Shear wave splitting in the Isparta angle, southwestern Turkey: Anisotropic complexity in the mantle

Abstract

This study presents shear wave splitting analysis results observed at ISP (Isparta) broadband station in the Isparta Angle, southwestern Turkey. We selected 21 good quality seismic events out of nearly 357 earthquakes and calculated splitting parameters (polarization direction of fast wave, φ and delay time between fast and slow waves, δt) from mainly SKS and a few SKKS phases of the selected 21 seismic events. Then, we compared calculated splitting parameters at ISP station (56 • ≤ φ ≤ 205 • ; 0.37 s ≤ δt ≤ 4 s) with those previously calculated at ANTO (Ankara) and ISK (İstanbul) stations (27 • ≤ φ ≤ 59 • ; 0.6 s ≤ δt ≤ 2.4 s and 26 • ≤ φ ≤ 54 • ; 0.6 s ≤ δt ≤ 1.5 s) which are located at 230 and 379 km away from ISP station in central and northwestern Turkey, respectively. The backazimuthal variations of the splitting parameters at ISP station indicate a different and complex mantle polarization anisotropy for the Isparta Angle in southwestern Turkey compared to those obtained for Ankara andİstanbul stations.

Shear wave splitting along a nascent plate boundary: the North Anatolian Fault Zone

“…Although we have a limited backazimuthal distribution for our results and we cannot completely rule out the presence of vertically varying anisotropy, the distribution of nulls and the consistency in observed splitting parameters favour a single layer anisotropic source. This one layer model is also consistent with previous observations by Vinnik et al (1992) and Şapaş & Boztepe‐Güney (2009), who analysed anisotropy beneath the long‐operating station ANTO and found no evidence of vertically varying anisotropy. The case of two‐layer anisotropy will be discussed further in the following section.…”

The Influence of the North Anatolian Fault and a Fragmenting Slab Architecture on Upper Mantle Seismic Anisotropy in the Eastern Mediterranean

“…(d) ISP station in the Isparta Angle. The dashed gray line represents the model of Şapaş and Boztepe‐Güney (2009) and the thick purple line indicates splitting parameters when stacking the eastern and western splits separately.…”

“…The authors propose two anisotropic layers, with the upper contained entirely within the crust. Depth-dependent anisotropy is also suggested beneath the central NAF by receiver function analysis (Vinnik et al, 2016) and there is evidence for backazimuth-dependent splitting parameters at station ISP in south-west Anatolia, interpreted as two anisotropic layers by Şapaş and Boztepe-Güney (2009). Contrastingly, recent anisotropic Rayleigh wave tomography is used by Legendre et al (2021) to suggest that anisotropy is weak throughout the Anatolian upper mantle, and XKS splitting therefore arises in the mantle transition zone.…”

Phylogeny and diversification of mountain vipers (Montivipera, Nilson et al., 2001) triggered by multiple Plio–Pleistocene refugia and high-mountain topography in the Near and Middle East

“…The time frame correlates with a prominent tectonic event in the Middle East, the uplift of the Turkish-Iranian plateau to an elevation of 1.5-2 km a.s.l. (Şapaş and Boztepe-Güney, 2009). Along with the increase of elevation, climatic, spatial, biotic and evolutionary factors changed.…”