Horizontally Polarized Shear Waves Research Articles

Extreme seismic anisotropy indicates shallow accumulation of magmatic sills beneath Yellowstone caldera

Understanding the distribution and mobility of crystal mushes within modern magmatic systems is crucial to volcanic hazard assessments as distinct pockets of mobile magma may become interconnected and lead to melt accumulation on shorter time scales than magma that is broadly distributed in a homogeneous mush. Here, we reveal that Yellowstone's upper-crustal magma reservoir in the top 20 km is heterogeneous in both melt concentration and texture. We exploit ambient noise in an unprecedented dense temporary seismic network to jointly constrain vertically- and horizontally-polarized shear wave speeds to create enhanced 3D isotropic and anisotropic shear velocity models. Our models show an exceptionally low-velocity (>20% reduction) layer 4–7 km beneath the surface, situated near the top of the reservoir previously-imaged by earthquake P-wave tomography. The presence of strong radial anisotropy (20%) within this layer indicates the uppermost portion of the modern Yellowstone reservoir is organized as a sill complex, with up to 28% of melt fraction in horizontally-elongated volumes at depths where rhyolite was commonly stored before past eruptions. The findings demonstrate that high-resolution anisotropic imaging through a dense seismic network can constrain both magma distribution and reservoir texture, which are important to understand the evolution and hazard assessment of volcanic systems like Yellowstone.

Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review.

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine it with enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade.

Effect of undulation on SH-wave propagation in corrugated magneto-elastic transversely isotropic layer

ABSTRACTThis article delves to study the effect of corrugated boundary surfaces on the propagation of horizontally-polarized shear waves (SH-waves) in a magnetoelastic transversely isotropic layer under a hydrostatic state of stress lying over an elastic half-space under gravity. A dispersion equation has been derived in closed-form and is found to be in good agreement to the classical Love-wave equation. The effect of magnetoelasticity, hydrostatic state of stress, gravity, corrugation, position parameter, and undulation on the phase velocity of the SH-wave has been identified. Numerical computation along with graphical demonstration has been carried out for cadmium, magnesium, and zinc materials of hexagonal symmetry to highlight some significant facts.

Three-dimensional localization of transient acoustic sources using an ice-mounted geophone

This paper presents an approach to three-dimensional (3D) localization of ocean acoustic sources using a single three-component geophone on Arctic sea ice. Source bearing is estimated by maximizing the radial signal power as a function of horizontal look angle, applying seismic polarization filters to suppress shear waves with transverse particle motion. The inherent 180° ambiguity is resolved by requiring outgoing (prograde) particle motion in the radial-vertical plane. Source range and depth estimates and uncertainties are computed by Bayesian inversion of arrival-time differences of the water-borne acoustic wave and ice seismic waves, including the horizontally-polarized shear wave and longitudinal plate wave. The 3D localization is applied to geophone recordings of impulsive sources deployed in the water column at a series of ranges (200 to 1000 m) and bearings (0° to 90°) for three sites in the Lincoln Sea characterized by smooth annual ice, rough/ridged annual ice, and thick multi-year ice. Good bearing estimates are obtained in all cases. Range-depth localization is successful for ranges over which ice seismic arrivals could be reliably detected, approximately 200 m on rough ice, 500 m on smooth ice, and 800 m on multi-year ice. Effects of environmental uncertainty on localization are quantified by marginalizing over unknown environmental parameters.

Residual Stress Behavior of Rolled Aluminum Alloy A2024T3 in a Thin Plate During Cyclic-Tension Fatigue Studied Using Ultrasonic Horizontally Polarized Shear Waves

The cyclic-tension fatigue in a rolled thin-plate of aluminum alloy Al-4Cu-1Mg was evaluated nondestructively using a horizontally polarized shear wave (SH) transmission method under optimized measuring and analyzing conditions. The propagation time of the SH waves, which contained elements of reflected waves, had three distinct stages, the first, middle and final ones, during the fatigue process. The variation of the propagation time was dominated by the residual-stress field during the fatigue progress, as an acoustoelastic effect. The change in the stage of the variation can be elucidated by balance points for the redistribution of the residual stress, which clearly told us the degree of progression of the fatigue in the thin plate.

Acoustic Effects on Cyclic-Tension Fatigue of Al-4Cu-1Mg Alloy by Ultrasonic Shear Wave Methods

Cyclic-tension fatigue of aluminum alloy Al-4Cu-1Mg has been determined by usage of vertically-polarized shear wave (SV) reflection and horizontally-polarized shear wave (SH) transmission methods. Internal friction measured by SV method begins to increase rapidly from normalized fatigue ratio of about 0.5, showing dominating interaction of movable dislocations with the waves, as viscoelastic effect. Propagation time and logarithmic damping ratio in the SH method decrease with an increase of the fatigue degree, due to a shift of residual stress as the acoustoelastic effect. The logarithmic damping ratio shows better correlation with the residual-stress shift than the propagation time because acoustic velocity is considered to be significantly affected by pile-up dislocation.

Surface acoustic wave biosensors: a review

This review presents an overview of 20 years of worldwide development in the field of biosensors based on special types of surface acoustic wave (SAW) devices that permit the highly sensitive detection of biorelevant molecules in liquid media (such as water or aqueous buffer solutions). 1987 saw the first approaches, which used either horizontally polarized shear waves (HPSW) in a delay line configuration on lithium tantalate (LiTaO(3)) substrates or SAW resonator structures on quartz or LiTaO(3) with periodic mass gratings. The latter are termed "surface transverse waves" (STW), and they have comparatively low attenuation values when operated in liquids. Later Love wave devices were developed, which used a film resonance effect to significantly reduce attenuation. All of these sensor approaches were accompanied by the development of appropriate sensing films. First attempts used simple layers of adsorbed antibodies. Later approaches used various types of covalently bound layers, for example those utilizing intermediate hydrogel layers. Recent approaches involve SAW biosensor devices inserted into compact systems with integrated fluidics for sample handling. To achieve this, the SAW biosensors can be embedded into micromachined polymer housings. Combining these two features will extend the system to create versatile biosensor arrays for generic lab use or for diagnostic purposes.

The Horizontally Polarized Shear Waves in Multilayered Piezo-Composites with 2-2 Connectivity

Following the advances in structural applications, composite structures are being used commonly in transducer applications to improve acoustic, mechanical and electrical performance of piezoelectric devices. Functional composite transducers for sensors and actuators generally consist of ceramics and polymers, the disadvantage of the brittleness nature of the piezoelectric ceramics can be overcome and the structures especially good for sensing can be allowed for building up. Propagation behavior of horizontally polarized shear waves (SH-waves) in piezoelectric ceramic-polymer composites with 2-2 connectivity is taken into account. The multilayer structures are consisted of piezoelectric thin films bonded perfectly with polymeric thin films alternately. The phase velocity equations of SH-waves propagation in the piezoelectric ceramic-polymer composites with 2-2 connectivity are obtained for the cases of wave propagation in the direction perpendicular to the layering and along the layering, respectively. Filter effect of this kind of structure and the effect of volume fraction and shear modulus ratio of piezoelectric layer to polymer layer on the phase velocity are discussed in detail, respectively. One practical combination of piezoelectric thin film-polymer thin film multilayer system is chosen to carry out the numerical simulation, some basic properties of SH-waves propagation in above multilayered structures are revealed.

Antiplane shear wave scattering from two curvedinterface cracks between a piezoelectric fiber and an elasticmatrix

Following the dynamic theory of linear piezoelectricity, we consider the scattering of horizontallypolarized shear waves from a single piezoelectric fiberpartially bonded to an elastic matrix. The debonding is assumedto be two curved interface cracks with non-contacting faces, andthe two cracks are symmetrically located with respect to theaxis of wave propagation. The wavefunction expansion method isused to reduce the problem to the solution of a pair of dualseries equations, the solution of which is then expressed interms of a singular integral equation introducing a dislocationdensity function. Numerical calculations for P7-epoxy andN8-epoxy composites are carried out, and the effects offrequency, crack angle and piezoelectric material constants onthe dynamic stress intensity factor, dynamic energy releaserate, scattering cross section and electrical signal are showngraphically.

Acoustic sensors based on surface-localized HPSWs for measurements in liquids

Acoustic wave probes based on horizontally polarized shear waves (HPSWs) in quartz plates are presented. These probes can be applied as physical or chemical sensors for measurements in liquids and to characterize thin solid films mechanically. An appropriate and comprehensive simulation tool has been developed and is used to work out the specific advantages of the proposed probing system, to interpret the experimental data and to optimize the probing devices for special measurement purposes. The use of additional coatings of known consistency is introduced, which leads to an enhanced sensitivity and a reduction of cross-sensitivities, in particular for surface-localized HPSWs in quartz, which have not yet been the subject of sensor research. Theoretical and experimental results confirm the huge potential of HPSW devices for sensing applications in liquids.

On the propagation of horizontally polarized shear waves in a thin composite laminate plate

This paper examines the propagation of horizontally polarized shear and quasi-shear waves in aluminium and carbon fibre reinforced composite thin plates. The theory of plane stress waves in orthotropic media is utilized to describe the deviation between the energy velocity and phase velocity. Owing to the non-uniform attenuation of the quasi-shear waves in unidirectional composites, a cross-correlation method is employed to measure the ultrasonic wave velocities. The measured horizontal polarized shear wave or quasi-shear wave velocities in both the aluminium and the unidirectional composite thin specimens are in accordance with those predicted by the theory. Furthermore, in the unidirectional composite specimen, the attenuation along the direction perpendicular to the fibre is found to be much higher than that along the fibre direction.

A numerical integration Green's function model for ultrasonic field profiles in mildly anisotropic media

A numerical integration technique utilizing a point source Green's function is introduced to analyze the wave behavior in transversely isotropic-type anisotropic media allowing us to make fast and accurate computations of the acoustic field. The centrifugally cast stainless steel (CCSS) used in nuclear power plants is chosen as a sample medium because of its columnar grain character leading to material anisotropy. A representative number of field profiles are computed and plotted to illustrate the quasi-longitudinal, quasi-transverse, and horizontally-polarized shear wave propagation in a transversely-isotropic medium. Phenomena such as beam skewing, beam splitting, beam focusing, unsymmetrical beams, and other anisotropic effects, some of which are already known from earlier experimental observations, emerge as a computational result of the introduced technique.

Scattering of horizontally-polarized shear waves by surface irregularities : Sills, L B Geophys J R Astr Soc, V54, N2, Aug 1978, P319– 348

Scattering of horizontally-polarized shear waves by surface irregularities : Sills, L B Geophys J R Astr Soc, V54, N2, Aug 1978, P319– 348

Scattering of horizontally-polarized shear waves by surface irregularities

The problem of the scattering of harmonic SH waves by an arbitrary surface irregularity in an otherwise semi-infinite elastic, homogeneous, isotropic two-dimensional half-space is examined in this study in order to ascertain the effect of topography on this type of seismic ground motion and to develop a useful scheme which can realistically handle arbitrary two-dimensional topography. Three geometric models are considered: a semicircular hill which is of academic interest; a mountain with a Gaussian shape which utilizes realistic dimensions and the combination of a ridge and a depression that models a region in Sylmar, California. A singular Fredholm integral equation of the second kind for the displacement at the free surface is developed and solved numerically. In the case of the semicircular hill, horizontal ground motion can be more than twice that occurring in the case of smooth topography. The mountain simulated by a Gaussian profile experiences at its crest amplifications for certain angles of incidence and de-amplifications for other angles of incidence, as well as displacements whose amplitudes vary slowly with frequency on the side of the mountain which is in the same direction as the incident waves. The ridge-depression combination which is approximated by a sixth-order polynomial actually experienced shattered earth at its ridge crest during the San Fernando, California earthquake of 1971. This amplification is also exhibited by the results of the analysis which predicts amplifications of over 75 per cent at the top of the ridge for waves arriving on the same side as the ridge.

Seismic Motion of Buildings with Buried Foundations

Transient and steady-state responses of a one-story building model with an embedded foundation subjected to plane horizontally-polarized shear waves are derived and analyzed. Soil-structure interaction effects are especially emphasized and a comparison of the rigorous results is made with the results for an analogous simplified model for which the interaction effects are neglected. It is shown that a conventional mass-dashpot-spring model fails to describe the actual complicated interaction effects associated with the scattering of waves around the foundation.

Crack propagation generated by a horizontally polarized shear wave

A plane horizontally-polarized shear wave propagates into an undisturbed brittle elastic material containing a void. This paper inquires into the conditions for initiation of crack propagation at an instantaneous velocity upon diffraction of the wave by the void. The investigation consists of two parts. In the first, the particle velocity and the shear stresses are determined for diffraction of a transient wave of arbitrary shape by a wedge-shaped void which produces a running crack at the instant the wave front strikes the tip of the wedge. In the second, the balance of rate-of-energy is employed to determine that shape of the incident pulse which is consistent with crack propagation at an instantaneous velocity. It is shown that near the wave front the incident displacement wave must be of the form of a square root of the general argument t− ax− by. For this particular type of incident wave, the instantaneous velocity of crack propagation is computed as a function of the angle of incidence, the “amplitude” of the incident wave, and of the material parameters.