Creep Burst Coincident With Faulting in Marble Observed in 4‐D Synchrotron X‐Ray Imaging Triaxial Compression Experiments. Issue 9 (12th September 2020)

• Record Type: Journal Article
• Authors: Renard, François; Kandula, Neelima; McBeck, Jessica; Cordonnier, Benoît
• Is Part Of: Journal of geophysical research. Volume 125:Issue 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-12
• Subjects: creep -- slow slip event -- Carrara marble -- faulting; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2020JB020354
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Faults in carbonate rocks show both seismic and aseismic deformation processes, leading to a wide range of slip velocities. We deformed two centimeter‐scale cores of Carrara marble at 25°C and imaged the nucleation and growth of faults using dynamic synchrotron X‐ray microtomography. The first sample experienced a constant confinement of 30 MPa and no pore fluid. The second sample experienced confinement in the range 35–23 MPa and water as a pore fluid at 10 MPa pore pressure. We increased the axial stress by steps until creep deformation occurred and imaged deformation in 4‐D. The samples deformed with a quasi‐constant or increasing strain rate when the differential stress was constant, a process called creep. However, for both samples, we also observed transient events that include the acceleration of creep, that is, creep bursts, phenomena similar to slow slip events that occur in continental active faults. During these transient creep events, strain rates increase and correlate in time with strain localization and the slow development of system‐spanning fault networks. In both samples, the acceleration of opening and shearing of microfractures accommodated creep bursts. High‐resolution time‐lapse X‐ray microtomography imaging and digital image correlation during triaxial deformation quantify creep in laboratory faults at subgrain spatial resolution. This work demonstrates that transient creep events, that is, creep bursts or slow slip events, correlate with the nucleation and slow growth of faults and not only with slip on preexisting faults. Plain Language Summary: Active faults may slip at velocities close to 1 m/s during earthquakes and may also slip at much slower rates, in creep. Sometimes such creep is continuous in time; sometimes it is transient and occurs as creep bursts, also called slow slip events. Using state‐of‐the‐art synchrotron X‐ray imaging of core samples of Carrara marble deformed under constant stress conditions and room temperature, we identified such creep bursts. Our 4‐D imaging technique allows seeing through the sample and characterizing the microphysical processes that produce creep bursts. Results show that the acceleration of microfractures nucleation, growth, and coalescence in the sample may lead to the formation of system‐spanning faults that coincide in time with the macroscopically observed creep burst. These results demonstrate that creep bursts may not only correspond to slow slip events on active preexisting faults but may also indicate the slow development of new active faults. Key Points: Transient creep bursts under constant stress conditions are detected in laboratory experiments The bursts correlate in time with increasing dilatancy, including microfracture opening and rotation The macroscopically detected bursts correlate in time with the microscopically observed nucleation, slow growth, and shearing of faults