SplitRacer; MATLAB code and GUI for semiautomated analysis and interpretation of teleseismic shear-wave splitting

We present a graphical user interface in the MATLAB environment for teleseismic shear-wave splitting analysis. In view of increasingly large seismological experiments, SplitRacer is designed to process large data sets quickly for which it integrates automatic and user-active steps. This enables a straightforward analysis based on the user's own quality criteria. SplitRacer offers a number of features designed to ensure precise measurements as well as user-friendliness. Data can be downloaded directly from all data centers that are part of the International Federation of Digital Seismograph Networks Web Services. Existing data can easily be used when cut into 1-hr three-component seismograms. A first automatic data check is followed by visual assessment of the phases in question. We account for a possible misalignment of the sensor by analyzing the particle motions and comparison with the theoretical back azimuths of the events recorded at a station. The shear-wave splitting analysis is based on the minimum (transverse) energy method (Silver and Chan, 1991), which constrains the fast-polarization direction and the delay time. Measurements can be repeated for a number of time windows to enable a statistical error analysis. SplitRacer provides an overview of single-phase splitting measurements per station that can be used to detect azimuthal dependencies. To infer the anisotropic properties beneath a station, SplitRacer offers the possibility to fit models of one or two anisotropic layers or a model of smoothly varying anisotropy to the observed data. Furthermore, SplitRacer also offers a multiphase joint-splitting analysis for one and two hypothetical layers in which all events at a given station are used simultaneously to constrain the anisotropic model. This significantly reduces the influence of noise and makes the measurement more robust. As an example, we apply SplitRacer to constrain seismic anisotropy beneath the permanent station BKS of the Berkeley Digital Seismic Network.