Orals: Fri, 2 May | Room G2
Fault zones in the brittle regime accommodate deformation across a wide range of spatial and temporal scales, from localized, rapid seismic events to extensive, slow aseismic creep. The initiation of large ruptures is a complex process, with diverse spatiotemporal patterns reflecting a range of physical mechanisms not yet fully integrated into a single theoretical framework.
Recent advances in laboratory experiments, using techniques analogous to seismic and geodetic methods, enable the monitoring of rock deformation across broad scales. We present results from triaxial rock failure tests employing a novel combination of acoustic emission (AE) sensors (to study seismic response) and fibre optic-based distributed strain sensing (DSS) systems (to map heterogeneous surface strain). A key theoretical challenge is understanding damage accumulation during the pre-failure phase and the transition to seismogenic behaviour. Our study leverages these technological advances to assess the heterogeneous evolution of rheology and its influence on earthquake preparation physics.
Experiments on intact and notched rock specimens reveal differing preparatory mechanics. In intact specimens, DSS measurements show silent, long-range stress redistribution followed by accelerated AE bursts only at sufficiently high stress levels. The failure of local heterogeneities produces intermittent changes in AE number and statistics, as well as in surface strain. In notched specimens, process zones generate self-arresting creep surges with increased AE rates, mirroring natural observations. We discuss numerical approaches to integrate these diverse behaviours.
How to cite: Selvadurai, P. A., Chen, H., Bianchi, P., Salazar Vasquez, A., Michail, S., Nikkhoo, M., Dal Zilio, L., Madonna, C., Giardini, D., and Wiemer, S.: Diverse Deformation: Novel Insights into Preparatory Earthquake Physics from the Laboratory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10707, https://doi.org/10.5194/egusphere-egu25-10707, 2025.
What makes slow and fast slip phenomena exhibit different statistics, in frequency distribution and temporal rate of moment? [1–3] Here, we experimentally demonstrate an exponential distribution of moment and a proportionality between moment and duration, as slow-slip phenomena. These statistics are realized by our novel rotary shear system using spherical particles floated on a liquid surface. By varying porosity and material of the particle layer, we suggest that low friction and/or low rigidity of particles distinguish slow-slip phenomena from fast slip. Our results imply that the amount and temporal rate of moment is limited by the strain localization and the fraction of pore or ductile phase.
We developed a quasi-two-dimensional rotary shear system using fault gouge analogue lubricated with fluid matrix. A granular layer of spherical particles (~ 4 mm in diameter) was prepared floating on a transparent heavy liquid (density 2.8 g/cm3). We recorded and tracked particle movements while measuring torque in real-time. The porosity of the layer was varied between 0.18 and 1 (pure liquid), using roughly 3900 particles at maximum. These measurements were conducted individually with soft, low-friction hydrogel particles and hard glass beads. A rotating cylinder connected to a torque meter via a torsion spring imposed shear on the layer at 0.6˚/s, 0.01 mm/s on the surface. The same particles were glued onto the cylinder.
Our findings can be summarized in the following three points:
(1) A decrease in porosity results in the transition from stable shear flow to stick-slip behaviors. Using hydrogel particles, the stress drop during slip events follows a scale-limited exponential distribution, irrespective of porosity. Similarly, using glass beads, exponential distributions are observed. Considering previous experimental studies confining dry frictional particles with power law [4–6], low friction by our lubrication might suppress force chain networking across particles and scale-invariant event generation.
(2) The moment of the hydrogel particle layer, calculated from measured torque and visually tracked slip area, also follows an exponential distribution. The characteristic moment increases with porosity decrease (pressure increase). The decrease in porosity is also accompanied by shear band localization. This localization is, thus, caused by compression of a higher porous shear band. The decrease in pore fluid and ductile phase could explain the seismic transition zone from slow to fast earthquakes on updip and downdip side, respectively.
(3) A nearly linear moment-duration scaling with an exponent of 1.0–1.3 is exhibited by hydrogel at any porosity, while glass beads exhibit an exponent of 1.3-2.3. This might correspond to the earthquake scaling: linear for slow-slip phenomena, and cubic for fast ones [2]. Moreover, for soft hydrogel particles, porosity decrease leads to the maximum moment rate, as expected to slow earthquakes [3]. In our analogue system, the maximum moment rate is limited by the minimum width of the localized shear band, suggesting similar mechanisms in natural slip systems.
[1] Chestler & Creager (2017) JGR
[2] Ide et al. (2007) nature
[3] Ide & Beroza (2023) PNAS
[4] Korkolis et al (2021) JGR
[5] Geller et al (2015) PRE
[6] Dalton & Corcoran (2001) PRE
How to cite: Sasaki, Y. and Katsuragi, H.: Lubricated soft granular shear explaining an origin of slow-slip phenomena's statistics: Experimental study using fault gouge analogue of spherical hydrogel particles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-327, https://doi.org/10.5194/egusphere-egu25-327, 2025.
Recent observations reveal that faults can host both slow and fast slip events, raising fundamental questions about their governing physics. Initially considered rare phenomena, slow slip events are now recognized as widespread features of fault zones, capable of releasing seismic moments comparable to large earthquakes, however, over longer time-scales.
We use laboratory experiments in a double-direct shear configuration with quartz gouge to explore fault slip behavior under varying normal stresses (8–22 MPa) and loading stiffness. The experiments were conducted on the BRAVA2 biaxial deformation apparatus, which features servo-controlled loading and high-frequency acoustic emission (AE) monitoring. By varying the stiffness ratio (k/kc), defined as the ratio of system stiffness (k) to fault stiffness (kc), we reproduced a spectrum of slip behaviors.
Our results reveal that the transition between slip modes is governed by the ratio (k/kc) of the loading system stiffness (k) to the fault critical stiffness (kc). We observe stable sliding when k/kc > 1.4, slow slip events clustering around k/kc ≈ 1, and fast events occurring when k/kc < 0.8, with peak slip velocities ranging from hundreds of μm/s to over 25 mm/s.
These slip modes exhibit distinct seismic signatures: slow slip events produce swarms of low-amplitude AEs (M0<10−2 Nm) corresponding to fault acceleration, while fast events generate concentrated high-amplitude bursts (M0>10−2 Nm). Despite differences in seismic signatures, our findings reveal continuous scaling across slip modes, with breakdown work (Wb) scaling with slip (Wb∝δ1.47) and seismic moment (Wb∝M00.25). The key difference lies in deformation partitioning: during slow slip, AEs occur in ~0.02% of the total slip duration, defined by the time during the stress drop, while fast slip events exhibit AEs over >10% of their duration. This indicates that slow slip is dominated by aseismic processes, whereas fast slip involves more seismic energy release.
Based on these observations, we suggest that slow and fast earthquakes represent end-members of a continuum. During slow slip, multiple small seismic patches develop during short inter-seismic periods, leading to distributed deformation. In contrast, fast slip events develop under longer inter-seismic periods, enabling the formation of larger, more coherent patches that fail simultaneously. This finding has important implications for understanding the spatiotemporal variations in fault slip behavior and suggests that changes in fault zone properties could trigger transitions between slip modes.
How to cite: Pignalberi, F., Mastella, G., Giorgetti, C., Marone, C., and Scuderi, M. M.: Understanding Fault Slip Modes Through AE Scaling and Seismic Partitioning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5800, https://doi.org/10.5194/egusphere-egu25-5800, 2025.
Fault healing is a crucial mechanism for the seismic cycle allowing faults to lock and restrengthen during the interseismic time. Several studies also suggested that the rate of fault healing controls the magnitude and recurrence time of earthquakes both in laboratory and nature. Experimental works show that fault healing, at the laboratory time-scale of 1 to 105 s, is dominantly a frictionally-driven process which derives from the time-dependent growth of the contact area due to plastic yielding of asperities. However, seismic cycles in nature are considerably longer and thus other healing mechanisms such as cementation are more effective. Cementation is a chemically-driven process commonly observed in the field where cataclasites characterize the core of several exhumed tectonic faults. Nevertheless, laboratory studies on the role of cementation on fault stability are still few because the limited time-frame of the laboratory approach which hinders an effective characterization of the process. Here we present a different experimental approach to overcome this limitation. By using an analogue fault gouge made of hydraulic cement in both nominally dry and fluid saturated conditions, we investigate how frictional and chemical (cementation) healing influence fault slip behavior. Microstructural analysis shows the pervasive precipitation of newly-formed minerals in the fluid-saturated gouge, coherently with the expected cementation reaction. In these experiments, cementation results in larger and non-log-linear restrengthening of the experimental fault compared to frictional healing. Our results show that cementation also promotes unstable slip, inducing a time-dependent increase of fault cohesive strength that scales with time as the observed stress drop during instabilities. We thus suggest that cementation is a fundamental mechanism during interseismic time that controls the seismic potential of faults, even at shallow depths, with relevant implications for natural and induced seismicity.
How to cite: Volpe, G., Affinito, R., Calzolari, L., Pozzi, G., Marone, C., and Collettini, C.: The influence of cementation on faults frictional stability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9023, https://doi.org/10.5194/egusphere-egu25-9023, 2025.
Premonitory slip and migrating foreshocks transitioning into an accelerating unstable rupture are commonly observed in experiments and less frequently in nature, but what controls their spatiotemporal evolution remains unclear. In this context, we conduct a series of displacement-driven triaxial compression experiments on porous sandstone samples containing a saw-cut fault under conditions of varying load point velocities (1 to 10 μm/s), confining pressures (35 to 75 MPa) and constant pore pressure (5 MPa). Integrating far-field mechanical and displacement measurements, near-fault strain gauge arrays, and a dense network of piezoelectric transducers, we find that local premonitory slip always occurs above a threshold stress, showing a crack-like propagating front with a slow speed up to 2 cm/s. Premonitory slip is accompanied by migrating small-magnitude precursory Acoustic Emissions (AEs) with dominantly shear-enhanced compaction source mechanisms transitioning to double-couple when approaching slip events. The transition from local premonitory slip to system-size slip event occurs once the premonitory slip front crosses the entire fault, followed by the emergence of system-size slip event with an accelerating rupture front in the opposite direction. Premonitory slip and precursory AE rates accelerate progressively, culminating in slow (< 5 µm/s slip rates) or fast (1 to 10 mm/s) slip events. With increasing load point velocities, average premonitory slip rates increase at reduced precursory time spans, leading to fast slip events. Increasing confining pressure causes increasing premonitory slip and off-fault precursory AEs, but does not affect premonitory slip rates. Precursory slip scales with co-seismic slip, and is predominately aseismic. Our results imply that local variations in loading conditions at slow slip and rupture velocities will affect spatiotemporal evolution of premonitory slip and potentially associated foreshock activity.
How to cite: Wang, L. and Dresen, G.: Propagation of premonitory slip leading up to system-size rupture events on laboratory faults in porous sandstone: Effects of loading rate and confining pressure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10473, https://doi.org/10.5194/egusphere-egu25-10473, 2025.
Natural fault systems exhibit a complex interplay of factors that govern the nucleation, propagation, and arrest of ruptures. Among these factors, the distribution of initial stress stands out as a key driver of rupture dynamics, influencing the size, recurrence interval, and spatial characteristics of seismic events. The fault system size further contributes to the complexity of the seismic cycle. This study investigates how heterogeneous initial stress conditions shape the seismic cycle of a long experimental fault.
We reproduce frictional ruptures on a biaxial direct shear apparatus hosting a 2.5 m long fault composed of analog material (PMMA). The initial stress distribution is controlled through a stopper that modifies the boundary conditions. Strain gauge rosettes, recording at 40 kHz, measure stress evolution.
Our results demonstrate that stress heterogeneity significantly affects seismic behavior, including nucleation location and complexity of the seismic sequences (from system size events to supercycles). Moreover, stress heterogeneity strongly influences the dynamics of main ruptures, leading to complex behaviors such as temporary arrest and re-nucleation of the rupture. Time delays (time intervals between arrest and re-nucleation) were found to span two orders of magnitude and were significantly larger than the dynamic propagation period. Numerical simulations corroborate these findings, revealing delayed triggering mechanisms such as creeping front-induced, dynamic wave-induced, or a combination of the two.
This study offers a framework for interpreting stress heterogeneity's spatial and temporal evolution along natural faults and its implications for earthquake predictability and rupture dynamics.
How to cite: Paglialunga, F., Passelègue, F., Ampuero, J. P., Latour, S., and Violay, M.: Impact of Heterogeneous Initial Stress on the Seismic Cycle and Rupture Dynamics of a Long Laboratory Fault, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12092, https://doi.org/10.5194/egusphere-egu25-12092, 2025.
Fluid injections can induce aseismic slip that propagates either behind or beyond the pore pressure diffusion front, depending on the initial stress state along the fault. In the latter case, the aseismic slip front may trigger seismicity at considerable distances from the injection well. In this study, we investigate the influence of the initial stress state and injection rate on the transition between these two end-member scenarios.
We performed triaxial experiments on a saw-cut Westerly granite sample oriented at an angle of 30° relative to the maximum principal stress. The fault was preloaded to 60% and 90% of its frictional strength before fluid injection was initiated. Fluid was injected along the fault through a borehole positioned at one edge of the fault, with fluid pressure rates ranging from 0.015 to 15 MPa/s.
The propagation of the fluid pressure front was monitored using three pressure sensors placed at varying distances along the fault. A deterministic inversion approach was employed to reconstruct the spatial and temporal evolution of hydraulic diffusivity during injection, up to the onset of instability. This method provided an optimal solution for the diffusion of pore pressure throughout the injection process. The slip front propagation was monitored using strain gauges distributed around the experimental fault. The initiation times of strain release recorded by these gauges were used as proxies for the passage of the slip front. The slip front velocity was inferred by assuming a quasi-circular geometry, as defined by the elastic properties of the tested rock.
Our results reveal that, regardless of the initial stress state, increasing the injection rate reduces the stress injection parameter induces T, allowing the transition between the two end-member cases: (1) aseismic slip front propagating behind the pore pressure diffusion front (λ<1) and (2) aseismic slip front propagating beyond the pore pressure diffusion front (λ>1). Furthermore, higher injection rates result in increased slip front velocities. These experimental observations are interpreted within the framework of fracture mechanics. Specifically, we demonstrate that reducing the initial stress state along the fault enhances the energy release rate (G) promoting the initiation of the slip front propagation. Secondly, higher injection rates generate larger values of G at the crack tip, explaining the observed increase in slip front velocities, and the transition between the two end member cases with increasing injection rates.
How to cite: Passelegue, F., Brantut, N., Dublanchet, P., Barnaby, F., and Chauris, H.: Influence of injection rate on the dynamic of fluid-induced aseismic slip fronts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15900, https://doi.org/10.5194/egusphere-egu25-15900, 2025.
Stick-slip on pre-existing faults has long been recognized as a source of shallow earthquakes, where "stick" is the interseismic period of elastic strain accumulation and "slip" is the earthquake. While stick-slip behavior has long been associated with velocity-dependent and time-dependent friction, the description has not adequately addressed position-dependent friction---an aspect that is relevant to spatially complex fault zones in nature. Here we state a frame-indifferent formulation of frictional contact between heterogeneous surfaces and introduce the notion that friction is a function of the states of the two surfaces in contact, each representing roughness and microstructural details of the surface. We show how the interaction between irregular surfaces results in heterogeneous Coulomb friction along the interface. We then conduct dynamic simulations of a spring-slider model and find that heterogeneity in Coulomb friction alone is capable of reproducing a wide range of complex fault slip behaviors, from fault creep and low frequency earthquakes to ordinary earthquakes and slow slip events. The different slip behaviors produced by our model occur at a spectrum with no sharp boundaries between them, which seem to agree with observations in various subduction zones. We also find that seismic moment-duration scaling span a broad continuum with upper bounds for fast and slow earthquakes adhering to cubic and linear relations, respectively. As a whole, our framework of position-dependent friction raises the prospect of alternative approaches to simulate earthquake dynamics in multidimensional models of geologic faults.
How to cite: Alghannam, M., Nordbotten, J., and Juanes, R.: Stick-slip from heterogeneous Coulomb friction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1948, https://doi.org/10.5194/egusphere-egu25-1948, 2025.
The contemporary model for tectonic earthquakes is based on the interplay between the frictional rheology of a potentially seismic fault and the electrodynamics of the surrounding medium. More specifically, it has been shown in many experimental and theoretical studies that a necessary condition for unstable sliding events on a fault is a weakening rate larger than the unloading stiffness of the surrounding rocks. By weakening rate, we refer here to the decrease of the resisting shear stress (i.e. of the instantaneous friction coefficient) with sliding. Conversely, by loading stiffness, we refer to the decrease of the loading shear stress with sliding.
We investigate the role and effect of the loading stiffness on the seismic cycles of a simulated granular fault. For this purpose, we build a numerical model based on the Discrete Element Method (DEM), inspired by laboratory experiments on fault gouge. In contrast to a typical DEM fault models, we employ an elastic loading system with user-controlled shear stiffness. We show that the coupling between fault granular rheology and country rock elasticity leads to seismic cycles with properties that are strongly influenced by their ratio. Stiff faults produce frequent contractional events with limited sliding distances and low to moderate stress drops, while soft faults produce rare dilatational events with large sliding distances and stress drops. Statistical distributions of events are extracted, and empirical scaling laws for the role of fault stiffness on these distributions are proposed.
We show that, on average, simulated events are well-described by a simple linear slip-weakening friction law, but that the weakening rate that best describes the events is tightly coupled with the loading stiffness. This contradicts the idea of an intrinsic friction law for the granular gouge layer and demonstrates the need to consider a fault as a tribosystem coupling the scale of the contact junction within the granular gouge and of the elastic surrounding medium. We conclude that, even in a highly-simplified model where the gouge layer is represented by a limited number of circular grains, there is no such thing as a “friction law” describing the behaviour of the interface. Rather, friction is a multiscale emerging property of the whole tribosystem defined by the interface and the elastic properties of the surrounding medium, as well as the past sliding history of the fault patch.
How to cite: Mollon, G., Casas, N., and Scuderi, M.: Seismic cycles in a DEM simulated granular gouge layer: influence of the loading stiffness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20352, https://doi.org/10.5194/egusphere-egu25-20352, 2025.
Prediction of subduction earthquakes mostly relies on interplate coupling models that provide patterns interpreted within the framework of rate-and-state friction laws. However, this framework has been challenged by recent observations, indicating that rheological and geometrical complexities must be considered in order to fully understand megathrust mechanics.
In this study, we investigate whether the strongly and weakly coupled patches could be related to the distribution of deformation along the plate interface, potentially associated with either basal erosion or underplating. Since both underplating and basal erosion impact forearc morphology, the location of such distributed deformation along the plate interface can be inferred from a simple mechanical analysis of the topography.
We first show that long-lived plate interface deformation is governed by aseismic processes. Through a comparison of erosive and accretionary margins, we show that large earthquakes propagate along well-localized and smoothed rate-weakening fault planes, bounded by elongate zones of underplating along accretionary margins, and by both basal erosion and underplating along erosive margins.
Comparing margins of different ages, we find that underplating occurs at shallower depth for younger subducting plates. Along erosive margins, two bands of underplating are observed: the shallow one likely corresponds to the underplating of eroded material, while the deeper would be related to the underplating of the altered oceanic plate. In cold subduction zones, Domain-C earthquakes take place between those two bands, while SSEs are found along warm subduction zones. These differences are discussed using thermo-mechanical simulations.
How to cite: Cubas, N., Gauthier, A., Soret, M., and Le Pourhiet, L.: Relationships Between Plate Interface Deformation and Earthquake Segmentation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17429, https://doi.org/10.5194/egusphere-egu25-17429, 2025.
In 2011 and 2016 two near-identical earthquakes near Mochiyama, Japan ruptured the same fault, in the same place, with a similar magnitude. The unusually short repeat time between the two earthquakes provides a rare opportunity to estimate the evolution of stress on a fault through an earthquake cycle, as the stress drop in the first earthquake provides a reference value from which we can infer variations through time in the stresses required to cause earthquake rupture. I will argue that the fault experienced a decrease of 1–5 MPa in the shear stresses needed to generate earthquake rupture (20-50% of the first earthquake’s stress drop). I will describe geodetic and seismological evidence of the inter-event period that might have hinted at the mechanisms that led to this fault weakening.
How to cite: Wimpenny, S.: Transient Weakening of a Natural Fault Zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2271, https://doi.org/10.5194/egusphere-egu25-2271, 2025.
Shallow aseismic fault creep has been observed for more than half a century (Steinbrugge et al., 1960). Aseismic creep can be manifest as continuous creep at a steady rate, can occur episodically in events with durations of hours or weeks, or can take the form of afterslip decaying in rate following an earthquake.
Upon closer inspection of the different types of aseismic slip recorded on creepmeters, this simple view may not be complete. Here, we present a new taxonomy for shallow aseismic slip based on 40 years of creepmeter data recorded at seventy-nine locations on creeping faults in California, Utah, Türkiye, and Pakistan. We identify at least six major forms of creep: steady creep, episodic creep events, afterslip, triggered slip, months-long creep surges, and creeplets (slip of ≤100 μm). The last two of these modes of aseismic slip have hitherto not been recognized, since they are often difficult to distinguish from environmental perturbations and/or instrumental artifacts. The creep event and creeplet classes of aseismic slip can form sequences of events that occur in close temporal spacing to one another. These six modes of creep may sometimes occur simultaneously (notably afterslip and creeplets/smaller creep events), combining to accommodate the overall fault motions.
Using these formalised definitions of aseismic slip, we have catalogued more than 5000 aseismic slip transients. In this global catalogue of mostly sub-centimetre amplitude shallow aseismic slip transients we observe over 4,400 creep events, over 800 creeplets and over 150 months-long creep surges. Using this catalogue we are able to form the following conclusions: the median duration of episodic creep events is 2.7 days with a median slip amplitude of 0.6 mm, creeplets have a median duration of 11 hrs with a median slip amplitude of 50 μm, and creep surges have a median duration of 1.5 months, and a median slip amplitude of 1.7mm. The catalogue will shortly be made available for public access.
How to cite: Gittins, D., Materna, K., and Bilham, R.: Taxonomy of shallow aseismic creep, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13682, https://doi.org/10.5194/egusphere-egu25-13682, 2025.
Dynamic triggering of local seismicity or slow-slip events by large earthquakes over vast distances is a well-documented phenomenon. Using satellite radar interferometry (InSAR) and seismic data, we identified a significant aseismic deformation signal in the Eastern Kura Basin, situated between the Lesser and Greater Caucasus thrust belts, at the diffuse boundary of the converging Eurasian and Arabian plates. This deformation is concentrated along the 170-km-long West Caspian Fault (WCF) and six shorter, sub-parallel faults (<70-km); it is also associated with unrest at 56 mud volcanoes over known hydrocarbon reservoirs.
Surface displacement fields from four InSAR tracks constrained the aseismic slip to a transient event between 4 and 9 February 2023, with no significant pre- or post-slip deformation. However, InSAR and GNSS analysis over a longer time-frame indicates that the WCF and sub-parallel faults are continuously creeping. Seismic analysis of data from a station 2 km away from the WCF identified 58 high-frequency local events at depths ranging 10–20 km, with magnitudes below 3.2. These events coincided with the arrival of surface waves from the 6 February 2023, M7.8/M7.6 Kahramanmaraş earthquakes in eastern Türkiye, over 1,000 km away. SAR coherence and interferometric phase maps also revealed eruptions and deformation at 56 mud volcanoes during this period, suggesting a fluid-mediated dynamic triggering mechanism. Our inversion of displacement fields indicates right-lateral strike-slip motion along the vertical WCF and sub-parallel faults, incorporating hydrocarbon reservoir inflation.
We interpret the observed aseismic slip as a fluid-mediated transient event dynamically triggered by the surface-waves of a 1000-km distant earthquake, which altered pore pressure and normal stress on optimally oriented faults in the Eastern Kura basin. This event represents one of the largest documented aseismic crustal slips in a continental collision zone. Despite the continuous creep and transient slip behavior observed along the WCF, its potential for generating large seismic events remains uncertain.
How to cite: Bayramov, Z., Viltres, R., Doubre, C., Maggi, A., Jolivet, R., and Rivera, L.: 1,000-km distant dynamic triggering of large aseismic fault slip and mud volcano unrest in the Eastern Caucasus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-909, https://doi.org/10.5194/egusphere-egu25-909, 2025.
The 80 km-long, NE-striking Pütürge segment of the East Anatolian fault in eastern Türkiye is bounded by two earthquake rupture zones. In the NE, it is underlain by the rupture zone of the M6.7 2020 Sivrice earthquake; at its SW end, it truncates close to the northeastern extent of the M7.8 2023 Pazarcık earthquake. There is a substantial gap of over 40 km between the two rupture zones. Previous authors (e.g. Çakir et al., 2023) have suggested that the 2020 event was arrested by creep on the NE Pütürge segment. In this study, we investigate whether the Pazarcik event was similarly arrested by creep at the Pütürge segment's SW end.
We process InSAR data from ascending and descending tracks of the Sentinel-1 satellites that cover the Pütürge segment, from three time periods – before, between, and after the two earthquakes – using the ISCE and MintPy software. We take short, fault-perpendicular profiles through the velocities and time series we produce to investigate possible shallow creep behavior, and downsample the cumulative displacements to constrain models of fault slip.
We find: 1) the Pütürge segment was creeping at the surface before the Sivrice earthquake (in the period 2014-2020), at rates that peak at ~6 mm/yr at its NE end, and decrease along-strike to effectively zero at its SW end; 2) the deformation following the Sivrice event includes ~10 cm of surface creep between February and July 2020 along the Sivrice rupture zone, followed by a M~5.8 aftershock and creep transient on the fault immediately to the SW of that zone; and 3) the post-Pazarcık earthquake deformation (~10 cm of surface creep in 8 months) is concentrated along the SW-most section of the Pütürge segment, where there had been little creep before or after the Sivrice earthquake. As we identify creep along the whole Pütürge segment, albeit at different times in different places, we suggest that creep did plausibly play a role in ending the Pazarcık rupture.
How to cite: Funning, G., Hofstetter, C., and Özarpacı, S.: Temporally variable creep behavior on the East Anatolian Fault and the arrest of the 2023 Pazarcık earthquake rupture, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15399, https://doi.org/10.5194/egusphere-egu25-15399, 2025.
Tectonic pseudotachylytes preserve key information of fossil earthquakes. They provide valuable insights into the activity and tectonic evolution of ancient faults. The >2000 km long South Tibetan Detachment System is one of largest fault systems in the world, and the exposure of its seismogenic zone can help understand formation of earthquakes. Our structural analysis reveals two phases of pseudotachylytes under different deformation conditions in the leucogranite of Ra Chu transect. Field investigations identify two types of pseudotachylytes: (1) M-PT type pseudotachylyte associated with mylonitization, and C-PT type pseudotachylyte that formed during cataclasis. The former develops parallel to the pervasive foliation of the host rock, while the latter crosscuts the foliation at a high angle. Microstructural observation suggests that both types of pseudotachylytes are produced by frictional melting. Geochemical analysis has revealed selective melting of minerals and trace element migration during the formation of pseudotachylytes, necessitating the involvement of external fluids. These fluids play an important role in process of earthquake nucleation by reducing the strength of fault zones. Geochronological constraints correlate the formation of pseudotachylytes to regional tectonics: Firstly, M-PT formed within the brittle-ductile transition zone at ~17 Ma and underwent ductile deformation together with the host rock. As the fault zone exhumed, C-PT and cataclasis superimposed in the shallow brittle zone at ~14 Ma. The coexistence of these two types of pseudotachylytes records the rapid cooling and exhumation history of the South Tibetan Detachment System over several million years, indicating that seismic sliding occurred repeatedly in the same section of a long-lived fault zone.
How to cite: Guo, Y., Chu, Y., Lin, W., Lei, Y., Liu, T., and Guo, L.: Two phases of pseudotachylytes in Ra Chu transect of South Tibetan Detachment System and its implications to fault activities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9628, https://doi.org/10.5194/egusphere-egu25-9628, 2025.
Seismic waves from distant earthquakes are known to trigger earthquakes and slow slip events on active faults. However, the underlying physics of such interaction is poorly understood. Dynamic rearrangement of grains in a granular medium, pore pressure changes within that same gouge or the response of a frictional interface have been proposed to explain such distant triggering. The main issue is the lack of observations at various scales of the same triggered slip event in nature, from seconds to years and from the local meter-scale to a full-scale image of induced slip on the fault.
We use data from a dense seismogeodetic network, InSAR imagery and four creepmeters located at Ismetpasa along the North Anatolian Fault to quantify the temporal and spatial evolution of a sequence of transient shallow slow slip events triggered by the passage of the waves from the 2023 Kahramanmaras doublet. Cumulative slip amounts to 1 cm over a few months and accumulates in the form of multiple mm-amplitude slip events lasting from minutes to weeks. Slip nucleated initially during the passage of surface waves from the M7.8 Kahramanmaras and M7.5 Elbistan earthquakes. High-rate (1s) GNSS time series were used to derive complete time series of dynamic aerial strain and stress tensors to compute the dynamic change in Coulomb stress change during the passage of surface waves. Although the timing of dynamic Coulomb stress change is consistent with the initiation of the first slip events, it is difficult to physically quantitatively relate the amplitude of the shaking with the amplitude of the slip events. Three of the creepmeters subsequently recorded multiple creep events with logarithmically decaying fault slip (Tau> 1.7 hours) following an initial offset of a few tens of microns. We note that the amplitude of the second slip event, triggered by the M7.5 Elbistan earthquake, is larger than that of the first one, triggered by the M7.8 Kahramanmaras earthquake. Subsequent events in the following weeks initiate when local atmospheric pressure drops severely, a feature that was not observed prior to the sequence. Finally, we observe that, for all these slow slip events, slip rate is slowed down by the local increase in atmospheric pressure with a logarithmic relationship between slip rate and pressure.
We interpret these slow slip events as the signature of the progressive weakening of the fault zone, weakening first initiated dynamically by the passage of the surface waves from distant earthquakes and progressively continued with the cumulation of slip along the fault. The first incoming waves from the Kahramanmaras earthquake dynamically re-arrange material in the fault gouge, initiating a slip instability at depth, potentially further facilitated by elevated pore pressure, then progresses to the surface and expands along the fault. Each wave train further weakens the fault plane allowing for more slip, which itself further weakens the fault. Once no strain is available, the fault recovers and regains its strength over time. Our study provides a first view of the dynamics of triggered events by combining seismological, geodetic and atmospheric observations.
How to cite: Jolivet, R., Jara, J., Martìnez-Garzón, P., Klein, É., Dérand, P., Becker, D., Çakir, Z., Özdemir, A., Bilham, R., Seydoux, L., Dogan, U., and Ergintav, S.: Progressive weakening of a fault by seismic waves revealed by dynamically triggered slow slip events on the North Anatolian Fault, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15756, https://doi.org/10.5194/egusphere-egu25-15756, 2025.
Stress accumulation on the plate interface of subduction zones is a key parameter that controls the location, timing and rupture characteristics of earthquakes. The diversity of slip processes occurring in the megathrust indicates that stress is highly variable in space and time. Based on GNSS and InSAR data, we study the evolution of the interplate slip-rate along the Oaxaca subduction zone, Mexico, from October 2016 through October 2020, with particular emphasis on the pre-seismic, coseismic and post-seismic phases associated with the June 23, 2020 Mw 7.4 Huatulco earthquake (also known as La Crucecita earthquake), to understand how different slip regimes contribute to the stress accumulation in the region. Our results show that continuous changes in both the aseismic stress-releasing slip and the coupling produced a high stress concentration prior to the event on the region with the highest moment release of the Huatulco earthquake and a stress deficit zone in the adjacent updip region . This region under negative stress accumulation can be explained by possible recurrent shallow Slow Slip Events (SSE) offshore Huatulco as well as by the stress shadow from adjacent locked segments. Two months prior to the event, a Mw 6.6 long-term SSE also occurred about 80 km northwest from the hypocenter, between 25 and 55 km depth. Transient increments of the interplate coupling around the adjacent 1978 (Mw 7.8) Puerto Escondido rupture zone correlate with the occurrence of the last three SSEs in Oaxaca far downdip of this zone, possibly associated with along-dip fluid diffusion at the subduction interface. Throughout the four-year period analyzed, the interface region of the 1978 event experienced a high CFS build up, primarily attributable to both the co-seismic and early post-seismic slip of the Huatulco rupture, that, considering the 55 year average return period of the region, indicates large earthquake potential near Puerto Escondido. Continuous monitoring of the interplate slip-rate thus provides a better estimation of the stress accumulation in seismogenic regions than those given by long-term, time-invariant coupling models, and improves our understanding of the megathrust mechanics where future earthquakes are likely to occur.
How to cite: Villafuerte, C., Cruz-Atienza, V., Tago, J., Solano-Rojas, D., Garza-Girón, R., Franco, S. I., Dominguez, L. A., and Kostoglodov, V.: Slow slip events and megathrust coupling changes contribute to the earthquake potential in Oaxaca, Mexico, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15266, https://doi.org/10.5194/egusphere-egu25-15266, 2025.
We report a rarely observed case of steady aseismic deformation in the context of a fold-and-thrust belt, with a well-documented structural and lithological background. We focus on a 12-km-long section across the foothills of southwestern Taiwan, where about 23 mm/yr of westward compression is observed. From west to east, the surface geological structures include an anticline, a thrust and a backthrust. We determine Holocene uplift rates based on fluvial terraces, invert the interseismic 3D velocity field using existing geodetic datasets, and build a geological cross-section to constrain the possible deep geometry for the structure responsible for the observed surface deformation. Geodetic vertical velocities and Holocene uplift rates show a similar pattern, with rates rapidly increasing eastward, then remaining relatively constant across the fold axis and thrust, and finally sharply decreasing across the backthrust, across which InSAR observations suggest a velocity discontinuity. Our observations show that active deformation is occurring mainly aseismically and involves the anticline (the Wushantou Anticline) and backthrust (the Kouhsiaoli Fault). Our cross-section illustrates a 4-5 km deep wedge with a passive roof thrust corresponding to the backthrust, on the hanging wall of which the anticline is located. A classical fault-bend fold model with a slip rate of 21±2 mm/yr can explain most of the observations, yet local misfit suggests a possible contribution to uplift from pure shear of clayey rocks in the anticline core. Based on published records from a deep well drilled across the fold core and backthrust, clay-rich lithology and elevated fluid content are likely to favor aseismic slip. Without instrumental earthquakes reported on these structures and in the lack of successful paleo-earthquake investigations, whether these structures ever generate M>6 events remains an open question.
How to cite: Le Béon, M., Chen, C.-C., Huang, W.-J., Ching, K.-E., Shih, J.-W., Tseng, Y.-C., Chiou, Y.-W., Liu, Y.-C., Hsieh, M.-L., Pathier, E., Lu, C.-H., and Fruneau, B.: Aseismic deformation within the fold-and-thrust belt in southwest Taiwan: Example from the Tsengwen River section, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19314, https://doi.org/10.5194/egusphere-egu25-19314, 2025.
Clay-rich fault gouges, such as those commonly found in mature fault zones, exhibit complex frictional-plastic behavior. The standard rate- and state-dependent friction law (RSF) can capture the macroscopic frictional behavior of geologic materials in laboratory experiments but offers limited insight into the underlying microphysical processes. Flow laws (FL), i.e. constitutive equations of material behavior with a microphysical basis, have been proposed as a suitable tool to explain the rate and temperature dependence of friction. Here, we use both frameworks, RSF and FL, to analyze the deformation behavior of kaolinite-rich gouges.
We report on the results of velocity stepping and slide-hold-slide friction experiments on dry and water-saturated kaolinite-rich powder (75 % kaolinite, 14 % muscovite/illite, 8 % K-feldspar, 3 % quartz), at a range of temperatures (20 oC to 180 oC) and load point velocities (0.03 µm/s to 100 µm/s, corresponding to bulk strain rates of ~3*10-5 s-1 to 10-1 s-1). The experiments were performed using two different experimental devices covering a broad range of normal stress, displacement, and sliding rate conditions: a triaxial direct shear apparatus (effective normal stress values of 60 MPa and 160 MPa) and a rotary shear apparatus (effective normal stress of 60 MPa). In the velocity stepping tests, we observed both velocity weakening and velocity strengthening friction. At 180 oC, we found that (a - b) decreased with increasing target velocity. At 20 oC, 70 oC, and 120 oC, there is no clear trend in (a - b) with respect to target velocity or step direction. The results of the slide-hold-slide tests suggest the activation of water-assisted, heat-driven mechanisms at temperatures above 70 oC: the healing rate β transitioned from positive values at 20 oC and 70 oC, to negative values at 120 oC and 180 oC, leading to net weakening at long hold times. For the saturated samples at 120 oC and 180 oC, the decrease in β was accompanied by a significant decrease in the stress exponent n to values below 50 with increasing temperature and decreasing strain rate, suggesting a switch in the dominant deformation mechanism as well. Overall, our preliminary findings demonstrate the complementarity of the RSF and FL frameworks in analyzing fault gouge deformation over a wide range of strain rates relevant for earthquake nucleation.
How to cite: Korkolis, E., Rempe, M., Niemeijer, A., and Faulkner, D.: Experimental deformation of clay-rich fault gouges within the rate-and state-dependent friction and flow law frameworks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9863, https://doi.org/10.5194/egusphere-egu25-9863, 2025.
Understanding the rheology of carbonates is crucial, as destructive earthquakes frequently occur in tectonically active carbonate regions (e.g., the Corinth Rift Zone, the Italian Apennines, and the Sichuan Basin, China), leading to fatalities and severe economic impacts. Seismic to aseismic deformation can be understood in terms of the frictional response, which is based on the underlying deformation mechanisms. To grasp the seismic potential of faults in carbonates, we studied the conditions under which dolomite fault gouge is frictionally unstable, based on the rate and state friction law (RSF) and complemented the mechanical results with microstructural observations to understand the active deformation mechanisms.
We will present results from experiments conducted using the hydrothermal rotary shear apparatus on simulated fault gouge of dolostone. These experiments were carried out at sub-seismic slip velocities ranging from nm/s to hundreds of µm/s, temperatures from room temperature to 600 °C, and at a constant effective normal stress and fluid pressure of 50 MPa. Our mechanical results show a strongly temperature dependent steady-state sliding strength during initial sliding, with Byerlee friction values of ~0.7 at low (< 300 °C) and the highest (600 °C) temperature, but values of ~0.4 at intermediate temperatures (300 – 500 °C). Additionally, the friction values show a strong dependence on both velocity and temperature, where cooler temperatures (< 300 °C) are mostly velocity strengthening and therefore conditionally stable, while higher investigated temperatures (400 – 600 °C) result in mostly velocity weakening, potentially unstable outcomes. An exception to this is found at the highest velocities (> 100 µm/s) at 400 – 500 °C and the slowest velocities (< 0.03 µm/s) at 600 °C. Further, we observed oscillatory and stick-slip behaviour at negative and near-zero RSF (a-b) values with amplitudes decreasing with increasing friction stability values. Microstructural observations on deformed samples revealed that brittle deformation mechanisms are active across all investigated temperatures. However, microstructural analysis using SEM-XRD, Raman, and FTIR on samples deformed at temperatures >300 °C provides evidence of dolomite decomposition into calcite and brucite. This dissolution-precipitation creep is enhanced with increasing temperature.
These results suggest a transition from stable to unstable behaviour at ~300 °C which continues until the highest temperature of 600 °C with frequently accompanied stick-slips, translating to a seismogenic depth range of 10 – 20 km, assuming a continental geothermal gradient of 30 °C/km.
How to cite: Kozlov, E., Niemeijer, A., de Bresser, H., and King, H. E.: Frictional Behaviour of Carbonates: Defining the Seismogenic Zone in Dolomite , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19622, https://doi.org/10.5194/egusphere-egu25-19622, 2025.
Subducted rough topography, such as seamounts, complicates seismic and aseismic slip behavior along megathrusts. The 2024 M 7.1 Hyuganada earthquake occurred along the megathrust with the subduction of Kyushu-Palau Ridge (KPR) offshore Kyushu, southwestern Japan. Therefore, this earthquake provides a valuable opportunity to observationally illustrate the role of subducted seamounts in modulating seismic and aseismic slip processes. We inferred coseismic slip and 1-week afterslip using GNSS coordinates. The inferred mainshock slip was located in the down-dip of the seamount, suggesting that this earthquake was initiated under enhanced compression due to the subducted seamount. Furthermore, considering that subducted seamounts might act as a soft barrier, the mainshock rupture was probably arrested by this seamount. The inferred 1-week afterslip peaked at the up-dip of the mainshock peak and overlapped with the seamount. This up-dip afterslip is accompanied by four aftershock clusters. Assuming that the activation timing of aftershocks marks the arrival of the afterslip front, various onset timings of these clusters suggest different migration rates of afterslip in different directions. In particular, the activation of a cluster up-dip of the seamount is delayed, suggesting that the migration rate of the afterslip front is slowed down along the path across the seamount. Little afterslip is inferred in a segment south of the mainshock, where the interseismic slip deficit rate is low. We interpret these observations that the megathrust there is somehow insusceptible to stress perturbation and seems to creep steadily across the mainshock occurrence. Our results geodetically highlight that the subducted KPR introduced mechanical heterogeneity of megathrust at an order of 10 km.
How to cite: Itoh, Y.: Coseismic slip and early afterslip of the 2024 Hyuganada earthquake modulated by a subducted seamount, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1671, https://doi.org/10.5194/egusphere-egu25-1671, 2025.
We use a 3-D finite-element model to invert the dense GNSS observations for coseismic and postseismic megathrust slip of the 2024 Mw 7.1 Hyuga-nada earthquake in westernmost Nankai subduction zone. The results reveal a quasi-circular, thrust-dominated rupture with a maximum slip of ~ 1.5 m, spanning depths of 15–30 km along the downdip edge of the subducting Kyushu-Palau ridge. Following the mainshock, a complex evolution of postseismic slip is observed. Initially, afterslip is concentrated predominantly within the coseismic rupture area. Over subsequent weeks, afterslip steadily migrates downdip to depths of 30–50 km, overlapping with regions historically associated with short- and long-term slow slip events (SSEs). Approximately one month after the earthquake, an additional episode of accelerated aseismic slip is detected at depths of 60–80 km, accompanied by a burst of M1–2 microseismicity. This distinct spatiotemporal evolution of megathrust slip suggests a complex interplay among the temperature and stress states of the subduction system, the megathrust rheology and the subducting Kyushu-Palau ridge. Through systematic resolution tests, we demonstrate that this event may represent the first well-constrained “seamount earthquake” captured by modern inland geodesy.
How to cite: Zhang, X., Li, S., and Chen, L.: Investigating megathrust slip during and following the 2024 Mw 7.1 Hyuga-nada earthquake in southwest Japan , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4673, https://doi.org/10.5194/egusphere-egu25-4673, 2025.
Back-propagating rupture (BPR), a phenomenon where seismic rupture migrates rapidly backward away from its advancing front, has been observed across various geological settings. Previous studies have proposed that the occurrence of BPR is attributed to fault zone complexity and heterogeneity, including the presence of fluids, but how fluid flow controls BPR behavior remains poorly understood. In this study, we use the Hydro-Mechanical Earthquake Cycles (H-MECs) model to explore the interplay between fluid flow and BPR in a fault with a poro-visco-elasto-plastic medium, governed by rate- and state-dependent friction. Our simulations show that back-propagating rupture can occur either on a homogeneous fault or fault zone with heterogeneous hydro-mechanical structure. By increasing the background pre-stress on a homogeneous fault, we observe different rupture modes, from steady pulse rupture with BPR, steady-growing pulse rupture to crack-like rupture, with rupture speed increasing linearly. Further simulations accounting for fault zone heterogeneity demonstrate that regions with low pore-fluid pressure are more likely to undergo seismic rupture, while regions with high pore-fluid pressure remain stable and creeping. BPR occurs when rupture transitions from a low to a high pore-fluid pressure region. This pore-fluid pressure transition induces oscillations in slip rate and shear stress, triggering a shift from pulse-like to crack-like rupture behavior, generating a secondary rupture front that propagates backward and causing re-rupture along the fault. Our findings indicate that the length of the high pore-fluid pressure region and background pre-stress significantly influence the occurrence and propagation of BPR — smaller background pre-stress and larger high pore-fluid pressure regions promote BPR, driven by a self-healing front behind the forward rupture. These results emphasize the critical role of pore-fluid pressure heterogeneity and stress conditions in fault dynamics, providing a plausible mechanism for back-propagating rupture consistent with observations.
How to cite: Ye, J., Dal Zilio, L., and Giardini, D.: Exploring the role of hydromechanics in back-propagating rupture dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8291, https://doi.org/10.5194/egusphere-egu25-8291, 2025.
Understanding and monitoring active faults provides useful information in understanding fault movement and constraining seismic hazards. Recently,
short-term deformation rates have been increasingly studied and can be compared with long-term geological data. This study utilises Interferometric Synthetic Aperture Radar (InSAR) data from the European Ground Motion Service (EGMS) spanning 2018 to 2023 to investigate vertical ground deformation rates along the Psathopyrgos and Rion-Patras faults in the Gulf of Corinth, Greece. These two faults represent some of the most active zones of deformation in the region. Our observations reveal a consistent vertical deformation signal, which when combined with topographic data from a 5 m Digital Elevation Model (DEM), helps to constrain the spatial extent of tectonic deformation. We hypothesise that the current deformation across these faults is primarily driven by aseismic creep and interseismic deformation, which is picked up by the EGMS. With increasing microseismicity and possible seismic risk in the area, we perform a seismic hazard analysis to evaluate the potential impact of linked fault ruptures, particularly concerning densely populated areas such as the city of Patras. We obtain Peak Ground Acceleration (PGA) values of 414 − 432 cm/s2 near the city of Patras and Rio. This research highlights the importance of integrating remote sensing data with geological and seismic observations to improve our understanding of fault behaviour and regional seismic risks.
How to cite: Pua, A., Whittaker, A. C., and Locher, V.: Reconciling fault growth histories in time and space and seismic hazard analysis: Western Gulf of Corinth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9527, https://doi.org/10.5194/egusphere-egu25-9527, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 2
EGU25-2323 | ECS | Posters virtual | VPS28
Seismic fault slip affected by pore pressure and cyclic normal stress – deduced by lab investigationsTue, 29 Apr, 14:00–15:45 (CEST) | vP2.19
Slip characteristics of tectonic faults are highly correlated with earthquake risks. However, the stress conditions in-situ are not static, because tides and seismic waves produce dynamic stress disturbances. The effect of fluids also needs to be considered. The fault slip evolution considering both, stress perturbation and fluid pressure is poorly investigated in the laboratory.
We performed direct shear tests on saw-cut granite joints using a shear box device with external syringe pump. The lower part of the specimen was driven by constant load point velocity, and static/dynamic normal loads were applied to the upper part. LVDTs recorded horizontal and vertical movements: fault slip and vertical dilatancy, respectively. The impact of two factors are studied in the experiment: pore fluid pressure and applied normal stress oscillation amplitude.
In conclusion, static pore fluid pressure reduces effective normal stress and shear stiffness of the sheared fault. Under constant normal stress, the reduction in fault shear stiffness caused by fluids synchronously competes with the reduction in critical stiffness (Kc) as the effective normal stress decreases. The stick-slip events are most intensive under low fluid pressure and high normal stress. Under oscillating normal stress, as the normal stress oscillation amplitude increases, the overall fault shear strength weakens continuously. Frictional strengthening and aseismic slips always occur in the normal stress loading stage. Normal stress unloading leads to multi-step stick-slip behavior of the sheared fault. The fault normal deformation is controlled by both normal loading/unloading and asperity overriding. Increasing pore pressure and superimposed normal stress magnitudes lead to more dramatic shear stress changes, but the degree of seismic slip is reduced.
How to cite: Tao, K., Konietzky, H., and Dang, W.: Seismic fault slip affected by pore pressure and cyclic normal stress – deduced by lab investigations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2323, https://doi.org/10.5194/egusphere-egu25-2323, 2025.
