Complete Synthetic Seismograms for High-Frequency Multimode SH-waves

1991 ◽  
pp. 529-560 ◽  
Author(s):  
N. Florsch ◽  
D. Fäh ◽  
P. Suhadolc ◽  
G. F. Panza
Keyword(s):  
High Frequency ◽  
Synthetic Seismograms ◽  
Sh Waves

scholarly journals Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes

Solid Earth ◽  
2014 ◽  
Vol 5 (1) ◽  
pp. 141-159 ◽  
Author(s):  
W. Friederich ◽  
L. Lambrecht ◽  
B. Stöckhert ◽  
S. Wassmann ◽  
C. Moos
Keyword(s):  
Oceanic Crust ◽  
High Frequency ◽  
Seismic Velocity ◽  
Synthetic Seismograms ◽  
Return Flow ◽  
Minor Importance ◽  
Seismic Velocities ◽  
Subduction Channel ◽  
Intermediate Depth ◽  
Subducted Oceanic Crust

Abstract. Return flow in a deep subduction channel (DSC) has been proposed to explain rapid exhumation of high pressure–low temperature metamorphic rocks, entirely based on the fossil rock record. Supported by thermo-mechanical models, the DSC is envisioned as a thin layer on top of the subducted plate reaching down to minimum depths of about 150 km. We perform numerical simulations of high-frequency seismic wave propagation (1–5 Hz) to explore potential seismological evidence for the in situ existence of a DSC. Motivated by field observations, for modeling purposes we assume a simple block-in-matrix (BIM) structure with eclogitic blocks floating in a serpentinite matrix. Homogenization calculations for BIM structures demonstrate that effective seismic velocities in such composites are lower than in the surrounding oceanic crust and mantle, with nearly constant values along the entire length of the DSC. Synthetic seismograms for receivers at the surface computed for intermediate depth earthquakes in the subducted oceanic crust for models with and without DSC turn out to be markedly influenced by its presence or absence. While for both models P and S waveforms are dominated by delayed high-amplitude guided waves, models with DSC exhibit a very different pattern of seismic arrivals compared to models without DSC. The main reason for the difference is the greater length and width of the low-velocity channel when a DSC is present. Seismic velocity heterogeneity within the DSC or oceanic crust is of minor importance. The characteristic patterns allow for definition of typical signatures by which models with and without DSC may be discriminated. The signatures stably recur in slightly modified form for earthquakes at different depths inside subducted oceanic crust. Available seismological data from intermediate depth earthquakes recorded in the forearc of the Hellenic subduction zone exhibit similar multi-arrival waveforms as observed in the synthetic seismograms for models with DSC. According to our results, observation of intermediate depth earthquakes along a profile across the forearc may allow to test the hypothesis of a DSC and to identify situations where such processes could be active today.

Asymptotic Expansions of Guided Elastic Waves

1972 ◽  
Vol 39 (2) ◽  
pp. 378-384 ◽  
Author(s):  
B. Rulf ◽  
B. Z. Robinson ◽  
P. Rosenau
Keyword(s):  
Elastic Waves ◽  
High Frequency ◽  
Rayleigh Waves ◽  
Lamb Waves ◽  
Two Dimensions ◽  
Guided Wave ◽  
Curved Surfaces ◽  
Sh Waves ◽  
Free Surfaces ◽  
Wave Problems

The problem of propagation of guided elastic waves near curved surfaces and in layers of nonconstant thickness is investigated. Rigorous solutions for such problems are not available, and a method is shown for the construction of high frequency asymptotic solutions for such problems in two dimensions. The method is applied to Love waves, which are SH-waves in an elastic layer, Rayleigh waves, which are elastic waves guided by a single free surface, and Lamb waves, which are SV-waves guided in a plate or layer with two free surfaces. The procedure shown breaks the second-order boundary-value problems which have to be solved into successions of simpler problems which can be solved numerically. Some numerical examples for Rayleigh waves are carried out in order to demonstrate the utility of our method. The method shown is useful for a large variety of guided wave problems, of which the ones we treat are just examples.

scholarly journals Synthetic seismograms for SH waves in anelastic transversely isotropic media

1994 ◽  
Vol 116 (3) ◽  
pp. 598-604 ◽  
Author(s):  
Lawrence H. T. Le ◽  
E. S. Krebes ◽  
Gerardo E. Quiroga-Goode
Keyword(s):  
Transversely Isotropic ◽  
Synthetic Seismograms ◽  
Sh Waves ◽  
Transversely Isotropic Media ◽  
Isotropic Media

Ray-synthetic seismograms for SH waves in anelastic media

1980 ◽  
Vol 70 (1) ◽  
pp. 29-46
Author(s):  
E. S. Krebes ◽  
F. Hron
Keyword(s):  
Plane Waves ◽  
Synthetic Seismograms ◽  
Body Waves ◽  
Plane Boundary ◽  
Theory Approach ◽  
Reflection And Transmission ◽  
Sh Waves ◽  
Transmission Coefficients ◽  
Mathematical Properties ◽  
Crustal Model

abstract The linear theory of viscoelasticity is used to study the effects of anelasticity on SH body waves propagating through a layered medium. The mathematical properties of SH waves in a viscoelastic medium are outlined. Reflection and transmission coefficients for SH plane waves impinging upon a plane boundary separating two anelastic media are calculated and compared with the coefficients for the perfectly elastic case. Synthetic seismograms for teleseismic SH body waves are computed for a plane-layered crustal model in both the elastic and anelastic cases, using a ray theory approach.

Body waves as normal and leaking modes. Part I: Introduction

1967 ◽  
Vol 57 (2) ◽  
pp. 191-198
Author(s):  
J. Cl. De Bremaecker
Keyword(s):  
Rayleigh Waves ◽  
Fourier Transformation ◽  
Normal Modes ◽  
Synthetic Seismograms ◽  
Body Waves ◽  
Apparent Velocity ◽  
S Wave ◽  
Sh Waves ◽  
P And Sv Waves ◽  
Method Of Residues

abstract Realistic artificial seismograms may be computed by considering body waves as sums of normal or leaking modes of surface waves: the S wave and those arriving after S may be considered as sums of higher normal modes of Rayleigh waves (RiN) and Love waves (LiN); in this case the apparent velocity c < βn. Earlier arrivals are generally due to the first kind of leaking modes of Rayleigh waves (RiL1) for which βn < c < αn. Deep reflections in seismic prospecting are RiL2 for which c > αn. Synthetic seismograms can be computed by double Fourier transformation in those two last cases. Alternately the method of residues followed by a single Fourier (or Laplace) transformation may be used in all cases. Earth-stretching approximations should give excellent results for SH waves and may give satisfactory results for P and SV waves.

Array analysis of seismic scattering

1990 ◽  
Vol 80 (6B) ◽  
pp. 2242-2260
Author(s):  
Anton M. Dainty ◽  
M. Nafi Toksöz
Keyword(s):  
Frequency Band ◽  
High Frequency ◽  
Spatial Separation ◽  
Forward Direction ◽  
Synthetic Seismograms ◽  
Array Analysis ◽  
Seismic Scattering ◽  
Phase Velocities ◽  
Lg Coda ◽  
Seismic Wavefield

Abstract The use of high frequency arrays permits investigation of the spatial as well as the temporal character of the seismic wavefield in the frequency band 1-10 Hz. The authors have carried out investigations into seismic scattering at NORESS, FINESA, and ARCESS. Two principal methods have been used, frequency-wavenumber analysis of coda and coherency analysis of seismic phases. For regional seismograms, frequency-wavenumber analysis of Lg coda shows that Lg-to-Lg scattering dominates and that scattering is initially concentrated in the forward direction, changing to isotropic backscatter later in the coda. The P coda is more complex, although all cases studied show that energy is concentrated in the on-azimuth direction. However, different phase velocities are found for the three different cases studied, indicating that P coda is made up of several different contributions whose balance varies in different situations. In previous work, we have found that the decay of coherency with spatial separation scales as the wavelength for the Lg phase of regional events in the frequency band 1-10 Hz, declining to about 0.5 within one wavelength. Analysis of synthetic seismograms for realistic models of the area suggests that this loss of coherency is not due to dispersion, reaffirming a scattering interpretation. However, the decline in coherency is isotropic, seemingly contradicting the finding of forward scattering found in the frequency-wavenumber analysis. This may reflect a sensitivity of the coherency analysis to scattering within or very close to the array, while the frequency-wavenumber analysis favors scatterers at greater distance.

Complete synthetic seismograms for high-frequency multimodeSH-waves

1991 ◽  
Vol 136 (4) ◽  
pp. 529-560 ◽  
Author(s):  
N. Florsch ◽  
D. F�h ◽  
P. Suhadolc ◽  
G. F. Panza
Keyword(s):  
High Frequency ◽  
Synthetic Seismograms
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