scholarly journals How deep ocean-land coupling controls the generation of secondary microseism Love waves

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Florian Le Pape ◽  
David Craig ◽  
Christopher J. Bean
Keyword(s):  
Rayleigh Waves ◽  
Love Wave ◽  
Deep Ocean ◽  
Sedimentary Basins ◽  
Order Effect ◽  
Wave Climate ◽  
Love Waves ◽  
Ocean Wave ◽  
Propagation Path ◽  
Wave Hindcast

AbstractWind driven ocean wave-wave interactions produce continuous Earth vibrations at the seafloor called secondary microseisms. While the origin of associated Rayleigh waves is well understood, there is currently no quantified explanation for the existence of Love waves in the most energetic region of the microseism spectrum (3–10 s). Here, using terrestrial seismic arrays and 3D synthetic acoustic-elastic simulations combined with ocean wave hindcast data, we demonstrate that, observed from land, our general understanding of Rayleigh and Love wave microseism sources is significantly impacted by 3D propagation path effects. We show that while Rayleigh to Love wave conversions occur along the microseism path, Love waves predominantly originate from steep subsurface geological interfaces and bathymetry, directly below the ocean source that couples to the solid Earth. We conclude that, in contrast to Rayleigh waves, microseism Love waves observed on land do not directly relate to the ocean wave climate but are significantly modulated by continental margin morphologies, with a first order effect from sedimentary basins. Hence, they yield rich spatio-temporal information about ocean-land coupling in deep water.

Wave-equation dispersion inversion of Love waves

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. R693-R705 ◽  
Author(s):  
Jing Li ◽  
Sherif Hanafy ◽  
Zhaolun Liu ◽  
Gerard T. Schuster
Keyword(s):  
Wave Equation ◽  
Wave Velocity ◽  
Rayleigh Waves ◽  
Love Wave ◽  
Field Data ◽  
Wave Dispersion ◽  
Dispersion Curves ◽  
Love Waves ◽  
S Wave ◽  
Love Wave Dispersion

We present a theory for wave-equation inversion of Love-wave dispersion curves, in which the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. Similar to inversion of Rayleigh-wave dispersion curves, the complicated Love-wave arrivals in traces are skeletonized as simpler data, namely, the picked dispersion curves in the [Formula: see text] domain. Numerical solutions to the SH-wave equation and an iterative optimization method are then used to invert these dispersion curves for the S-wave velocity model. This procedure, denoted as wave-equation dispersion inversion of Love waves (LWD), does not require the assumption of a layered model or smooth velocity variations, and it is less prone to the cycle-skipping problems of full-waveform inversion. We demonstrate with synthetic and field data examples that LWD can accurately reconstruct the S-wave velocity distribution in a laterally heterogeneous medium. Compared with Rayleigh waves, inversion of the Love-wave dispersion curves empirically exhibits better convergence properties because they are completely insensitive to the P-velocity variations. In addition, Love-wave dispersion curves for our examples are simpler than those for Rayleigh waves, and they are easier to pick in our field data with a low signal-to-noise ratio.

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.

scholarly journals Local Coupling and Conversion of Surface Waves due to Earth’s Rotation. Part 1: Theory

2020 ◽  
Author(s):  
Roel Snieder ◽  
Christoph Sens-Schönfelder
Keyword(s):  
Rayleigh Wave ◽  
Surface Waves ◽  
Coriolis Force ◽  
Rayleigh Waves ◽  
Love Wave ◽  
Mode Conversion ◽  
Love Waves ◽  
Earth’S Rotation ◽  
Earth's Rotation ◽  
Phase Velocities

Summary Earth’s rotation affects wave propagation to first order in the rotation through the Coriolis force. The imprint of rotation on wave motion has been accounted for in normal mode theory. By extending the theory to propagating surface waves we account for the imprint of rotation as a function of propagation distance. We describe the change in phase velocity and polarization, and the mode conversion of surface waves by Earth’s rotation by extending the formalism of Kennett (1984) for surface wave mode conversion due to lateral heterogeneity to include the Coriolis force. The wavenumber of Rayleigh waves is changed by Earth’s rotation and Rayleigh waves acquire a transverse component. The wavenumber of Love waves in not affected by Earth’s rotation, but Love waves acquire a small additional Rayleigh wave polarization. In contrast to different Rayleigh wave modes, different Love wave modes are not coupled by Earth’s rotation. We show that the backscattering of surface waves by Earth’s rotation is weak. The coupling between Rayleigh waves and Love waves is strong when the phase velocities of these modes are close. In that regime of resonant coupling, Earth’s rotation causes the difference between the Rayleigh wave and Love wave phase velocities that are coupled to increase through the process of level-repulsion.

scholarly journals Excitation of mantle Love waves and definition of mantle wave magnitude

1969 ◽  
Vol 59 (2) ◽  
pp. 923-933
Author(s):  
James N. Brune ◽  
Gladys R. Engen
Keyword(s):  
Rayleigh Waves ◽  
Love Wave ◽  
Strike Slip ◽  
Love Waves ◽  
Excitation Curve ◽  
Kamchatka Earthquake ◽  
Set Up ◽  
Definition Of ◽  
Large Earthquakes ◽  
Slip Motion

abstract A study is made of the excitation of mantle Love waves of 100 seconds period as a function of magnitude. 153 measurements of Love wave spectral density for earthquakes since 1930 ranging in magnitude from 6.0 to 8.9 are used to determine an excitation curve. The observations were first corrected to a standard distance of 90°. The excitation curve supports earlier results for mantle Rayleigh waves and, for strike-slip motion, an earlier curve for seismic moment versus mantle-wave magnitude. For dip-slip motion, the moments should be multiplied by a factor of about 212. A definition of mantle wave magnitude MM, is set up, and the largest earthquake since 1930 found on this scale is the Alaskan earthquake of March 28, 1964 where MM = 8.9. Other comparably large earthquakes, MM = 8.8, were the Kamchatka earthquake of November 4, 1952 and the Chilean earthquake of May 22, 1960. It is suggested that mantle-wave magnitudes be used as a diagnostic aid in estimating the Tsunami potential of earthquakes.

scholarly journals Dynamical Downscaling of ERA5 Data on the North-Western Mediterranean Sea: From Atmosphere to High-Resolution Coastal Wave Climate

2021 ◽  
Vol 9 (2) ◽  
pp. 208
Author(s):  
Valentina Vannucchi ◽  
Stefano Taddei ◽  
Valerio Capecchi ◽  
Michele Bendoni ◽  
Carlo Brandini
Keyword(s):  
Mediterranean Sea ◽  
Wind Wave ◽  
Dynamical Downscaling ◽  
Wave Climate ◽  
Western Mediterranean ◽  
Limited Area ◽  
Computational Domain ◽  
Wave Hindcast ◽  
The North ◽  
Western Mediterranean Sea

A 29-year wind/wave hindcast is produced over the Mediterranean Sea for the period 1990–2018. The dataset is obtained by downscaling the ERA5 global atmospheric reanalyses, which provide the initial and boundary conditions for a numerical chain based on limited-area weather and wave models: the BOLAM, MOLOCH and WaveWatch III (WW3) models. In the WW3 computational domain, an unstructured mesh is used. The variable resolutions reach up to 500 m along the coasts of the Ligurian and Tyrrhenian seas (Italy), the main objects of the study. The wind/wave hindcast is validated using observations from coastal weather stations and buoys. The wind validation provides velocity correlations between 0.45 and 0.76, while significant wave height correlations are much higher—between 0.89 and 0.96. The results are also compared to the original low-resolution ERA5 dataset, based on assimilated models. The comparison shows that the downscaling improves the hindcast reliability, particularly in the coastal regions, and especially with regard to wind and wave directions.

scholarly journals Deep ocean wave energy conversion using a cycloidal turbine

2011 ◽  
Vol 33 (2) ◽  
pp. 110-119 ◽  
Author(s):  
S.G. Siegel ◽  
T. Jeans ◽  
T.E. McLaughlin
Keyword(s):  
Energy Conversion ◽  
Wave Energy ◽  
Deep Ocean ◽  
Ocean Wave ◽  
Wave Energy Conversion ◽  
Ocean Wave Energy

scholarly journals Surface waves in multilayered elastic media I. Rayleigh and Love waves from buried sources in a multilayered elastic half-space

1964 ◽  
Vol 54 (2) ◽  
pp. 627-679
Author(s):  
David G. Harkrider
Keyword(s):  
Surface Waves ◽  
Frequency Domain ◽  
Half Space ◽  
Rayleigh Waves ◽  
Elastic Half Space ◽  
Love Waves ◽  
Displacement Fields ◽  
Matrix Formulation ◽  
Total Displacement ◽  
Rayleigh And Love Waves

ABSTRACT A matrix formulation is used to derive integral expressions for the time transformed displacement fields produced by simple sources at any depth in a multilayered elastic isotropic solid half-space. The integrals are evaluated for their residue contribution to obtain surface wave displacements in the frequency domain. The solutions are then generalized to include the effect of a surface liquid layer. The theory includes the effect of layering and source depth for the following: (1) Rayleigh waves from an explosive source, (2) Rayleigh waves from a vertical point force, (3) Rayleigh and Love waves from a vertical strike slip fault model. The latter source also includes the effect of fault dimensions and rupture velocity. From these results we are able to show certain reciprocity relations for surface waves which had been previously proved for the total displacement field. The theory presented here lays the ground work for later papers in which theoretical seismograms are compared with observations in both the time and frequency domain.

scholarly journals Ambient noise cross-correlation observations of fundamental and higher-mode Rayleigh wave propagation governed by basement resonance

2021 ◽  
Author(s):  
Martha Savage ◽  
FC Lin ◽  
John Townend
Keyword(s):  
Rayleigh Wave ◽  
Correlation Functions ◽  
Rayleigh Waves ◽  
Ambient Noise ◽  
Cross Correlation ◽  
Amplitude Ratio ◽  
Sedimentary Basins ◽  
Longitudinal Motion ◽  
Resonance Frequencies ◽  
Noise Cross Correlation

Measurement of basement seismic resonance frequencies can elucidate shallow velocity structure, an important factor in earthquake hazard estimation. Ambient noise cross correlation, which is well-suited to studying shallow earth structure, is commonly used to analyze fundamental-mode Rayleigh waves and, increasingly, Love waves. Here we show via multicomponent ambient noise cross correlation that the basement resonance frequency in the Canterbury region of New Zealand can be straightforwardly determined based on the horizontal to vertical amplitude ratio (H/V ratio) of the first higher-mode Rayleigh waves. At periods of 1-3 s, the first higher-mode is evident on the radial-radial cross-correlation functions but almost absent in the vertical-vertical cross-correlation functions, implying longitudinal motion and a high H/V ratio. A one-dimensional regional velocity model incorporating a ~ 1.5 km-thick sedimentary layer fits both the observed H/V ratio and Rayleigh wave group velocity. Similar analysis may enable resonance characteristics of other sedimentary basins to be determined. © 2013. American Geophysical Union. All Rights Reserved.

A survey of the microseisms recorded at Aberdeen in 1955, together with a review of the meteorological conditions under which they may have arisen

1958 ◽  
Vol 48 (1) ◽  
pp. 65-76
Author(s):  
A. E. M. Geddes
Keyword(s):  
Fast Moving ◽  
Rayleigh Waves ◽  
Standing Waves ◽  
Meteorological Conditions ◽  
Love Waves ◽  
Norwegian Coast ◽  
Pressure Distributions ◽  
Moving Storm ◽  
Set Up ◽  
Rocky Coast

Abstract As observations of microseisms at Aberdeen appeared to indicate that microseisms may arise from a cause or causes other than from standing waves set up by reflection from a steep rocky coast or by a mixture of waves in a fast-moving storm, a survey of Aberdeen records for 1955 has been carried out and a comparison made with the meteorological conditions prevailing at the time. A noticeable feature on the weather charts was the frequent occurrence of pressure distributions with two centres, while the occasions on which fast-moving storms occurred, or reflection from rocky coasts, were rare. Consequently there seemed to be grounds for supposing that the standing waves arose from the interference of two sets of wave systems generated by double low-pressure centres. Further, single low centres off either the Norwegian coast or that of America produced very little effect at Aberdeen. The survey suggests that the principal regions where such microseisms were produced appeared to be in the Atlantic north of 50° N and off the rocky coast of northwest Scotland. From a comparison of the displacements on the E-W and N-S records there is some support for the hypothesis that microseisms are due to a mixture of Rayleigh waves and Love waves.

Contributions to love-wave transformation theory: Earth-flattening transformation for love waves from a point source in a sphere

1973 ◽  
Vol 63 (3) ◽  
pp. 983-993
Author(s):  
Edgar Kausel ◽  
Fred Schwab
Keyword(s):  
Point Source ◽  
Love Wave ◽  
Love Waves ◽  
Wave Transformation ◽  
Transformation Theory ◽  
Flat Structure ◽  
Wave Response

abstract By means of the Biswas-Knopoff (1970) transformation, programs for the computation of the Love-wave response to a point source in a flat structure can be modified, quite easily, to compute the response in a sphere.

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