Imaging the Lithosphere-Asthenosphere Boundary Using Iterative Method of Receiver Function Analysis: A Synthetic Seismogram Approach
Abstract:Our study is based on the receiver-function (RF) analysis of a hypothetical regional geological model that extends from oceanic to thick cratonic lithosphere. RF techniques are used to study the interior of Earth. Teleseismic P waves are followed by a series of scattered waves, which occur due to P-to-S converted phases. The sequence of these scattered waves on a time series can be represented by receiver function (RF) for the station and may vary with the incidence angle and azimuth of the incoming P-wave. Here we use iterative deconvolution method to study receiver functions, which provides RF estimates with low noise levels. This method is based on least-squares minimization of the difference between the observed horizontal seismogram and a predicted signal generated by the convolution of an iterative spike train with the vertical-component of seismogram.
The study is based on a hypothetical model (800x800x400km) on a mesh with 10 km grid spacing that is smoothly embedded within a standard global Earth model. Physical properties of the regional model match with prescribed surface heat-flow and geoid boundary conditions computed using an approach based on thermodynamics, mineral physics, and solid-Earth geophysics. The model also incorporates seismic anisotropy in the mantle beneath the hypothetical continent. A three dimensional model is computed that approximates the mantle flow around the hypothetical continental lithospheric keel. The anisotropy is computed from the flow model and is incorporated to the model. Synthetic seismograms are computed using SPECFEM3D_GLOBE, which provides full wave-equation modelling of seismic wave propagation incorporating material properties such as anisotropy, attenuation and fluid-solid interfaces. To ensure a realistic (non-ideal) azimuthal distribution, the event locations are based on a subset of a ten-year global catalog from 2001 to 2010 within the magnitude range from 6.0 to 7.0.