Erina Prastyani

• Prastyani, Erina; Wang, Lei; McBeck, Jessica; Cordonnier, Benoît; Rybacki, Erik & Dresen, Georg [Vis alle 7 forfattere av denne artikkelen] (2026). Transition From Faulting to Dilatant Cataclastic Flow in Carrara Marble Revealed by Acoustic Monitoring and 4D X‐Ray Imaging. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 131(8). doi: 10.1029/2026jb034160. Fulltekst i vitenarkiv Vis sammendrag

  The brittle–ductile transition, typically located near the base of the seismogenic zone, controls strain localization and the evolution of physical properties, with direct implications for fluid transport and fault mechanics. However, quantitative constraints on strain partitioning and porosity evolution across this transition remain limited, particularly in low‐porosity carbonate rocks. We conducted triaxial compression experiments on dry Carrara marble at confining pressures of 5 and 100 MPa using two complementary techniques: (a) acoustic emission (AE) monitoring coupled with P‐wave velocity measurement, and (b) in situ X‐ray microtomography combined with digital volume correlation (DVC). AE activity remains low at all pressures, with source mechanisms becoming increasingly compaction‐dominated at the highest confinement. P‐wave velocities fall markedly during deformation by up to 60% at 5–10 MPa, ∼50% at 40 MPa, and ∼40% at 100 MPa, reflecting pervasive microcrack development. DVC reveals that the proportion of dilative volumetric strain decreases with confinement from nearly 90% at 5 MPa to 50% at 70–90 MPa, yet dilation remains a major component and is comparable to compaction even at the highest pressures. X‐ray–derived bulk porosity increases from <1% to ≈1.5% at low confinement prior to failure, and to 10% at higher confinements, indicating substantial porosity generation during distributed dilatant cataclastic flow. Together, these results provide the first quantitative link between P‐wave velocity reduction, volumetric strain partitioning, and transient porosity generation across the brittle to semi‐ductile transition, revealing how the interplay of dilation and compaction governs both elastic properties and strain localization in low‐porosity crystalline carbonate.

• Prastyani, Erina; Cordonnier, Benoit & Renard, Francois (2025). Generation of large transient porosity at the brittle to semi-ductile transition. Earth and Planetary Science Letters. ISSN 0012-821X. doi: 10.1016/j.epsl.2025.119805. Fulltekst i vitenarkiv Vis sammendrag

  Fluid circulation within Earth’s crust is contingent on the presence of connected porosity. Yet, at depths near the brittle to ductile transition regimes, where the base of the seismogenic zone is located, high pressure compacts the rock, reducing porosity and inhibiting fluid circulation. At greater depths, plastic mechanisms during ductile deformation further reduce the likelihood of porosity generation. In this study, we experimentally simulated the brittle to semi-ductile transition in Carrara marble by performing triaxial deformation experiments coupled with time-lapse 3D synchrotron Xray microtomography at five confining pressures, ranging from 5 MPa to 70 MPa at room temperature and tracked the evolution of porosity over time. Contrary to the prevailing belief, our results show that porosity increases with increasing axial stress at stresses corresponding to the brittle to semi-ductile transition, where fluid circulation is thought to be impeded. In both the semi-brittle and semi-ductile regimes, porosity exhibits similar values, close to 18%, at equivalent axial strain. Although the porosity is comparable, the dominant deformation mechanisms differ: localized shear zones and distributed microcracking characterize the semi-brittle regime, whereas distributed microcracking, without localization, becomes more prominent in the semi-ductile regime. Our findings reveal the formation of high porosity within the semi-brittle and semi-ductile regimes and offer new insight into how this porosity, interpreted as transient within the crust, may enable fluid circulation at the base of the seismogenic zone in Earth's crust.

• Prastyani, Erina; Cordonnier, Benoit; Beck, Jessica Ann Mc; Weiss, Jérôme & Renard, Francois (2025). Mixed-mode deformation in a rock bridge between two fault segments. Tectonophysics. ISSN 0040-1951. 897. doi: 10.1016/j.tecto.2025.230624. Fulltekst i vitenarkiv Vis sammendrag

  Analyzing how fracture networks develop from preexisting isolated fault segments in immature faults may provide knowledge of the preparation process leading to fault growth and dynamic rupture. We reproduce this process experimentally using triaxial compression experiments coupled with time-lapse in-situ synchrotron X-ray tomography in Westerly granite core samples (10 mm diameter, 20 mm height) that contain two parallel notches oriented at 30° with respect to the axis of the cylinder. We conducted the experiments at room temperature with a constant confining pressure of 20 MPa. We image microfracture development, characterize the microphysical processes of damage and fault growth in an intact rock bridge between the notches, and analyze the evolution of fractures oriented at 0°–17° (extensile) and 17°–32° (shear) as the rock approached failure. We also elucidate the strain localization process in the deforming rock using digital volume correlation. Our study offers a detailed comparison of microfracture and strain field development during fault growth. Results indicate that the rock bridge between the notches becomes damaged with a damage rate and a fracture rate diverging as the rock approaches macroscopic failure. Immediately preceding failure, shear fractures dominate the fracture networks. DVC analysis showed that the deformation process is mixed-mode, accommodated by dilation and shear strain, with the shear strains being more localized than the dilation. Furthermore, regions of high dilative strain host both extensile and shear fractures. These findings provide valuable insights into the fault growth process within an intact rock bridge between two fault segments in nature, demonstrating how mixed-mode deformation facilitates fault maturation.

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• Prastyani, Erina; Renard, Francois; Cordonnier, Benoit & McBeck, Jess (2026). 4D Imaging of Brittle to Semi-ductile Deformation in Crystalline Rock. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  This thesis investigates the fundamental links between strain localization, porosity evolution, and deformation mechanisms across the brittle-to-semi-ductile transition in crystalline rock. Using a multidisciplinary approach that combines triaxial deformation experiments with in-situ 4D X-ray microtomography and acoustic emission monitoring, this work quantifies the seismic and aseismic processes governing deformation. In the brittle regime, this work elucidates how strain partitioning between dilation and shear drives fault growth within intact rock bridges. As deformation reaches the semi-ductile regime, this research captures the evolution of substantial transient porosity and pore connectivity, quantifying the volumetric strain partitioning that might influence fault stability and fluid transport in the middle crust. By challenging the view of the brittle-ductile transition as a static, low-porosity barrier, this thesis provides a dynamic framework for understanding the occurrence of slow slip events, aseismic creep, and deep fluid migration near the base of the seismogenic zone.

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