Seismotectonic analysis around the Mont Terri rock laboratory (Switzerland): a pilot study

For this pilot study we used recorded seismic events from the SED permanent network and data from a dedicated SNS network to improve the seismotectonic understanding of very weak seismicity in the vicinity of the Mont Terri underground laboratory. We combined field data on faults with microseismic events and modelling of stress and focal mechanisms. Eighty-six events with very low magnitudes (ML ≈ −2.0 to 2.0) recorded between July 2014 and August 2015 were located within a radius of 10 km of the underground laboratory and used for modelling. We compiled 234 fault/striation data from laboratory tunnels and regional geology, and also from seismic/borehole data on basement faults. With this database we defined seven groups of main faults in the cover and four groups in the basement. For each of these groups we computed a synthetic focal mechanism that was subsequently used to determine a synthetic P-phase waveform. The synthetic waveforms were then correlated with the microseismic events of the cover and the basement respectively. Of these, 78 events yielded satisfactorily correlation coefficients that we used for a regional seismotectonic interpretation. The synthetic focal mechanism can be linked to the main regional structural features: the NNE–SSW-oriented reactivated faults associated with the Rhine Graben development, and the NE–SW-oriented reverse faults related to the thrust development of major folds such as the Mont Terri anticline. The results for this pilot study confirm that our affirmative method can be used to augment local and regional seismotectonic interpretations with very weak-intensity earthquake data

Cenozoic granitoids in the Dinarides of southern Serbia: age of intrusion, isotope geochemistry, exhumation history and significance for the geodynamic evolution of the Balkan Peninsula

Two age groups were determined for the Cenozoic granitoids in the Dinarides of southern Serbia by high-precision single grain U-Pb dating of thermally annealed and chemically abraded zircons: (1) Oligocene ages (Kopaonik, Drenje, Željin) ranging from 31.7 to 30.6Ma (2) Miocene ages (Golija and Polumir) at 20.58-20.17 and 18.06-17.74Ma, respectively. Apatite fission-track central ages, modelling combined with zircon central ages and additionally, local structural observations constrain the subsequent exhumation history of the magmatic rocks. They indicate rapid cooling from above 300°C to ca. 80°C between 16 and 10Ma for both age groups, induced by extensional exhumation of the plutons located in the footwall of core complexes. Hence, Miocene magmatism and core-complex formation not only affected the Pannonian basin but also a part of the mountainous areas of the internal Dinarides. Based on an extensive set of existing age data combined with our own analyses, we propose a geodynamical model for the Balkan Peninsula: The Late Eocene to Oligocene magmatism, which affects the Adria-derived lower plate units of the internal Dinarides, was caused by delamination of the Adriatic mantle from the overlying crust, associated with post-collisional convergence that propagated outward into the external Dinarides. Miocene magmatism, on the other hand, is associated with core-complex formation along the southern margin of the Pannonian basin, probably associated with the W-directed subduction of the European lithosphere beneath the Carpathians and interfering with ongoing Dinaridic-Hellenic back-arc extensio

The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units

A correlation of tectonic units of the Alpine-Carpathian-Dinaridic system of orogens, including the substrate of the Pannonian and Transylvanian basins, is presented in the form of a map. Combined with a series of crustal-scale cross sections this correlation of tectonic units yields a clearer picture of the three-dimensional architecture of this system of orogens that owes its considerable complexity to multiple overprinting of earlier by younger deformations. The synthesis advanced here indicates that none of the branches of the Alpine Tethys and Neotethys extended eastward into the Dobrogea Orogen. Instead, the main branch of the Alpine Tethys linked up with the Meliata-Maliac-Vardar branch of the Neotethys into the area of the present-day Inner Dinarides. More easterly and subsidiary branches of the Alpine Tethys separated Tisza completely, and Dacia partially, from the European continent. Remnants of the Triassic parts of Neotethys (Meliata-Maliac) are preserved only as ophiolitic mélanges present below obducted Jurassic Neotethyan (Vardar) ophiolites. The opening of the Alpine Tethys was largely contemporaneous with the Latest Jurassic to Early Cretaceous obduction of parts of the Jurassic Vardar ophiolites. Closure of the Meliata-Maliac Ocean in the Alps and West Carpathians led to Cretaceous-age orogeny associated with an eclogitic overprint of the adjacent continental margin. The Triassic Meliata-Maliac and Jurassic Western and Eastern Vardar ophiolites were derived from one single branch of Neotethys: the Meliata-Maliac-Vardar Ocean. Complex geometries resulting from out-of-sequence thrusting during Cretaceous and Cenozoic orogenic phases underlay a variety of multi-ocean hypotheses, that were advanced in the literature and that we regard as incompatible with the field evidence. The present-day configuration of tectonic units suggests that a former connection between ophiolitic units in West Carpathians and Dinarides was disrupted by substantial Miocene-age dislocations along the Mid-Hungarian Fault Zone, hiding a former lateral change in subduction polarity between West Carpathians and Dinarides. The SW-facing Dinaridic Orogen, mainly structured in Cretaceous and Palaeogene times, was juxtaposed with the Tisza and Dacia Mega-Units along a NW-dipping suture (Sava Zone) in latest Cretaceous to Palaeogene times. The Dacia Mega-Unit (East and South Carpathian Orogen, including the Carpatho-Balkan Orogen and the Biharia nappe system of the Apuseni Mountains), was essentially consolidated by E-facing nappe stacking during an Early Cretaceous orogeny, while the adjacent Tisza Mega-Unit formed by NW-directed thrusting (in present-day coordinates) in Late Cretaceous times. The polyphase and multi-directional Cretaceous to Neogene deformation history of the Dinarides was preceded by the obduction of Vardar ophiolites onto to the Adriatic margin (Western Vardar Ophiolitic Unit) and parts of the European margin (Eastern Vardar Ophiolitic Unit) during Late Jurassic to Early Cretaceous time

Tectono-metamorphic and magmatic evolution of the Internal Dinarides (Kopaonik area, southern Serbia) and its significance for the geodynamic evolution of the Balkan Peninsula

The study is devoted to the tectono-metamorphic and magmatic evolution of the Internal Dinarides and it furthermore addresses the geodynamic evolution of the Balkan Peninsula. The investigated area is located in the internal-most part of the Dinarides and covers the contact zone between the Dinaridic orogen that essentially formed in Latest Cretaceous to Paleogene times and the “Serbo–Macedonian Massif“, that is a part of the Carpatho–Balkan orogen (Dacia Mega-Unit) which is characterised by older (pre-Turonian) deformations. The widespread occurrences of ophiolitic rocks, separated by different fragments of continental basement rocks led to a ,multi-ocean‘ concept whereby the oceans were separated by elongate continental terranes or micro-plates. By investigating the stratigraphic and tectonic evolution of the various continent-derived units and by studying their relation with the intervening ophiolitic belts this ,multi-terrane/multi-ocean‘ problem is critically addressed and a one-ocean model is preferred. Thereby the continental terranes simply represent the passive margin of Adria, exposed in windows below the ophiolites, which were obducted in Late Jurassic times. Strongly deformed and metamorphosed meta-sediments crop out in the Studenica valley and the Kopaonik area representing the easternmost occurrences of Triassic sediments within the Dinarides. Upper Paleozoic terrigeneous sediments are overlain by Lower Triassic siliciclastics and limestones, followed by Anisian shallow-water carbonates. A pronounced facies change to hemipelagic and distal turbiditic, cherty meta-limestones (Kopaonik Formation) testifies to a late Anisian drowning of the former shallow-water carbonate shelf. Sedimentation of the Kopaonik Formation was contemporaneous with shallow-water carbonate production on nearby and more proxi- mal carbonate platforms that were the source areas of diluted turbidity currents reaching the depositional area of this formation. The Kopaonik Formation was dated by conodont faunas as late Anisian to Norian and possibly extends into the Early Jurassic. It is therefore considered an equivalent of the grey Hallstatt facies of the Eastern Alps, the Western Carpathians and the Albanides–Hellenides. The coeval carbonate platforms were generally located in more proximal areas of the Adriatic margin, whereas the distal margin was dominated by hemipelagic/ pelagic and distal turbiditic sedimentation, facing the evolving Neotethys Ocean to the east. A similar arrangement of Triassic facies belts can be recognised all along the evolving Meliata–Maliac–Vardar branch of Neotethys, which is in line with a ‘one-ocean-hypothesis’ for the Dinarides: all ophiolites presently located southwest of the Drina–Ivanjica and Kopaonik thrust sheets are derived from an area to the east, and the Drina–Ivanjica and Kopaonik units emerge in tectonic windows from below this ophiolite nappe. On the base of the Triassic facies distribution neither arguments for an independent Dinaridic Ocean nor evidence for isolated terranes or blocks was seen. Two age groups for the Cenozoic granitoids in the Dinarides of southern Serbia were determined by high precision single grain U–Pb dating of thermally annealed and chemically abraded zircons: (i) Oligocene ages (Ko- paonik, Drenje, Željin) ranging from 31.7 to 30.6 Ma and (ii) Miocene ages (Golija and Polumir) at 20.58–20.17 and 18.06–17.74 Ma, respectively. Apatite fission-track central ages and modelling combined with zircon central ages, together with local structural observations, constrain the subsequent exhumation history of the magmatic rocks. They indicate rapid cooling from above 300 to ca. 80 °C between 16 and 10 Ma for the Oligocene and the Miocene age group, caused by extensional exhumation of the plutons that are located in the footwall of core-complexes. Miocene magmatism and core-complex formation thus not only affected the Pannonian basin but also a part of the mountainous areas of the internal Dinarides. Four different deformation phases (D1–D4) are distinguished in the study area. D1 to D3 are related to com- pression and metamorphism that pre-date the intrusion of I-type Oligocene plutons in Early Oligocene times, whereas the fourth deformation phase (D4) is related to extensional tectonics and exhumation that are contempo- raneous with the intrusion of Miocene S-type granitoids. The first event (D1) is probably linked to the obduction of the Western Vardar Ophiolitic Unit onto the distal Adriatic continental margin. It is associated with top-NW shear-senses observed in sigma-clasts in a ductilely deformed and slightly metamorphosed ophiolitic mélange as well as with a penetrative foliation and a stretching lineation coupled to greenschist facies metamorphism in the Late Paleozoic to Early Jurassic sediments. During the Late Cretaceous (110–85 Ma) these sediments witnessed a metamorphic event that occurred under lowermost greenschist-facies conditions, associated with the ductile deformation phase (D2) represented by a well developed foliation and isoclinal folds overprinting D1. A higher greenschist- to amphibolite-facies overprint is observed during Middle to Late Eocene (45–35 Ma) due to nappe- stacking caused by out-of-sequence thrusting (D3). This event is associated with the E–W-oriented compression related to and following the closure of the Sava suture. During the Miocene the entire area of investigation un- derwent rapid exhumation, accompanied by intense N–S-oriented ductile stretching (D4). This extension is correlated with the Miocene extension in the Pannonian basin whose location is in the back-arc area of the W-directed subduction of the European lithosphere beneath the Carpathians

Long term investigations at the Mont Terri rock laboratory of tilt and their near and far field influences 

&amp;lt;p&amp;gt;Underground research laboratories provide advantageous conditions to observe a broad range of various rock parameters to characterise rock matrix and geological features, and to enhance knowledge of their dynamic behaviour, all under relatively undisturbed conditions. One of their favorable features is that the overburden protects against large environmental changes, although those influences cannot be mitigated in full. Especially for long term investigations, a holistic observation of ambient environmental parameters is necessary on the local scale and beyond.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Swiss Mont Terri rock laboratory is situated in the Jura Mountains about 250 m below the surface. Starting in 1996, the international Mont Terri Consortium has conducted about 150 experiments in the native Opalinus Clay. Embedded in several of the ongoing in situ experiments, platform tiltmeters assist in the often interdisciplinary investigations. Two different types of biaxial instruments with resolutions of 0.1 urad and better than nrad are distributed throughout the laboratory, together forming a small, growing array, with the first tiltmeters installed in April 2019.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Tiltmeters observe the direct local deformation, they are exposed to near field but also far field impacts. Known local influences are mainly temperature, air pressure, and humidity. In Mont Terri, all of these parameters are registered directly at the location of the tilt sensors with the same relatively high sampling of once every few seconds. In addition, Mont Terri&amp;#039;s comprehensive database imparts valuable complementing information. However, the detected deformation pattern is also influenced on a much larger spatial scale, e.g. far field, extensive changes in weather patterns, earth tides, and teleseismic events.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Therefore, to allow detection, identification, and realistic interpretation of complex signal responses on different spatial scales, it is mandatory to distinguish transient and long term signals, natural and anthropogenic disturbances. Their understanding is essential for the evaluation of stability and the safety of a rock laboratory for the benefit of its personnel and visitors. Obviously, long term, continuous data series require long term commitments. But the efforts pays off, not the least, as decade-long deformation studies contribute to multifaceted technical and scientific aspects of long term behavior of barrier rocks, and these are relevant for the exploitation of the deep geological subsurface such as nuclear waste disposal, geological storage of carbon dioxide, use of geothermal energy, or inter-seasonal thermal energy storage.&amp;lt;/p&amp;gt;</jats:p

Zehn Jahre geodätisches Grundlagen- und Überwachungsnetz im Felslabor Mont Terri: Präzisions-Tunnelvermessung für die Entwicklung und Austestung eines Überwachungskonzepts für zukünftige Tiefenlager

Im Felslabor Mont Terri in St - Ursanne wird seit 1996 ein internationales Forschungsprogramm durchgeführt mit dem Ziel, die spezifischen Eigenschaften des Opalinustons hinsichtlich Machbarkeit und Sicherheit eines geologischen Tiefenlagers für radioaktive Abfälle abzuklären. Ein seit 2007 laufend weiter entwickeltes, hochpräzises geodätisches Grundlagen- und Deformationsnetz bietet die Basis, um kleinste dreidimensionale Veränderungen bedingt durch natürliche und/oder künstlich (durch Bauprojekte und Experimente) erzeugte Veränderungen zu detektieren; zudem sollen geochemische und geotechnische Sensoren damit georeferenziert werden. Der vorliegende Artikel beschreibt die in den letzten 10 Jahren durchgeführten Arbeiten und dokumentiert die erreichten Resultate und Erkenntnisse.https://www.tugraz.at/events/iv2017/home

Investigations based on biaxial tiltmeter array and uniaxial hydrostatic levelling system at the Mont Terri rock laboratory

&amp;lt;p&amp;gt;In order to enable investigations and further comprehensive understanding of dynamical processes, it is clear one has to identify all relevant parameters and aim to record them all under best conditions concerning e.g. resolution, coverage in space, and in many cases on a multitude of scales in time. Obviously, it is also difficult to satisfy all these constrains in full. Especially scientific long-term observations often suffer the lack of necessary lasting commitment; secure funding, continual high quality maintenance, protected environment, or sufficient planning stability. Fortunately, the Swiss Mont Terri rock laboratory, with its history of now 25&amp;amp;#160;years of forefront scientific expertise, a long-standing fruitful cooperation formed by the partners of the consortium and in consequence thereof state-of-the-art results obtained through 100&amp;amp;#160;completed individual experiments and 45&amp;amp;#160;additional experiments actually ongoing, ensures the conditions listed above.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Based on this favorable prospect, a now growing tiltmeter array is established at the underground laboratory. The instruments are embedded in several multidisciplinary experiments, dedicated to numerous, different scientific questions. Starting in April 2019, the first two platform tiltmeters became operational. Less than two years later, ten biaxial instruments are quasi-continuously monitoring deformation at various locations within the galleries and niches at Mont Terri. The envisioned, increasing spatial coverage of the network will facilitate geodetic observations of the underground rock laboratory as a whole and of its subregions as well.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Already in September 2012, a 50&amp;amp;#160;m long hydrostatic levelling system (HLS) was installed along a gallery in the underground laboratory to detect displacements across an active geological fault zone. The combination of both, i.e. the uniaxial, integral deformations data provided by HLS together with the array of biaxial, point measurements acquired by the tiltmeters offers a unique concerted opportunity to achieve detailed deformation data in a large underground rock laboratory and to survey the associated dynamical processes occurring on timeframes covering seconds to decades.&amp;lt;/p&amp;gt;</jats:p

The Saint-Ursanne earthquakes of 2000 revisited: evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt

AbstractThe interpretation of seismotectonic processes within the uppermost few kilometers of the Earth’s crust has proven challenging due to the often significant uncertainties in hypocenter locations and focal mechanisms of shallow seismicity. Here, we revisit the shallow seismic sequence of Saint-Ursanne of March and April 2000 and apply advanced seismological analyses to reduce these uncertainties. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which is currently evaluated as a possible site for the development of a deep geothermal project. Template matching analysis for the period 2000–2021, including data from mini arrays installed in the region since 2014, suggests that the source of the 2000 sequence has not been persistently active ever since. Forward modelling of synthetic waveforms points to a very shallow source, between 0 and 1 km depth, and the focal mechanism analysis indicates a low-angle, NNW-dipping, thrust mechanism. These results combined with geological data suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the Saint-Ursanne sequence. Together with two other more recent shallow thrust faulting earthquakes near Grenchen and Neuchâtel in the north-central portion of the Jura fold-and-thrust belt (FTB), these new findings provide new insights into the present-day seismotectonic processes of the Jura FTB of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely &lt; 0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement.</jats:p

Long term deformation and seismic observations at the Mont Terri rock laboratory&amp;#160;

&amp;lt;p&amp;gt;The Mont Terri rock laboratory, located in the Swiss Jura Mountains, is dedicated to research on argillaceous rocks. Since its founding in 1996, the objective is the hydrogeological, geochemical, and geotechnical characterisation of Opalinus Clay in the context of nuclear waste repositories. More recently, the work has broadened to additional fields, covering potential uses of the deep geological subsurface such as geological storage of carbon dioxide and geothermal energy. With the excellent infrastructure, a comprehensive database, and the broad scientific and technological expertise, knowledge is enhanced e.g. through the advancement and comparison of approaches as well as the development and testing of novel investigation methods. These, as well as studies on feasibility and risk assessment, are of benefit also for underground laboratories in general and in situ explorations in different rock types worldwide. Due to the long-term commitment and the available gallery space of the research facility, elaborate as well as decade-long experiments can be implemented.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In order to detect, quantify, and understand short- and long-term deformations in the Mont Terri rock laboratory, quasi continuous time series are established employing various monitoring techniques. The latter complement each other in regard to their spatial dimensions, operational frequency optima, and their point or integral information. The approach combines&amp;lt;/p&amp;gt;&amp;lt;ul&amp;gt;&amp;lt;li&amp;gt;a 50&amp;amp;#160;m long uniaxial hydrostatic levelling system (HLS, Type &amp;amp;#8220;PSI&amp;amp;#8221;, positioned along a gallery wall, measuring principle: electrical plate capacitors),&amp;lt;/li&amp;gt; &amp;lt;li&amp;gt;four mini-arrays of very-broad-band triaxial seismometers, installed in the rock laboratory (one under the HLS) as well as outside the rock laboratory at the surface,&amp;lt;/li&amp;gt; &amp;lt;li&amp;gt;and an array of high resolution, biaxial platform tiltmeters, with instruments situated close to the HLS and in various parts of the rock laboratory, integrated in other in situ experiments.&amp;lt;/li&amp;gt; &amp;lt;/ul&amp;gt;&amp;lt;p&amp;gt;The observed signals and their analysis differ in space and time. They range from the detection of local nanoseismic as well as large tele seismic events, to the determination of earth tides, and to the identification of seasonal trends versus other long term geodetic movements. Besides the mutual comparison of the three deformation measurements, the time series provide valuable input for numerous scientific questions such as the stability of the rock laboratory as a whole or in its parts, the influence of excavation, ventilation, or fluid injection on rock matrix and faults. Long data series of ambient parameters, essential for interpretation of the deformation records, such as temperature, pressure, and humidity, are recorded by sensors integrated in the above listed instruments and are also of interest in further experiments performed by the Mont Terri Consortium.&amp;lt;/p&amp;gt;</jats:p

The Saint-Ursanne earthquakes of 2000 revisited: Evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt

&amp;lt;p&amp;gt;The interpretation of seismotectonic processes within the uppermost few kilometers of the Earth&amp;amp;#8217;s crust has proven challenging due to the often significant uncertainties in hypocenter locations and focal mechanisms of shallow seismicity. Here, we revisit the shallow seismic sequence of Saint-Ursanne of March and April 2000 and apply advanced seismological analyses to reduce these uncertainties. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (M&amp;lt;sub&amp;gt;L&amp;lt;/sub&amp;gt;) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which is currently evaluated as a possible site for the development of a deep geothermal project. Template matching analysis for the period 2000-2021, including data from mini arrays installed in the region since 2014, suggests that the source of the 2000 sequence has not been persistently active ever since. Forward modelling of synthetic waveforms points to a very shallow source, between 0 and 1 km depth, and the focal mechanism analysis indicates a low-angle, NNW-dipping, thrust mechanism. These results combined with geological data suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the Saint-Ursanne sequence. Together with two other more recent shallow thrust faulting earthquakes near Grenchen and Neuch&amp;amp;#226;tel in the north-central portion of the Jura fold-and-thrust belt (FTB), these new findings provide new insights into the present-day seismotectonic processes of the Jura FTB of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely &amp;lt;0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement. This trenspressive regime is confirmed by the ML4.1 R&amp;amp;#233;cl&amp;amp;#232;re earthquake of December 24. 2021, which occurred ~20 kilometres west of St. Ursanne in the uppermost crust.&amp;lt;/p&amp;gt;</jats:p