Three-dimensional, wavefield imaging of broadband seismic array data

• Authors: Gary L. Pavlis
• Venue: Computers & Geosciences
• Year: 2011

This paper describes an implementation of a three-component, three-dimensional plane wave migration method to image P-to-S converted waves that arrive following the direct P waves of teleseismic earthquakes. The programs described assume that the input data have been deconvolved to produce a set of vector impulse response functions with the initial P pulse centered at time 0. This method was implemented as three different application programs called pwstack, pwmig, and gridstacker. pwstack produces local-scale plane wave decompositions using the pseudostation concept. The output of pwstack is an estimate of the plane wave response over a grid of slowness vectors interpolated onto a regular grid in space. The Gaussian smoother that is used for the pseudostation method has the additional benefit of serving as a type of spatial antialiasing filter. The program called pwmig takes the output of pwstack and inverts the plane wave data for radial and transverse scattering potential using an inverse generalized Radon transform. Data can be back-projected using a conventional longitudinal, radial, transverse coordinate system or a novel depth-variable method that computes a transformation matrix linking each vector sample to an equivalent dipping-layer coordinate system at the corresponding scattering point. Because pwmig is a prestack method, a final program, gridstacker, is needed to stack data from multiple events that characterize real data. gridstacker is a general solution for stacking data with different grid geometries and variable data quality. Weighting functions can be defined externally by a user-supplied recipe or one can use a set of robust estimation methods coded in gridstacker. The programs are validated with simulation data produced by recently developed elastic finite-difference code and a model that simulates the edge of a subduction zone. Finally, I show an example of an application of these programs to image the western United States with the USArray.