An investigation into the fundamental relationships between attenuation, phase dispersion, and frequency using seismic refraction profiles over sedimentary structures

Geophysics ◽  
1987 ◽  
Vol 52 (1) ◽  
pp. 72-87 ◽  
Author(s):  
R. S. Jacobson
Keyword(s):  
Frequency Dependence ◽  
Seismic Waves ◽  
Velocity Dispersion ◽  
Seismic Refraction ◽  
Systematic Investigation ◽  
Data Sets ◽  
Frequency Dependent ◽  
Frequency Independent ◽  
Apparent Attenuation ◽  
Seismic Refraction Data

Despite many attenuation measurements which indicate a linear functional frequency dependence of absorption or constant [Formula: see text] in sediments, several theories predict no such linear dependence. The primary justification for rejecting a first‐power frequency dependence of attenuation is that it implies that seismic waves cannot propagate causally. Seismic waves must also travel with some velocity dispersion to satisfy causality, yet there is a lack of velocity dispersion measurements in sediments. In‐situ attenuation is caused by two distinct mechanisms: anelastic heating, and scattering due to interbed multiples. Apparent, or scattering, attenuation can produce both frequency‐dependent and non‐frequency‐dependent effects. Accurate measurements of attenuation and velocity dispersion are difficult; it is not surprising that a systematic investigation into the frequency dependence of absorption and velocity has not been made. A reinvestigation into two seismic refraction data sets collected over thickly stratified deep‐sea fans indicates that [Formula: see text] should not be assumed to be independent of frequency. Further, significant frequency‐independent absorption is present, indicating a high degree of apparent attenuation. Phase, or velocity, dispersion was also measured, but the results are more ambiguous than those for attenuation, due to inherent limitations of digital signals. Nevertheless, the absorption and velocity dispersion results are largely compatible, suggesting that if apparent attenuation is observed, then the scattered waves propagate causally.

APPARENT ATTENUATION DUE TO INTRABED MULTIPLES, II

Geophysics ◽  
1978 ◽  
Vol 43 (4) ◽  
pp. 730-737 ◽  
Author(s):  
M. Schoenberger ◽  
F. K. Levin
Keyword(s):  
Seismic Data ◽  
Field Data ◽  
Seismic Waves ◽  
Synthetic Seismograms ◽  
Frequency Dependent ◽  
Total Attenuation ◽  
The World ◽  
Apparent Attenuation

In a paper with the same title published in Geophysics (June 1974), we showed that synthetic seismograms from two wells gave a frequency‐dependent attenuation due to intrabed multiples of about 0.06 dB/wavelength. This loss was 1/3 to 1/2 of the total attenuation found for field data on lines near the wells. Our data sufficed to confirm the conclusion of O’Doherty and Anstey that attenuation caused by intrabed multiples may be appreciable, but the number of wells was insufficient to establish the magnitude of that attenuation in general. To get a better feel for intrabed multiple‐generated attenuation, we have computed losses for 31 additional wells from basins all over the world. Sonic and, where available, density logs were digitized every foot and converted into synthetic seismograms with 50 orders of intrabed multiples. Using the technique of the 1974 paper of extending the logs and placing an isolated reflector 2000 ft below the bottom of the wells, we computed attenuation constants for plane seismic waves that had traveled down and back through the subsurfaces defined by the logs. Computed constants varied from 0.01 dB/wavelength to 0.22 dB/wavelength. Total traveltimes ranged from 0.7 to 2.7 sec; the average was 1.9 sec. Attenuation constants computed from surface seismic data near four of the 31 wells gave values 1.3 to 7 times the corresponding intrabed constants. Thus, attenuation due to intrabed multiples accounts for an appreciable fraction of the observed attenuation but by no means all of it.

Frequency dependence of CO2 elimination and respiratory resistance in monkeys

1985 ◽  
Vol 58 (2) ◽  
pp. 653-657 ◽  
Author(s):  
J. W. Watson ◽  
A. C. Jackson
Keyword(s):  
Frequency Dependence ◽  
Nonlinear Frequency ◽  
Frequency Dependent ◽  
Dependent Behavior ◽  
Frequency Independent ◽  
Respiratory System Resistance ◽  
The Relationship ◽  
High Frequency Oscillatory ◽  
Large Frequency ◽  
Co2 Elimination

In dogs, respiratory system resistance (Rrs) is frequency independent, and during high-frequency oscillatory ventilation (HFO) the relationship between CO2 elimination (VCO2) and frequency is linear. In contrast, we found in rabbits a large frequency-dependent decrease in Rrs with increasing frequency along with a nonlinear relationship between frequency and VCO2 (J. Appl. Physiol. 57: 354–359, 1984). We proposed that frequency dependent mechanical properties of the lung account for inter-species differences in the frequency dependence of gas exchange during HFO. In the current study we tested this hypothesis further by measuring VCO2 and Rrs as a function of frequency in a species of monkey (Macaca radiata). In these monkeys, Rrs decreased minimally between 4 and 8 Hz and in general increased at higher frequencies, whereas VCO2 was linearly related to frequency. This is further evidence supporting the hypothesis that nonlinear frequency-VCO2 behavior during HFO is related to frequency-dependent behavior in Rrs.

scholarly journals Merge-Optimization Method of Combined Tomography of Seismic Refraction and Resistivity Data

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Andy A. Bery
Keyword(s):  
High Resolution ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Optimization Method ◽  
Detailed Knowledge ◽  
Data Sets ◽  
Geophysical Surveys ◽  
Data Points ◽  
Geophysical Imaging ◽  
Seismic Refraction Data

This paper discussed a novel application called merge-optimization method that combines resistivity and seismic refraction data to provide a detailed knowledge of the studied site. This method is interesting because it is able to show strong accuracy of two geophysical imaging methods based on many of data points collected from the conducted geophysical surveys of disparate data sets based strictly on geophysical models as an aid for model integration for two-dimensional environments. The geophysical methods used are high resolution methods. The resistivity imaging used in this survey is able to resolve the subsurface condition of the studied site with low RMS error (less than 2.0%) and 0.5 metre electrodes interval. For seismic refraction method, high resolution of seismic is used for correlation with resistivity results. Geophones spacing is 1.0 metre and the total number of shot-points is 15, which provides very dense data point. The algorithms of merge-optimization have been applied to two data sets collected at the studied site. The resulting images have been proven to be successful because they satisfy the data and are geometrically similar. The regression coefficient found for conductivity-resistivity correlation is 95.2%.

scholarly journals Simulation study of 6–10 kV cable lines for transient processes calculation during earth faults

Vestnik IGEU ◽  
2021 ◽  
pp. 30-40
Author(s):  
V.A. Shuin ◽  
Yu.D. Kutumov ◽  
N.V. Kuzmina ◽  
T.Yu. Shadrikova
Keyword(s):  
Frequency Dependence ◽  
Single Phase ◽  
Transient Processes ◽  
Cable Line ◽  
Frequency Dependent ◽  
Cable Networks ◽  
Ground Fault ◽  
Three Phase ◽  
Frequency Independent ◽  
Cable Lines

As a rule, researchers do not consider the dependence of the inductance of cable lines on frequency in their scientific papers devoted to the calculation of transient processes during single phase-to-ground fault in 6–10 cable networks. In some cases, it can lead to significant errors in evaluation of current and voltage transient components parameters. Therefore, it is an urgent task to estimate defined errors and the scope of application of frequency-independent equivalent circuits and models of 6–10 kV cable lines during calculation and simulation of transient processes in case of single phase-to-ground fault. The authors applied PSCAD / EMTDC software to study the effect of the frequency dependence of the inductances of 6–10 kV cable lines on the calculation accuracy of transient processes during single phase-to-ground fault. It allows to simulate electric power systems models with the usage of both frequency-dependent and frequency-independent cable line models with round conductors only. To check the adequacy of the frequency-dependent three phase cable model developed in PSCAD software, the authors have used a frequency-dependent model of 6–10 kV three-phase cable with sector-shaped conductors designed in COMSOL Multiphysics software. The authors have developed an approach to develop of 610 kV cable lines models with frequency-dependent and frequency-independent parameters. The authors have obtained error estimation in transient current and voltage parameters during single phase-to-ground fault in cable networks models that do not consider the frequency dependence on inductance (for discharge components the error is 1520 %, for charging components the error is equal to 510 %). It is shown that models with cable line parameters defined according to spreading speed of electromagnetic wave, can be used for approximate calculation of transient current and voltage to solve most of tasks of investigation of transient processes during single phase-to-ground faults. Application of the developed recommendations to determine three phase medium voltage cable lines parameters will increase the calculation accuracy of transient processes during single phase-to-ground faults in 6–10 kV cable networks. Only application of frequency-dependent models of cable lines allows us to provide required accuracy to develop methods of distant earth fault localization in 6–10 kV networks.

scholarly journals High resolution seismic refraction data interpretation: an example from Xiakou landslide, Sichuan, China

1999 ◽  
Vol 19 ◽  
Author(s):  
Surendra Raj Pant ◽  
T. Li ◽  
A. Wagner ◽  
Fu Wei Yi ◽  
Cao Jiaman
Keyword(s):  
Seismic Waves ◽  
Seismic Refraction ◽  
Data Interpretation ◽  
Velocity Inversion ◽  
Electrical Sounding ◽  
Electrical Soundings ◽  
Conventional Methods ◽  
Thick Overburden ◽  
Seismic Refraction Data ◽  
Landslide Zone

Among several data processing and interpretation techniques available in seismic refraction, the Generalised Reciprocal Method (GRM) is now widely used. In the thick landslide zone of Xiakou, Sichuan, China, the depths to bedrock obtained from the conventional refraction interpretation by the Plus-Minus Method (Method t0) differed considerably from the results of electrical soundings and drilling. The conventional methods were not able to accommodate to the more likely geological situations (i.e. undetected layers and velocity inversion) in a thick landslide zone. Thicker the overburden more the variation occurred between the results of the GRM and conventional methods. The velocity of seismic waves in the refractor calculated by the Plus-Minus Method was also affected significantly from the bedrock topography. After applying the GRM, the calculated depths were found to be very near to those of the drilling and electrical sounding. The GRM also revealed that the changes in refractor velocity (recorded by conventional methods) were fictitious. The fictitious changes in refractor velocity were caused by the target refractor topography and surface topography. In this paper two profiles are taken for discussion. The profile B-B' represents a case of thick overburden (more than 30 m) whereas the profile D-D' is taken from a thin overburden (less than 15 m) above the target refractor.

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