AlpArray Austria 2

The scientific goal of this project and its international project context, AlpArray, is to better understand the structure, deformation, and evolution of the lithosphere beneath the Alps, from the surface down to the mantle transition zone. We focus on the Eastern Alps with a set of specific questions and hypotheses about the subsurface: What is the structure of the crust and the lithosphere under Austria and neighboring countries? It has been shown that a large part of the Eastern Alps extrudes to the East, but it is unclear at which depth the associated deformation takes place, within the lower crust, or rather in the upper mantle, the so-called asthenosphere. We will try to answer that question. How is the subsurface structure different between Alps, Pannonian Basin, the Dinarides and the Carpathians, and how and where does the transition between these regions take place within the Earth? How deep do the sedimentary basins in the region extend, e.g. under the Vienna Basin? To answer these questions, we will use data from the AlpArray network, a 400-station backbone across the entire Alpine region, with homogeneous spacing of 40-60 km between the stations. This network of portable stations complements the permanently installed stations in the area, e.g. that of the Central Institute for Meteorology and Geodynamics (ZAMG). We will make use of different seismological techniques, based on the analysis of seismological body waves, surface waves and ambient noise, to produce (tomographic) images of velocity structure, seismic anisotropy (that constrains deformation in the Earth), and also use hypothesis testing techniques that can directly respond to questions of geodynamic nature, such as those presented above. The data will also be used to contribute to societally-important questions as the detection of distant landslides and man- made signals. For all this it is very important to gather enough information about the subsurface. Beside learning about the structure of the subsurface and its deformation, it is also important for better understanding seismic hazard in the area. That earthquakes can occur has been documented by infrequent, but disastrous earthquakes in the past (e.g., Villach in 1348, Vienna in 1590). Gaining more such base data about seismicity in and around Austria and the tectonic faults along which they occur is of paramount importance.

AlpArray was an initiative to study the greater Alpine area with high-quality broadband seismological experiments. We have gathered infrastructure and expertise from institutions around Europe to work together on data acquisition, processing, and better understanding the subsurface under the Alps. Beyond the permanently installed stations, portable broadband stations were placed into a 400-station << backbone >> to achieve a homogeneous network of broadband seismological instruments over the entire Alpine area with 40-60 km spacing. This has provided information on subsurface structure and deformation with homogeneous and even resolution. Beside the backbone, there were also be densely-spaced stations along swaths across key parts of the Alpine chain. The main scientific goal of AlpArray was to better understand the structure, deformation, and evolution of the lithosphere beneath the Alps, from the surface down to the mantle transition zone, using the full set of seismological techniques for imaging structure and deformation, and for localizing seismicity. The geodynamic interpretation of the acquired data was and will be complemented by other Earth Science subdisciplines such as gravity and magnetotellurics, structural geology, and numerical and analogue modeling. The role of the project AlpArray Austria 2, as continuation of AlpArray Austria, was to assemble the Austrian contribution to the backbone network. Instrumentation for the project was supplied by the University of Vienna (UW), complementing the permanent network maintained by the Central Institute for Meteorology and Geodynamics (ZAMG). The gathered dataset is unprecedented in the Alpine region, for its spatial coverage and quality, and it allows us to perform cutting-edge research for the entire Alpine region, and especially for the Eastern Alps and their transition to the foreland and the Carpathians/Dinarides. The dataset gathered in this project is of considerable value also for better understanding seismic hazard in the area. Earthquakes have in the past caused much damage in Austrian and neighboring cities (e.g., Villach in 1348, Vienna in 1590), and this will happen again. Gaining more base data about seismicity in and around Austria and the tectonic faults along which they occur is therefore of paramount importance.