On the joint inversion of seismic waveforms and gravimetric anomalies - Application to the Pyrenees

The Pyrenees is a continental collisional orogen characterized by complex tectonic settings, with continental subduction of the Iberian plate, shallow mantle bodies exhumed during the Cretaceous episode of rifting and foothill sediment basins. High resolution imaging of the deep global architecture of the Pyrenees is thus a very challenging problem. In this work, we perform joint inversions of teleseismic waveforms and gravimetric anomalies in order to obtain finely resolved 3D models of seismic velocities and density of the Pyrenees. We developed a 3D tele-seismic full waveform inversion framework based upon the open source Python package SeisFlows. Forward and adjoint simulations are based on the improved/speed-up SEM-FK hybrid method in SPECFEM3D. The gravity inversion is based upon the parallel TOMOFAST3D code. Seismic waveforms allow us to constrain the elastic parameters while gravity data allow us to better resolve the density structure. We designed several synthetic tests to find the best strategy for the joint inversion of these two types of data. We will then apply the joint inversion method to real data, using ~160000 gravity measurements from the global database of the Bureau Gravimétrique international and the seismological datasets from the PYROPE and OROGEN projects, as well as those from the permanent broadband seismological network stations. This will provide us a high resolution 3D velocity and especially density model of the Pyrenean lithosphere.