Azimuthal and Spatial Variations of Shear-Wave Splitting Parameters at Long-Running Seismic Stations in the Area Affected by the India-Eurasian Collision


Most previous shear-wave splitting studies presented the results in the form of station-averaged splitting parameters. This practice is valid only when the parameters do not vary significantly with the geographic location of the ray-piercing points at the depth of the source of anisotropy, and/or with the arriving azimuth of the XKS (including SKS, SKKS, and PKS) ray-paths. Here we present results of XKS splitting measurements at about 15 long-running seismic stations in the part of East Asia that is influenced by Cenozoic orogenic events associated with the India-Eurasian collision, aiming at evaluating the pervasiveness of complex anisotropy in the vicinity of the stations. Our results show that based on the spatial/azimuthal variation of the splitting parameters, the stations can be divided into 4 groups. Those in Group A (stations AAK, LSA, ULN, WMQ, WUS) demonstrate a clear azimuthal variation with a 90-degree periodicity which is suggestive of double-layer anisotropy. Resulting splitting parameters at Group B stations (BJT, ENH, HIA, LZH, TLY) show clear dependence on the geographic location of the ray-piercing points (and thus dependence on the back-azimuth also), but the azimuthal dependence is complex and is not a periodic function. In most cases those stations are located near major tectonic boundaries and the splitting parameters from events with ray-piercing points on the same tectonic province are similar. Stations in Group C (CHTO, MAKZ, XAN) have a decent azimuthal coverage and show insignificant azimuthal and spatial variations, suggesting simple anisotropy. The remaining two stations (GAR, KMI) have a limited azimuthal coverage and thus a conclusive categorization cannot be made until more events become available. Observations at those stations suggest that at least in the study area, complex anisotropy is pervasive (10 out of 13 stations with a sufficient azimuthal coverage), and consequently, station-averaged splitting parameters may not be representative of the actual anisotropic structure beneath a station and should be used with caution. The study also highlights the importance of long-running seismic stations in the realization of complex anisotropy.

Meeting Name

Western Pacific Geophysics Meeting (2010: Jun, 22-25, Taipei, Taiwan)


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Body waves; Mantle; Lithosphere

Document Type

Article - Conference proceedings

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