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We present a novel three-dimensional model of compressional wave attenuation (1/QP) for the Eastern and eastern Southern Alps in Europe that includes the eastern part of the Adriatic indenter, termed here the Dolomites Sub-Indenter. Our approach employed waveform data from the SWATH-D network, a dense temporary network operational between 2017 and 2019, as well as selected stations of the larger AlpArray Seismic Network. A spectral inversion method using frequency-independent quality factor QP, was applied to derive 3578 path-averaged attenuation values (t*) from 126 local earthquakes. These were then inverted using the damped least square inversion (local earthquake tomography) for the attenuation structure. The resulting QP model, which builds on and complements a previously calculated 3-D velocity model (VP and VP/VS), exhibits good resolution down to ~ 20 km depth. Several anomalies can be correlated with the distribution of other physical parameters (VP and VP/VS) and regional tectonic features. Notably, the Friuli-Venetian region exhibits the highest attenuation (lowest QP) anomaly, coinciding with low VP values and increased VP/VS. This anomaly is likely associated with a high density of faults and fractures, as well as the presence of fluid-filled sediments along the active thrust front in the eastern segment of the Southern Alps. Another intriguing observation is the low attenuation (high QP) anomaly along the northwestern edge of the Dolomites Sub-Indenter (NWDI), located south of the Periadriatic fault and east of the Giudicarie fault, where seismicity is notably absent. This anomaly coincides with Permian magmatic rocks at the surface and may be a measure of their strength at depth. [ABSTRACT FROM AUTHOR]

Neogene indentation of the Adriatic plate into Europe led to major modifications of the Alpine orogenic structures and style of deformation in the Eastern and Southern Alps. The Giudicarie Belt is a prime example of this, as it offsets the entire Alpine orogenic edifice; its activity has been kinematically linked to strike-slip faulting and lateral extrusion of the Eastern Alps. Remaining questions on the exact role of this fold-and-thrust belt in the structure of the Alpine orogen at depth necessitate a quantitative analysis of the shortening, kinematics, and depth of decoupling beneath the Giudicarie Belt and adjacent parts of the Southern Alps. Tectonic balancing of a network of seven cross sections through the Giudicarie Belt parallel to the local NNW–SSE shortening direction reveals that this belt comprises two kinematic domains that accommodated different amounts of shortening during overlapping times. These two domains are separated by the NW–SE-oriented strike-slip Trento-Cles–Schio-Vicenza fault system, which offsets the Southern Alpine orogenic front in the south and merges with the Northern Giudicarie Fault in the north. The SW kinematic domain (Val Trompia sector) accommodated at least ∼ 18 km of Late Oligocene to Early Miocene shortening. Since the Middle Miocene, this domain experienced at least ∼ 12–22 km shortening, whereas the NE kinematic domain accommodated at least ∼ 25–35 km shortening. Together, these domains contributed an estimated minimum of ∼ 40–47 km of sinistral strike-slip motion along the Northern Giudicarie Fault, implying that most offset of the Periadriatic Fault is due to Late Oligocene to Neogene indentation of the Adriatic plate into the Eastern Alps. Moreover, the faults linking the Giudicarie Belt with the Northern Giudicarie Fault reach ∼ 15–20 km depth, indicating a thick-skinned tectonic style of deformation. These fault detachments may also connect at depth with a lower crustal Adriatic wedge that protruded north of the Periadriatic Fault and are responsible for N–S shortening and eastward, orogen-parallel escape of deeply exhumed units in the Tauern Window. Finally, the E–W lateral variation of shortening across the Giudicarie Belt indicates internal deformation and lateral variation in strength of the Adriatic indenter related to Permian–Mesozoic tectonic structures and paleogeographic zones. [ABSTRACT FROM AUTHOR]

We study the crustal structure under the Eastern and Southern Alps using ambient noise tomography. We use cross-correlations of ambient seismic noise between pairs of 71 permanent stations and 19 stations of the Eastern Alpine Seismic Investigation (EASI) profile to derive new 3D shear velocity models for the crust. Continuous records from 2014 and 2015 are cross-correlated to estimate Green's functions of Rayleigh and Love waves propagating between the station pairs. Group velocities extracted from the cross-correlations are inverted to obtain isotropic 3D Rayleigh- and Love-wave shear-wave velocity models. Our models image several velocity anomalies and contrasts and reveal details of the crustal structure. Velocity variations at short periods correlate very closely with the lithologies of tectonic units at the surface and projected to depth. Low-velocity zones, associated with the Po and Molasse sedimentary basins, are imaged well to the south and north of the Alps, respectively. We find large high-velocity zones associated with the crystalline basement that forms the core of the Tauern Window. Small-scale velocity anomalies are also aligned with geological units of the Austroalpine nappes. Clear velocity contrasts in the Tauern Window along vertical cross sections of the velocity model show the depth extent of the tectonic units and their bounding faults. A mid-crustal velocity contrast is interpreted as a manifestation of intracrustal decoupling in the Eastern Alps that accommodated eastward escape of the Alcapa block. [ABSTRACT FROM AUTHOR]

We aim to link fault kinematics along the orogenic front of the Eastern Southern Alps with deformation of the Adriatic indenter since Miocene time. The main structure in this area, the Schio-Vicenza Fault, is a steep fault system that trends NW-SE, perpendicular to the strike of frontal thrusts of the Eastern Southern Alps and oblique to NNE-SSW striking Giudicarie fold-and-thrust belt. This belt was active in Miocene time and offsets the main edifice of the Alps, including the Periadriatic Fault.The steep fault surfaces of the Schio-Vicenza Fault carry two generations of striations: (1) older subhorizontal striations with sinistral slip indicators; and (2) younger SW-dipping striations indicating oblique downthrow of the SW block. Faults with the Schio-Vicenza Fault trend can be traced NW to the end of the ENE-WSW-trending Valsugana Thrust. However, the Schio-Vicenza Fault does not merge with or truncate the Giudicarie Belt as shown on previous maps of the area.East of the Schio-Vicenza Fault, the orogenic front of the Eastern Southern Alps comprises the Bassano thrust system. This system is associated with an ENE-WSW trending ramp anticline that folds and tilts Mio-Pliocene strata. Southwest of the Schio-Vicenza Fault, the front comprises the Marana Thrust, which emplaces the Upper Triassic Dolomia Principale to the SSE onto Lower Cretaceous strata ('Maiolica'). Fault-slip analysis of this thrust and NE-SW trending fold axes indicate NNW-SSE shortening. At the SW end of the Marana Thrust, m-scale chevron folds in the footwall strata ('Maiolica') trend NW-SE, at a high angle with this shortening direction.Sinistral motion along the Schio-Vicenza Fault indicates that it acted as a clutch to accommodate differential Neogene-to-recent shortening associated with Adriatic indentation in the Eastern Southern Alps. NW-SE-directed shortening was greater NE of the Schio-Vicenza Fault along the Bassano Thrust than SW along the Marana Thrust. The observation that the Schio-Vicenza Fault terminates in the NW, near the end of the Valsugana Thrust, rather than merging with the Giudicarie Belt, indicates that the latter was kinematically decoupled from post-Oligocene shortening along the orogenic front. Together with the anomalously low seismicity just north of the Valsugana Thrust, this suggests that ongoing shortening is taken up between this thrust and the active orogenic front.The NW-SE trending folds in the footwall of the Marana Thrust do not fit with the typical Neogene Alpine ENE-WSW strike of folds and thrusts in this area and the timing of the thrusting is not well constrained. Work is underway to determine whether these folds represent a different deformational phase or formed due to interference with a local Oligocene normal fault. In addition, the oblique normal motion to the SW along the Schio-Vicenza Fault is inconsistent with Neogene Alpine shortening and could reflect flexural extension in the foreland bulge of the Apennines. [ABSTRACT FROM AUTHOR]