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First motions from seismic sources in a semi-infinite homo-geneous medium overlain by an inhomogeneous layer


 The problem of seismic radiation from buried sources situated at a depth H below the free surface of an inhomogeneous layer of thickness h(< H) overlying a semi-infinite homogeneous medium is considered. First-motion solutions have been obtained at the free surface. Three point sources—slip on a horizontal plane, strike slip on a vertical plane and dip slip on a plane dipping at 45°—are considered in detail. Numerical results are computed for a linear increase of P and S velocities in the layer. Amplitude variations and first-motion signs of P, SV and SH waves are shown graphically for homogeneous and inhomogeneous media.