EFFECT OF SINUSOIDAL INTERFACES ON TELESEISMIC P-WAVE RECEIVER FUNCTIONS

Using the T-matrix, or extended boundary condition, method, we model seismic wave scattering from earth models with irregular interfaces. This is motivated by numerous observations that surface and subsurface topography is responsible for the amplification and de-amplification of seismic waves and the generation of coda waves. We demonstrate that irregular Moho and free-surface scattering significantly affects teleseismic P-wave receiver function waveforms. Receiver functions are routinely used to obtain detailed crustal and upper mantle structure. For a layer-over-halfspace model, we perform a sensitivity study on the effects of ray parameter, interface roughness and wavelength, receiver position, and incident wave frequency content. The free-surface responses vary significantly with receiver position, interface wavelength and with incident wave frequency content. Using frequency-wavenumber analysis, the coda is shown to contain scattered Rg waves and S waves. Receiver functions are formed from the free-surface responses by deconvolution, and these are then inverted, as synthetic 'data', for plane-layered velocity structure, to show how scattered energy maps onto the final velocity models. Spurious structure models result, with the amplitude of the spurious features (for example low-velocity zones) decreasing with interface roughness. The resulting velocity models also vary appreciably with receiver position.