European tectosphere and slabs beneath the greater Alpine area – Interpretation of mantle structure in the Alps-Apennines-Pannonian region from teleseismic V_p studies

Based on recent results of AlpArray, we propose a new model of Alpine collision that involves subduction and detachment of thick (180–200 km) European tectosphere. Our approach combines teleseismic P-wave tomography and existing Local Earthquake Tomography (LET) allowing us to image the Alpine slabs and their connections with the overlying orogenic crust at an unprecedented resolution. The images call into question the conventional notion that slabs comprise only seismically fast lithosphere and suggest that the mantle of the downgoing European Plate is heterogeneous, containing both positive and negative Vp anomalies of up to 5–6%. We interpret these as compositional rather than thermal anomalies, inherited from the Variscan and pre-Variscan orogenic cycles. They make up a kinematic entity referred to as tectosphere, which presently dips beneath the Alpine orogenic front. In contrast to the European Plate, the tectosphere of the Adriatic Plate is thinner (100–120 km) and has a lower boundary approximately at the interface between positive and negative Vp anomalies. Horizontal and vertical tomographic slices reveal that beneath the Central and Western Alps, the downgoing European tectospheric slab dips steeply to the S and SE and is only locally still attached to the Alpine crust. However, in the Eastern Alps and Carpathians, the European slab is completely detached from the orogenic crust and dips steeply to the N-NE. This along-strike change in attachment coincides with an abrupt decrease in Moho depth below the Tauern Window, the Moho being underlain by a pronounced negative Vp anomaly that reaches eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted to represent hot upwelling asthenosphere that was instrumental in accommodating Neogene orogen-parallel lateral extrusion of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the east. A European origin of the northward-dipping, detached slab segment beneath the Eastern Alps is likely since its imaged down-dip length (300–500 km) matches estimated Tertiary shortening in the Eastern Alps accommodated by south-dipping subduction of European tectosphere. A slab anomaly beneath the Dinarides is of Adriatic origin and dips to the northeast. There is no evidence that this slab dips beneath the Alps. The slab anomaly beneath the northern Apennines, also of Adriatic origin, hangs subvertically and is detached from the Apenninic orogenic crust and foreland. Except for its northernmost segment where it locally overlies the southern end of the European slab of the Alps, this slab is clearly separated from the latter by a broad zone of low Vp velocities located south of the Alpine slab beneath the Po Basin. Considered as a whole, the slabs of the Alpine chain are interpreted as attenuated, largely detached sheets of continental margin and Alpine Tethyan lithosphere that locally reach down to a slab graveyard in the Mantle Transition Zone (MTZ).

Time for a change of paradigm for Alpine subduction?

<p>The prevailing paradigm of mountain building in the Alps entails subduction of European continental lithosphere some 100km thick beneath the Adriatic plate. Based on recent results of AlpArray, we propose a new model that involves subduction and wholesale detachment of locally much thicker (200-240 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing Local Earthquake Tomography (LET) to image the Alpine slabs and their connections with the overlying orogenic crust at unprecedented resolution. The images call into question the simple notion that slabs comprise only seismically fast lithosphere and suggest that the mantle of the downgoing European plate is compositionally heterogeneous, containing both positive and negative seismic anomalies of up to 5%. We interpret these as compositional rather than thermal anomalies, inherited from the Paleozoic Variscan orogenic cycle and presently dipping beneath the Alpine orogenic front. In contrast to the European Plate, the lithosphere of the Adriatic Plate is thinner (100-120 km) and has a more poorly defined lower boundary approximately at the interface between positive and negative Vp anomalies.</p><p> </p><p>Horizontal and vertical tomographic slices reveal that beneath the Central and Western Alps, the downgoing European Plate dips steeply to the S and SE and is locally detached from the Alpine crust. However, in the Eastern Alps and Carpathians east of the central Tauern Window, the Alpine slab anomaly occupies the 150-400 km depth interval and dips steeply to the N-NE, having completely detached from the  Alpine orogenic crust. This along-strike change coincides with an abrupt eastward decrease in Moho depth (Kind et al., this session), the Moho being underlain by a pronounced negative Vp anomaly reaching eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted to represent hot upwelling asthenosphere that was instrumental in accommodating Neogene orogen-parallel lateral extrusion of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the E.  An Adriatic origin of the northward-dipping, detached slab segment beneath the Eastern Alps is unlikely since its imaged down-dip length (200-300 km) matches estimated Tertiary shortening in the Eastern Alps accommodated by south-dipping subduction of European lithosphere, whereas shortening in the south-vergent eastern Southern Alps is only ≤ 70 km.</p><p> </p><p>A slab anomaly beneath the northernmost Dinarides, laterally adjoining the Eastern Alps, is missing. The slab anomaly beneath the northern Apennines, of Adriatic origin und dipping beneath the Tyrrhenian backarc, hangs subvertically and appears to be almost detached from the Apenninic orogenic crust. Except for its westernmost segment where it meets the Alpine slab, this slab is clearly separated from the latter by a broad extent of upwelling asthenosphere located south of the Alpine slabs beneath the Po Plain, i.e., just south of the Alpine subduction zone. Considered as a whole, the slabs beneath the Alpine chain are interpreted as attenuated, largely detached sheets of continental margin and Alpine Tethyan lithosphere that locally reach down to a slab graveyard in the Mantle Transition Zone (MTZ).</p>

Crustal shear wave blockage in and around the Eastern Alps from the 2016 Alland earthquake

<p>Earthquakes in the Eastern Alps are characterized by strongly elongated isoseismals, documenting significantly more efficient propagation of seismic waves towards the foreland (F) than into the orogen (O). In an effort to understand this phenomenon we analysed the local to regional wavefield of a single earthquake with ML4.2 / mb3.6 and epicenter WSW of Vienna (Alland) using instrumental data with unprecedented dense coverage (including AlpArray) and rich macroseismic observations. This earthquake with characteristic asymmetry of isoseismals and with the source located in the basement of the European plate just beneath the frontal thin-skinned thrust of the Penninic units is considered a representative example of the stronger historical and potential future earthquakes from this regionally important seismogenic source area. The analysis of macroseismic intensities and PGA, PGV and spectral content within time windows tied to Sg+Lg wavetrains and other interpreted phases indicates a very good match of smoothed high precision instrumental and high resolution macroseismic wavefields, which allows their joint interpretation. In the F-direction, a very small decrease of intensity and PGA values at an epicentral distance range between 30-50 km and 130-180 km is well approximated by intensity prediction equations derived for central and eastern North America. On the other hand, a sudden drop of respective values is observed at a distance of 20-30 km in the O-direction, correlating with the seismically active fault zone of Mur-Mürz line. The geographic distribution of regional distance-corrected PGA perturbations (dPGA) reveals several well-defined domains with internally limited variance whose boundaries partly correlate with known major geologic structures. Special attention has been paid to description of contrasts between the Foreland domain (Bohemian Massif + autochthonous sediments), the North Alpine domain (between the frontal thrust and Mur-Mürz line + its WSW continuation, i.e. close to southern limits of stable European plate) and the South Alpine domain (south of the former to the southern limits of the region of interest at latitude 46.2°N). The ratio of mean dPGA values observed in these three neighbouring domains is 1.00 : 0.27 : 0.05, respectively. Furthermore, significant contrast between the three domains is observed in terms of spectral content. High frequency signal above 10Hz is characteristic for the Foreland domain and strongly reduced in the South Alpine domain, suggesting that the structures related to the margin of stable European plate act here as an efficient high-cut frequency filter. While map isolines of high frequency spectral amplitude are strongly elongated in F-direction, in agreement with PGA and macroseismic intensity, for frequencies below ~5Hz the isolines of spectral amplitude are quasi-isometric around the epicenter at least within distance of ~120 km. Combination of several mechanisms is considered to explain the wave energy propagation, including intrinsic attenuation at fault zones, blockage at waveguide inhomogeneities and Q(f) contrasts between the crustal domains. Numerous other interesting observations from the whole region including the Carpathian and Pannonian domains, demonstrate the strong potential of densely sampled earthquake wavefields for studies of crustal structure and seismic hazard in the generally low-rate seismicity areas.</p>

Receiver Function mapping of mantle transition zone discontinuities beneath Western Alps using scaled 3-D velocity corrections

<p>The Alpine orogenic belt is the result of the continental collision and convergence between the Adriatic microplate and European plate during the Mesozoic. The Alps orogenic belt has a complex tectonic history and the deformation in and around the Alps are significantly affected by several microplates (e.g., Adriatic and Iberia) and blocks, in particular the Apennines, Betics, Dinarides. The mantle transition zone is delineated by seismic velocity discontinuities around the depths of 410 and 660 km which are generally interpreted as polymorphic phase changes in the olivine system and garnet-pyroxene system.The subduction depth of the European plate and the origin of the mantle flow behind the plate plays crucial roles for our understanding of regional geodynamic (Zhao et al., 2016; Hua et al., 2017). Therefore, we use receiver function method to study the seismic features of discontinuities beneath the Western Alps to constrain the structure of subducted plate and study the geodynamic origin of the low velocity anomaly behind the subduction zone and its relationship with the high-relief topography. </p><p>This study uses data collected from 293 permanent and temporary broadband seismic stations (e.g., CIFALPS). Teleseismic events are selected from 30<sup>o</sup> to 90<sup>o </sup>epicentral distrance with magnitudes (Mw) between 5.3 and 9.0. Data are carefully checked by automated and manual procedures to to give a total of 24904 receiver functions. Both 1D velocity model of the IASP91 and 3D velocity model of the EU60 (Zhu et al., 2015) are used for time-to-depth migration. The results show that using 3D velocity model to image the two discontinuities may obtain a more accurate structure image of the mantle transition zone.</p><p>In the northern part of the study area, along the alpine orogenic belt, we find a localized arc-shaped thinning area with a depressed 410 discontinuity, which is attributed to hot mantle upwellings. The uplift is hardly seen on the 660 discontinuity, suggesting that the thermal anomaly is unlikely to be interpreted as a mantle plume. The uplift of the 410-km can be interpreted as the European plate subducting to the depth of the upper transition zone. The depression of the 660-km  is likely attributed to the remnants from the oceanic mantle lithosphere that detached from the Eurasian plate after closure of the Alpine Tethys. Our results show a good agreement between the thinning area of MTZ and the area of topographic uplift, the mantle upwelling promotes the temperature increase which is conducive to the uplift of topographic.</p><p>Reference</p><p>Zhao L , Paul A , Marco G. Malusà, et al. Continuity of the Alpine slab unraveled by high-resolution P-wave tomography. Journal of Geophysical Research: Solid Earth, 2016, 121.</p><p>Hua, Y., D. Zhao, and Y. Xu (2017), P wave anisotropic tomography of the Alps, J. Geophys. Res. Solid Earth, 122, 4509–4528, doi:10.1002/2016JB013831.</p><p>Zhu H,Bozdag E and Tromp J.Seismic structure of the European upper mantle based on adjoint tomography.Geophys. J. Int. 2015, 201, 18–52</p>

Integrating Data under the European Plate Observing System from the Regional and Selected Local Seismic Networks in Poland

High-quality and open-access seismic data are of great importance for both research and increasing public awareness of actual seismic hazards and risks. We present four seismic networks that currently operate in Poland: the backbone Polish Seismological Network (PLSN), which monitors natural teleseismic events as well as regional events from Poland, and three networks that mainly serve the monitoring of anthropogenic seismicity. The acquired data from all four networks are openly available through the European Plate Observing System (EPOS) Information Technology (IT) facilities: the PLSN data within the Observatories and Research Facilities for European Seismology–European Integrated Data Archive and the anthropogenic seismicity data episodes through the induced seismicity-EPOS platform of EPOS Thematic Core Service Anthropogenic Hazards. For each network, we describe briefly the recorded seismic activity, the equipment and composition of the network, the acquisition system, and the data availability. Information from recent studies is used to demonstrate the scientific potential of the acquired anthropogenic seismicity data.

The Transversal Seismicity Action RESIF: A Tool to Improve the Distribution of the French Seismicity Products

In recent years, the French seismological, geodetic, and gravimetric community has been structured within Réseau Sismologique et géodésique Français (RESIF) (French seismological and geodetic network). In addition to instrumental developments, RESIF has structured the work on French seismicity (metropolitan and overseas) within the RESIF transverse seismicity action (ATS). The purpose of this article is to present the ATS and the way it is structured to propose to the community different products: seismicity bulletin and catalog, historical and instrumental macroseismicity data, and ShakeMaps. The places where these products can be found are indicated, as well as the way they are realized and the improvements in progress for a better realization and availability. The link with European plate observing system is also underlined.

Placodont remains (Sauropsida, Sauropterygia) from the Triassic of Hungary (Transdanubian Range and Villány Mountains)

New placodont remains from the Triassic of Hungary are described here. They come from two different tectonic units: the Transdanubian Range Unit representing Alpine type sedimentary basins and the Villány-Bihar Unit that was part of the southern passive margin of the European Plate during the Triassic. The fossils came from four stratigraphic levels with the oldest specimen, a maxilla fragment found in the upper Anisian of Forrás Hill, near Felsőörs (Transdanubian Range). Based on dental morphology, the specimen is referred to here as Paraplacodus broilii. This site is similar in age to the Monte San Giorgio (Switzerland and Italy) locality. A Carnian occurrence of placodonts from this tectonical unit is a dentary fragment and two isolated teeth referred to here as Placochelys placodonta. The youngest specimen from this unit is a placochelyid tooth fragment from the Rhaetian of the Keszthely Mountains (Transdanubian Range). The richest assemblage of new placodont remains is from the Ladinian of the Villány Mountains, southern Hungary. Cranial elements are referred to here as Cyamodus sp. Teeth from this site are similar to that of Cyamodus sp. described from Slovenia, and both assemblages are among the last occurrences of the genus in the European Triassic. The Villány site is considered as a gap locality because of the rarity of Ladinian placodont occurrences in the German-Alpine sedimentary basins.

High-temperature acid magmatic rocks from the Late Cretaceous suture zone between European plate and Adria microplate (Croatia)

<p>The Late Cretaceous magmatic rocks within the southwestern part of the Pannonian Basin basement (Croatia) occur in two areas: Voćin volcanic mass (VVM) at the northwestern part of Mt. Papuk (near town of Voćin, covering the area of ~10km<sup>2</sup>) and volcanic mass of Mt. Požeška Gora (PVM, area of ~30 km<sup>2</sup>). Both volcanic masses consist of basalts and rhyolites, and in lesser extent of pyroclastic material. Granite can be found it the PVM. Interconnection of this two masses and Late Cretaceous ages have been proposed based on the petrography and mineralogical features of previously studied samples and rather arguable data: K-Ar dating on basalts from VVM (~73−52 Ma) and Rb-Sr isochron age on granite and rhyolite from PVM (~72 Ma). The age has been recently refined with the zircon LA-ICP-MS age dating (~82 Ma), but the magma source of this bimodal formation, geotectonic position, setting and its regional importance still have not been explained in detail.</p><p>In order to conduct preliminary research, two localities with acid effusive rocks were sampled from the VVM (Rupnica geosite and Trešnjevica quarry), and three more from PVM (near the village of Vesela, Pakao Creek and the granite from quarry near the village of Gradski Vrhovci).</p><p>Acid rocks are characterized by a highly siliceous composition (up to 75 wt.% SiO<sub>2</sub>), enrichment in alkalies (high-K calc-alkaline towards to shoshonite series) and aluminium (peraluminous affinity), followed by high FeO<sub>T</sub>/(FeO<sub>T</sub>+MgO) ratios matching ferroan magmas. They classify as rhyolites or alkali-rhyolites/granite. Microelements including REE show that studied rocks have characteristics of A<sub>2</sub>-type of post-collisional/post-orogenic acid rocks, most common A-type of rocks formed during rifting caused by extension and thinning of continental crust. According to geotectonic classification diagrams, rocks from PVM show geochemical signature of volcanic arc, while VVM shows signature of within plate environment.</p><p>External zircon morphology seems to be uniform with prevailing J3−J5-type for rhyolites and D-type for granite and with average ratio of 2.2:1. Those types are characteristic for the high-temperature magmas (confirmed with the calculated Zr-saturation temperature of 850−930°C) originating from the lower crust or even upper mantle. Inclusions of hematite, F-apatite and anatase have been detected with Raman spectrometry in zircon from all samples, with the most significant findings of kumdykolite and kokchetavite inclusions detected in samples from Vesela and Gradski Vrhovci. Latter inclusions are metastable phases crystallized from enclosed melt and are indicators of a rapid cooling of the host magma.</p><p>According to the results presented here, acid rocks show rather uniform geochemistry, which speaks in favor of the early ideas of the unique magmatic complex, although today at the surface they are separated by ~35 km in distance. Those rocks show potential to be of great regional importance bearing new information about the evolution in the Late Cretaceous in the area of Sava Zone, a suture zone between Tisia Mega-Unit (European plate) and Adria microplate, which spatially and temporally marks the closure of the Neotethys Ocean.</p><p>Support by the Croatian Science Foundation (IP-2014-09-9541) is acknowledged.</p>

EUROVOLC: Building the European volcanological community and opening access to Research Infrastructures of Volcano Observatories and Volcano Research Institutions

<p>Volcanic systems are complex and volcanic eruptions are difficult to predict. The volcanoes present multiple hazards, where eruptions often result in cascading effects. The European volcano monitoring and research community, including volcano observatories and their close collaborating volcanic research institutions, play a key role in mitigating volcanic risk in Europe by providing key scientific information and interpretation during volcanic crises. However, to fully benefit society, access to these infrastructures and propagation of advances in volcanological research and know-how across the European volcanological community need to be improved. The H2020 EUROVOLC Infrastructure project is addressing this need by promoting collaboration and community building within the European volcanological community and between the community and its stakeholders, advancing new research and discoveries for the benefit of improved volcano hazard monitoring and management and opening access to European volcanological Research Infrastructures.</p><p>EUROVOLC’s objectives are to overcome the fragmentation of the European volcanology community. This fragmentation is portrayed by the scattered distribution of volcano observatories across the European plate and European overseas territories, the wide range of scientific disciplines involved in volcanology, the short and time-fragmented duration of research projects and, in some cases, the lack of community standards and test beds to test new theories and methodologies. The project builds upon developments of its forerunners, the volcano Supersite projects FUTUREVOLC and MED-SUV and will rely on collaboration with the e-Infrastructures of the EPOS (European Plate Observing System) Organization to sustain long-term access to the data and products made available in EUROVOLC. The consortium includes all the main European volcano observatories and many of the strongest volcano research institutions, as well as Civil Protection agencies and geothermal industry and IT companies.</p><p>The project is structured around activities contributing to the advancement of four main themes: (i) Community building, (ii) Sub-surface processes, (iii) Volcano-atmosphere interactions, and (iv) Volcanic hazard preparedness and risk management, where within each theme the three traditional categories of Infrastructure project activities are carried out: Networking people and data, Joint Research, and Access to Research Infrastructures, both virtual and trans-national.</p><p>EUROVOLC has already substantially enriched opportunities for volcanological research in Europe through the project’s two open calls for research proposals, offering trans-national access to the Research Infrastructures of European volcano observatories and laboratories and modeling facilities of volcano research institutions. From the first call in summer 2018 twelve projects were funded, most of which were carried out during 2019. The selected proposals submitted to the second call in 2019 will be carried out during 2020. Additionally, virtual access has been constructed to several new or improved data and modeling services. In the Networking activities new standards for observations and hazard communication are being developed, suitable data sets defined for benchmarking ash-dispersion models and new data sets opened. In the Joint Research activities new methodologies for ash-dispersion modeling and pre-eruptive unrest detection are being developed, a new catalogue of European volcanoes created, and hazard tools developed and tested.</p><p>The ingredients, activities and achievements of EUROVOLC will be summarized in the presentation.</p>

Open access to geological information and 3D modelling data sets in the European Plate Observing System platform (EPOS)

<p>The European Plate Observing System (EPOS, www.epos-ip.org) is a multidisciplinary pan-European research infrastructure for solid Earth science. It integrates a series of domain-specific service hubs such as the Geological Information and Modelling Technical Core Service (TCS GIM) dedicated to access data, data products and services on European boreholes, geological and geohazards maps, mineral resources as well as a catalogue of 3D models. These are hosted by European Geological Surveys and national research organisations.</p><p>Even though interoperability implementation frameworks are well described and used (ISO, OGC, IUGS/CGI, INSPIRE …), it proved to be difficult for several data providers to deploy in the first place the required OGC services supporting the full semantic definition (OGC Complex Feature) to discover and view millions of geological entities. Instead, data are collected and exposed using a simpler yet standardised description (GeoSciML Lite & EarthResourceML Lite). Subsequently, the more complex data flows are deployed with the corresponding semantics.</p><p>This approach was applied to design and implement the European Borehole Index and associated web services (View-WMS and Discovery-WFS) and extended to 3D Models. TCS GIM exposes to EPOS Central Integrated Core Services infrastructure a metadata catalogue service, a series of “index services”, a codeList registry and a Linked Data resolver. These allow EPOS end users to search and locate boreholes, geological maps and features, 3D models, etc., based on the information held by the index services.</p><p>In addition to these services, TCS GIM focussed particularly on sharing European geological data using the Linked Data approach. Each instance is associated with a URI and points to other information resources also using URIs. The Linked Data principles ensure the best semantic description (e.g. URIs to shared codeList registries entries) and also enrich an initial “information seed” (e.g. a set of Borehole entries matching a search) with more contents (e.g. URIs to more Features or a more complex description). As a result, this pattern including Simple Feature and Linked Data has a positive effect on the IT architecture: interoperable services are simpler and faster to deploy and there is no need to harvest a full OGC Complex Feature dataset. This architecture is also more scalable and sustainable.</p><p>The European Geological Services codeList registries have been enriched with new vocabularies as part of the European Geoscience Registry. In compliance with the relevant European INSPIRE rules, this registry is now part of the INPIRE Register Federation, the central access point to the repository for vocabulary and resources. European Geoscience Registry is available for reuse and extension by other geoscientific projects.</p><p>During the EPOS project, this approach has been developed and implemented for the Borehole and Model data services. TCS GIM team provided feedback on INSPIRE through the Earth Science Cluster, contributed to the creation of the OGC GeoScience Domain Working Group in 2017, the launch of the OGC Borehole Interoperability Experiment in 2018, and proposed evolutions to the OGC GeoSciML and IUGS/CGI EarthResourceML standards.</p>