A large data set of surface wave phase velocity measurements is compiled to study the structures of the crust and upper mantle underneath the Alpine continental collision zone. Records from both ambient‐noise and earthquake‐based methods are combined to obtain a high‐resolution 3‐D model of seismic shear velocity. The applied techniques allow us to image the shallow crust and sedimentary basins with a lateral resolution of about 25 km. We find that complex lateral variations in Moho depth as mapped in our model are highly compatible with those obtained from receiver function studies; this agreement with entirely independent data is a strong indication of the reliability of our results, and we infer that our model has the potential to serve as reference crustal map of shear velocity in the Alpine region. Mantle structures show nearly vertical subducting lithospheric slabs of the European and Adriatic plates. Pronounced differences between the western, central, and eastern Alps provide indications of the respective geodynamic evolution: we propose that in the southwestern and northeastern Alps, the European slab has broken off. The complex anomaly pattern in the upper mantle may be explained by combination of remnant European slab and Adriatic subduction. Along‐strike changes in the upper mantle structure are observed beneath the Apennines with an attached Adriatic slab in the northern Apennines and a slab window in the central Apennines. There is also evidence for subduction of Adriatic lithosphere to the east beneath the Pannonian Basin and the Dinarides down to a maximum depth of about 150 km.

Dynamic glacier activity is increasingly observed through passive seismic monitoring. We analysed near-regional-scale seismicity on the Arctic archipelago of Svalbard to identify seismic icequake signals and to study their spatialÁ temporal distribution within the 14-year period from 2000 until 2013. This is the first study that uses seismic data recorded on permanent broadband stations to detect and locate icequakes in different regions of Spitsbergen, the main island of the archipelago. A temporary local seismic network and direct observations of glacier calving and surging were used to identify icequake sources. We observed a high number of icequakes with clear spectral peaks between 1 and 8 Hz in different parts of Spitsbergen. Spatial clusters of icequakes could be associated with individual grounded tidewater glaciers and exhibited clear seasonal variability each year with more signals observed during the melt season. Locations at the termini of glaciers, and correlation with visual calving observations in situ at Kronebreen, a glacier in the Kongsfjorden region, show that these icequakes were caused dominantly by calving. Indirect evidence for glacier surging through increased calving seismicity was found in 2003 at Tunabreen, a glacier in central Spitsbergen. Another type of icequake was observed in the area of the Nathorstbreen glacier system. Seismic events occurred upstream of the glacier within a short time period between January and May 2009 during the initial phase of a major glacier surge. This study is the first step towards the generation and implementation of an operational seismic monitoring strategy for glacier dynamics in Svalbard.

The increasingly dense coverage of Europe with broad-band seismic stations makes it possible to image its lithospheric structure in great detail, provided that structural information can be extracted effectively from the very large volumes of data. We develop an automated technique for the measurement of interstation phase velocities of (earthquake-excited) fundamental-mode surface waves in very broad period ranges. We then apply the technique to all available broadband data from permanent and temporary networks across Europe. In a new implementation of the classical two-station method, Rayleigh and Love dispersion curves are determined by cross-correlation of seismograms from a pair of stations. An elaborate filtering and windowing scheme is employed to enhance the target signal and makes possible a significantly broader frequency band of the measurements, compared to previous implementations of the method. The selection of acceptable phase-velocity measurements for each event is performed in the frequency domain, based on a number of fine-tuned quality criteria including a smoothness requirement. Between 5 and 3000 single-event dispersion measurements are averaged per interstation path in order to obtain robust, broad-band dispersion curves with error estimates. In total, around 63,000 Rayleigh-and 27,500 Love-wave dispersion curves between 10 and 350 s have been determined, with standard deviations lower than 2 per cent and standard errors lower than 0.5 per cent. Comparisons of phase-velocity measurements using events at opposite backazimuths and the examination of the variance of the phase-velocity curves are parts of the quality control. With the automated procedure, large data sets can be consistently and repeatedly measured using varying selection parameters. Comparison of average interstation dispersion curves obtained with different degrees of smoothness shows that rough perturbations do not systematically bias the average dispersion measurement. They can, therefore, be treated as random but they do need to be removed in order to reduce random errors of the measurements. Using our large new data set, we construct phase-velocity maps for central and northern Europe. According to checkerboard tests, the lateral resolution in central Europe is ≤150 km. Comparison of regional surface-wave tomography with independent data on sediment thickness in North-German Basin and Polish Trough confirms the high-resolution potential of our phase-velocity measurements. At longer periods, the structure of the lithosphere and asthenosphere around the Trans-European Suture Zone (TESZ) is seen clearly. The region of the Tornquist-Teisseyre-Zone in the southeast is associated with a stronger lateral contrast in lithospheric thickness, across the TESZ compared to the region across the Sorgenfrei-Tornquist-Zone in the northwest.

SUMMARY This study images upper‐mantle structure beneath different tectonic and geomorphological provinces in southern Scandinavia by P‐wave traveltime tomography based on teleseismic events. We present results using integrated data from several individual projects (CALAS, MAGNUS, SCANLIPS, CENMOVE and Tor) with a total of 202 temporary seismological stations deployed in southern Norway, southern Sweden, Denmark and the northernmost part of Germany. These stations, together with 18 permanent stations, yield a high density data coverage and enable presentation of the first high resolution 3D seismic velocity model for the upper mantle for this region, which includes the entire northern part of the prominent Tornquist Zone and the Southern Scandes Mountains. P‐wave arrival time residuals of up to ±1 s are observed indicating large seismic velocity contrasts at depths. Relative regional as well as absolute global tomographic inversion is carried out and consistently show upper‐mantle velocity variations relative to the ak135 global reference model of up to ±2–3 per cent corresponding to P‐wave velocity differences of 0.4–0.5 km s–1 from depths of about 100 km to more than 300 km. High upper‐mantle velocities are observed to great depth to the east in Baltic Shield areas of southwestern Sweden suggesting the existence of a deep lithosphere keel. Lower velocities are found to the west and southwest beneath the Danish and North German sedimentary basins and in most of southern Norway. A well defined, generally narrow and deep boundary is observed between areas of contrasting upper‐mantle seismic velocity. In the southern part of the study area, this boundary is localized along and east of the Sorgenfrei–Tornquist Zone. It seems to follow the eastern boundary of a zone of significant Late Carboniferous–Permian volcanic activity from southwestern Sweden to the Oslo Graben area. To the north, it crosses shield units, Caledonides as well as areas of high topography. Supported by independent results of surface wave studies, we interpret this velocity boundary as a first order lithosphere boundary representing the southwestern edge of thick shield lithosphere. In basin areas to the southwest, low upper‐mantle velocities are associated with asthenosphere beneath thinned lithosphere and velocity contrasts are likely to arise mainly from temperature differences. To the north structural and geodynamic relations are more complex and both temperature and compositional differences may play a part. Reduced upper‐mantle velocity beneath southern Norway also seems, despite relatively low heat flow, to be associated with areas of thinned lithosphere, pointing towards increased temperatures and reduced density in the upper mantle. This feature extends over large areas and seems not directly correlated to the shorter wavelength high topography of the Scandes Mountains, but may contribute with some isostatic buoyancy on a regional scale. For this northern area, there is no obvious geodynamic explanation to reduced upper‐mantle velocity. A...

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