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SUMMARY We present new methods for the interpretation of 3‐D seismic wide‐angle reflection and refraction data with application to data acquired during the experiments CELEBRATION, 2000 and ALP 2002 in the area of the Eastern Alps and their transition to the surrounding tectonic provinces (Bohemian Massif, Carpathians, Pannonian domain, Dinarides). Data was acquired on a net of arbitrarily oriented seismic lines by simultaneous recording on all lines of seismic waves from the shots, which allows 2‐D and 3‐D interpretations. Much (80%) of the data set consists of crossline traces. Low signal to noise (S/N) ratio in the area of the young orogens decreases the quality of travel time picks. In these seismically heterogeneous areas it is difficult to assign clearly defined arrivals to the seismic phases, in particular on crossline record sections. In order to enhance the S/N ratio, signal detection and stacking techniques have been applied to enhance the Pg‐, Pn‐ and PmP phases. Further, inversion methods have been developed for the interpretation of WAR/R‐data, based on automated 1‐D inversion (Pg) and the application of the delay time concept (Pn). The results include a 3‐D velocity model of the crust based on Pg waves, time and depth maps of the Moho and a Pn‐velocity map. The models based on stacked data are robust and provide a larger coverage, than models based on travel time picks from single‐fold (unstacked) traces, but have relatively low resolution, especially near the surface. They were used as the basis for constructing models with improved resolution by the inversion of picks from single‐fold data. The results correlate well with geological structures and show new prominent features in the Eastern Alps area and their surrounds. The velocity distribution in the crust has strong lateral variations and the Moho in the investigation area appears to be fragmented into three parts.

[1] During the last decade, a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the Eastern Alps and their adjacent tectonic provinces. A fragmentation of the lithosphere into three blocks, Europe (EU), Adria (AD), and the new Pannonian fragment (PA), was interpreted and a triple junction was inferred. The goal of this study has been to relate these deep crustal structures to active tectonics. We used elastic plate modeling to reconsider the Moho fragmentation. We interpret subduction of EU below AD and PA from north to south and underthusting of AD mantle below PA from southwest to northeast. The Moho fragmentation correlates well with major upper crustal structures and is supported by gravity, seismic, and geodetic data. An analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central Eastern Alps and thickening of the Adriatic indenter under the Southern Alps. According to the velocity relations at the triple junction, PA moves relative to EU and AD along ENE and SE striking faults, mainly by strike slip. An eastward directed extensional component is compensated by the lateral extrusion of the central Eastern Alps. The Periadriatic (Insubric) line east of the triple junction and the mid-Hungarian fault zone have relatively recently lost their role as first-order active structures. We favor the idea that the Pannonian fragment and the TISZA block merged to a "soft" microplate surrounded by the Eastern and Southern Alpine, Carpathian, and Dinaric orogens. Citation: Brückl, E.,

A B S T R A C TIn regions where active source seismic exploration is constrained by limitations of energy penetration and recovery, cost and logistical concerns, or regulatory restrictions, analysis of natural source seismic data may provide an alternative. In this study, we investigate the feasibility of using locally-generated seismic noise in the 2-6 Hz band to obtain a subsurface model via interferometric analysis. We apply this technique to three-component data recorded during the La Barge Passive Seismic Experiment, a local deployment in south-western Wyoming that recorded continuous seismic data between November 2008 and June 2009. We find traffic noise from a nearby state road to be the dominant source of surface waves recorded on the array and observe surface wave arrivals associated with this source up to distances of 5 kms. The orientation of the road with respect to the deployment ensures a large number of stationary points, leading to clear observations on both in-line and cross-line virtual source-receiver pairs. This results in a large number of usable interferograms, which in turn enables the application of standard active source processing methods like signal processing, common offset stacking and traveltime inversion. We investigate the dependency of the interferograms on the amount of data, on a range of processing parameters and on the choice of the interferometry algorithm. The obtained interferograms exhibit a high signal-to-noise ratio on all three components. Rotation of the horizontal components to the radial/transverse direction facilitates the separation of Rayleigh and Love waves. Though the narrow frequency spectrum of the surface waves prevents the inversion for depth-dependent shear-wave velocities, we are able to map the arrival times of the surface waves to laterally varying group and phase velocities for both Rayleigh and Love waves. Our results correlate well with the known geological structure. We outline a scheme for obtaining localized surface wave velocities from local noise sources and show how the processing of passive data benefits from a combination with well-established exploration seismology methods. We highlight the differences with interferometry applied to crustal scale data and conclude with recommendations for similar deployments.

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Global warming is causing an apparent rapid retreat of many glaciers worldwide. In addition to mass-balance investigation, the determination and monitoring of total glacial ice volume and ice-thickness distribution are important parameters for understanding the interactions between climate and the complex glacier system. Because of spatially irregular and sparse datasets, scaling of volume and ice-thickness distribution is often a challenging problem. This study focuses on two small (<2 km2) temperate glaciers in the Hohe Tauern (Eastern Alps) region of central Austria. The period 2003–04 saw the first use of ground-penetrating radar (GPR) to determine the total ice volume and ice-thickness distribution of the two glaciers. A centre frequency of 20 MHz was used in point measuring mode. Despite variable data quality, bedrock reflections up to depths of >100m were identified in the data. The acquired GPR data are irregularly distributed and the spatial density is too low to calculate reasonable bedrock topography with standard interpolation approaches. Thus one main focus of this study was to develop an appropriate interpolation technique. Eventually, kriging technique and a glacial mechanically based interpolation parameter were used. Mean calculated ice thicknesses for the two investigated glaciers are 40–50 m, with a maximum of 150–165 m. No direct validation data are available, so different considerations support the computed bedrock topography.

Earthen dams and levees are prone to progressive failure through internal erosion of their structure. Internal erosion is often invisible to current methods of inspection until it manifests itself at the exterior surface. This study focuses on the novel use of passive seismic interferometry to monitor temporal changes in earthen embankments caused by internal erosion. This technique uses the ambient seismic noisei.e. ambient vibrationspropagating through the structure. Laboratory-scale and field-scale embankment failure experiments are monitored. Seismic impulse responses are reconstructed from the ambient noise and temporal variations in seismic wave velocities are observed throughout each test. The application of seismic interferometry on a canal embankment tested to failure by internal erosion revealed up to 20% reductions in surface wave velocity as internal erosion progressed. The monitoring of a field embankment loaded to partial failure revealed a 30% reduction in averaged surface wave velocity. Some local velocity variations showed good agreement with local pore water pressure responses.

SUMMARY The subject of this paper concerns the seismic modelling of the crustal structure in the transition zone from the Bohemian Massif, across the Molasse basin and the Eastern Alps to the Southern Alps, mainly on the territory of Austria. The CEL10/Alp04 profile crosses the triple point of the European plate, Adriatic microplate and the recently identified Pannonian fragment. The seismic data along the presented profile originate from two large experiments: CELEBRATION 2000 and ALP 2002. The wavefield observed in the Eastern Alps is more complex than in the Bohemian Massif. Strong first arrivals (Pg) are distinct up to 60–90 km offset and are characterized by large variations in apparent velocity and amplitude. The contact between the Molasse basin and the Eastern Alps represents a barrier for seismic waves. Mid‐crustal reflections (Pc) are usually recorded at short distance intervals (20–50 km) and are also characterized by variations in apparent velocity and amplitude. The Moho reflections are usually strong and well correlated, while Pn arrivals are only fragmentarily recorded. Detailed 2‐D forward modelling of all refracted, post‐critical and reflected phases, identified in the correlation process, was undertaken using a ray‐tracing technique. The P‐wave velocity in the crystalline upper crust of the Bohemian Massif and Molasse basin is about 6.15 km s−1, which is slightly higher than in the Alpine area (about 6.0 km s−1). Below the northern accretionary wedge of the Eastern Alps low‐velocity sediments penetrate towards the southwest (SW) down to about 10 km depth. In the middle crust of the Alpine part, a reflective zone was modelled by a lamellae structure with alternating high and low velocities and thicknesses of about 2–3 km. The lower crust in this part of the model is more homogeneous, with a velocity of about 6.9 km s−1. In the Bohemian Massif, a high‐velocity (HV) body (VP∼ 7 km s−1) of a few kilometres thickness was delineated in the depth interval 18–23 km. The crustal thickness along the CEL10/Alp04 profile changes from about 42–44 km in the SW (Alpine part), to around 40 km in the central part of the profile (Molasse basin), and 38–40 km in the NE (Bohemian Massif). The velocity in the uppermost mantle determined from Pn wave traveltimes is about 8 km s−1 along the whole profile. The interpretation of the seismic wavefield is supplemented by an existing 3‐D P‐wave velocity model of the area. Main features derived by 2‐D modelling (low velocities beneath the accretionary wedge, high velocities in the lower crust of the Bohemian Massif, Moho topography) well correlate with the 3‐D model. Furthermore, the 3‐D model allows assessing the lateral extent of significant features alongside the CEL10/Alp04 profile. This area is affected by both collision and escape tectonics. The high‐reflectivity zone in the middle crust is explained by intermediate to mafic intrusions, rather than by ductile extensional deformation as generally observed in the lower crust.