Mapping mantle structure of the European plate based on seismic full-waveform inversion methods

The European continent undergoes a series of complicated tectonic processes since the closure of the Tethyan Ocean, including oceanic plate subduction, continental plate subduction, continental collision and orogeny. High resolution 3-D mantle structure under the European plate is key to investigate its geodynamic evolution history. Full waveform seismic inversion for mantle structure has become feasible with the advent of accurate 3D wave propagation codes and the use of adjoint sources to compute the gradient of misfit functions between data and synthetics. The adjoint source, in this approach, depends on how a misfit is defined between data and synthetics. The time or phase shift between data and synthetic has been used in most full waveform inversions for mantle structure. Waves that sample the upper mantle, however, are almost always multi-pathed due to discontinuities, the low velocity zone as well as large amplitude lateral variations, leading to complex waveforms that cannot be fully captured by time/phase shifts. Here we use the normalized correlation coefficient between data and synthetics as a misfit function to simultaneously capture both the phase and relative amplitude information of the waveform, and perform full waveform inversion on a large data set of three component seismic data from Europe. The global 3-D tomography model S362WMANI combined with crustal model EPcrust comprises our starting model. The adopted numerical solver for the wave equation is SPECFEM3D_GLOBAL, a high-accuracy numerical simulation package based on the spectral-element method. We adopt multi-stage inversion method to iteratively enhance the frequency range of the inversion. Our preliminary results show significant improved resolution of the upper mantle structure and provide key constraints on the deep subduction processes of micro-plates in the Europe region.