Analysis Of Love Waves Research Articles

Analysis of Love Waves in an Initially Stressed Transversely Isotropic Porous Layer Over Heterogeneous Half Space with Parabolic Irregularity

Analysis of Love Waves in an Initially Stressed Transversely Isotropic Porous Layer Over Heterogeneous Half Space with Parabolic Irregularity

Analysis of Love Waves in Pre-Stressed Layer Sandwiched between Dry Sandy Layer and Couple Stress Substrate

Analysis of Love Waves in Pre-Stressed Layer Sandwiched between Dry Sandy Layer and Couple Stress Substrate

Multichannel analysis of Love waves in a 3D seismic acquisition system

Multichannel analysis of Love waves (MALW) analyzes high-frequency Love waves to determine near-surface S-wave velocities, and it is getting increasing attention in the near-surface geophysics and geotechnique community. Based on 2D geometry spread, in which sources and receivers are placed along the same line, current MALW fails to work in a 3D seismic acquisition system. This is because Love-wave particle motion direction is perpendicular to its propagation direction, which makes it difficult to record a Love-wave signal in 3D geometries. We have developed a method to perform MALW with data acquired in 3D geometry. We recorded two orthogonal horizontal components (inline and crossline components) at each receiver point at the same time. By transforming the raw data from rectangular coordinates (inline and crossline components) to radial-transverse coordinates (radial and transverse components), we recovered Love-wave data along the transverse direction at each receiver point. To achieve a Love-wave dispersion curve, the recovered Love-wave data were first transformed into a conventional receiver offset domain, and then transformed into the frequency-velocity ([Formula: see text]-[Formula: see text]) domain. Love-wave dispersion curves were picked along the continuous dispersive energy peaks in the [Formula: see text]-[Formula: see text] domain. The validity of our proposed method was verified by two synthetic tests and a real-world example.

Love waves from local traffic noise interferometry

Surface-wave interferometry on local scale usually aims at recovering Rayleigh waves. This is because of the predominant use of vertical component geophones in exploration seismology and the fact that Rayleigh waves occur for any given subsurface structure. On the other hand, Love waves are present only in layered media and require horizontal component geophones for their observation. As they depend on shear-wave velocity structure and density only, the analysis of Love waves provides a potentially powerful supplement to Rayleigh wave inversion. Perhaps surprisingly, recent studies show that low-frequency Love waves (0.05–0.1 Hz) excited by the interaction of ocean waves with the ocean floor (the Earth's microseism) can be recovered by interferometry, and that their S/N is high compared to Rayleigh waves (Lin et al., 2008). On a regional scale, Jay et al. (2012) analyzed the ambient noise field in a volcanic region and found that Love waves with frequencies of about 0.3 Hz are observed more clearly than corresponding Rayleigh waves. In this article, we show that Love waves in the frequency band of 1.5 to 5 Hz can be obtained from local noise interferometry, and that they are of comparable S/N as Rayleigh waves. Thus they may also be used to constrain the near-surface structure.

The 2012 Mw 8.6 Sumatra earthquake: Evidence of westward sequential seismic ruptures associated to the reactivation of a N‐S ocean fabric

The 11 April 2012 Mw 8.6 earthquake offshore Sumatra is the largest of the rare great intraplate earthquakes of the instrumental era. This major strike‐slip event occurred in the diffuse zone of deformation that accommodates differential rotation between Indian and Australian plates. We perform a back projection analysis – calibrated with well‐located aftershocks – of short‐period teleseismic P‐waves recorded by the European array to image the rupture process during the mainshock. In complement, a Love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio‐temporal extent. The combined analysis reveals a complex rupture pattern, characterized by three main episodes of energy release, the latest being located 370 km west of the epicenter, on the Ninety East Ridge, with a delay of 120 s. We interpret the 11 April 2012 Mw 8.6 offshore Sumatra earthquake as a complex westward‐propagating sequence of dynamically triggered strike‐slip fault ruptures, associated to the reactivation of the inherited NNE–striking sea floor fabric. The dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids.

The shear wave velocity underneath Bucharest city, Romania, from the analysis of Love waves

SUMMARY From the dispersion of Love waves, we infer models of shear wave velocity structure underneath Bucharest (Romania) at depths down to 2 km that can contribute to seismic hazard estimation. Waves from eight regional events recorded during 10 months with a network of 34 seismic broad-band stations of the URban Seismology (URS) experiment are used. Although these events provide poor azimuthal coverage the data reliably constrain a shear wave velocity model with an interface between the Neogene and the Cretaceous sediments that is dipping northwards towards the Carpathian mountains. Array processing techniques that account for non-uniform wave propagation are used to estimate the dispersion of structural phase velocity. From this, we infer subsurface structure at three different latitudes. The Neogene sediments are represented by a gradient layer with no significant lateral variation. Shear wave velocity increases from approximately 400 m s −1 near the surface to 1 km s −1 at 1 km depth and 5 km in the south, and to 1.35 km s −1 at 1.5 km depth and 5 km in the north from the centre of Bucharest, respectively. For the half-space representing the Cretaceous sediments, we obtain shear wave velocities of 2.7–2.9 km s −1 . The results are consistent with results from boreholes and shallow seismics for the near-surface structure and results from receiver function studies and crustal refraction seismic studies for the deeper structure. The details of the Neogene layer comprising a vertical gradient fill a gap in existing models of the subsurface structure of Bucharest and can contribute to modelling of seismic hazard for the city. Since the signalto-noise ratio restricted useful data to the frequency range from 90 to 290 mHz, the inversion could not constrain the near-surface velocity independently. Due to strong trade-off between near-surface velocity and depth of half-space, the latter had to be introduced as ap rioridata from previous studies.

On the Spectral Analysis of Love Waves

The focus of this study is an analytical and computational platform for shallow seismic profiling via the dispersion and attenuation analysis of Love surface waves. Although the Rayleigh waves are now commonly used as an engineering tool for nonintrusive identification of shallow subsurface stratigraphy, little attention has been paid so far to utilizing their horizontally polarized, Love-wave counterpart. The proposed methodology revolves around a causal viscoelastic model for the wave motion in a layered half-space caused by action of a surficial, torsionally vibrating disc. It is shown that the use of Love waves as a sounding tool reduces the number of material parameters relevant to viscoelastic site characterization by precluding the effect of Poisson’s ratio and of the compressional-wave quality factor of each subterranean layer. For practical purposes, solution to the inverse problem is reduced to the minimization of a spectral misfit between experimental observations and theoretical predictions of the horizontally polarized surface ground motion. To maintain the rigor and computational effectiveness of the inverse solution, sensitivities of the viscoelastodynamic model with respect to relevant layer parameters are determined analytically. The Love-wave testing methodology for which this article establishes a necessary theoretical framework may be used either in a stand-alone fashion or as a complement to the (well-established) spectral analysis of Rayleigh waves. The proposed technique may be especially useful for (1) shallow surveying applications in which material dissipation is important and (2) accurate characterization of saturated layers in which vertically polarized waves find limited use owing to their sensitivity to the pore fluid.

First evidence for high anelastic attenuation beneath the Red Sea from Love Wave Analysis

Attenuation coefficients of Love waves are determined for two seismic paths along the Red sea. The attenuation coefficients are obtained using the multiple filter method for periods from 25 to 130 s along one path and from 40 to 130 s along the second one. The two sets of observations are in good agreement with anomalously high attenuation coefficients similar to those reported across a young part of the Pacific ocean. Indeed, the values lie on average between 3.3 ± 0.6 and 1.1 ± 0.3(10−4km−1), higher values being observed at shorter periods. In a second part of the paper, these apparent attenution observations are interpreted in terms of a distribution of intrinsic absorption in the upper mantle. A frequency independent Qβ model is obtained using a trial‐and‐error method. The best fit to the data required a large and very low Qβ (30–50) zone below a depth of 50 km, underlying a thin and high Qβ (200–300) lid. These results are consistent with high heat flows and low velocities which characterize this tectonically active area, and corroborate the inference of anomalously high temperatures and low viscosity in the upper mantle beneath the Red Sea from recent seismological results.

Higher mode interference and observed anomalous apparent Love wave phase velocities

For a representative selection of spherical earth models compatible with seismic observations, there is a significant frequency range over which the fundamental and first higher Love mode group velocity curves approach each other closely or actually overlap. Higher Love modes can be excited comparably to the fundamental mode for both shallow and deep sources under a variety of circumstances, and thus higher mode interference is an important factor to be taken into account in the proper interpretation and analysis of Love waves. Simple theoretical computations reveal the nature of the effect of mode contamination on measured phase velocities, and biases in the selection and analysis of surface wave data make it appear likely that fundamental mode Love waves experiencing higher mode interference will exhibit anomalously high apparent phase velocities, as observed in the United States midcontinent and in Japan. Thus it is suggested that it may not be necessary to resort to complex or anisotropic models to explain these observations. Consideration of the effects of mode interference, as well as knowledge of source parameters (type, depth, orientation), are important in determining dependable fundamental and higher Love mode phase velocity dispersion over a broad frequency band. Phase velocity filtering across a large array could effectively separate the modes. Love waves traversing continental regions from the source will suffer little or no contamination from higher modes for wave periods of less than about 60 sec and thus are preferred to oceanic paths in obtaining reliable fundamental mode data in this restricted frequency range.