A comprehensive high resolution 3D P- and S-wave velocity model for the Alpine mountain chain using local earthquake data: Constraining crustal structure, lithologies and mountain-building processes

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Description:The dense AlpArray Seismic Network (AASN) allows for the first time to image in high resolution the seismic properties of the crust and mantle lithosphere beneath the Alps. Although numerous studies and seismic experiments have been conducted to decipher the mountain building processes in the Alps, only in the Western Alps some degree of consensus has been reached. However, for the Eastern Alps structure and tectonic processes leading to mountain building are still controversially discussed. The tectonic revolution in the Eastern Alps as discussed by Handy et al. in the introduction to the second period of the SPP must find its expression in the crust, most notably as large scale crustal decoupling horizons; however, their location and extend are not constrained yet by geophysical images. Additionally, the possible polarity flip of subduction in the Eastern Alp is still hotly debated, but if existent should be accompanied by a Moho jump.In this proposal we will use Local Earthquake Tomography (LET) to image the P- and S-wave velocities and corresponding Poisson ratio (Vp/Vs) and precise earthquake hypocenters in the Alpine crust and mantle lithosphere providing essential geophysical images and constraints to unravel the processes involved in the tectonic revolution. For the analysis of the waveform data (picking/identification of phases) we will use methods related to artificial intelligence and machine learning. We will directly address Theme 1: Reorganisations of the lithosphere during mountain building by delineating intra-crustal structures and Moho topography. Our comprehensive velocity model will also address Theme 2: crustal response of changes in mountain structure by linking the investigated surface structures in MB4D with high resolution images of mantle processes that are currently debated in the seismological community (e.g. slab polarity flip). The work is part of a cluster of proposals with complementary goals and approaches to investigate the Neogene Orogenic Revolution of the Alps. This cluster will provide the necessary complimentary expertise in Alpine geology, numerical modelling, and seismology needed to unravel the mountain building processes in the Eastern Alps. Deliverables:• 3D high resolution P- and S-wave velocity (and Poisson ratio) model of the Alps• High resolution earthquake locations and associated uncertainties• Crustal corrections for upper mantle tomography studies• A comprehensive waveform database and event database (including travel times) for further analysis