Imaging the Effects of Subducting Slabs on the Mantle Transition Zone with Pds Receiver Functions Beneath Southern Europe

Abstract:

The mantle is delineated by seismic discontinuities between 300 and 800 km depth. Variations in topography, width and occurrence of the discontinuities indicate lateral variations in temperature, composition and water content, as these variations influence the mantle phase transitions. Seismic studies of the conversions of pressure to shear waves (Pds phases) are an important tool to observe lateral variations in these discontinuities.

Here we collect a Pds data set across all European seismic stations since 2000 that are available through ORFEUS or IRIS; resulting in ~500,000 event-station pairs. We deconvolve the radial component by the vertical component – assumed to represent the source component- using the iterative deconvolution method to obtain receiver functions. We assess the quality of a receiver function by the signal-to-noise ratio and by evaluating how well the radial component is reproduced when reconvolving the receiver function with the vertical component. This results in ~36,000 high quality receiver functions across Europe.

Our receiver functions show little lateral variation in the depth of the transition zone discontinuities across the East European Craton, and we use this region as a reference to the more tectonically unstable regions. Around the Mediterranean, we look for signature of slabs ponding or penetrating at the discontinuity around 660 km. The Hellenic slab, which in tomographic models extends into the lower mantle, causes a signature of a disappearing '410' and a deeper, broader '660'. There are also potential signatures of '300' and '520' discontinuities in the slab region.

To explain our observations we compute synthetic Ps receiver functions for mantle transition zone models of various temperatures for various compositional models. The synthetic seismic velocity models are computed using Perple_X (Connolly, 2005) with the mineral parameter database of Stixrude and Lithgow-Bertolloni (2011). The synthetics are computed with the reflectivity method. The data and synthetics need to be compared to use the observations as a thermometer or indicator of slab composition or water content.