Love Waves Research Articles

Analysis of integrated effect of irregularity and corrugated interfaces of doubly layered half space on torsional surface wave propagation

Present geophysical model analyzes the propagation characteristics of torsional wave in an inhomogeneous viscoelastic fiber‐reinforced layer sandwiched between superior porous layer and transversely isotropic piezoelectric subspace with imperfect interfaces. Porous layer and intermediate reinforced layer are endowed with initial stress and corrugated interfaces, whereas the lower piezoelectric half space possesses rectangular cavity at the welded contact. Earth's adjacent layers near mountainous region often endowed with initial stresses resemble the present geological setup. The material properties of intermediate layer are considered to be varying exponentially. Particular cases have been deduced for electrically open and short condition for validation with the standard Love wave expressions. Effects of the relevant parameters on resultant torsional velocity have been explored through numerical simulation and depicted for electrically short and open conditions. Findings of present model may be utilized in the field of signal testing, sensors design, seismic acoustic wave (SAW) devices, and geophysical application concerned with torsional wave based on non‐destructive evaluation.

Shear Wave Velocities in the San Gabriel and San Bernardino Basins, California

AbstractWe construct a new shear velocity model for the San Gabriel, Chino and San Bernardino basins located in the northern Los Angeles area using ambient noise correlation between dense linear nodal arrays, broadband stations, and accelerometers. We observe Rayleigh and Love waves in the correlation of vertical (Z) and transverse (T) components, respectively. By combining Hilbert and Wavelet transforms, we obtain the separated fundamental and first higher mode of the Rayleigh wave dispersion curves based on their distinct particle motion polarization. Basin depths constrained by receiver functions, gravity, and borehole data are incorporated into the prior model. Our 3D shear wave velocity model covers the upper 3–5 km of the crust in the San Gabriel, Chino and San Bernardino basin area. The Vs model is in agreement with the geological and geophysical cross‐sections from other studies, but discrepancies exist between our model and a Southern California Earthquake Center community velocity model. Our shear wave velocity model shows good consistency with the CVMS 4.26 in the San Gabriel basin, but predicts a deeper and slower sedimentary basin in the San Bernardino and Chino basins than the community model.

Investigation of Acoustic Emission Wave Propagation Pattern with Defect Locations in a Multilayer Structure

Acoustic emission (AE) is used to monitor conditions of various structures across many industrial sectors, including containment vessel or storage tank of nuclear materials. Periodic monitoring, inspection, and analysis of structure conditions can help prevent failure and accidents. Understanding the transient elastic waves in multi-layered structures (planar or rounded types) has long been of great interest. This paper experimentally investigates changes in AE wave propagation patterns in multilayer planar structures (detecting and assessing the effect of coating layers, assumed surrogate of deposits or protective layer). Epoxy phenolic coated two mild steel plates were assembled (without any adhesion), and two piezoelectric AE sensors were placed on the coating layer. The pencil lead break (PLB) test was used to initiate the AE waves from the surface and cross-section of different layers. From wavelet transforms (WT) analysis, significant energy zone changes were observed up to the 450 kHz frequency level with PLB on the surface and cross-section of different layers. Love wave propagation on the coated plate structure resulted in wave pattern changes with PLB locations and layers. Wave duration, energy, energy ratio, and peak amplitude levels were also analysed to characterise the AE wave pattern relationship with defect location in a multilayer plate-like (planar) structure. The approaches used in this work could potentially be useful in providing a greater understanding of defects within multilayer nuclear containment structures, and also offering an alternative way to monitor corrosion related degradation of structures with insulations.

Love wave propagation in a piezoelectric layer imperfectly bonded over a cracked porous half-space

This article explores the characteristics of Love wave in a piezoelectric layer imperfectly bonded over a heterogeneous fluid-saturated cracked dual porous half-space. The governing equations of the piezoelectric layer are solved analytically to determine mechanical displacement and electrical potential. Dispersion equations have been established using suitable boundary conditions for electrically open and electrically short conditions. In a particular case, the dispersion equation is reduced to the classical Love wave equation, which validates the present mathematical model. The effect of different parameters (like imperfection, dielectric constant, piezoelectric, and inhomogeneity) on phase velocity has been discussed theoretically and graphically, along with a comparative study by considering two piezoelectric materials, namely, PZT-4 and BaTiO3.

In situ estimation of effective rock elastic moduli by seismic ambient vibrations

In this study, we performed a non-invasive ambient noise investigation of unsaturated rock structures in the Bohemian Paradise (Bohemian Cretaceous Basin, Czech Republic). Our study focused on two key topics: 1) An in situ elastic moduli estimate of competent, horizontally deposited sandstone layers using ambient noise array measurements. Recordings were processed using an f-k array analysis, from which frequency-dependent Love and Rayleigh wave dispersion curves, as well as Rayleigh wave ellipticity, were retrieved. Data were inverted for the P- and S-wave velocity profiles, from which Young's and shear moduli were successfully estimated. 2) A study of the local response of the Kapelník rock tower. We analysed a dataset of ambient noise recordings obtained from the top of the tower and its foot. Information regarding tower oscillation frequencies and directions, together with amplification ratios, were retrieved from a particle motion polarisation analysis and from site-to-reference spectral ratios. Euler-Bernoulli beam theory was also employed for interpreting measured data using elastic moduli estimated from noise array measurements.

Surface wave dispersion curve inversion using mixture density networks

SUMMARYIn many seismological, environmental and engineering applications a detailed S-wave velocity model of the shallow subsurface is required. This is generally achieved by the inversion of surface wave dispersion curves using various inversion methods. The classical inversion approaches suffer from several shortcomings, such as inaccurate solutions due to local minima or large computation times in case of a wide parameter space. A number of machine learning (ML) approaches have been suggested to tackle these problems, which however do not provide probabilistic solutions and/or constrain layer number and layer thickness to a fixed value. In this study, we develop a novel neural network (NN) approach in order to characterize the shallow velocity structure from Love and Rayleigh wave dispersion curves. The novelty of our method lies in the simultaneous estimation of layer numbers, layer depth and a complete probability distribution of the S-wave velocity structure. This is achieved by a two-step ML approach, where (1) a regular NN classifies the number of layers within the upper 100 m of the subsurface and (2) a mixture density network outputs the depth estimates together with a fully probabilistic solution of the S-wave velocity structure. We show the advantages of our ML approach compared to a conventional neighbourhood inversion and a Markov chain Monte Carlo algorithm. Our ML approach is then applied to dispersion curves extracted from recorded noise data in Munich, Germany. The resulting velocity profile is in accordance with lithologic information at the site, which highlights the potential of our approach.

Love‐like wave dispersion in a highly non‐homogeneous viscoelastic orthotropic layer under the effect of non‐local elasticity

This paper examines the effects of non‐local elasticity on the propagation of Love‐like waves in a Voigt‐type viscoelastic layer over an elastic half‐space. The model's geometry is considered orthotropic, highly non‐homogeneous, and initially stressed media in the context of non‐local continuum mechanics. The non‐homogeneity functions are regarded as binomial functions with a positive real exponent. Two different non‐local parameters have been defined by considering different internal characteristic lengths for the layer and half‐space. Modified Bessel functions of the first and second kinds are used to determine displacement functions. Asymptotic representations of derivatives of modified Bessel's functions have been derived to get the compact form of the dispersion equation. A comparison of phase velocity equations with classical Love wave equations has demonstrated the validity of our model. It is found that different modes of Love‐like waves are dispersive and highly affected by the attenuation coefficient. Additionally, non‐local parameters significantly influence the limitation of phase velocity modes of Love‐like waves. The phase and damped velocity versus non‐local parameters have been depicted with the effect of different parameters in the model. It has been found that the non‐local parameters decrease the particle displacement amplitude in elastic half‐space and rapidly eliminate waves with depth.

Quantitative analysis of surface‐wave propagation in the Mexico City Valley

AbstractThe Mexico City basin is an extreme example of an alluvial geological structure that induces long duration and large amplification on ground motions. Researchers have established that the seismic wavefield within the Mexico City basin is composed primarily of surface waves. In the present work, we present a quantitative analysis of the surface‐wave field propagating in the Mexico City basin and generated by thrust‐ and normal‐faulting events. Surface waves are identified and extracted from three‐component ground motion recordings using a technique that exploits the polarization of ground motion. The spatial analysis of the extracted waves clearly shows that the basin response, is strongly dominated by low‐frequency ( to ) Love waves. For all seismic events considered, we found that the identified Love waves can reach amplitudes three times larger as compared to Rayleigh waves. Our analysis indicates that surface wave amplification (as defined in the present work) increases with the 1D fundamental resonant site‐period T1, and appears to be independent of earthquake magnitude. We also quantify the mean delay time of the central frequency f0 of the extracted waves. We found that the of Love waves is spatially more coherent as compared to that of Rayleigh waves. The parameter T1 appears to be a good “proxy” of surface wave effects. This is manifested by a reciprocal relation that was established between T1 and the frequency f0 of the extracted Love waves. Equally important, the latter reciprocal relation turns out to be independent of earthquake magnitude.

Remnants of magma underplating by the Emeishan mantle plume within the lithosphere beneath southeastern margin of the Tibetan Plateau

The Emeishan Large Igneous Province (ELIP) is located along southeastern margin of the Tibetan Plateau, where long-wavelength crustal thickening and surface uplift have been attributed to the influx of weak crustal material from central Tibet into the lower crust beneath the Yangtze Craton. We have developed a new shear-wave velocity model for the lithosphere beneath eastern Tibet, based on a two-step linearized joint inversion technique of P-wave receiver functions (PRFs) with Rayleigh wave dispersion (10–60 s period) and Love wave dispersions (8–30 s period) for three dense seismic arrays. We applied bootstrap resampling technique to calculate the results of inversion. The resulting shear velocity model revealed two major low-velocity features in the middle–lower crust beneath southeastern Tibet. The horizontally extensive low-velocity zone (LVZ) beneath the northern Sichuan–Yunnan diamond-shaped block (SYDSB) can be interpreted as possible lower crustal flow from central Tibet, whereas the low-velocity anomaly observed beneath the Xiaojiang Fault is consistent with the presence of a partially molten layer enhanced by shear deformation along large faults. These two LVZs are separated by a lithospheric-scale high-velocity zone (HVZ) that is situated beneath the geologically inferred core of the ELIP. Based on other geophysical and geological evidence, we interpret this high-velocity anomaly body as remnants of the Emeishan plume-strengthened lithosphere that originally formed during the Permian volcanism, and we speculate that it has acted as a barrier to the hypothesized flow of lower crustal material from central Tibet since the late Cenozoic.

Bright and Dark Solitary Love Waves in a Heterogeneous Semi-Space Coated with a Heterogeneous Elastic Layer

The propagation of nonlinear Love waves in an elastic, vertically heterogeneous crust laid upon an elastic, heterogeneous semi-space is considered. By employing the multiple scales method, the amplitude function of Love waves is represented by a nonlinear Schrödinger equation which includes the nonlinear material and heterogeneity parameters of the layered semi-space in its coefficients. This study numerically investigates the influence of heterogeneity as well as the nonlinear properties of the media on the presence of bright and dark solitary Love waves. Moreover, the remarkable effects of nonlinear and heterogeneous material properties of both layer and semi-space on the wave evolution of bright and dark solions are graphically shown.

Combining Love and Rayleigh waves in detecting and locating seismic sources

SUMMARY Surface waves are critical in detecting and locating seismic sources that do not produce much high-frequency radiation. For such sources, typical approaches using body waves for detecting and locating earthquakes are less effective. Slow earthquakes and exotic seismic sources often have this seismic radiation characteristic, and array analyses of surface waves recorded on global and regional seismic networks have proven effective in recognizing such sources. Most approaches have relied on Rayleigh waves, whereas Love waves have rarely been used. Here we develop a new approach using multiscale arrays to detect and locate seismic sources with both Love and Rayleigh surface waves. The method first forms three-station subarrays and then uses three-component records of the stations to independently estimate three sets of surface wave propagation directions and centroid arrival times. The subarray estimates are then assembled to locate seismic sources and their origin times. We find that using multiple, disconnected global networks improves location accuracy and that using both types of surface waves can enhance detection sensitivity and robustness.

Reply to comment on Malkoti et al. () by Haney and Nakahara

SUMMARY We acknowledge errors in the surface wave Green's tensor shown by Malkoti et al., as pointed out in the Comment by Haney and Nakahara. Using their expressions for Love and Rayleigh wave Green's tensors valid in the near-field, we recompute multicomponent cross-correlation waveforms required for H/V amplitude ratio calculations. All else being equal, these new waveforms are practically indistinguishable from those of Malkoti et al. Differences due to the use of corrected Green's tensors, appear only when the receivers are placed close to the edges of the modelling domain, that is when the receiver separation is large compared to the domain size. Since Malkoti et al. used a modelling domain much larger than the receiver separation, their H/V calculations, and all associated findings, stand.

Fault Damage Zone Effects on Ground Motions during the 2019 Mw 7.1 Ridgecrest, California, Earthquake

ABSTRACT We have simulated 0–3 Hz deterministic wave propagation in the Southern California Earthquake Center Community Velocity Model (CVM) version CVM-S4.26-M01 for the 2019 Mw 7.1 Ridgecrest earthquake. A data-constrained high-resolution fault zone model (Zhou et al., 2022) is incorporated into the CVM to investigate the effects of the near-fault low-velocity zone (LVZ) on the resulting ground motions, constrained by strong-motion data recorded at 161 stations. The finite-fault source used for the simulation of the Ridgecrest event was obtained from the Liu et al. (2019) kinematic inversion, enriched by noise following a von Karman correlation function above ∼1 Hz with a f−2 high-frequency decay. Our results show that the heterogeneous near-fault LVZ inherent to the fault zone structure significantly perturbs the predicted wave field in the near-source region, in particular by more accurately generating Love waves at its boundaries. The fault zone decreases the 0.1–0.5 Hz mean absolute Fourier amplitude spectrum bias to seismic recordings for all sites in the model and in the Los Angeles basin area (∼200 km from the source) by 16% and 26%, respectively. The fault zone structure generally improves modeling of the long-period features in the data and lengthens the coda-wave trains, in better agreement with observations. The favorable fit to data was obtained with a model including high-resolution surface topography, a 700-m-thick geotechnical layer and frequency-dependent anelastic attenuation in the model domain, with QS=0.1VS and QS(f)=0.1VSf0.5 (VS in m/s) for frequencies lower and higher than 1 Hz, respectively. We recommend that a data-constrained fault zone velocity structure, where available, be included in ground-motion modeling to obtain the least-biased fit to observed seismic data.

Structure Along the Martian Dichotomy Constrained by Rayleigh and Love Waves and Their Overtones

AbstractUsing seismic recordings of event S1222a, we measure dispersion curves of Rayleigh and Love waves, including their first overtones, and invert these for shear velocity (VS) and radial anisotropic structure of the Martian crust. The crustal structure along the topographic dichotomy is characterized by a fairly uniform vertically polarized shear velocity (VSV) of 3.17 km/s between ∼5 and 30 km depth, compatible with the previous study by Kim et al. (2022), https://doi.org/10.1126/science.abq7157. Radial anisotropy as large as 12% (VSH > VSV) is required in the crust between 5 and 40 km depth. At greater depths, we observe a large discontinuity near 63 ± 10 km, below which VSV reaches 4.1 km/s. We interpret this velocity increase as the crust‐mantle boundary along the path. Combined gravimetric modeling suggests that the observed average crustal thickness favors the absence of large‐scale density differences across the topographic dichotomy.

Highly sensitive and fast response Love wave mode humidity sensor based on MoS2@Ti3C2Tx hierarchical structure

Humidity sensing is crucial for food production, environmental monitoring, microelectronic manufacture, and common living conditions. Thus, there is a high demand for development of high-performance humidity sensors with good stability, high precision and fast responses. In this study, Love wave mode humidity sensors were prepared using quartz-based SAW devices coated with composite sensing layers of accordion-like Ti3C2Tx, MoS2 nanoflowers and MoS2 @Ti3C2Tx hierarchical structure, respectively. The hydrophilic Ti3C2Tx was used to provide abundant surface functional groups for adsorption of water molecules, and the hydrophobic MoS2 enabled rapid adsorption and desorption of water molecules from the surface of MoS2 @Ti3C2Tx. The MoS2 @Ti3C2Tx coated Love wave humidity sensor presented an ultra-high sensitivity of 0.67 kHz/% RH in the wide humidity range from 11.3% RH to 97.3% RH, mainly attributed to the hierarchical structure of MoS2 @Ti3C2Tx with large specific surface areas, abundant adsorption sites and superhydrophilicity. Meanwhile, this Love wave humidity sensor showed fast response/recovery rates, great repeatability and long-term stability, indicating its great prospects in humidity detection applications.

Influence of low-velocity superficial layer on long-period basin-induced surface waves in eastern Osaka basin

The long-period strong ground motions with periods above 1 s have, in the case of farther or deeper earthquakes, potential to cause serious damage to structures with low eigen frequency, such as long bridges, oil tanks, or artificially damped structures, such as high-rise buildings. This work focuses on wave propagation due to the deep large earthquake representing rare deep damaging events of the region, with relatively sparse data coverage, studied for simple geological models computed by 2D finite differences. We model the wave propagation by finite differences using up-to-date 3D structural model of the Osaka basin. The strong surface waves in the region are not directly generated by these deep sources, but they originate by refraction mostly at the edges of the bedrock–sediments interface. The objective of this research is to model observed surface Love wave generated in the eastern part of the basin that propagates approximately westwards and is recorded by several surface stations. At these stations, the 3D finite-difference modeling provides a good fit with the observed surface wave in terms of waveform, amplitude, and arrival time for the most detailed 3D velocity model that contains topmost 50–250 m structure with the lowest S-wave velocities of 250 m/s. The semblance analysis of the synthetic wave field reveals that the respective synthetic surface wave is a result of interfering waves arriving in OSA and WOS stations from NE and SE directions. Performed tests reveal that such a synthetic wave field is extremely sensitive to the presence of the superficial 50—250 m thick low-velocity structure which is only a small fraction of the propagating surface wave length and occupies only part of the surface area. The ability to model the surface wave in terms of amplitude and time arrival validates the 3D structural model for long-period Osaka Bay earthquake scenario computations.Graphical

Interacting Seismic Waveguides: Multimode Surface Waves and Leaking Modes

Recent developments in seismic recording provide dense sampling of the seismic wavefield that allows the extraction of higher surface wave modes as well as the fundamental, and in some circumstances also P-dominated modes. The character of the modal branches and their dispersion with frequency and phase speed depends on interactions between different aspects of the seismic structure and between wavetypes. The influence of P waves becomes quite strong in the very near surface when there are strong wavespeed gradients. An effective tool for understanding the nature of the modal interactions due to structure is provided by the seismic response in frequency-phase speed space, the kernel for seismogram calculation. Such displays for all three-components of the surface response extract the full modal response, including leaking modes effects, for Rayleigh and Love waves and an indication of the way that the modes are excited.

Modelling of coupled magnetoelastic waves in structure containing thin antiferromagnetic films on an elastic substrate

In this work we present a model explaining the properties of magnetoelastic waves propagation in the heterostructure containing an antiferromagnetic layer on a non-magnetic elastic substate. Horizontally polarized shear surface waves (SH-waves) propagating in thin film are Love waves. The dispersion characteristic of magnetoelastic waves in such structure was obtained, and the effect of variation of the thickness of the antiferromagnetic layer and the external magnetic field on the frequency of the magnetoelastic resonance was also studied. It was found that an increase in the magnetic field magnitude leads to the increase in the magnetoelastic resonance frequency, and, on the contrary, with an increase in the thickness of the AFM layer the magnitude of the magnetoelastic resonance frequency decreases. The obtained results can be used to develop devices for generating and processing signals in the GHz and THz frequency ranges.

Tunable metasurfaces for seismic Love wave manipulation: A theoretical study

Seismic Love waves are horizontally polarized surface waves propagating within an overlying layer, which have been shown to pose potential hazards to infrastructures. In this study, we propose an original analytical formulation to investigate the interaction between seismic Love waves and a metasurface that is composed of a cluster of tunable anti-plane resonators. The formulation utilizes the Green's function of a layered half-space subjected to a surface SH source, to describe both the source-induced incident field and the resonator-excited scattered field. Based on the multiple scattering theory, we obtain the total wavefield of the layered half-space equipped with surface resonators by coupling the incident field and the scattered field. Besides, a closed-form dispersion relation governing the hybrid Love waves is derived by utilizing the effective medium approximation. We demonstrate the capabilities of our analytical formulation by modelling Love waves propagating across a pair and a cluster of resonators, evidenced by some complex phenomena (e.g., surface-to-bulk wave conversion and higher-order hybridized surface modes). The hybridization features of different Love modes and metasurface resonances are clearly revealed. We anticipate the proposed tunable metasurface and the formulation can shed light on versatile control of Love wave propagation.

S1222a—The Largest Marsquake Detected by InSight

AbstractNASA's InSight has detected a large magnitude seismic event, labeled S1222a. The event has a moment magnitude of 4.7, with five times more seismic moment compared to the second largest event. The event is so large that features are clearly observed that were not seen in any previously detected events. In addition to body phases and Rayleigh waves, we also see Love waves, minor arc surface wave overtones, and multi‐orbit surface waves. At long periods, the coda event exceeds 10 hr. The event locates close to the North‐South dichotomy and outside the tectonically active Cerberus Fossae region. S1222a does not show any evident geological or tectonic features. The event is extremely rich in frequency content, extending from below 1/30 Hz up to 35 Hz. The event was classified as a broadband type event; we also observe coda decay and polarization similar to that of very high frequency type events.