Deep focus

Abstract: Summary The relation between p-A curves for surface and deep focus sources is investigated in order to construct synthetic body wave seismograms for non-zero focal depths by the quantized ray theory algorithm. The transformation of a surface focus p-A curve into a deep focus p-A curve is defined in terms of that curve which corresponds to surface focus rays reflected from the depth at which the deep focus is located. By analogy with the geometry of the surface focus formulation, paths of integration to obtain absolute travel-time and velocity-depth curves can be defined in the p-A plane. Explicit inversion from deep focus data is possible only when the velocity-depth structure above the depth of focus is known. Through a comparison of short period quantized ray theory synthetic seismograms with similar Cagniard-de Hoop computations, it is shown that quantized ray theory can be used for accurate predictions of body wave amplitude behaviour corresponding to a wide range of focal depths.