New shear wave splitting measurements using broadband seismic data recorded by the BX seismological network in Botswana

Abstract

New measurements shear-wave splitting (SWS) were determined using a teleseismic dataset from 21 broadband seismic stations belonging to the GSN-BX network in Botswana archived at IRIS-DMC. The stations are distributed across major geologic terrains such as the Kaapvaal craton, Limpopo Mobile Belt and Zimbabwe Craton. Earthquakes with magnitude larger than 5.2 mb with epicentral distances in the range of 90° and 180° were analyzed for SKS (S-wave traversing the core as P-wave) and SKKS (S-wave traversing the core as P-wave with one reflection from inner side of the Core Mantle Boundary) phases, while PKS (P-wave bottoming in the core and converting to S-wave at the Core Mantle Boundary) phases were analyzed in the range of 130°–165°. SWS parameters were calculated at each station by minimizing the energy on the transverse component of the PKS, SKKS, and SKS phases (hereafter collectively called XKS). The measurement included the polarization direction ϕ, which gives a reliable indication of the alignment of olivine in the upper mantle, and, the delay time dt between the arrival times of the fast and slow travelling split shear waves. The value of dt is related to the intrinsic anisotropy and thickness of the anisotropic layer. The SWS parameters provide insights into the present and past deformation processes of upper mantle.