Measuring Seismic Anisotropy Using Teleseismic Direct S Waves: A Differential Splitting Intensity Method

Abstract Seismic anisotropy provides constraints on the lithospheric deformation and mantle flow. SKS splitting analysis is a common approach to investigate anisotropy, but tends to suffer from potentially insufficient back‐azimuthal coverage. Teleseismic direct S waves provide complementary constraints; however, they cannot be directly used in conventional splitting analysis due to source‐side anisotropy and phase contamination. In this study, we propose a new method based on splitting intensity (SI) to measure receiver‐side seismic anisotropy under stations. The method calculates differential SI between adjacent stations in which the similar contribution of source‐side anisotropy and phase contamination may be eliminated properly. Data with polarization directions within the ranges of 0°–30°, 75°–105°, and 150°–180° referred from the back azimuths and epicentral distances of 30°–80° are considered useful. Splitting parameters obtained from our new method are comparable to those from SKS splitting measurements. We further apply this method to a data set from the southeastern Tibetan Plateau. Using records at 95 permanent stations from 2,783 events, we obtain 36,185 high‐quality SI measurements, which yield 11,185 differential SI measurements. Our results present a similar anisotropy pattern to those revealed by previous research, that is, dominant transition of fast polarizations from N‐S to the north and E‐W to the south of 26°N. The new method largely expands the application of shear wave splitting analysis, which increases the data coverage in many regions worldwide. Absolute SI measurements appear to be necessary for homogeneous anisotropic structures, although this still requires further investigation.