Recent developments in the study of crustal response to seismic waves it have necessitated research on the effect of an inclined or a concaved interface of discontinuity in the crust or upper mantle structure. In this paper, the effect of the inclination on the observed spectrum at the surface is examined by an experimental method (two-dimensional model seismology).
Ray-theoretical consideration is found to be valid even for dip angles as large as 30°. We can readily explain the main features of recorded waves and their spectra (or the transfer functions) in terms of the following properties: multiple reflections within a dipping layer; conversions between P and S phases at the free surface and at the bottom boundary of the layer; polarities of S waves.
It has been experimentally established that dip angles of the layer of less than about 5°-10°, the amplitude characteristics of the transfer functions show only slight changes in forms and in peak frequencies.
The key point of the experiment for studying the effects of a dipping layer on the transfer function is the generation of plane waves. For this purpose, many sources of cylindrical waves are used taking advantange of the superposition principle.

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Surface displacements due to a fault model in a semi-infinite medium are obtained in the near field. Final solution can be found only by evaluating definite integrals. It is shown that displacements due to a moving dislocation can also be obtained by evaluating similar definite integrals.

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A mathematical expression of elastic waves reflected due to slight heterogeneity of the medium is presented explicitly to the first order approximation in the case of one-dimensional problems. The approximate solution of elastic waves propagated through a heterogeneous medium is obtained by regarding the effect of the heterogeneity as that of equivalent dynamical sources scattered within the medium and by applying Green's function to the first-order approximate wave equation.
Comparison between the approximate reflected wave and the exact one shows the validity of the present theory.
The applications of the solution are found in such problems as attenuation of elastic waves passing through a heterogeneous medium and interpretation of reflected waves from a certain layered structure.
The finite difference method is applied to the wave equation with the aid of the present theory in order to demonstrate the nature of elastic waves propagated through a heterogeneous medium.

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The expression for a stress drop of a fault with finite length and width is derived, and the mean stress drop over the fault plane is computed as a function of fault dimension.
The geometrical factor J is related to the stress drop by (21) in the text. Plots of the mean J value, J, versus the ratio (length/width) in Fig. 5 enables us to determine the stress drop for a finite fault. It is shown that for earthquakes, whose stress drops were estimated to be very large by applying the expressions derived on the basis of an assumption of an infinitely long narrow fault, stress drops are reduced when taking account of the finiteness of fault demension.

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Many aftershocks of very small magnitude were detected at Caliente, Nevada, seven and a half months after the southeastern Nevada earthquake of August 16, 1966.
An observation was made for 10 days at Caliente in the framework of the Japan-U.S. microearthquake program. Observed were 2600 events per day where the S-P time was shorter than 2 seconds. A b value was determined to be 1.10 for the magnitude range from -1.1 to 0.2.

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