Frictional heterogeneities on carbonate‐bearing normal faults: Insights from the Monte Maggio Fault, Italy

Abstract

Observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and/or spatial heterogeneity of fault frictional behavior. Such complex slip patterns have been observed for earthquakes on normal faults throughout central Italy, where many of the M w 6 to 7 earthquakes in the Apennines nucleate at depths where the lithology is dominated by carbonate rocks. To explore the relationship between fault structure and heterogeneous frictional properties, we studied the exhumed Monte Maggio Fault, located in the northern Apennines. We collected intact specimens of the fault zone, including the principal slip surface and hanging wall cataclasite, and performed experiments at a normal stress of 10 MPa under saturated conditions. Experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 MPa stress drop as the fault surface fails, then velocity-neutral frictional behavior and significant frictional healing. Overall, our results suggest that (1) earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface; (2) postseismic slip is more likely to occur in areas of the fault where gouge is present; and (3) high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop.

Effect of Fluid Chemistry on the Interfacial Composition, Adhesion, and Frictional Response of Calcite Single Crystals—Implications for Injection‐Induced Seismicity

“…The friction coefficients measured in this work ( μ <0.1) are much smaller than those corresponding to calcite‐rich fault gouge in macroscopic experiments ( μ ~0.6 under saturated conditions) (Carpenter et al, ; Carpenter et al, ; Verberne et al, ). A similar discrepancy between the friction coefficients measured at different length scales has been reported before for other materials, such as mica (Horn & Deere, ; Ma et al, ), quartz (Chester, ; Donose et al, ), and graphite (Liu et al, ).…”

Frictional behavior of talc‐calcite mixtures

“…The frictional strength for pure calcite is consistent with results from other studies on limestone and calcite‐rich fault rock at low stress and room temperature [e.g., Weeks and Tullis , ; Scuderi et al ., ; Carpenter et al ., ; Tesei et al ., ; Verberne et al ., ]. For pure talc, our data are in good agreement with results from other experiments conducted on synthetic talc gouges at variable normal stress and temperature representative of the shallow crustal conditions [e.g., Escartín et al ., ; Moore and Lockner , ; Niemeijer et al ., ; Hirauchi et al ., ].…”

“…In addition, we noticed that, whereas at 5 MPa normal stress, the velocity dependence does not show a clear trend as a function of velocity, at 50 MPa ( a − b ) values systematically decrease with increasing step velocity. From a theoretical point of view, the rate and state friction law states that a and b are constitutive properties of the material and independent of sliding velocity [e.g., Dieterich , ]; however our experiments, as well as previous studies, show that a velocity dependence of the a and b parameters exists [e.g., Ikari et al ., ; Niemeijer et al ., ; Ikari et al ., ; Moore and Lockner , ; Carpenter et al ., ; Verberne et al ., ]. We suggest that in our experiments this rate dependence of ( a − b ) can derive in part from a low‐temperature plastic deformation of both talc lamellae [ Beeler et al ., ] and calcite [e.g., De Bresser et al ., ; Schubnel et al ., ], being more efficient at higher normal stresses.…”

Mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20–600°C: Implications for natural faults in limestones

“…Treating these data in terms of an apparent friction coefficient ( ) yielded μ values of ~0.7 at low displacements (Stage I, τ I ), at room temperature, decreasing to ~0.6 at 100–200°C (Table ). These values are similar to the friction coefficient obtained in previous studies on simulated calcite gouge conducted at 20°C to 140°C, at low (≤53 MPa) effective normal stresses using relatively low displacement rates (1 to 300 µm/s) [ Verberne et al ., , ; Tesei et al ., ; Carpenter et al ., ; Chen et al ., ].…”