• Multiscale nature of wave fields and fractures in geomaterials
• Rotational mechanisms of wave and fracture propagation
• Strong rock and rock mass non-linearity (such as bilinear stress-strain curve with high modulus in compression and low in tension) and its effect on wave propagation
• Triggering effects and instability in geomaterials
• Active nature of geomaterials (e.g., seismic emission induced by stress and pressure wave propagation)
• Synchronization in fracture processes including earthquakes and volcanic activity
It is anticipated that studying these and related phenomena can lead to breakthroughs in understanding of the stress transfer and multiscale failure processes in the Earth's crust, ocean and atmosphere and facilitate developing better prediction and monitoring methods.
The session is designed as a forum for discussing these and similar topics.
Posters on site: Tue, 5 May, 08:30–10:15 | Hall X4
Stress-dependent seismic velocities in fractured rocks arise from the coupled deformation of a macroscopically continuous background matrix and stress-sensitive microstructures such as microcracks and aligned fractures. To capture this multi-source nonlinearity together with microstructural size effects, we develop a unified third-order strain-gradient acoustoelastic framework that embeds nonlocal strain-gradient micromechanics into classical acoustoelasticity based on third-order elastic constants, enabling micro–macro coupling through a total strain-energy function.
We validate the theory using ultrasonic transmission measurements on two artificial sandstones sharing the same background matrix: an intact sample containing native microdefects and a cracked sample with uniformly implanted aligned penny-shaped cracks. Measurements were conducted under dry conditions at 500 kHz with hydrostatic pressure from 5 to 50 MPa, and anisotropic velocities were constrained using propagation directions normal and parallel to the bedding/crack plane. The proposed model reproduces the strongly nonlinear velocity–pressure trends in the low-pressure regime dominated by progressive crack closure, while remaining consistent with the near-linear regime at higher pressure.
A key outcome is a physically interpretable characteristic scale 𝑔 representing an evolving microstructural length associated with stress-driven changes in compliant pore space. We show that 𝑔 exhibits an asymptotic pressure dependence consistent with cumulative compliant-porosity evolution, and that these quantities are systematically correlated. Using effective-medium parameterizations for penny-shaped cracks (Hudson and Padé–Hudson), we further demonstrate that 𝑔2 scales approximately linearly with fracture (crack) porosity across a range of crack aspect ratios and parameter ranges, supporting a robust micro–macro linkage.
These results provide a physics-guided route to connect stress-driven microstructural evolution with macroscopic wave observables, with implications for fracture characterization and seismic monitoring in stressed crustal systems.
How to cite: Fu, L.-Y., Yang, H., Tang, J., and Zheng, H.: Macroscopically microstructural effects on wave propagation in highly stressed fractured rocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2532, https://doi.org/10.5194/egusphere-egu26-2532, 2026.
Sliding of a fault with gouge leads to rotation of gouge particles. Since the particles are not spherical, their rotation in the presence of pressure normal to the fault can exhibit local negative shear stiffness. Another mechanism of local negative shear stiffness is rotations of couples of temporary connected particles. These rotations affect the relation between the shear sliding stress and normal stress creating the effect of apparent friction coefficient, which, in some locations, can become negative [1]. The value (and the sign) of the local stiffness and the apparent friction coefficient depend upon the initial pressure and the stiffness of the surrounding rock. When elastic p-wave approaches a fault in normal direction it causes both normal and shear oscillations of one fault face against the other. If the amplitude of the wave-generated normal oscillations exceeds a certain threshold which depends upon fault and particles’ geometry and rock stiffness, then the shear oscillations reach the negative stiffness stage and become unstable. This leads to unstable periodic fault sliding resulting in seismic events.
The proposed concept will form a basis for developing realistic models of sliding and periodic seismicity of fault with gouge. It will also facilitate developing models of monitoring of fractures affecting thermal spallation mechanics.
Acknowledgement. The authors acknowledge financial support from of the Australian Research Council through project DP250103594.
1. Pasternak, E. and A. Dyskin, 2025. Negative stiffness induced and controlled by constriction. Status Solidi B DOI: 10.1002/pssb.202500428 (in print).
How to cite: Dyskin, A. and Pasternak, E.: P-wave triggering of periodic fault sliding. Negative friction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9269, https://doi.org/10.5194/egusphere-egu26-9269, 2026.
Traces of Mode I fractures in rocks (cracks in rock samples, hydraulic fractures, magmatic dikes, Mis-Ocean Ridges) are usually not straight; they exhibit interruptions and overlappings [1]. These are 2D features belonging to a particular cross-sectional view. In 3D interruptions and overlappings represent local bridges connecting the opposite sides of the fracture and distributed all over it. These bridges constrict the fracture opening and reduce the values of the stress intensity factor. The dimensions, the number and the geometry of the bridges depend upon the rock structure (at the scale microscopic with respect to the fracture length). Therefore, understanding the effect of bridges on the stress intensity factor can shed light on the rock microstructure. The combined effect of uniformly distributed bridges is accounted for by the introduction of constriction length [1]. As a result, under the given stress the stress intensity factor depends on both the fracture length and the ratio of fracture length to the constriction length.
Fracture propagation is controlled by fracture toughness, which is usually determined by measuring/estimating the fracture length, and the load at which fracture propagates. For this the conventional models neglecting the effect of bridges are employed. This shows a scale effect, the increase of fracture toughness with fracture length [2-5]. We used the model of constricted fracture propagation and found that for each scale there exists a constriction length such that scale effect of fracture toughness disappears and the fracture toughness remains constant.
Determination of constriction length allows more realistic monitoring of fracture growth and provides insight into the rock structure. It will also allow developing a more realistic scaling of fracture growth in strain rock burst and thermal spallation.
Acknowledgement. The authors acknowledge financial support from of the Australian Research Council through project DP250103594.
1. Dyskin, A.V., E. Pasternak, S. Shapiro and A. Bunger, 2025. Scaling laws for hydraulic fractures with constricted opening. Engineering Fracture Mechanics, 327 (2025) 111464.
2. Kobayashi, R., K. Matsuki and N. Otsuka, 1986. 2. Size Effect in The Fracture Toughness of Ogino Tuff. J. Rock Mech. Min. Sci. & Geomech. Abstr. 23, 13-18.
3. Shlyapobersky, J. 1985. Energy analysis of hydraulic fracturing. 26th US Symposium on Rock Mechanics / Rapid City, SD / 26-28 June 1985, 539-546.
4. Delaney, P.T. and D.D. Pollard, 1981. Deformation of host rocks and flow of magma during growth of Minette Dikes and Breccia-bearing intrusions near Ship Rock, New Mexico. Geological Survey Professional Paper 1202, 1-61.
5. Macdonald, K.C., D.S. Scheirer and S.M. Carbotte, 1991. Mid-Ocean Ridges: Discontinuities, segments and giant cracks. Science, 253, 986-994.
How to cite: Pasternak, E. and Dyskin, A.: Mode I fractures with distributed bridges. Scaling and monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9365, https://doi.org/10.5194/egusphere-egu26-9365, 2026.
The long time evolution of wave trains involves various nonlinear stages, with significant differences in the wave group shape at each stage. To further investigate the characteristics of nonlinear wave group interaction during the long time evolution of wave trains, the High-Order Spectral method and wavelet transform analysis are employed, and a novel spatial wave group identification method suitable for long time evolution process is introduced. Then the wave groups in the evolution process are classified into four types based on the wave group length. The results show that during the stage of modulation instability, all wave groups are of Type I, which is a result of modulation instability. In this stage, all wave groups propagate at the same velocity without any energy exchange between them, maintaining independent evolution. The appearance of the other three types of wave groups indicates the presence of nonlinear wave group interaction. Under the dominance of nonlinear wave group interaction, the number and length of wave groups no longer remain constant, with significant changes observed in their characteristic parameters. Additionally, the propagation velocities of the wave groups evolve continuously. When two wave groups with different velocities merge, the resulting group accelerates rather than decelerates. In the subsequent evolution, the participating wave groups begin to separate again, with the wave group that was initially trailing overtaking the one that was leading, and their velocities eventually approaching. It is worth noting that the different types of wave groups are the result of nonlinear interactions and also serve as the fundamental units for the subsequent nonlinear interaction processes.
How to cite: Xie, S., Tao, A., Fan, J., Zheng, J., and Wu, C.: Nonlinear wave group interaction in the long time evolution of wave trains, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16230, https://doi.org/10.5194/egusphere-egu26-16230, 2026.
Crack propagation in heterogeneous materials is strongly influenced by the combined effects of temperature, microstructural disorder, and dissipation mechanisms, particularly in subcritical fracture regimes. Recent experiments performed on pressure-sensitive adhesive (PSA) tapes by S.Santucci et al at the École Normale Supérieure de Lyon (France) have revealed complex slow fracture dynamics, including intermittent and thermally activated propagation regimes under quasi-static loading conditions.
While these studies provide a detailed experimental characterization of adhesive peeling and fracture processes, the present work focuses on a theoretical investigation aimed at interpreting the underlying physical mechanisms observed experimentally. Within the framework of linear elastic fracture mechanics, we develop a model describing the time-dependent crack propagation kinetics by accounting for thermally activated processes and material disorder, in connection with energy-based approaches of the Griffith type. The model relates the elastic energy release rate and the stress intensity factor to the crack propagation velocity and allows us to analyze the influence of temperature on the transition from slow crack growth to unstable fracture. The results highlight the key role of thermal fluctuations in subcritical fracture processes and provide a consistent theoretical framework for interpreting experimental observations in adhesive materials.
How to cite: Kebci, D.: Influence of Thermal Effects and Material Disorder on Fracture Propagation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21671, https://doi.org/10.5194/egusphere-egu26-21671, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 1b
EGU26-5765 | ECS | Posters virtual | VPS23
Research on the mechanical behaviors of multi-fractured blocky rock massesThu, 07 May, 16:15–18:00 (CEST) vPoster Discussion
Deep rock masses have complex internal structures, which results in significant discreteness and blocky structures. With the increase in the depth of engineering construction and energy extraction, the unique pendulum-type waves emerge in deep blocky rock masses under the action of dynamic loads from mining and blasting, and they are characterized by low frequency, low velocity, large displacement amplitude and high kinetic energy, distinguishing them fundamentally from conventional seismic waves. Pendulum-type waves can induce alternating stress states of relative compression and separation within blocky rock masses, and may lead to rockburst disasters and even engineering-induced seismicity, thus posing great challenges to the safety of underground engineering such as tunnel construction and mining. In this paper, experimental research is conducted on the mechanical behaviors and typical characteristics of pendulum-type waves of multi-fractured blocky rock masses under static and dynamic loads. Firstly, the strength, deformation and failure mode were analysized based on uniaxial compression tests. The weak structural layers will significantly reduce the uniaxial compressive strength and enhance the ultimate deformation capacity of rock masses. Fractured rock masses have significant nonlinear deformation and may develop macroscopic fractures (vertical splitting failure, with the failure mode transitioning from brittle failure to ductile failure) at the stress level significantly lower than their uniaxial compressive strengths. Subsequently, based on the dynamic impact tests, the dynamic response, overall displacement, wave velocity and the mechanism of anomalously low friction were investigated, and the typical characteristics of pendulum-type waves, including the low frequency (177 Hz and 153 Hz in this experiment, which are much lower than the natural frequency of the rock itself), low velocity (about 900 m/s in this experiment, which is significantly lower than those of P-waves and S-waves), large displacement amplitude (it is more than two orders of magnitude larger than the deformation of an intact rock under an identical load) and high kinetic energy (The total kinetic energy accounts for 40% and 28% of the total energy in this experiment, which has its particularity and cannot be ignored) were quantitatively described. This study holds significant research importance for understanding the nonlinear waves in deep fractured rock masses and their dynamic behaviors, as well as for preventing and controlling engineering disasters in deep rock masses.
How to cite: Jiang, K., Qi, C., and Hu, X.: Research on the mechanical behaviors of multi-fractured blocky rock masses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5765, https://doi.org/10.5194/egusphere-egu26-5765, 2026.
EGU26-8596 | ECS | Posters virtual | VPS23
Waveform signatures of acoustic emission from thermally and mechanically induced microfracture in centrally apertured basaltThu, 07 May, 16:15–18:00 (CEST) vPoster Discussion
Acoustic emission (AE) monitoring is widely applied to track damage development in brittle rock, although relating recorded signals to specific fracture mechanisms can remain uncertain, particularly when comparing thermal and mechanical loadings. This contribution presents a preliminary assessment of AE waveform characteristics measured during two heating-only experiments and two uniaxial compressive strength (UCS) experiments performed on 100 mm diameter basalt specimens containing a central axial circular hole. This geometry provides a consistent configuration that promotes stress redistribution and damage localisation around an opening, allowing fracture processes to be compared within a common specimen form.
Full AE waveforms were acquired throughout each test using broadband piezoelectric sensors coupled to the specimen surface, with pre-amplification and digital acquisition. Event features were extracted in the time and frequency domains, including rise angle, duration, hit counts, average frequency, peak frequency, peak amplitude, and amplitude distributions. Feature-space comparisons were then used to evaluate whether thermally and mechanically induced microfracturing exhibit separable signal characteristics.
The thermal experiments were associated with a single dominant fracture initiating along the shortest ligament between the aperture boundary and the nearest specimen edge. In contrast, UCS loading produced a more complex fracture network consistent with mixed tensile and shear microfracturing. Rise angle versus hits per duration plots indicated that thermal events occupied a more restricted region, whereas UCS events displayed a broader spread, which may reflect greater variability in source processes during complex damage evolution. Frequency-based comparisons further highlighted the differences: thermally induced events clustered mainly within a lower-frequency band (approximately 100-300 kHz), while the UCS tests exhibited an additional higher-frequency population (approximately 400-600 kHz), alongside the lower-frequency component. Amplitude distributions were also differed, with thermal events tending toward a narrower amplitude range relative to the wider distribution observed under UCS loading. Collectively, these observations suggest that the combined time-domain, frequency-domain, and amplitude-based AE features support mechanism-informed discrimination between thermally driven tensile fracture and mechanically driven complex fracture networks providing a basis for subsequent statistical or learning-based classification in coupled thermomechanical experiments
How to cite: De Alwis, A., Serati, M., Dyskin, A., Pasternak, E., Martin, D., and Williams, D.: Waveform signatures of acoustic emission from thermally and mechanically induced microfracture in centrally apertured basalt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8596, https://doi.org/10.5194/egusphere-egu26-8596, 2026.
EGU26-8985 | ECS | Posters virtual | VPS23
Non-linear rotational waves and complex rotation patterns in a chain of blocks with elbowingThu, 07 May, 16:15–18:00 (CEST) vPoster Discussion
Block elbowing, the process in which rotating blocks push neighbouring blocks apart, influences both geological deformation and the stability of mining excavations in blocky rock masses. A clearer understanding of elbowing is essential for improving rock mass modelling and maintaining the safety of engineering structures. To this end, we analyse a chain of stiff blocks connected by springs, with one or two end active (driving) blocks – the blocks whose rotation is externally induced. All other - passive blocks - have translational and rotational degrees of freedom. The results show that block rotation is sequential (starting from driving blocks) producing a rotational wave with strongly configuration-dependent rotational patterns.
Opposite to a single driving block system, a double-driving block system exhibits more complex behaviour, as the active blocks may rotate in the same direction (Case I) or in opposite directions (Case II). In Case I passive blocks can exhibit anticlockwise rotation that is opposite to the clockwise rotating driving blocks, while in Case II all passive blocks do not rotate at all.
Further deformation patterns arise from block geometry, introduced by varying block corner rounding to represent spheroidal weathering. The results reveal a transition from reversible to irreversible passive block kinematics. Reversible responses include either clockwise rotation followed by full recovery or no rotation. The boundary between these types of block behaviour is defined by a linear relationship between the active-passive and passive-passive contact friction coefficients, with the intercept related to block corner rounding. In contrast, irreversible kinematics characterised by residual rotation emerge only for highly rounded blocks. This irreversible behaviour is restricted to short block chains and disappears in chains of five blocks suggesting a critical size of the Cosserat like zone with independent rotational degrees of freedom. This study provides new insights for modelling the stability and long-term evolution of blocky rock masses.
How to cite: Zhang, M., Dyskin, A., and Pasternak, E.: Non-linear rotational waves and complex rotation patterns in a chain of blocks with elbowing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8985, https://doi.org/10.5194/egusphere-egu26-8985, 2026.
EGU26-11339 | Posters virtual | VPS23
Estimation of potential magnitudes of induced seismic events based on direct numerical simulation of fluid injection near an active tectonic fault.Thu, 07 May, 16:15–18:00 (CEST) vPoster Discussion
The subject of this study is the process of hydraulic stimulation of a tectonic fault, leading to induced seismicity. We consider a scenario in which fluid injected near an existing fault, causing a localized change in pore pressure and a reduction in effective stresses. This, in turn, initiates slippage of the fault segments and the formation of a slip zone, the size and slip velocity of which determine the magnitude of the resulting seismic events. The goal of this study was to develop a relatively simple model for estimating the potential magnitude of induced seismic events based on a limited set of governing parameters. The primary objectives of the study were to identify the key factors that have the greatest impact on the characteristics of the slip zone and to determine how fluid injection parameters (rate and injected fluid volume) affect earthquake magnitude by changing slip dynamics. The model obtained is based on the results of a series of numerical experiments analyzing the hydromechanical behavior of the fault under various injection conditions. The modeling was performed using a two-parameter rate-and-state friction law, which, unlike a single-parameter model, allows for a wider range of slip regimes to be simulated and accurately describes the transition from stable slip to dynamic failure.
The functional relationships were established between the initial system parameters and the key obtained slip characteristics. It was shown that the final slip zone length is almost linearly related to the length of the initial unstable zone, and the maximum slip velocity increases exponentially with increasing pore pressure rate. At the same time, in the area of high loading rates, the saturation of the sliding velocity is observed at a characteristic level, which leads to a limitation of the possible magnitudes of earthquakes induced by fluid injection.
How to cite: Turuntaev, S., Baryshnikov, N., and Riga, V.: Estimation of potential magnitudes of induced seismic events based on direct numerical simulation of fluid injection near an active tectonic fault., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11339, https://doi.org/10.5194/egusphere-egu26-11339, 2026.
