SEISMIC ANISOTROPY IN WESTERN MAKRAN SUBDUCTION ZONE

We performed shear wave splitting (SWS) of SKS, SKKS and PKS (XKS) phases from six broad-band stations across the western makran subduction zone (WMSZ) to investigate seismic anisotropy in the region (Figure 1). For each waveform, the energy minimization method of Silver and Chan (1991) is used to find the SWS parameters. An exampleof such analysis is shown in Figure 2. For stations located on the Oman Sea coastline, the fast directions are oriented approximately trench-perpendicular and for stations JASK and JSK1 the fast directions are oriented trench-oblique (Figure 1). It seems that the main source of the anisotropy is residing in the upper mantle. As the lithosphere of theWMSZ is thin (about ~ 20 km) (Entezar-Saadat et al., 2017), therefore we expect the splitting contribution from the continental lithosphere to be negligible. The location of these stations provides several advantages that ameliorate some of the challenges inherent in interpreting XKS analysis in a subduction zone like the study done by Eakin et al. (2015) on Peruvian subduction zone. In west Makran, first, in the subduction regime, the slab starts with a very shallow gentle dip (∼ 8◦) and increases to about 55◦, where it plunges into the asthenosphere beneath the volcanic arc (Shad Manaman et al., 2010). So in this subduction region, dipping anisotropy is less likely (Eakin et al., 2015).

کلیدواژه ها:

Anisotropy ، Shear wave splitting ، Makran subduction zone ، Trench-perpendicular