Stratigraphic filtering of seismic waves: The influence of mode conversion multiples onP-wave andS-wave phase and attenuation     

I. Lerche 《Pure and Applied Geophysics》1987,125(5):717-751

We demonstrate how multiples, generated at the interfaces of plane parallel beds, modify the propagation characteristics of an originally coherent seismic wave. For waves propagating at an angle to the bedding plane we find that theSV andP-waves couple so that neither is a pure mode. TheSH-wave, while modified in its propagation characteristics by multiples, remains a pure mode. The coupling ofSV-multiples into the quasi-P-mode appears weaker than the coupling ofP-wave multiples into the quasi-SV mode; at least this is so for the two simple cases of (a) density fluctuations only and (b) correlatedV _p andV _s fluctuations which conserve Poisson's ratio.We also find that the coupling is sensitive to both the angle of propagation and frequency. In addition there is a cut-off angle forP-wave multiples influencing the quasi-SV mode. Propagation angles larger than the cut-off permit theP-multiples to modify the phase of the quasi-SV mode, but not its effective attenuation. No such cut-off effect is found for SV-multiples influencing the quasi-P mode, whose angle-dependent and frequency-dependent phase distortion and effective attenuation are influenced both byP-wave multiples andSV-multiples.In view of the mathematical complexity of the expressions describing the phase, and effective attenuation of modes when allowance is made forP-andS-wave multiples, we strongly advocate numerical coding of the major mathematical formulae. By so doing a systematic study can be undertaken of the frequency and offset dependence of seismic waves as a function of seismic source input and power spectral behavior of the fluctuations in density and elastic constants of beds. It is our opinion that the full mathematical expressions are too involved to permit an analytic, systematic investigation to be given of the phase and attenuation of seismic waves with any degree of sophistication or generality.  相似文献   

Viscid and inviscid self-similar blast waves: Spherical,isothermal flows and inferences for supernova remnants     

I. Lerche 《Astrophysics and Space Science》1977,47(2):347-360

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On phase and ray directions of magnetosonic waves     

I. Lerche 《Astrophysics and Space Science》1978,57(1):233-239

The behavior of phase speed for the slow and fast magnetosonic waves is well documented in the literature. Not so well documented is the behavior of the ray direction and its relation to the phase direction — indeed we have not found the ray behavior recorded in most of the standard plasma physics texts. We rectify this situation and point out some of the curiosities associated with the direction of the slow ray relative to the direction of the slow phase wave. These calculations have been performed as a necessary basis for discussion of phase and ray evolution of magnetosonic waves in differentially shearing plasmas, which subject is the topic of a later paper.  相似文献   

Inversion of multiple thermal indicators: Quantitative methods of determining paleoheat flux and geological parameters IV. Case histories using thermal indicator tomography     

Z. He  I. Lerche 《Mathematical Geology》1989,21(5):523-541

A quantitative tomographic method to determine simultaneously several geological, geochemical, and geothermal parameters associated with reconstruction of the geohistory and thermal history of sediments in a well is presented. Using vitrinite reflectance data from the well Inigok-1, National Petroleum Reserve of Alaska, the numerical algorithm was tested and found to be effective in delineating the variation of heat flux with time. In addition, the size and timing of a major unconformity also were bracketed. Application of tomography using apatite fission track distributions with depth as a thermal indicator enabled not only the thermal history of two wells in the NW Canning Basin of Australia to be determined, but also the chemical parameters associated with fission track annealing to be constrained. Results of both the Alaska study and the Australian study were consistent with the qualitative behavior inferred from current geological models.  相似文献   

Inversion of dynamical indicators in quantitative basin analysis models. II. Synthetic tests and a case history using dynamical indicator tomography     

K. Zhao  I. Lerche 《Mathematical Geology》1993,25(2):107-123

The dynamical evolution of sediments in basins, and their compaction, is the underpinning keystone on which rests the ability to model thermal history of the basin and hydrocarbon generation, migration, and accumulation histories. A presentation is given of the dynamical tomography method, which inverts dynamical indicators to evaluate the parameters in a 1-D fluid-flow/compaction model, including values dealing with geological events as well as values dealing with intrinsic, or assumed, lithologic equations of state. Synthetic tests illustrate the operation of the system. Using observed downhole quantities: total depth, formation thicknesses, variation of porosity, permeability, and total fluid pressure with depth from the Navarin Basin COST No. 1 well, Bering Sea, Alaska, the numerical algorithm was tested and found to be effective in a nonlinear inverse sense to determine and/or constrain the parameters entering quantitative models of dynamical sedimentary evolution. The predictions of present day total depth, formation thicknesses, porosity, permeability, and fluid pressure with depth are close to the measured data. The minimization provides the uncertainty in each parameter and so the geohistory of a well can be defined better.  相似文献   

On pair production in intense electromagnetic fields occurring in astrophysical situations     

J. K. Daugherty  I. Lerche 《Astrophysics and Space Science》1975,38(2):437-445

We show that the pair production rate in a strong magnetic field is substantially altered when an electric field is also included. We illustrate and emphasize this significant alteration by considering a few special cases. In the vicinity of the polar cap of a rotating magnetized neutron star it is currently though thatboth steady electric and magnetic fields must be present. The results presented here then indicate that some considerable degree of caution must be exercised in applying pair production rates calculated under the assumption of zero electric field to the problems of pulsar emission and the generation and maintence of pulsar magnetospheres. In general such rates are very different from the rate computed allowing for the existence of an electric field.  相似文献   

Soliton solutions and their stability for the flow of relativistic fluids through channels     

I. Lerche  P. J. Wiita 《Astrophysics and Space Science》1980,68(1):207-219

We analyze the flow of a perfect relativistic fluid in a confining channel of variable cross-section — a situation that is relevant for models of radio galaxies. Families of soliton-like solutions are found and their topologies described. However, a perturbative investigation of these solutions indicates that all such soliton modes are unstable, and would eventually decay.  相似文献   

The effect of turbulent fluctuations in the interstellar gas and magnetic field on Faraday rotation     

I. Lerche 《Astrophysics and Space Science》1970,6(3):481-491

The effect of fluctuations in both the interstellar electron number density and galactic magnetic field on the propagation of high frequency radio waves is discussed in terms of the frequency dependent Faraday rotation. It is shown that when the fluctuations are representative of large scale disturbances (1–10² pc) in the interstellar medium, then the observed Faraday rotation is not a measure of the line of sight integral of the product of the magnetic field with the electron number density.Since evidence has been presented elsewhere for believing that such large scale disturbances do exist in our galaxy, some care must be exercised in the physical interpretation of Faraday rotation measurements.Alfred P. Sloan Foundation Fellow.  相似文献   

On the propagation of magneto-ionic rays in a shearing plasma     

I. Lerche 《Astrophysics and Space Science》1979,63(1):79-102

Using the geometrical optics approximation, we give the behavior of fast and slow magneto-ionic rays passing through a plasma which possesses a differential shear. Depending upon the orientation of the ambient magnetostatic field with respect to the flow direction, it is shown that the effects of the shear can cause ray paths to propagateupstream ordownstream. The fact that in an homogeneous plasma the slow magneto-ionic wave has a group angle which is oppositely directed to its phase angle causes the slow rays to exhibit properties which are extremely curious relative to those obtaining for the fast rays — which are themselves interesting. We have done these calculations to show that the effects of velocity shear in an otherwise homogeneous plasma lead to interesting ray behaviors which, presumably, bear upon the more general question of magneto-ionic energy transport in inhomogeneous plasmas.  相似文献   

The Georges Bank Basin: a quantitative basin analysis study     

J. Liu  I. Lerche  K.K. Bissada†  J. Lacey† 《地学学报》1991,3(1):70-83

Using a one-dimensional (1D) fluid flow/compaction model applied to wells of the Georges Bank Basin, east coast, USA, has enabled a simulation to be made of the history of the sedimentation, basement subsidence, tectonic activity, geoheat flux evolution, maturation of organic matter, hydrocarbon generation, and migration tendency.
Based on the analysis of the basement tectonic activity, the basin's development is related to the formation and the evolution of the east edge of the North American plate. Through the simulation of geoheat flux variation, maturation of organic material and hydrocarbon generation at different positions in the basin at different time periods are analysed. Additionally, from the modelling of excess fluid pressure, porosity and permeability variations in the strata, the potential hydrocarbon migration tendency and stratigraphic traps in the basin are discussed.  相似文献