THE DIRECTIVITY PROBLEM FOR A BURIED LINE SOURCE

Geophysics ◽  
1961 ◽  
Vol 26 (5) ◽  
pp. 626-634 ◽  
Author(s):  
Freeman Gilbert ◽  
Leon Knopoff
Keyword(s):  
Radiation Pattern ◽  
Line Source ◽  
First Motion ◽  
Motion Approximation

A method based on the first motion approximation is presented for determining the radiation pattern of a buried line source. If measurements at the surface are used to obtain the P and S components of the source, the multipolar distribution of the source may be determined. The multipolar distribution is not unique since several distributions can have the same radiation pattern. Some examples are presented for simple sources. The method is applicable to real sources or virtual sources such as centers of diffraction or scattering.

First motions from seismic sources

1960 ◽  
Vol 50 (1) ◽  
pp. 117-134 ◽  
Author(s):  
Leon Knopoff ◽  
Freeman Gilbert
Keyword(s):  
Radiation Pattern ◽  
Fault Plane ◽  
Displacement Vector ◽  
Strain Tensor ◽  
Dislocation Model ◽  
Double Couple ◽  
First Motion ◽  
Sudden Release ◽  
Deep Focus ◽  
Dynamic Dislocation

ABSTRACT An application of dynamic dislocation theory gives the elastodynamic radiation resulting from the sudden occurrence of an earthquake due to faulting. The fault plane is visualized as a geometrical discontinuity across which there exists a sudden discontinuity in either one component of the strain tensor or one component of the displacement vector. It is shown that there are eight independent models, if unilateral faulting is assumed; and an argument is presented to demonstrate the likelihood that unilateral faulting does not exist in nature. For bilateral faulting the eight independent models are reduced in number to five. Of these five, two are more likely to occur in nature than the others. One of these, the displacement dislocation model, has a first-motion radiation pattern formally identical with that of a double couple in an unfaulted medium. The second, the shearstrain dislocation model, has a first-motion radiation pattern formally identical with that of an isolated force in an unfaulted medium. The latter type of mechanism may occur in deep-focus earthquakes. Another type of radiation, corresponding to the single couple in an unfaulted medium, results from the sudden release of shear strain in a laminar region.

ELECTROMAGNETIC RADIATION-PATTERN EFFECTS OF DIELECTRIC LAYERS

1967 ◽  
Vol 45 (9) ◽  
pp. 3119-3128 ◽  
Author(s):  
J. H. Harris
Keyword(s):  
Electromagnetic Radiation ◽  
Radiation Pattern ◽  
Line Source ◽  
Magnetic Line ◽  
Dielectric Layers

A formulation for the radiation pattern of a grounded magnetic line source in the presence of dielectric layers is obtained and the effects of differing permittivity variations are investigated. It is shown that relatively simple bounding functions may be established, and that layers may be employed to obtain both directive and smoothed patterns.

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.

Sign in / Sign up

Export Citation Format

Share Document