Markus Rast

Last Name

Rast

First Name

Markus

ORCID

0000-0001-9211-7545

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09636 - Behr, Whitney / Behr, Whitney

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Publications 1 - 10 of 14

Effects of Energy Dissipation on Precursory Seismicity During Earthquake Preparation
Bianchi, Patrick; Selvadurai, Paul Antony; Dal Zilio, Luca; et al. (2024)
Seismica
The b-value of the magnitude distribution of natural earthquakes appears to be closely influenced by the faulting style. We investigate this in the laboratory for the first time by analyzing the moment tensor solutions of acoustic emissions detected during a triaxial compression test on Berea sandstone. We observe systematic patterns showing that faulting style influences the b-value and differential stress. Similar trends are observed in a complementary physics-based numerical model that captures mechanical energy dissipation. Both the differential stress and dissipation are found to be inversely correlated to the b-value. The results indicate that, at late stages of the test, the dissipation increases and is linked to a change in AE faulting style and drop in b-value. The patterns observed in the laboratory Frohlich diagrams could be explained by the integrated earthquake model: damaged rock regions form as microcracks coalesce, leading to strain localization and runaway deformation. The modeling results also align with the micromechanics responsible for dissipation at various stages of the experiment and agrees with moment tensor solutions and petrographic investigations. The integration of physics-based models that can capture dissipative processes of the earthquake cycle could assist researchers in constraining seismic hazard in both natural and anthropogenic settings.
Importance of Water-Clay Interactions for Fault Slip in Clay-Rich Rocks
Rast, Markus; Madonna, Claudio; Selvadurai, Paul Antony; et al. (2024)
Journal of Geophysical Research: Solid Earth
Clay-rich rocks are integral to subduction zone dynamics and of practical importance, for example, as barriers in nuclear waste and CO2 repositories. While the effects of swelling strain on the self-sealing capabilities of these rocks are relatively well-established, the implications of polar fluids interacting with charged clay particles on the frictional behavior, and the role of swelling stress in initiating slip in critically stressed faults, remain ambiguous. To address these uncertainties, we conducted triaxial friction experiments using saw-cut samples, with the upper half composed of Opalinus claystone (OPA) and the lower half of Berea sandstone (BER). The frictional strength of the non-wetted OPA-BER interface was estimated based on experiments at confining pressures of 4–25 MPa and constant axial loading rate (0.1 mm/min). Fluid injection friction experiments were performed using decane (non-polar fluid) or deionized water (polar fluid) at 10 and 25 MPa confining pressures and constant piston displacement control. Macroscopic mechanical data were complemented by distributed strain sensing on the sample surface. Compared to decane, the frictional strength of the OPA-BER interface tended to decrease when injecting water, which is attributed to phyllosilicate lubrication and the transition of the OPA from a solid rock to an incohesive mud near the saw-cut surface. When injecting water, slip was initiated during initial hydration of the OPA-BER interface, although the apparent stress state was below the yield stress. To explain this behavior, we propose that the swelling stress is a crucial factor that should be integrated into the effective stress model.
Laboratory‐Constrained Seismic Properties of the COSC‐2 Borehole, Scandinavian Caledonides: Implications for Crustal Anisotropy and Reflectivity
Rast, Markus; Madonna, Claudio; Schweizer, Nora; et al. (2025)
Journal of Geophysical Research: Solid Earth
Seismic surveys are essential for studying the Earth's subsurface. However, the interpretation of seismic surveys requires a link between field data and rock physical properties by linking laboratory‐derived data from drill core samples with borehole information and seismic images. Here, we study the seismic properties of the second “Collisional Orogeny in the Scandinavian Caledonides” borehole (COSC‐2), which intersects parautochthonous turbidites, highly deformed black shales (Alum Shale), autochthonous sediments, and the underlying Baltic basement. We selected six core samples of the major lithologies (graywacke, lithic arenite, Alum Shale, arkosic arenite, porphyry, and dolerite) to measure ultrasonic P‐ and S‐wave velocities (V_P and V_S) under dry conditions at confining pressures of 10–240 MPa. For anisotropic sedimentary samples, we measured V_P and V_S in three mutually perpendicular sub‐samples oriented relative to foliation and lineation. Combining our measurements with theoretical concepts of elasticity, we estimated key influences on seismic properties. Our results show: (a) Pressure solution seams in arenites have little effect on seismic anisotropy. (b) Strongly anisotropic graywacke and Alum Shale samples have orthorhombic or lower symmetry, challenging the common transverse isotropy assumption for clay‐rich rocks. Accounting for laboratory‐derived anisotropy may improve the reflectivity in seismic surveys. (c) Organic matter in Alum Shale reduces seismic velocities, enhances seismic anisotropy, and causes Alum Shale to be a prominent reflector. (d) Despite the low porosity, microcracks in the dolerite cause velocities to be significantly higher under saturated conditions than under dry conditions, which must be considered when interpreting the reflectivity of dolerites intruded into porphyries.
Numerical shear experiments of quartz-biotite aggregates: Insights on strain weakening and two-phase flow laws
Rast, Markus; Ruh, Jonas B. (2021)
Journal of Structural Geology
For progressively deforming multi-phase aggregates, it is unclear to what extent the change in geometry and orientation of the involved phases leads to textural strain weakening and thus may control strain localization. Consequently, the question arises how the ductile flow of multi-phase rocks can be described or determined. To contribute to the understanding of these knowledge gaps, two-dimensional numerical shear experiments of quartz-biotite aggregates were conducted at variable conditions. Textural variations after a shear strain of γ ≈ 10 appear to be dependent on the viscosity contrast between the minerals involved. To estimate whether a numerical experiment is undergoing strain weakening or hardening, the temporal evolution of the mean second invariant of the deviatoric stress tensor was tracked. The results suggest that strain weakening occurs if biotite is distinctly isolated in form of strong or weak inclusions and that it is more effective under conditions with larger viscosity contrasts between matrix and inclusions. However, observed stress drops in experiments purely based on textural strain weakening are low compared to other strain weakening processes. Numerical results from experiments with variable strain rate, temperature and biotite content were combined to determine two-phase flow law parameters for quartz-biotite aggregates, which are in broad agreement with existing analytical mixed-aggregate flow laws.
Fault reactivation in clay-rich rocks – eﬀects of water-clay interactions
Rast, Markus; Madonna, Claudio; Selvadurai, Paul Antony; et al. (2024)
EGUsphere
Clay-rich rocks play an important role in critical practical applications, particularly as natural barriers in nuclear waste repositories and subsurface caprocks for CO2 storage. The interaction between electrostatically charged clay minerals and polar fluids (e.g., water) can lead to swelling or, under confined conditions, build-up of swelling stress. Fault closure by swelling in clay-rich rocks has been the focus of many studies. However, it remains unclear how water-clay interactions affect the stability of pre-existing faults, considering that in addition to changes in frictional properties, the stress state may also change due to the build-up of swelling stress. This study addressed this gap by conducting triaxial friction experiments on oblique saw-cut cylindrical samples. The upper half of the sample consisted of a clay-rich rock (Opalinus claystone) and the lower half of a permeable sandstone (Berea sandstone). The first set of experiments determined the friction slip envelope of the sandstone-claystone interface without fluid injection, at confining pressures ranging from 4 to 25 MPa, and a constant axial loading rate of 0.1 mm/min. These experiments showed a frictional strength well below Byerlee’s law, indicating that the Opalinus claystone dictates the strength of the two-material interface. Friction experiments with fluid injection were then performed at confining pressures of 10 and 25 MPa with a constant piston position (no axial loading) and an initial differential stress of about 70% of the expected yield stress. The aim was to compare the fluid pressures required to initiate slip in scenarios with and without fluid-clay interactions. For this, the experiments involved stepwise increases in fluid pressure through the injection of either deionized water (a polar fluid) or decan (a non-polar fluid). In one of the decane and one of the water injection experiments, fibre-optic strain sensors were attached to the sample surface. This allowed us to differentiate between poroelastic deformation within the matrix, deformation due to water-clay interaction, and elastic relaxation due to slip along the saw cut. The friction slip envelope based on decane injection experiments is within the uncertainty of the friction slip envelope based on the experiments with no fluid injection. In contrast, the water injection experiments indicate a weakening of the frictional interface. We interpret this weakening to be due to the transition of the claystone from a solid rock to a mud close to the saw-cut surface. This weakening was evident even at ambient fluid pressure, although the apparent stress state was below the yielding stress, indicating the need to consider swelling stress in initial water injection scenarios. In summary, our data suggest that water-clay interactions may reactivate pre-existing faults due to (1) the change of the frictional properties and (2) the build-up of swelling stress.
The COSC-2 drill core and its well-preserved lower Palaeozoic sedimentary succession - an unexpected treasure beneath the Caledonian nappes
Lehnert, Oliver; Almqvist, Bjarne; Anderson, Mark; et al. (2024)
Estonian Journal of Earth Sciences
The Collisional Orogeny in the Scandinavian Caledonides (COSC) project focuses on processes related to the closure of the Iapetus Ocean, causing the Ordovician-Silurian continent- continent collision between Baltica and Laurentia. The rock succession in the second drill core (COSC-2) from the J & auml;mt land County, central Sweden, provides the base for detailed sedi- mentological, stratigraphic, geophysical, geochemical, geothermal and structural studies. The basement, comprising 1.66-1.65 Ga Transscandinavian Igneous Belt porphyries intruded by 1.47 Ga and 1.27-1.26 Ga mafic dykes and sills, is heavily weathered towards the top. Here it grades into typical saprock and saprolite (including immature soil reflecting the sub-Cambrian peneplain). The overlying sedimentary sequence starts with basal conglomerates and heterogeneous sediments with shell fragments, indicating an early Cambrian rather than a Neoproterozoic age for the marine transgression in the area. The developing early Cambrian basin was rapidly filled, initially by mostly coarse-grained sediment gravity flows. These strata are covered by sandstone turbidites that show an upward transition into the Alum Shale Formation, representing a tectonically quieter period (mid-Cambrian/Maolingian to Early Ordovician/Tremadocian). The upper part of the Alum Shale Formation is overlain by a late Early Ordovician turbidite succession. Local sources of sediments below the Alum Shale Formation and the extended deposition period may indicate continuous sedimentation in a pull-apart basin pre served in a window beneath the Caledonian thrust sheets.
Fault slip in clay-rich rocks – inﬂuence of the interaction between water and clay minerals
Rast, Markus; Madonna, Claudio; Selvadurai, Paul Antony; et al. (2024)
1st Caprock Integrity & Gas Storage Symposium 2024 – Extended Abstracts
Laboratory Observations Linking Fault Surface Characteristics to the Onset and Evolution of Frictional Sliding and Off-fault Damage
Michail, Sofia; Selvadurai, Paul Antony; Leach Cebry, Sara Beth; et al. (2022)
AGU Fall Meeting Abstracts
The onset and evolution of frictional sliding can provide insight into processes prior to earthquake nucleation such as frictional heterogeneity imposed by variations of the asperity population. Foreshocks in nature are localized frictional instabilities prior to a mainshock. They are believed to be connected to variations in frictional strength and linked to the preparatory slow slip accumulating along the principal rupture plane prior to the mainshock. In dry and bare surfaces, the contact is established through asperities, which are topographical heights where the normal stress concentrates, hence imposing variations in fault strength. In this study, we perform triaxial tests on saw-cut Carrara Marble samples in dry and unlubricated conditions. During the tests, the frictional sample remained initially locked then transitioned to sliding. During sliding, we observed a velocity weakening phase followed by a velocity strengthening phase with increasing slip. Two types of technologies were used to study this frictional response in space and time: (1) an array of acoustic emission sensors monitored localized precursory seismicity and (2) quasi-static deformation in the fault-parallel strain was monitored using novel distributed strain sensing (DSS) using fiber optics. The high-density fault-parallel strain measurements displayed a significant heterogeneous distribution in time and space and experienced sudden reorganization at various phases of the experiment. Major strain reorganization was observed and appears to be collocated to the non-uniform wear, which appeared as grooving and off-fault damage. Worn regions exhibited high normal stress and were determined experimentally using a pressure sensitive film. These regions may explain the strain concentrations observed and potential locations of acoustic emission on the frictional interface. An accurate understanding of the stress and strain heterogeneity on and near the fault may help to improve our understanding of how precursory seismicity and aseismic preslip appear at larger scales.
Geology, Geochronology and Rock Magnetics Along Bedretto Tunnel (Gotthard Massif, Central Alps) and Numerical Modelling of Quartz-Biotite Aggregates
Rast, Markus (2020)
Hydromechanical Behavior of Rocks in Shallow Tectonic Settings: Implications for Natural and Engineered Systems
Rast, Markus (2025)
The hydromechanical behavior of rocks in shallow tectonic settings is essential to understand key processes in both natural deformation systems and engineered subsurface applications. Collisional tectonic settings, including subduction zones and fold-and-thrust belts in the foreland of mountain ranges, are of significant interest because they host large and devastating earthquakes. Attention has been given to phyllosilicate-rich rocks because the internal structure of phyllosilicate minerals causes unique hydromechanical properties, such as low frictional strength, low permeability, and the ability to swell. These properties play a key role in localizing deformation and controlling fluid flow. They also make phyllosilicate-rich formations relevant to engineered systems, such as carbon capture and storage (CCS) facilities and radioactive waste repositories. However, many aspects of how phyllosilicate minerals influence the hydromechanical behavior of rocks in shallow tectonic settings are not fully understood. This thesis addresses some of these knowledge gaps through three studies. The first study investigates the factors that control the occurrence and spatial distribution of different slip modes - such as seismogenic slip, slow slip events (SSEs), and aseismic creep - within an accretionary wedge, as well as how these slip modes are influenced by rock type and physical conditions. To address this, the exhumed McHugh Accretionary Complex in Alaska was used as an analog for the shallow subduction interface. Field observations, compositional analyses, and microstructural data were combined with laboratory friction experiments using representative fault materials and host rocks. Friction experiments were performed under dry and water-saturated conditions at effective normal stresses representative of shallow subduction zones. The results show that increased phyllosilicate content - especially when combined with increased organic matter and water-saturated conditions - reduces the frictional strength and enhances velocity-strengthening behavior, favoring aseismic creep. These findings align with field observations of strain localization in argillitic lithologies. Conversely, frictionally stronger rocks, such as some altered basalts and cherts, may host seismic slip or SSEs depending on their degree of deformation. Lithological contrasts mapped across the McHugh Complex may produce stress and fluid pressure concentrations, which may also influence slip initiation. The second study examines how rock composition and fabric influence seismic properties and the interpretation of subsurface geophysical data, particularly in fold-and-thrust belts. To accomplish this, core samples were analyzed from the second borehole of the "Collisional Orogeny in the Scandinavian Caledonides" project (COSC-2). This borehole intersects various lithologies of an exhumed, inactive fold-and-thrust belt, including turbidites, black shale, and basement rocks. Ultrasonic P- and S-wave velocity measurements were performed on six representative lithologies under different confining pressures. Rocks rich in phyllosilicates, such as graywacke and black shale, show strong seismic anisotropy of orthorhombic or higher symmetry. This challenges the common assumption that phyllosilicate-rich rocks are transverse isotropic. The organic matter in the black shale reduces seismic velocities and further amplifies anisotropic behavior. This may make major thrust faults, which often localize in weak shales, prominent reflectors. In contrast, phyllosilicate-poor samples are weakly anisotropic or isotropic, but seismic velocities can be significantly affected by microcracks, depending on the degree of water saturation. The third study focuses on how polar fluids alter the frictional behavior of phyllosilicate-rich rocks, as well as the effect of swelling stress on the overall stress state. Triaxial friction experiments were performed on Opalinus claystone-Berea sandstone interfaces under non-wetted conditions and with the injection of polar and non-polar fluids (water and decane, respectively). Macroscopic mechanical data were complemented by distributed strain sensing using optical fibers. The results of these experiments show that water reduces the frictional strength, likely due to phyllosilicate lubrication and the transition of the Opalinus claystone into an incohesive mud. Notably, slip occurred during the initial injection of water, even when the apparent stress state was below the yield stress. These findings emphasize the importance of incorporating swelling-induced stress into models of fault reactivation and highlight implications for the integrity of clay-based sealing formations in engineered storage facilities. Together, these three studies advance our understanding of the hydromechanical properties of rocks in shallow tectonic settings, offering new insights into slip behavior, seismic imaging, and fluid-driven fault activity.

Publications 1 - 10 of 14

Markus Rast

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