Enhancement of Teleseismic Body Phases with a Polarization Filter

A time domain polarization filter, originally proposed by Flinn, has been modified and is used to increase the signal to noise ratio of teleseismic body phases. Both the rectilinearity and direction of particle motion is obtained from the co-variance matrix for three components of ground motion over a small time interval. The estimate of rectilinearity is found by diagonalizing the matrix and forming a function that involves the ratio of the largest and intermediate principle axes of the matrix. The direction of polarization is found from the eigenvector of the largest principle axis. A set of time-varying operators are then obtained which act as a point by point gain control to modulate the digital seismic records. This non-linear filter is useful for enhancing P, pP, sP, PP, S and other compressional or shear phases. When applied to an array of three-component stations it appears to be possible to identify multiple events in the source function of some earthquakes.