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Underground laboratories have become indispensable in the understanding of physical processes during e.g., hydraulic stimulation and seismic monitoring of deep geothermal reservoirs or CO2 storage target reservoirs. They provide a test bench and constitute the bridge between small-scale laboratory studies and full-scale pilot sites. Here, we present results from multiple active source seismic campaigns in one of the Swiss underground laboratories: the Mont Terri Rock Laboratory. Here, DAS fibres are cemented behind the casing of multiple monitoring boreholes and active shots are taken with a P-wave sparker. This dense array of active seismic measurements enables us to obtain a baseline characterisation of the P-wave velocity of the rock before any activity (e.g., injection) takes place. During stimulations, dynamic measurements with an active sparker source are recorded, followed by a time-lapse monitoring approach where seismic measurements are collected through active seismic campaigns in set time intervals in the months after stimulations. In this way we can create high-resolution, four-dimensional monitoring and characterisations of the rock body and potential earthquakes during the full monitoring period. We show different configurations and measurements settings with their effect on the DAS recordings of active signals.

The sealing characteristics of the geological formation located above a CO2 storage reservoir, the so-called caprock, are essential to ensure efficient geological carbon storage. In case CO2 were to leak through the caprock, temporal changes in fluid geochemistry can reveal fundamental information on migration mechanisms and induced fuid-rock interactions. Here, we present the results from a unique in-situ injection experiment, where CO2-enriched fluid was continuously injected in a faulted caprock analogue. Results show that the CO2 migration follows complex path- ways within the fault structure. The joint analysis of noble gases, ion concentrations and carbon isotopes allow us to quantify mixing between injected CO2-enriched fluid and resident formation water and to describe the temporal evolution of water-rock interaction processes. The results presented here are a crucial complement to the geophysical monitoring at the fracture scale highlighting a unique migration of CO2 in fault zones.

Carbon capture and storage in geological reservoirs is essential to mitigate carbon dioxide emissions, but is only effective if long-term storage is ensured and no leakage occurs, for example through unknown faults in the caprock that seals the reservoir. To test how the integrity of a caprock can be monitored non-invasively, we conducted an injection experiment directly into a faulted caprock analog at the Mont Terri Rock Laboratory. We monitored the experiment using active seismic techniques, along with strain, fluid pressure, and microseismicity measurements. Pulse injection with pressures of up to 4.8 MPa caused a perturbation of effective stress, which we observed through a reduction of seismic P-wave velocities by around 1 %. This perturbation was not sensed by means of microseismicity, even though a sudden pressure drop indicated that the injection caused the opening of some fractures within the fault zone. Substantial rock deformation was also only detected at the injection borehole but not in surrounding monitoring boreholes. Thus, with seismic velocity monitoring, processes can be detected within a faulted caprock for which other methods may be blind. This demonstrates the value of seismic velocity monitoring as a tool to complement a monitoring system., Geophysics, 87 (4), ISSN:0016-8033, ISSN:1942-2156

The increased interest in subsurface development (e.g., unconventional hydrocarbon, deep geothermal, waste disposal) and the associated (triggered or induced) seismicity calls for a better understanding of the hydro-seismo-mechanical coupling in fractured rock masses. Being able to bridge the knowledge gap between laboratory and reservoir scales, controllable meso-scale in situ experiments are deemed indispensable. In an effort to access and instrument rock masses of hectometer size, the Bedretto Underground Laboratory for Geosciences and Geoenergies (‘Bedretto Lab’) was established in 2018 in the existing Bedretto Tunnel (Ticino, Switzerland), with an average overburden of 1000 m. In this paper, we introduce the Bedretto Lab, its general setting and current status. Combined geological, geomechanical and geophysical methods were employed in a hectometer-scale rock mass explored by several boreholes to characterize the in situ conditions and internal structures of the rock volume. The rock volume features three distinct units, with the middle fault zone sandwiched by two relatively intact units. The middle fault zone unit appears to be a representative feature of the site, as similar structures repeat every several hundreds of meters along the tunnel. The lithological variations across the characterization boreholes manifest the complexity and heterogeneity of the rock volume, and are accompanied by compartmentalized hydrostructures and significant stress rotations. With this complexity, the characterized rock volume is considered characteristic of the heterogeneity that is typically encountered in subsurface exploration and development. The Bedretto Lab can adequately serve as a test-bed that allows for in-depth study of the hydro-seismo-mechanical response of fractured crystalline rock masses., Solid Earth Discussions, ISSN:1869-9537

We use Distributed Strain Sensing (DSS) through Brillouin scattering measurements to characterize the reactivation of a fault zone in shale (Opalinus clay), caused by the excavation of a gallery at...

Metamorphic and deformed rocks in thrust zones show particularly high seismic anisotropy causing challenges for seismic imaging and interpretation. A good example is the Seve Nappe Complex in central Sweden, an old exhumed orogenic thrust zone that is characterized by a strong but incoherent seismic reflectivity and considerable seismic anisotropy. However, only little is known about their origin in relation to composition and structural influences on measurements at different seismic scales. Here, we present a new integrative study of cross-scale seismic anisotropy analyses combining mineralogical composition, microstructural analyses, and seismic laboratory experiments from the COSC-1 borehole, which sampled a 2.5-km-deep section of metamorphic rocks deformed in an orogenic root now preserved in the Lower Seve Nappe. While there is strong crystallographic preferred orientation in most samples in general, variations in anisotropy depend mostly on bulk mineral composition and dominant core lithology as shown by a strong correlation between these. This relationship enables to identify three distinct seismic anisotropy facies providing a continuous anisotropy profile along the borehole. Moreover, comparison of laboratory seismic measurements and electron-backscatter diffraction data reveals a strong scale dependence, which is more pronounced in the highly deformed, heterogeneous samples. This highlights the need for comprehensive cross-validation of microscale anisotropy analyses with additional lithological data when integrating seismic anisotropy over seismic scales., Journal of Geophysical Research: Solid Earth, 126 (5), ISSN:2169-9313, ISSN:0148-0227, ISSN:2169-9356

The Bedretto Underground Laboratory for Geosciences and GeoEnergies, located in the Swiss Alps and situated under more than 1 km of granitic overburden, offers a unique field site to study processes in fractured rock. Currently, a total of six boreholes are available, four of them being permanently instrumented with monitoring equipment, and two dedicated as stimulation boreholes. One of the monitoring boreholes contains permanent packed-off intervals which record pressure changes and flow rate. The remaining three are instrumented with a variety of sensors, including fiber-optic micro-strain sensors, temperature monitoring, permanent geophones and accelerometers. All monitoring boreholes are either sealed with packers or cemented, and only the stimulation boreholes allow for outflow. During a period of several weeks, we were able to seal the two stimulation boreholes and allow the reservoir to approach ambient pressure conditions (more than 3 MPa at the wellhead) while we monitored the response of the reservoir. The pressure buildup shows not only in the pressure data, but also as stress changes in the reservoir. During a depressurization phase, we quickly opened one borehole and subsequently performed time-lapse single-hole Ground Penetrating Radar (GPR) measurements. At a second depressurization phase, we continued the GPR measurements while opening the second borehole in a controlled manner. The changes in strain, pressure and GPR reflectivity illuminate the response of the reservoir when moving from ambient to atmospheric pressure at the wellhead, and reveal processes such as wellbore storage, pore-pressure variations and ultimately permeability changes in the reservoir.

The transport of chemically reactive fluids through fractured clay-rich rocks is fundamental to many subsurface engineering technologies. Here, we present results of direct-shear laboratory experiments with simultaneous imaging by X-ray Computed Tomography in Opalinus claystone with subsequent fluid injection to unravel the interplay between mechanical fracture deformation, fluid sorption, and flow. Under constant radial stress (σc = 1.5 MPa), the average mechanical aperture (Formula presented.) increases with shear displacement. Upon brine injection, (Formula presented.) is reduced by 40% relative to initial conditions ((Formula presented.) μm) and fluid-sorption induces a divergent displacement of the two sample halves (Δh = ±50 − 170 μm) quantified by digital image correlation. None of these changes are observed in a control experiment with decane, indicating that creep is subordinate to swelling in sealing the fracture. Swelling-induced changes in permeability within the fracture are heterogeneous and largely affect the fracture flow field, as computed using numerical simulations., Geophysical Research Letters, 48 (5), ISSN:0094-8276, ISSN:1944-8007

Metamorphic and deformed rocks in thrust zones show particularly high seismic anisotropy causing challenges for seismic imaging and interpretation. A good example is the Seve Nappe Complex in Jämtland, Sweden, an exhumed orogenic thrust zone characterized by a strong but incoherent seismic reflectivity and considerable seismic anisotropy. However, only little is known about the origin of the anisotropy in relation to composition, structural influences, and implications for measurements at different seismic scales. We present an integrative study of the seismic anisotropy at different scales combining mineralogical composition, microstructural analyses and seismic laboratory experiments from samples of the 2.5 km-deep COSC-1 borehole. While there is a pronounced crystallographic preferred orientation in most of the core samples, variations in anisotropy correlate strongly with bulk mineral composition and dominant core lithology. Based on three major lithologic different facies (felsic gneiss, amphibole-rich rocks, and mica schists), we propose an anisotropy model for the full length of the borehole, which indicates two prevailing anisotropic units. Comparison of laboratory seismic measurements and electron-backscatter diffraction (EBSD) data reveals a strong scale-dependence, which is more pronounced in the highly deformed, heterogeneous samples. This highlights the need for comprehensive cross-validation of microscale anisotropy analyses with additional lithological data when integrating seismic anisotropy through seismic scales.

The success of geological carbon storage depends on the assurance of a permanent confinement of the injected CO2 in the storage formation at depth. One of the critical elements of the safekeeping of CO2 is the sealing capacity of the caprock overlying the storage formation, despite faults and/or fractures, which may occur in it. In this work, we present an ongoing injection experiment performed in a fault hosted in clay at the Mont Terri underground rock laboratory (NW Switzerland). The experiment aims at improving our understanding on the main physical and chemical mechanisms controlling i) the migration of CO2 through a fault damage zone, ii) the interaction of the CO2 with the neighbouring intact rock, and iii) the impact of the injection on the transmissivity in the fault. To this end, we inject a CO2-saturated saline water in the top of a 3 m think fault in the Opalinus Clay, a clay formation that is a good analogue of common caprock for CO2 storage at depth. The mobility of the CO2 within the fault is studied at decameter scale, by using a comprehensive monitoring system. Our experiment aims to the closing of the knowledge gap between laboratory and reservoir scales. Therefore, an important aspect of the experiment is the decameter scale and the prolonged duration of observations over many months. We collect observations and data from a wide range of monitoring systems, such as a seismic network, pressure temperature and electrical conductivity sensors, fiber optics, extensometers, and an in situ mass spectrometer for dissolved gas monitoring. The observations are complemented by laboratory data on collected fluids and rock samples. Here we show the details of the experimental concept and installed instrumentation, as well as the first results of the preliminary characterization. Analysis of borehole logging allow identifying potential hydraulic transmissive structures within the fault zone. A preliminary analysis of the injection tests helped estimating the transmissivity of such structures within the fault zone, as well as the pressure required to mechanically open such features. The preliminary tests did not record any induced microseismic events. Active seismic tomography enabled a sharp imaging the fault zone.

Understanding potential caprock failure through fault zone leakage is crucial for the safe, long-term containment of a CO2 storage site. Thus, the presence of faults in caprocks will greatly affect the site characterization process in terms of the safety assessment. The CS-D experiment at the Mont Terri Lab aims at investigating caprock integrity by determining CO2-rich water mobility in a fault zone. Seven boreholes were drilled in the clay rock, all crosscutting a fault at depths of 17-30 m below the niche floor. The boreholes were fully cored, and the samples analysed in various laboratories. All boreholes were instrumented for monitoring geochemical and geomechanical changes induced by fluid injection for prolonged time, with the goal to better understand mechanisms of CO2 leakage in a faulted caprock. We deployed a multi component monitoring setup measuring pressure, axial and 3D deformation, seismic activity and cross-hole electrical resistivity. A borehole was fully dedicated to the monitoring of the injection front, as well as geochemical in-situ measurements and fluid sampling. A portable mass spectrometer for direct measurements of gas has been installed in a dedicated borehole interval. Injection and monitoring activities started in December 2018, with multiple injection tests with saline water at pressures up to 6 MPa, in order to characterize the hydraulic response of the fault. A prolonged injection of CO2-saturated water at constant head pressure started in June 2019 and lasted for about 8 months. In this contribution, we will present the analysis of the data collected during the fault characterization (hydraulic, geophysics, and core analysis) as well as results of the continuous months-long injection. Preliminary interpretation of the monitoring data suggests that a fault does not necessarily form a pathway for the fluid to escape at shallow depth.

Tunnel excavations are known to perturb the hosting rock mass at long distances, with changes in the hydrogeological flow affecting, as well as deforming the rock mass, inducing subsidence in a zone above the tunnel. During the extension of the Mont Terri Underground Rock Laboratory, we had the unique opportunity to monitor the final part of the excavation of Gallery18 and the final breaktrough.The joint effort of two experiments (CS-D lead by ETH Zurich and FS-B lead by LBNL) allowed for a detailed characterization of the poro-elastic response of the rock mass and the Mont Terri Main Fault Zone to the excavation. Geophysical, geomechanical, and hydrogeological monitoring include: (1) pressure monitoring in several borehole intervals; (2) deformation at a chain potentiometer and fiber optics grouted in boreholes (normal to bedding and parallel to fault zone), and platform-tilmeters installed at the tunnel floor, as well as detailed 3D displacement at the SIMFIP probe.All monitoring systems detected major perturbations starting from 15 days before the breakthrough and continuing for several days after it. We summarize the observations and will combine numerical modelling and observed trend to conceptualized the pattern of poro-elastic deformation. The results of the analysis could help shedding light on the poro-elastic behaviour of clay, providing interesting hints for the modeling community and helping in planning of future nuclear waste repositories in such material.

Deeply rooted thrust zones are key features of tectonic processes and the evolution of mountain belts. Exhumed and deeply eroded orogens like the Scandinavian Caledonides allow us to study such systems from the surface. Previous seismic investigations of the Seve Nappe Complex have shown indications of a strong but discontinuous reflectivity of this thrust zone, which is only poorly understood. The correlation of seismic properties measured on borehole cores with surface seismic data can constrain the origin of this reflectivity. To this end, we compare seismic velocities measured on cores to in situ velocities measured in the borehole. For some intervals of the COSC-1 borehole, the core and downhole velocities deviate by up to 2 km s−1. These differences in the core and downhole velocities are most likely the result of microcracks mainly due to depressurization. However, the core and downhole velocities of the intervals with mafic rocks are generally in close agreement. Seismic anisotropy measured in laboratory samples increases from about 5 % to 26 % at depth, correlating with a transition from gneissic to schistose foliation. Thus, metamorphic foliation has a clear expression in seismic anisotropy. These results will aid in the evaluation of core-derived seismic properties of high-grade metamorphic rocks at the COSC-1 borehole and elsewhere., Solid Earth, 11 (2), ISSN:1869-9510, ISSN:1869-9529

Confirming the permanent containment is a key challenge for the storage of CO2 in deep underground reservoirs. Faults in the cap rock of such reservoirs are potential flow paths for the CO2 to escape. Our decametre-scale experiment at the Mont Terri Rock Laboratory aims to better understand mechanisms of CO2 leakage trough a fault, and to test strategies to monitor the propagation of CO2-saturated water through faults.Two boreholes were drilled through the main fault in Mont Terri with packer-intervals dedicated to fluid-injection and hydraulic/geochemical monitoring. Another five boreholes in the close surrounding were equipped with various instruments for geotechnical and geophysical observations. During the first phase of the experiment, the hydraulic response of the fault was characterized with injections of formation water in a step-up mode at pressures up to 6.0 MPa. The second phase, which was still on-going at the time of the abstract submission, consists of a long-term (several months) injection of CO2-saturated formation water at a constant head of 4.5 MPa, which is below the fault opening pressure. All injection activities were monitored with active seismic measurements, along with a comprehensive set of hydraulic-, mechanical-, geochemical- and other geophysical surveys. We will present the active seismic imaging results from the step-up injection test and compare them with the other surveys. Additionally, preliminary results will be shown acquired during the long-term injection of CO2-saturated formation water into the fault.

Given shale's potential to serve as both a caprock for geological carbon sequestration and as the host for nuclear waste disposal, this study focuses on the structural characterization around a 1.5–3 m thick fault within the Opalinus Clay host rock and petrophysical characterization of both the host rock and fault core. Seven boreholes were drilled at the Mont Terri Rock laboratory in late 2018 to constrain the orientation of the so-called ‘Main Fault’ and several fracture families within the fault core using core and image logs. Contrary to typical fault models, matrix permeability and seismic velocity measurements show similarities in the host rock and within the Main Fault. In the clay-rich samples, measurements performed in laboratory at varying confining pressures indicate p-wave velocities range from 2.60 to 2.95 km/s perpendicular to foliation and 3.38–3.58 km/s parallel to foliation at near in-situ confining pressures, which increase with similar anisotropy at higher confining pressures (200 MPa). Since the permeability of the host rock and fault zone is very low (10−19–10−21 m2) flow is expected to prevail along fractures, where critical stress fault analysis suggests that potential hydraulically conductive fractures are actually conjugate to the Main Fault trend.

Recent drilling of the first Collisional Orogeny in the Scandinavian Caledonides scientific borehole (COSC-1) near Are, Sweden permitted a laboratory investigation of seismic anisotropy on high met ...

Mineral alignment can provide valuable information on a rock's geological history. Many structural, tectonic, or geodynamic studies rely on determining the preferred orientation of rock-forming minerals, either by direct texture determination or using anisotropy measurements as proxies. Robust interpretations of anisotropy require detailed understanding of its relationship with texture. This study investigates the texture, magnetic and seismic anisotropies of ultramafic rocks from the Ivrea-Verbano Zone (IVZ), Northern Italy, with a special focus on the interplay between anisotropy contributions carried by different minerals. Texture was obtained from electron backscatter diffraction, magnetic anisotropy from low- and high-field anisotropy of susceptibility measurements, and seismic anisotropy from P- and S-wave velocities along the three principal directions of the macroscopic fabric, using 22 mm diameter cores. Texture-based models of magnetic anisotropy agree well with corresponding measurements. Larger variability is observed for seismic anisotropy. Possible explanations are (1) velocities were measured in three directions, insufficient to determine the full elasticity tensor, and (2) seismic anisotropy depends on grain boundaries, pores, and cracks in addition to crystallographic preferred orientation. The contributions to magnetic and seismic anisotropy of each constituent mineral can interfere positively, leading to a larger overall anisotropy, or negatively, resulting in a weaker anisotropy. Seismic anisotropy is mostly controlled by olivine, whereas magnetic anisotropy can be dominated by olivine, pyroxene, or hornblende. This study illustrates that, although the relationship between texture and anisotropy can be complex, it is possible to quantitatively predict magnetic, and to a lesser degree seismic, anisotropy from texture data. Even though both magnetic and seismic anisotropies are common proxies for texture, they are not coaxial, and no simple relationship between the degree of magnetic and seismic anisotropy was found. These results underline the importance of understanding different minerals' contributions to anisotropy in upper mantle rocks.

The Ivrea-Verbano Zone offers a unique opportunity to study lower crust/upper mantle rocks unaffected by serpentinization. Peridotites from Finero (North-East Ivrea-Verbano Zone) have been collected to investigate the influence of individual mineral phases on seismic anisotropy. The methods involve experimental ultrasonic P-wave velocity measurements using a hydrostatic pressure vessel, and electron backscatter diffraction (EBSD) analysis to investigate the crystallographic preferred orientation (CPO). CPO was analyzed by large area EBSD scans for major minerals including olivine, orthopyroxene, but also for metasomatic hornblende. The CPO of olivine is confirmed to be the major source of detected seismic anisotropy. Minor influence can arise from hornblende if it is sufficiently abundant.

Geophysical Research Letters, 41 (20), ISSN:0094-8276, ISSN:1944-8007

A recent reinterpretation of the existing DSS profiles [Scarascia and Cassinis, Tectonophysics 271 (1997) 157–188] led to a reconstruction of the Moho boundary and of the lower crust, in the central-eastern Alpine sector, where the European and the Adriatic domains are deeply indented. In that work a complex crust–mantle transition, composed of alternating low- and high-velocity layers, was observed in the deepest bottom of the European crust. In the same work it was confirmed that the European lower crust beneath the Alpine Range is characterised by a very low seismic velocity, while the velocity of the Adriatic lower crust reaches the average values found in collisional belts. The interpretation of these features has been performed employing a data-base of ultrasonic seismic measurements. The Ivrea–Verbano Zone has been assumed as an analogue of crust–mantle transition. A statistical approach was used to associate the bodies of the interpreted seismic models to the lithotypes. A petrological model is attempted in order to suggest an explanation of the observed phenomena, assuming physical and compositional constraints appropriate to the Alpine collisional belt. Cumulitic peridotites and pyroxenites lenses in a gabbroic host rock fit the observed seismic structure of the crust–mantle transition. The upper mantle lies below a transition zone and is characterised by a velocity of 8.2 km/s, detected by P n phases. In our study it is interpreted as a spinel-to-garnet peridotite. The anomalous low velocity of the European lower crust is discussed but still remains an open subject.

The Campi Flegrei Deep Drilling Project (CFDDP) entered the operative phase during the second half of 2012, with the pilot hole drilling. The Project was initiated to address two kinds of problems: 1) purely volcanological, to understand in detail the dynamics of the most explosive and yet mostly unknown volcanism on the Earth with the potential to generate global catastrophes, and 2) to mitigate the highest volcanic risk in the World, namely the one associated with the metropolitan area of Naples where more than 3,000,000 people are exposed to extreme risk. The CFDDP Project offers the only direct means to understand the physics driving the on-going ground uplift affecting the area since at least six centuries, through in situ and laboratory measurements of rock rheology and permeability. In particular, direct investigation at depth by drilling is essential for understanding the extent that shallow magma intrusion is involved in the uplift of 15 to 20 m accumulated over the last centuries. Such a high cumulative uplift corresponds to 1-10 km3 of new magma intruded into the system, depending on details of the model used. Such an erupted volume should be conservatively assumed as the worst scenario for a future eruption. This corresponds to a massive eruption, largest than any other one after the caldera-forming Yellow Tuff eruption of 15,000 y BP and not much smaller than that, which would anyway require evacuation of some millions people. An alternative possibility is that the cumulative uplift is mostly due to shallow geothermal perturbations as described in several recent publications. Both possibilities, each with widely differing hazard implications, rely strongly on as yet poorly known conditions at depth beneath the caldera. It is thus crucial to discriminate between these two opposing possibilities in order to clarify the worst scenario for a future eruption and to provide an invaluable tool for civil defence at this densely populated area. This presentation describes preliminary results obtained from CFDDP pilot hole, reaching a final depth of 502 m, which show considerable promise in answering the main open questions. From a volcanological point of view, they enlighten in an unprecedented way the dynamics of the Bagnoli-Fuorigrotta plain, the easternmost part of the caldera and the most densely populated because it includes the city of Naples. Furthermore, they allowed for the first in-situ measurements, at 500 m of depth, of loading stress and fluid-dynamical parameters like permeability, thus already representing a large step forward towards a complete fluid-dynamical interpretation of the ground uplift episodes called ‘bradyseism’.

In order to determine the seismic properties of rocks representing the continental crust/upper mantle transition, a structural and petrographical study of peridotites of the Ivrea-Verbano zone (N. Italy) has been undertaken. The seismic behaviour (Vp, Vs, birefringence, orientation of the fast shear-wave polarisation plane) has been calculated from the modal composition of rock samples, together with the crystallographic preferred orientation and the single crystal elastic constants, using the methods of Mainprice (1990). It is shown that the intrinsic anisotropy of peridotites is mainly due to the lattice preferred orientation (LPO) of olivine and to the competing effects due to the LPO of orthopyroxene. If present, well-oriented hydrous phases such as phlogopite, leads to both P- and S-waves velocities becoming drastically reduced, but the anisotropy and the S-wave splitting (mainly on the foliation plane) is increased. An attempt has been made to apply this petrologic and microstructural approach to understand the seismic properties of ultramafic rocks with the aid of a mobile seismic network set up in the Ivrea-Verbano zone. Five recording units with 3-component geophones were installed on the most representative lithologies of the Ivrea-Verbano zone: kinzigites, gabbros, stronalites, and on metapelites of the adjacent outcrop of the Serie dei Laghi. During five months the seismic network recorded 49 events that were mainly regional earthquakes. The preliminary analysis of the first arrival revealed a high-velocity anomaly near the Finero ultramafic massif. Rough calculations indicated that this anomaly could be due to a shallow-depth, peridotitic body about six kilometres thick. S-wave polarisation analysis was carried out on the horizontal components of the seismograms of four regional earthquakes that showed a first arrival propagating almost vertically at the recording sites. Four earthquakes were chosen in order to reconstruct the orientation of the polarisation plane of the shear phases. The preliminary results of this analysis have shown a qualitatively good agreement between the orientation of the polarisation plane of the fast shear-wave and the strike of the foliation at the station near Finero, located on kinzigites of the Ivrea-Verbano zone, although the relationships between the local structural setting and the polarisation orientations at the other recording sites is not yet so clear.

In this paper the elastic properties of amphibolites from the Serie dei Laghi and the Ivrea zone (Southern Alps, N-Italy) were investigated as a function of their mineralogical composition, microfabric and density. Three orthogonal cores were cut parallel and normal to foliation and lineation; from those, bulk and grain density were measured and the interconnected porosity was calculated. Bulk density varies from 2.75 to 3.07 g/cm 3 and calculated porosity ranges from 0.02 to 0.88%. The same cores were also used to measure seismic velocity of ultrasonic waves at room temperature and at increasing confining pressure up to 300 MPa. At high pressure the matrix properties are separated from the crack-induced properties. P-wave velocity varies with respect to the direction of propagation: the slowest direction is always normal to foliation and the fastest parallel to the mineral lineation. The mineral lineation is typically defined by the elongation of amphibole crystals, in which the fastest Vp direction is parallel to the c axis, that is also the elongation axis. The Vp ranges between 6.76 and 7.54 km/s in the direction parallel to lineation and between 6.32 and 7.06 km/s in the direction normal to foliation. This defines a Vp anisotropy of up to 14%, whose shape varies from orthorhombic to axially symmetric (either prolate or flattened). It was observed that both Vp and Vp anisotropy increase with the amount of amphibole and decrease with the amount of plagioclase. Moreover, the c axis distribution of amphiboles is responsible of the Vp anisotropy intensity and shape, in agreement with observations from previous studies. The seismic properties calculated with the approach of Mainprice (1990), using the fabric data, the elastic constants and the modal composition, gave results in good agreement with the measurements. Exposed rocks in the Ivrea and Serie dei Laghi zones show that amphibolites are interlayered with metapelites on a scale from 1 to 100 m. Because of the very large acoustic impedance contrast (20.34±1.75 for amphibolites, 17.16±0.4 for metapelites), they represent a very reflective portion in the middle-lower crust. © 2007 Elsevier B.V. All rights reserved.

The magnetic fabric of a rock, defined by the anisotropy of magnetic susceptibility (AMS), is often used as a tectonic indicator. In order to establish a quantitative relationship between AMS and mineral texture, it is important to understand the single crystal intrinsic AMS of each mineral that contributes to the AMS of the rock. The AMS and crystallographic preferred orientation (CPO) of amphiboles, olivine and pyroxenes has been analyzed in a series of amphibolites, peridotites and pyroxenites that do show preferred mineral alignment. The CPO of each mineral phase was determined based on electron backscatter diffraction (EBSD). Whole- rock AMS was computed based on the CPO and single crystal AMS of the respective minerals. A comparison between measured and modelled magnetic anisotropy shows that the directions of the principal susceptibility axes agree well in amphibolite and peridotite. Pyroxenite is a good example for competing AMS fabrics in polyphase rocks.

Six types of rocks of Alpine origin were investigated for their suitability for high-temperature packed-bed thermal-energy storage. The rocks were thermally cycled in laboratory furnaces between about 100 °C and 600 ° C with a heating rate of 2.6 ° C /min and assessed in terms of their specific heat capacity and porosity as well as the degree of cracking, fracturing, and disintegration. Thermal cycling was found to lead to decreases in the specific heat capacity and increases in the porosity of the rocks. These changes are explained by physical and chemical reactions such as mineral dehydration, deserpentinization, decarbonation, and the quartz-inversion reaction. Simulations of a 23 MWh industrial-scale thermal-energy storage show that the decrease in the specific heat capacity does not have a significant impact on the effective storage capacity, utilization factor, and exergy efficiency. To avoid fracturing of rocks, foliated rocks and rocks rich in calcite and/or quartz, such as limestones and sandstones, are found to be unsuitable when exposed to temperatures higher than about 600 ° C or 573 ° C , respectively. Mafic rocks, felsic rocks, serpentinite, and quartz-rich conglomerates are judged to be suitable for high-temperature thermal-energy storage.

The CARMA project investigated the potential of Carbon dioxide capture and storage (CCS) in Switzerland and the country-specific difficulties on the way to implementation. CCS may play a major role in the future Swiss energy scenario as a bridging technology between the phase out of nuclear energy and the establishment of an entirely renewable energy system. The key findings of the CARMA project with respect to CCS implementation are summarized. A pilot CO2-injection test on a small scale is proposed to prove the suitability of the considered geological formations for durable and safe CO2 storage, and to gain information about the deep Swiss subsurface. Furthermore, such a field test would support the development of the legal framework needed for CCS and initiate knowledge transfer to the Swiss public. The successful test site in Ketzin, Germany adapted to the Swiss context can serve as a role model., Energy Procedia, 37, ISSN:1876-6102, GHGT-11 Proceedings of the 11th International Conference on Greenhouse Gas Control Technologies

A key challenge for CO2 geological storage is the integrity of the caprock. This challenge is addressed by executing a decameter-scale experiment at the Mont Terri Underground Rock Laboratory in Switzerland, under the umbrella of ELEGANCY (Enabling a Low-Carbon Economy via Hydrogen and CCS). ELEGANCY is an European project aiming at advance sustainable geo-energy processes through studies on risk mitigation, characterization and public perception, whose achievements will benefit the fields of carbon dixode sequestration. The experiment will investigating the mechanisms and the physical parameters governing the migration of CO2-rich brine through a faults. In particular, the test seeks to understand the conditions for slip activation (seismic vs. aseismic slip) and the stability of clay faults, as well as the coupling between fault slip, pore pressure, fluid migration and possible induced “micro” seismicity. To this end, we will inject CO2-rich brine into the fault core for a period of about eight months, while monitoring its geo-mechanical response. Additional tracer and transmissivity tests will be conducted at regular time intervals to determine the fluid path evolution of the injected fluid and to infer the potential evolution of CO2 from the brine. Numerical simulation work assist the different phases of the field experiment.