13 results on '"Rayleigh-Waves"'
Search Results
2. Depth constraints on azimuthal anisotropy in the Great Basin from Rayleigh-wave phase velocity maps
- Author
-
Beghein, C, Snoke, JA, and Fouch, MJ
- Subjects
Rayleigh-waves ,anisotropy ,lithosphere ,asthenosphere ,crust ,USArray ,Great Basin ,Geochemistry & Geophysics ,Physical Sciences ,Earth Sciences - Abstract
We present fundamental-mode Rayleigh-wave azimuthally anisotropic phase velocity maps obtained for the Great Basin region at periods between 16 s and 102 s. These maps offer the first depth constraints on the origin of the semi-circular shear-wave splitting pattern observed in central Nevada, around a weak azimuthal anisotropy zone. A variety of explanations have been proposed to explain this signal, including an upwelling, toroidal mantle flow around a slab, lithospheric drip, and a megadetachment, but no consensus has been reached. Our phase velocity study helps constrain the three-dimensional anisotropic structure of the upper mantle in this region and contributes to a better understanding of the deformation mechanisms taking place beneath the western United States. The dispersion measurements were made using data from the USArray Transportable Array. At periods of 16 s and 18 s, which mostly sample the crust, we find a region of low anisotropy in central Nevada coinciding with locally reduced phase velocities, and surrounded by a semi-circular pattern of fast seismic directions. Away from central Nevada the fast directions are ∼ N-S in the eastern Great Basin, NW-SE in the Walker Lane region, and they transition from E-W to N-S in the northwestern Great Basin. Our short-period phase velocity maps, combined with recent crustal receiver function results, are consistent with the presence of a semi-circular anisotropy signal in the lithosphere in the vicinity of a locally thick crust. At longer periods (28-102 s), which sample the uppermost mantle, isotropic phase velocities are significantly reduced across the study region, and fast directions are more uniform with an ∼ E-W fast axis. The transition in phase velocities and anisotropy can be attributed to the lithosphere-asthenosphere boundary at depths of ∼ 60 km. We interpret the fast seismic directions observed at longer periods in terms of present-day asthenospheric flow-driven deformation, possibly related to a combination of Juan de Fuca slab rollback and eastward-driven mantle flow from the Pacific asthenosphere. Our results also provide context to regional SKS splitting observations. We find that our short-period phase velocity anisotropy can only explain ∼ 30% of the SKS splitting times, despite similar patterns in fast directions. This implies that the origin of the regional shear-wave splitting signal is complex and must also have a significant sublithospheric component. © 2009 Elsevier B.V. All rights reserved.
- Published
- 2010
3. Variable water input controls evolution of the Lesser Antilles volcanic arc
- Author
-
Cooper, George F., Macpherson, Colin G., Blundy, Jon D., Maunder, Benjamin, Allen, Robert W., Goes, Saskia, Collier, Jenny S., Bie, Lidong, Harmon, Nicholas, Hicks, Stephen P., Iveson, Alexander A., Prytulak, Julie, Rietbrock, Andreas, Rychert, Catherine A., Davidson, Jon P., Davy, Richard G., Henstock, Tim J., Kendall, Michael J., Schlaphorst, David, van Hunen, Jeroen, Wilkinson, Jamie J., Wilson, Marjorie, Natural Environment Research Council (NERC), and Natural Environment Research Council [2006-2012]
- Subjects
Volcanic hazards ,RAYLEIGH-WAVES ,010504 meteorology & atmospheric sciences ,General Science & Technology ,SUBDUCTION ZONE ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle (geology) ,Lithosphere ,INVERSION ,Convergent boundary ,EXCHANGE ,Petrology ,CRUSTAL STRUCTURE ,0105 earth and related environmental sciences ,geography ,Science & Technology ,Multidisciplinary ,geography.geographical_feature_category ,Volcanic arc ,Subduction ,Continental crust ,MANTLE ,Crust ,SERPENTINIZATION ,VoiLA team ,BORON ,Multidisciplinary Sciences ,ISOTOPE VARIATIONS ,INSIGHTS ,Science & Technology - Other Topics ,Geology - Abstract
Oceanic lithosphere carries volatiles, notably water, into the mantle through subduction at convergent plate boundaries. This subducted water exercises control on the production of magma, earthquakes, formation of continental crust and mineral resources. Identifying different potential fluid sources (sediments, crust and mantle lithosphere) and tracing fluids from their release to the surface has proved challenging1. Atlantic subduction zones are a valuable endmember when studying this deep water cycle because hydration in Atlantic lithosphere, produced by slow spreading, is expected to be highly non-uniform2. Here, as part of a multi-disciplinary project in the Lesser Antilles volcanic arc3, we studied boron trace element and isotopic fingerprints of melt inclusions. These reveal that serpentine—that is, hydrated mantle rather than crust or sediments—is a dominant supplier of subducted water to the central arc. This serpentine is most likely to reside in a set of major fracture zones subducted beneath the central arc over approximately the past ten million years. The current dehydration of these fracture zones coincides with the current locations of the highest rates of earthquakes and prominent low shear velocities, whereas the preceding history of dehydration is consistent with the locations of higher volcanic productivity and thicker arc crust. These combined geochemical and geophysical data indicate that the structure and hydration of the subducted plate are directly connected to the evolution of the arc and its associated seismic and volcanic hazards. Serpentine subducted below the Lesser Antilles volcanic arc supplies water to the arc, controlling the location of seismicity, volcanic productivity and thickness of crust.
- Published
- 2020
4. Analysis of Rupture Directivity for the 2004 Sumatra Earthquake from the Rayleigh-Wave Phase Velocity.
- Author
-
Jo-Pan Chang, Ruey-Der Hwang, Chien-Ying Wang, Guey-Kuen Yu, Wen-Yen Chang, and Tzu-Wei Lin
- Subjects
- *
EARTHQUAKES , *RAYLEIGH waves , *SEISMIC networks - Abstract
The rupture directivity for the 2004 Sumatra earthquake is analyzed by examining differences between the phase-delay times of Rayleigh-waves (in the 140 - 160 sec period range) arising from the main shock and reference earthquakes. A long source-process time (-463.0 sec) and large rupture length (-1164.0 km) are derived from this analysis of rupture directivity. The source-process time for this earthquake is larger than for either the 1960 Chile or 1964 Alaska earthquakes. This might be due to the length of the rupture that occurred during earthquake faulting. The estimated rise time for the 2004 Sumatra earthquake, 92.0 sec, is approximately 20% of the whole source duration and also larger than those for the 1960 Chile and 1964 Alaska earthquakes. This likely reflects a fundamental difference between the frictional properties of these earthquakes. When the rise time is taken into account, an estimated rupture velocity of approximately 3.1 km sec-1 is obtained. This value is higher than that found in previous studies carried out on the basis ofhydroacoustic data and regional seismic networks. In this study, we obtain additional evidence from analysis of the surface-wave phase-delay time which confirms the basic features of the rupturing of the 2004 Sumatra earthquake. The results can also provide some constraints for the study of source rupturing for this earthquake. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
5. Shear modulus determination versus temperature up to the melting point using a laser-ultrasonic device
- Author
-
Nadal, M.-H., Hubert, C., and Ravel-Chapuis, G.
- Subjects
- *
ALUMINUM , *MELTING points , *ALUMINUM alloys , *FLUID dynamics - Abstract
Abstract: Shear modulus versus temperature μ(T) is determined by an innovating laser-ultrasonic facility. Bulk and surface wave velocities are measured versus temperature and compared. The analysis of the Rayleigh-wave is related to the shear modulus leading to a high sensitivity measurement independent of the thermal expansion coefficient. This last point is of great interest especially to establish the behavior of materials including phase transition associated with high volume changes. This paper focuses on results up to the melting point on tin, pure aluminum and an aluminum alloy. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
6. Rayleigh, Love and Stoneley waves in a transversely isotropic saturated poroelastic media by means of potential method.
- Author
-
Mahmoodian, Mohammadreza, Eskandari-Ghadi, Morteza, and Nikkhoo, Ali
- Subjects
- *
ELASTIC wave propagation , *POROELASTICITY , *RAYLEIGH waves , *EQUATIONS of motion , *ATTENUATION coefficients , *SURFACE waves (Fluids) , *ELASTIC waves , *POTENTIAL functions - Abstract
Investigation of propagation of surface waves, and also interfacial waves in a saturated either homogeneous or coated half-space in the framework of a simplified version of Biot theory known as u − p formulation is the target of this paper. Both the half-space and the coating are fluid-saturated transversely isotropic in both transport and elastic points of view. The coupled fluid continuity equation and equations of motion are decoupled by virtue of a set of two scalar potential functions. Based on the boundary and/or continuity conditions and appropriate form of scalar potential functions, a secular equation for determination of each of Rayleigh-, Love- and Stoneley-wave velocity and related attenuation coefficients is derived. Moreover, the characteristic equations of different waves are degenerated to explicit forms for some special cases, i.e., saturated isotropic and single-phase materials of either isotropic or transversely isotropic. Furthermore, the effects of hydraulic and mechanical parameters on elastic wave propagation are studied in detail. The dependency of wave velocities and corresponding attenuation coefficients to material parameters are shown graphically and explained in physical point of view. In addition, some wave characteristics are tabulated for a deep understanding of the physical behavior of different waves. Besides, the results are compared with previous studies in special simpler cases, where exact agreements may be discovered from which the validity of the results and the accuracy of numerical computations are evident. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
7. Subsurface crack determination by one-sided ultrasonic measurements
- Author
-
D. G. Aggelis, E. Leonidou, Theodore E. Matikas, and Mechanics of Materials and Constructions
- Subjects
velocity ,rayleigh-waves ,Materials science ,Acoustics ,Fiber-reinforced concrete ,Bending ,FREQUENCY ,Steel bar ,law.invention ,symbols.namesake ,cement-based materials ,solids ,Materials Science(all) ,law ,surface-breaking ,General Materials Science ,Geotechnical engineering ,Rayleigh wave ,Rayleigh waves ,attenuation ,corrosion ,nondestructive testing ,subsurface damage ,scattering ,Building and Construction ,wave-propagation ,Physics::Classical Physics ,Corrosion ,Wavelength ,Acoustic emission ,frequency ,symbols ,concrete ,Subsurface damage ,Ultrasonic sensor ,rayleigh waves ,Longitudinal wave - Abstract
Corrosion of steel reinforcement in concrete is a common type of damage. The cracks propagate from the steel bar to the surface without giving any visual sign prior to surface crack formation. As long as the surface material is intact, the sensitivity of the longitudinal wave velocity to the subsurface cracks is doubtful. In this paper, cracks were created in steel fiber reinforced concrete specimens by four point bending. Wave measurements took place on the intact surfaces (compression side) using common acoustic emission transducers. Although there was no visual sign of the crack, Rayleigh as well as longitudinal wave velocities clearly decreased relative to those of the sound material. Other parameters like the amplitude and the experimental scatter of the waves were much more sensitive to damage. Numerical simulations were conducted in order to make a parametric study concerning the depth of the sound layer, the propagating wavelength and the measured wave parameters and propose a firm methodology. It is concluded that by scanning a surface with simple acoustic one-sided measurements, the identification of the location of the subsurface damage is possible, while the propagating wave gives information about the depth of the crack. (C) 2011 Elsevier Ltd. All rights reserved. Cement & Concrete Composites
- Published
- 2012
8. Application of Surface-Wave Methods for Seismic Site Characterization
- Author
-
Matteo Picozzi, Stefano Parolai, Dario Albarello, Sebastiano Foti, Sebastiano, Foti, Stefano, Parolai, Dario, Albarello, and Picozzi, Matteo
- Subjects
Inverse problems ,velocity ,RAYLEIGH-WAVES ,Seismic noise ,Acoustics ,Seismic characterization ,Surface waves ,Shear wave ,Rayleigh waves ,VERTICAL SPECTRAL RATIOS ,LONG-PERIOD MICROTREMORS ,MONTE-CARLO ,INVERSION ,COLOGNE AREA GERMANY ,AVERAGE H/V RATIOS ,AMBIENT NOISE ,PHASE-VELOCITY ,DISPERSION-CURVES ,JOINT INVERSION ,550 - Earth sciences ,symbols.namesake ,Geochemistry and Petrology ,Rayleigh wave ,Spectral ratio ,Wave velocity ,Experimental data ,Inverse problem ,Geophysics ,Surface wave ,symbols ,Geology - Abstract
Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic.
- Published
- 2011
9. Generation of narrowband antisymmetric lamb waves using a formed laser source in the ablative regime
- Author
-
C. Cosenza, Shant Kenderian, Robert E. Green, B. Boro Djordjevic, A. Pasta, COSENZA C, KENDERIAN S, B BORO DJORDJEVIC, RE GREEN, and PASTA A
- Subjects
RAYLEIGH-WAVES ,Acoustics and Ultrasonics ,Acoustics ,Line source ,Displacement (vector) ,Acoustic dispersion ,Settore ING-IND/14 - Progettazione Meccanica E Costruzione Di Macchine ,Sonication ,symbols.namesake ,Lamb waves ,Optics ,COMPOSITES ,Scattering, Radiation ,Computer Simulation ,Electrical and Electronic Engineering ,Rayleigh wave ,SURFACE ACOUSTIC-WAVES ,LINE SOURCE ,Dispersion (water waves) ,Instrumentation ,Physics ,ULTRASONIC-WAVES ,NONCONTACT ,business.industry ,AIR ,Lasers ,Equipment Design ,Acoustic wave ,VELOCITY ,Models, Theoretical ,INSPECTION ,Equipment Failure Analysis ,Surface wave ,symbols ,Computer-Aided Design ,business ,POINT - Abstract
A formed laser source, using a four-element lenticular array, is used in the ablative regime to generate select, narrowband, acoustic plate waves. The arrangement of the array produces acoustical signals that have frequencies compatible with the response of the broadband capacitive air-coupled transducer used in this study. A simplified concept is presented to explain the effect of a line array source on the frequency content of acoustic waves. The analytical model for a point pulse surface displacement is derived from the point load solution to Lamb's problem. The point pulse displacement elements of a line array source are summed mathematically, taking into account all applicable propagation modes and dispersion of plate waves. The model considers only the out-of-plane displacement of the antisymmetric plate modes to represent the detection capability of the broadband receiver. The distribution function of the laser beam energy profile is modified to depict the actual energy distribution that illuminates the surface of the plate. Filtering functions are made compatible with the sensitivity of the broadband receiver so as to retain only the detected frequencies in the model. The theoretical model showed good agreement with experimental results.
- Published
- 2007
10. Shear velocity structure of the laterally heterogeneous crust and uppermost mantle beneath the Indian region
- Author
-
G. Mohan, G.F. Panza, and S. S. Rai
- Subjects
Shear Velocity ,Phase-Velocity ,Lithosphere ,Regionalization ,Evolution ,Mantle (geology) ,Volcanism ,Monte Carlo Technique ,Oceanic crust ,Shear velocity ,Petrology ,Earth-Surface Processes ,geography ,geography.geographical_feature_category ,Subduction ,Plate-Tectonics ,Bengal ,Crust ,Surface-Wave Dispersion ,Craton ,Rayleigh Wave ,Geophysics ,Shield ,Hotspots ,Indian Shield ,Geology ,Seismology ,Rayleigh-Waves - Abstract
The shear velocity structure of the Indian lithosphere is mapped by inverting regionalized Rayleigh wave group velocities in time periods of 15-60 s. The regionalized maps are used to subdivide the Indian plate into several geologic units and determine the variation of velocity with depth in each unit. The Hedgehog Monte Carlo technique is used to obtain the shear wave velocity structure for each geologic unit, revealing distinct velocity variations in the lower crust and uppermost mantle. The Indian shield has a high-velocity (4.4-4.6 km/s) upper mantle which, however, is slower than other shields in the world. The central Indian platform comprised of Proterozoic basins and cratons is marked by a distinct low-velocity (4.0-4.2 km/s) upper mantle. Lower crustal velocities in the Indian lithosphere generally range between 3.8 and 4.0 km/s with the oceanic segments and the sedimentary basins marked by marginally higher and lower velocities, respectively. A remarkable contrast is observed in upper mantle velocities between the northern and eastern convergence fronts of the Indian plate. The South Burma region along the eastern subduction front of the Indian oceanic lithosphere shows significant velocity enhancement in the lower crust and upper mantle. High velocities (approximate to 4.8 km/s) are also observed in the upper mantle beneath the Ninetyeast ridge in the northeastern Indian Ocean.
- Published
- 1997
11. Depth constraints on azimuthal anisotropy in the Great Basin from Rayleigh-wave phase velocity maps
- Author
-
Matthew J. Fouch, J. Arthur Snoke, and Caroline Beghein
- Subjects
USArray ,bepress|Physical Sciences and Mathematics ,Geochemistry & Geophysics ,bepress|Physical Sciences and Mathematics|Earth Sciences ,crust ,anisotropy ,EarthArXiv|Physical Sciences and Mathematics|Earth Sciences ,Mantle (geology) ,Physics::Geophysics ,bepress|Physical Sciences and Mathematics|Earth Sciences|Geophysics and Seismology ,Geochemistry and Petrology ,Asthenosphere ,Receiver function ,Lithosphere ,Earth and Planetary Sciences (miscellaneous) ,Physical Sciences and Mathematics ,Rayleigh-waves ,Great Basin ,Anisotropy ,Crust ,Geophysics ,EarthArXiv|Physical Sciences and Mathematics ,asthenosphere ,Space and Planetary Science ,Physical Sciences ,EarthArXiv|Physical Sciences and Mathematics|Earth Sciences|Geophysics and Seismology ,Earth Sciences ,Phase velocity ,Geophysics and Seismology ,lithosphere ,Geology ,Seismology - Abstract
We present fundamental-mode Rayleigh-wave azimuthally anisotropic phase velocity maps obtained for the Great Basin region at periods between 16 s and 102 s. These maps offer the first depth constraints on the origin of the semi-circular shear-wave splitting pattern observed in central Nevada, around a weak azimuthal anisotropy zone. A variety of explanations have been proposed to explain this signal, including an upwelling, toroidal mantle flow around a slab, lithospheric drip, and a megadetachment, but no consensus has been reached. Our phase velocity study helps constrain the three-dimensional anisotropic structure of the upper mantle in this region and contributes to a better understanding of the deformation mechanisms taking place beneath the western United States. The dispersion measurements were made using data from the USArray Transportable Array. At periods of 16 s and 18 s, which mostly sample the crust, we find a region of low anisotropy in central Nevada coinciding with locally reduced phase velocities, and surrounded by a semi-circular pattern of fast seismic directions. Away from central Nevada the fast directions are ∼ N-S in the eastern Great Basin, NW-SE in the Walker Lane region, and they transition from E-W to N-S in the northwestern Great Basin. Our short-period phase velocity maps, combined with recent crustal receiver function results, are consistent with the presence of a semi-circular anisotropy signal in the lithosphere in the vicinity of a locally thick crust. At longer periods (28-102 s), which sample the uppermost mantle, isotropic phase velocities are significantly reduced across the study region, and fast directions are more uniform with an ∼ E-W fast axis. The transition in phase velocities and anisotropy can be attributed to the lithosphere-asthenosphere boundary at depths of ∼ 60 km. We interpret the fast seismic directions observed at longer periods in terms of present-day asthenospheric flow-driven deformation, possibly related to a combination of Juan de Fuca slab rollback and eastward-driven mantle flow from the Pacific asthenosphere. Our results also provide context to regional SKS splitting observations. We find that our short-period phase velocity anisotropy can only explain ∼ 30% of the SKS splitting times, despite similar patterns in fast directions. This implies that the origin of the regional shear-wave splitting signal is complex and must also have a significant sublithospheric component. © 2009 Elsevier B.V. All rights reserved.
- Published
- 2010
12. Identification of lateral discontinuities via multi-offset phase analysis of surface wave data
- Author
-
Giulio Vignoli and Giorgio Cassiani
- Subjects
Offset (computer science) ,RAYLEIGH-WAVES ,0211 other engineering and technologies ,02 engineering and technology ,Classification of discontinuities ,010502 geochemistry & geophysics ,01 natural sciences ,symbols.namesake ,Geochemistry and Petrology ,medicine ,INVERSION ,Rayleigh wave ,Seismogram ,DISPERSION-CURVES ,VELOCITY ,SITE ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Mathematical analysis ,Geophysics ,Inverse problem ,Bruit ,Surface wave ,symbols ,Phase velocity ,medicine.symptom ,Geology - Abstract
Surface wave methods are based on the inversion of observed Rayleigh wave phase-velocity dispersion curves. The goal is to estimate mainly the shear-wave velocity profile of the investigated site. The model used for the interpretation is 1D, hence results obtained wherever lateral variations are present cannot be considered reliable. In this paper, we study four synthetic models, all with a lateral heterogeneity. When we process the entire corresponding seismograms with traditional f-k approach, the resulting 1D profiles are representative of the subsurface properties averaged over the whole length of the receivers lines. These results show that classical analysis disregards evidences of sharp lateral velocity changes even when they show up in the raw seismograms. In our research, we implement and test over the same synthetic models, a novel robust automated method to check the appropriateness of 1D model assumption and locate the discontinuities. This new approach is a development of the recent multi-offset phase analysis with the following further advantages: it does not need previous noise evaluation and more than one shot. Only once the discontinuities are clearly identified, we confidently perform classical f-k dispersion curve extraction and inversion separately on both sides of the discontinuity. Thus the final results, obtained by putting side by side the 1D profiles, are correct 2D reconstructions of the discontinuous S-wave distributions obtained without any additional ad-hoc hypotheses.
- Published
- 2010
13. Ultrasonic characterization of surfaces and interphases
- Author
-
Rokhlin, S. I. and Matikas, T. E.
- Subjects
metal-matrix composites ,2 solids ,multilayered fibers ,boundary-conditions ,rayleigh-waves ,thin-film ,wave interaction ,acoustic microscopy ,velocity data ,oxidation damage - Abstract
Mrs Bulletin
- Published
- 1996
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