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

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.

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.

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

2013 ◽  
Vol 5 (2) ◽  
pp. 1461-1509
Author(s):  
W. Friederich ◽  
L. Lambrecht ◽  
B. Stöckhert ◽  
S. Wassmann ◽  
C. Moos
Keyword(s):  
Oceanic Crust ◽  
High Frequency ◽  
Seismic Waves ◽  
High Amplitude ◽  
Synthetic Seismograms ◽  
Return Flow ◽  
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 to 6 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 structure with eclogitic blocks floating in a serpentinite matrix. Homogenization calculations for block-in-matrix 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. In models with channel, P and S waveforms are dominated by delayed high-amplitude guided waves emanating from the waveguide formed by oceanic crust and DSC. Simulated patterns allow for definition of typical signatures and discrimination between models with and without DSC. These signatures stably recur in slightly modified form for earthquakes at different depths inside subducted oceanic crust. Comparison with available seismological data from intermediate depth earthquakes recorded in the forearc of the Hellenic subduction zone reveal similar multi-arrival patterns 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.

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

STRATIGRAPHIC TRAP STUDY IN COTTONWOOD CREEK FIELD, BIG HORN BASIN, WYOMING

Geophysics ◽  
1962 ◽  
Vol 27 (4) ◽  
pp. 427-444 ◽  
Author(s):  
R. L. Sengbush
Keyword(s):  
Cross Sections ◽  
High Frequency ◽  
Synthetic Seismograms ◽  
Tape Recording ◽  
Theory Approach ◽  
Filter Theory ◽  
Seismic Method ◽  
Magnetic Tape Recording ◽  
Seismic Records ◽  
Facies Change

Stratigraphic trap production in the Cottonwood Creek field is controlled by loss in porosity and facies change in the “E” zone of the Phosphoria dolomite. The edge of the field was delineated on the seismic records through loss in amplitude of the high‐frequency “E” zone reflection due to thinning and decrease in velocity contrast of the “E” zone. Variable‐area cross‐sections show vividly this stratigraphic change. This study indicates that present techniques of magnetic tape recording and processing coupled with synthetic seismograms and the attendant filter theory approach to the seismic method have increased the capability of the seismic method to find stratigraphic traps.

Modeling dolomitized carbonate‐ramp reservoirs: A case study of the Seminole San Andres unit—Part II, Seismic modeling, reservoir geostatistics, and reservoir simulation

Geophysics ◽  
1998 ◽  
Vol 63 (6) ◽  
pp. 1876-1884 ◽  
Author(s):  
Fred P. Wang ◽  
Jiachun Dai ◽  
Charles Kerans
Keyword(s):  
Reservoir Simulation ◽  
Seismic Data ◽  
High Frequency ◽  
Block Size ◽  
Synthetic Seismograms ◽  
Carbonate Ramp ◽  
High Porosity ◽  
Seismic Modeling ◽  
Rock Fabric ◽  
Seismic Resolution

In part I of this paper, we discussed the rock‐fabric/petrophysical classes for dolomitized carbonate‐ramp rocks, the effects of rock fabric and pore type on petrophysical properties, petrophysical models for analyzing wireline logs, the critical scales for defining geologic framework, and 3-D geologic modeling. Part II focuses on geophysical and engineering characterizations, including seismic modeling, reservoir geostatistics, stochastic modeling, and reservoir simulation. Synthetic seismograms of 30 to 200 Hz were generated to study the level of seismic resolution required to capture the high‐frequency geologic features in dolomitized carbonate‐ramp reservoirs. At frequencies <70 Hz, neither the high‐frequency cycles nor the rock‐fabric units can be identified in seismic data because the tuning thickness of seismic data is much greater than the average thickness of high‐frequency cycles of 6 m. At frequencies >100 Hz, major high‐porosity and dense mudstone units can be better differentiated, while the rock‐fabric units within high‐frequency cycles can be captured at frequencies higher than 200 Hz. Seismic inversion was performed on the 30- to 200-Hz synthetic seismograms to investigate the level of seismic resolution required to recover the high‐resolution inverted impedance logs. When seismic data were noise free, wavelets were known and sampling rates were high; deconvolution techniques yielded perfect inversion results. When the seismic data were noisy, the inverted reflectivity profiles were poor and complicated by numerous high‐frequency spikes, which can be significantly removed using the moving averaging techniques. When wavelets were not known, the predictive deconvolution gave satisfactory inversion results. These results suggest that interwell information required for reservoir characterization can be recovered from low‐frequency seismic data by inversion. Outcrop data were collected to investigate effects of sampling interval and scale‐up of block size on geostatistical parameters. Semivariogram analysis of outcrop data showed that the sill of log permeability decreases and the correlation length increases with an increase of horizontal block size. Permeability models were generated using conventional linear interpolation, stochastic realizations without stratigraphic constraints, and stochastic realizations with stratigraphic constraints. The stratigraphic feature of upward‐shoaling sequences can be modeled in stochastic realizations constrained by the high‐frequency cycles and rock‐fabric flow units. Simulations of a fine‐scale Lawyer Canyon outcrop model were used to study the factors affecting waterflooding performance. Simulation results show that waterflooding performance depends strongly on the geometry and stacking pattern of the rock‐fabric units and on the location of production and injection wells.

scholarly journals Glorified optics and wave propagation in nonplanar structure

1978 ◽  
Vol 68 (5) ◽  
pp. 1313-1330
Author(s):  
Tai-Lin Hong ◽  
Donald V. Helmberger
Keyword(s):  
High Frequency ◽  
Spreading Rate ◽  
Synthetic Seismograms ◽  
Time Behavior ◽  
Nonplanar Structure ◽  
Transmission And Reflection Coefficients ◽  
First Motion ◽  
Motion Approximation ◽  
Ray Path ◽  
Transmission And Reflection

abstract Waves propagating in varying nonplanar structure can produce many interesting phenomena, such as focusing, caustics, and triplications. A high-frequency technique based on the first-motion approximation, referred to as glorified optics, has been developed to generate synthetic seismograms for these types of problems. The technique, in its simplest form, uses the spreading rate of a beam with transmission and reflection coefficients along each possible ray path. The time behavior of each arrival is either that of the original pulse or its Hilbert transform depending on the position of caustics. The geophysically interesting structure of a soft basin over a half-space is investigated in detail by this method. Synthetic seismograms appropriate for various locations are compared with the results of finite difference and finite element methods. The technique appears rich in insight and should prove very useful in modeling problems.

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