipath Propagation ◽  
Continental Margins ◽  
Period Range ◽  
Analysis Technique ◽  
High Resolution Analysis ◽  
Resolution Analysis ◽  
Propagation Paths ◽  
Using Data ◽  
Almost All

Abstract An investigation has been made of the multipath propagation of Rayleigh waves by using data obtained from the large aperture seismic array (LASA). The use of the LASA in conjunction with a high-resolution analysis technique provides a greater angular resolution and accuracy than was previously possible for the analysis of the multipath propagation. Measurements have been made of this phenomenon for the Rayleigh waves of 26 events distributed at various azimuths and distances from LASA. On the bas of these measurements reasonably good conjectures are made concerning the actual propagation paths for groups in the 20- to 40-sec period range. It is shown that in almost all cases these propagation paths can be associated with refractions and reflections at the continental margins.

scholarly journals Using multicomponent ambient seismic noise cross-correlations to identify higher mode Rayleigh waves and improve dispersion measurements

2020 ◽  
Vol 222 (3) ◽  
pp. 1590-1605 ◽  
Author(s):  
Avinash Nayak ◽  
Clifford H Thurber
Keyword(s):  
Rayleigh Wave ◽  
Group Velocity ◽  
Particle Motion ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Vertical Plane ◽  
Ambient Seismic Noise ◽  
Cross Correlations ◽  
The Individual

SUMMARY Ambient seismic noise cross-correlation with three-component sensors yields a nine-component empirical Green's tensor, in which four components of the radial–vertical plane contain Rayleigh waves. We exploit the retrograde elliptical nature of particle motion of the fundamental mode Rayleigh wave to correct the phase of the four radial–vertical components and stack them to obtain an average fundamental mode Rayleigh-wave time-series. This technique can suppress incoherent noise and wave packets that do not follow the targeted elliptical particle motion. The same technique can be used to isolate the first higher mode Rayleigh wave that follows prograde elliptical particle motion. We first demonstrate the effectiveness of the method on synthetic waveforms and then apply it on noise cross-correlations computed in Central California. Using this method, we isolate 1st higher mode Rayleigh waves on noise cross-correlations in the Great Valley, California, which provides new phase velocity constraints for estimating velocity structure in the sedimentary basin. We also obtain improved estimates of fundamental mode Rayleigh-wave dispersion for surface-wave tomography. The waveforms stacked assuming retrograde particle motion return at least ∼20 per cent more group velocity dispersion measurements satisfying a minimum signal-to-noise ratio (SNR) criterion than the individual components for periods ∼4–18 s. For equivalent group velocity measurements, SNR for the stacked estimate of the fundamental mode Rayleigh wave is on average 40 per cent greater than that measured on the individual components at periods less than 10 s. The technique also provides an easy way to detect large errors in sensor orientation.

Higher-mode Rayleigh waves as an aid to seismic discrimination

1976 ◽  
Vol 66 (3) ◽  
pp. 827-841
Author(s):  
Donald W. Forsyth
Keyword(s):  
Rayleigh Wave ◽  
Central Asia ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Multipath Propagation ◽  
Focal Depth ◽  
Seismic Source ◽  
High Ratio ◽  
Reliable Estimate ◽  
Related Factors

abstract Long-period records of surface waves from earthquakes in central Asia are often complex, with rapid amplitude fluctuations and apparent multiple arrivals of energy of the same frequency. Comparison of records from closely spaced earthquakes shows that the complexity is not caused by multipath propagation, but is associated with the seismic source geometry. The multiple arrivals are higher-mode Rayleigh waves traveling with group velocities faster than the fundamental mode. A relatively high ratio of higher-mode to fundamental-mode energy can be produced when an unusual combination of source depth and focal mechanism leads to poor excitation of the fundamental-mode Rayleigh wave, in which case, the amplitude of the higher mode yields a more reliable estimate of the size of the event than the amplitude of the fundamental mode. Several anomalous events in central Asia, which are characterized by unusually low Ms : mb ratios and hence could be suspected to be nuclear explosions, are reclassified as earthquakes when the new, higher-mode scale, Mhs, is employed. The focal depth and mechanism of these anomalous events apparently causes poor excitation of the fundamental-mode Rayleigh wave without significantly affecting the amplitude of the higher mode. Elimination of these source-related factors from traditional Ms : mb discriminants is an essential tool for reliable discrimination between earthquakes and nuclear underground tests.

The propagation of short elastic surface waves on a slowly rotating earth

1962 ◽  
Vol 52 (4) ◽  
pp. 823-846
Author(s):  
G. E. Backus
Keyword(s):  
Angular Velocity ◽  
Rayleigh Wave ◽  
Half Space ◽  
Rayleigh Waves ◽  
Love Wave ◽  
Transversely Isotropic ◽  
Wave Number ◽  
Classical Particle ◽  
Wave Group ◽  
First Order

abstract The effects of slow rotation with angular velocity Ω on Love and Rayleigh waves with given horizontal wave vector k on a plane-layered, transversely isotropic half-space have been calculated to first order in Ω. The frequency of Love waves is unaffected by rotation, while the frequency of Rayleigh waves is increased by k−1R(k)Ω · (z^ × k) where z^ is the unit outward normal to the boundary of the half-space and R(k) is a dimensionless function of k, the length of k. R(k) lies between −1 and 1, and vanishes identically for a homogeneous, isotropic halfspace with Poisson ratio 14. The vertical and longitudinal particle motions in a Love wave do not vanish and are neither in phase nor in quadrature with the transverse motion. The transverse particle motion in a Rayleigh wave does not vanish and is neither in phase nor in quadrature with the vertical and longitudinal motions. It has been shown that a group of short, multicomponent waves on an anisotropic curved surface behaves like a classical particle, whose Hamiltonian is generated by the local dispersion relation and the curvilinear coordinates used to describe the surface. This extension of Hamilton's eikonal theory, together with the plane dispersion relations just derived, has been applied to Love and Rayleigh waves of given wave number k on a radially stratified, transversely isotropic sphere of radius a rotating slowly with angular velocity Ω. Correct to first order in Ω and (ak)−1, the trajectory of a Love wave group is unaffected by rotation, while the plane of the great circle trajectory of a Rayleigh wave group maintains its inclination to the axis of rotation and precesses about that axis with angular velocity (ak)−)R(k)Ω. Because of this precession, at a fixed seismograph the direction of arrival of 333 second mantle Rayleigh waves from a point impulsive source changes systematically by about 2R degrees after each circuit of the earth.

Methods to isolate retrograde and prograde Rayleigh-wave signals

2019 ◽  
Vol 219 (2) ◽  
pp. 975-994 ◽  
Author(s):  
Gabriel Gribler ◽  
T Dylan Mikesell
Keyword(s):  
Rayleigh Wave ◽  
Time Domain ◽  
Fundamental Mode ◽  
Poisson Ratio ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Low Frequencies ◽  
Retrograde Motion ◽  
Mode Identification ◽  
Time Frequency

SUMMARY Estimating shear wave velocity with depth from Rayleigh-wave dispersion data is limited by the accuracy of fundamental and higher mode identification and characterization. In many cases, the fundamental mode signal propagates exclusively in retrograde motion, while higher modes propagate in prograde motion. It has previously been shown that differences in particle motion can be identified with multicomponent recordings and used to separate prograde from retrograde signals. Here we explore the domain of existence of prograde motion of the fundamental mode, arising from a combination of two conditions: (1) a shallow, high-impedance contrast and (2) a high Poisson ratio material. We present solutions to isolate fundamental and higher mode signals using multicomponent recordings. Previously, a time-domain polarity mute was used with limited success due to the overlap in the time domain of fundamental and higher mode signals at low frequencies. We present several new approaches to overcome this low-frequency obstacle, all of which utilize the different particle motions of retrograde and prograde signals. First, the Hilbert transform is used to phase shift one component by 90° prior to summation or subtraction of the other component. This enhances either retrograde or prograde motion and can increase the mode amplitude. Secondly, we present a new time–frequency domain polarity mute to separate retrograde and prograde signals. We demonstrate these methods with synthetic and field data to highlight the improvements to dispersion images and the resulting dispersion curve extraction.

Quantification of Effects of Ridge and Valley Topography on the Rayleigh Wave Characteristics

2018 ◽  
Vol 12 (03) ◽  
pp. 1850007 ◽  
Author(s):  
J. P. Narayan ◽  
A. Kumar
Keyword(s):  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Large Scale ◽  
Research Work ◽  
Vertical Component ◽  
Staggered Grid ◽  
Long Span ◽  
Shape Ratio ◽  
Day By Day ◽  
Ridge And Valley

The effects of ridge and valley on the characteristics of Rayleigh waves are presented in this paper. The research work carried out has been stimulated by the day by day increase of long-span structures in the hilly areas which are largely affected by the spatial variability in ground motion caused by the high-frequency Rayleigh waves. The Rayleigh wave responses of the considered triangular and elliptical ridge and valley models were computed using a fourth-order accurate staggered-grid viscoelastic P-SV wave finite-difference (FD) program. The simulated results revealed very large amplification of the horizontal component and de-amplification of the vertical component of Rayleigh wave at the top of a triangular ridge and de-amplification of both the components at the base of the triangular valley. The observed amplification of both the components of Rayleigh wave in front of elliptical valley was larger than triangular valley models. A splitting of the Rayleigh wave wavelet was inferred after interaction with ridge and valley. It is concluded that the large-scale topography acts as a natural insulator for the surface waves and the insulating capacity of the valley is more than that of a ridge. This insulation phenomenon is arising due to the reflection, diffraction and splitting of the surface wave while moving across the topography. It is concluded that insulating potential of the topography for the Rayleigh waves largely depends on their shape and shape-ratio.

An algorithm for automated tsunami warning in French Polynesia based on mantle magnitudes

1989 ◽  
Vol 79 (4) ◽  
pp. 1177-1193
Author(s):  
Jacques Talandier ◽  
Emile A. Okal
Keyword(s):  
Rayleigh Wave ◽  
Seismic Moment ◽  
Rayleigh Waves ◽  
French Polynesia ◽  
Tsunami Warning ◽  
Period Range ◽  
Wave Duration ◽  
T Wave ◽  
The Moment ◽  
Historical References

Abstract We have developed a new magnitude scale, Mm, based on the measurement of mantle Rayleigh-wave energy in the 50 to 300 sec period range, and directly related to the seismic moment through Mm = log10M0 − 20. Measurements are taken on the first passage of Rayleigh waves, recorded on-scale on broadband instruments with adequate dynamical range. This allows estimation of the moment of an event within minutes of the arrival of the Rayleigh wave, and with a standard deviation of ±0.2 magnitude units. In turn, the knowledge of the seismic moment allows computation of an estimate of the high-seas amplitude of a range of expectable tsunami heights. The latter, combined with complementary data from T-wave duration and historical references, have been integrated into an automated procedure of tsunami warning by the Centre Polynésien de Prévention des Tsunamis (CPPT), in Papeete, Tahiti.

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.

Period equation for Rayleigh waves in a layer overlying a half space with a sinusoidal interface

1962 ◽  
Vol 52 (4) ◽  
pp. 807-822 ◽  
Author(s):  
John T. Kuo ◽  
John E. Nafe
Keyword(s):  
Wave Propagation ◽  
Boundary Conditions ◽  
Half Space ◽  
Rayleigh Waves ◽  
Wave Length ◽  
Linear Equations ◽  
Wave Number ◽  
Interface Plane ◽  
Period Equation ◽  
Phase And Group Velocities

abstract The problem of the Rayleigh wave propagation in a solid layer overlying a solid half space separated by a sinusoidal interface is investigated. The amplitude of the interface is assumed to be small in comparison to the average thickness of the layer or the wave length of the interface. Either by applying Rayleigh's approximate method or by perturbating the boundary conditions at the sinusoidal interface, plane wave solutions for the equations which satisfy the given boundary conditions are found to form a system of linear equations. These equations may be expressed in a determinant form. The period (or characteristic) equations for the first and second approximation of the wave number k are obtained. The phase and group velocities of Rayleigh waves in the present case depend upon both frequency and distance. At a given point on the surface, there is a local phase and local group velocity of Rayleigh waves that is independent of the direction of wave propagation.

Use of reciprocity theorem for obtaining Rayleigh wave radiation patterns

1966 ◽  
Vol 56 (4) ◽  
pp. 925-936 ◽  
Author(s):  
I. N. Gupta
Keyword(s):  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Three Dimensional ◽  
Reciprocity Theorem ◽  
Point Sources ◽  
Dimensional Case ◽  
Wave Radiation ◽  
Radiation Patterns ◽  
Homogeneous Half Space ◽  
Double Couple

abstract The reciprocity theorem is used to obtain Rayleigh wave radiation patterns from sources on the surface of or within an elastic semi-infinite medium. Nine elementary line sources first considered are: horizontal and vertical forces, horizontal and vertical double forces without moment, horizontal and vertical single couples, center of dilatation (two dimensional case), center of rotation, and double couple without moment. The results are extended to the three dimensional case of similar point sources in a homogeneous half space. Haskell's results for the radiation patterns of Rayleigh waves from a fault of arbitrary dip and direction of motion are reproduced in a much simpler manner. Numerical results on the effect of the depth of these sources on the Rayleigh wave amplitudes are shown for a solid having Poisson's ratio of 0.25.

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