Determination of S-wave Backazimuth from a Linear Array of Receivers

Locations of seismic events from a linear array of receivers may require determination of slowness vectors of arriving waves. In an isotropic medium, P-waves are polarized along the slowness vector, which enables direct determination of backazimuth (i.e. azimuth of a source at a receiver) from P-wave polarization. In contrast, S-waves are polarized in a plane perpendicular to their slowness vectors, which prevents direct determination of their backazimuth. We have developed a novel technique to determine the slowness vector of S-waves detected in a linear array of receivers in an isotropic medium. We combine the S-wave polarization measurements and the derivative of the S-wave slowness vector along the array to obtain the full slowness vector and backazimuth. The proposed method allows location of seismic events from a single linear array of receivers using only shear waves, which usually have much larger signal-to-noise ratio than P-waves. This technique is not affected by SV-waves, which is shown by a test on a synthetic dataset. We also test the method on two real microseismic datasets from a hydraulic fracturing treatment and show that it outperforms the backazimuth determination from P-waves and from horizontal polarization of S-waves.