Applying scattered wave tomography and joint inversion of high-density (SWATH D) geophysical and petrophysical datasets to unravel Eastern Alpine crustal structure

点击翻译按钮获取中文摘要

This project harnesses the high density of seismic stations in the AlpArray complementary experiment SWATH D, conducted during the first phase of the SPP 2017 “Mountain Building Processes in 4D”, and also incorporates the wide transects EASI and the older TRANSALP, in order to understand how the crustal structure of the Alps seen today reflects the dramatic changes in mountain building style and reorganisation of plate boundaries at about 20 Ma. Uniform SE-directed subduction of European lithosphere during the Paleogene gave way to a more complex system involving not only the (partial) continuation of European subduction but the onset of Adriatic subduction below the Carpathians, the Apennines, and possibly the Alps. On the surface this revolution was reflected by laterally migrating subsidence patterns and infill in foreland basins as well as the development of different styles of accommodating shortening across the orogen. Within the crust, these changes must be accommodated by large scale decoupling horizons, but their geometry and relation to the structures seen at the surface, and even whether they are inside the crust or at the Moho, is disputed and probably differs laterally along the strike direction of the orogen. A still unresolved question concerns the existence of a possible polarity flip in the sense of subduction between the Central and Eastern Alps. If part of the continental crust is subducted, a characteristic jump in the Moho is expected, while a detachment at the base of the crust would lead to a kink in Moho topography. With this proposal we are directly addressing Theme 1 "Reorganisations of the lithosphere during mountain building" with a clear focus on mapping the possible reorganisations within the crust and of the topography of the Moho. We address Theme 2 "Surface and crustal responses" indirectly by constraining the different scenarios of crustal evolution that could have led to the current structure, and thereby provide a guide to those groups studying processes directly observable at the surface. By including experts in both seismological analysis as well as Alpine geology and petrophysics of the continental crust, we aim to go beyond merely delivering images of seismic properties by associating lithology. This proposal is part of a group of proposals with complementary goals and approaches devoted to understanding the Neogene Orogenic Revolution of the Alps.The project is structured into two work packages: The first focuses on the waveform inversion of high-frequency scattered and converted waves to image small-scale heterogeneities and discontinuities in the crust. The second employs a joint inversion of receiver functions and surface wave dispersion data using fully probabilistic Bayesian techniques. Constraints from geology and petrology will be used already at the model inference stage, not just at the interpretation stage, to best exploit the seismological data in the light of available prior knowledge.