Point source radiation in inhomogeneous anisotropic structures

Ivan Psencik & Telesson Neves Teles


The ray formulae for the radiation from point sources in unbounded inhomogeneous isotropic as well as anisotropic media consist of two factors. The first one depends fully on the type and orientation of the source and on the parameters of the medium at the source. We call this factor the directivity function. The other factor depends on the parameters of the medium surrounding the source and this factor is the well-known geometrical spreading. The displacement vector and the radiation pattern defined as a modulus of the amplitude of the displacement vector measured on a unit sphere around the source are both proportional to the ratio of the directivity function and the geometrical spreading.

For several reasons it is desirable to separate the two mentioned factors. For example, there are methods in exploration seismics, which separate the effects of the geometrical spreading from the observed wave field (so-called true amplitude concept) and thus require the proposed separation. The separation has also an important impact on computer time savings in modeling seismic wave fields generated by point sources by the ray method. For a given position in a given model, it is sufficient to calculate the geometrical spreading only once. A great variety of various types of point sources with a different orientation can then be calculated at negligible additional cost.

In numerical examples, we show the effects of anisotropy on the geometrical spreading, the directivity function and the radiation pattern. Ray synthetic seismograms due to a point source situated in an anisotropic medium are also presented and compared with seismograms for an isotropic medium.

Whole paper

The reprint is available in PDF (1742 kB !).

PAGEOPH, 148 (1996), 591-623.
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