Abstract
The strength, shape, and ultimately seismic behavior of many thin-skinned fold and thrust belts, including marine accretionary wedges, are strongly controlled by large-scale faults that develop from weak, clay-rich sedimentary horizons (decollements). The increase of temperature with depth along clay-rich faults promotes the so-called smectite-illite transition, which may influence the fault strength, fluid distribution, and possibly the onset of seismicity. Here we report on the frictional properties of intact fault rocks retrieved from two large decollements, which were exhumed from depths above and below the smectite-illite transition. We find that all tested rocks are characterized by very low friction (μ = 0.17–0.26), velocity-strengthening behavior, and low rates of frictional healing, suggesting long-term fault weakness. Combining our experimental results with the critical taper theory, we computed the effective friction, F , of megathrusts beneath several accretionary wedges around the world; the result was extremely low (0.03 < F < 0.14), and in agreement with other independent estimates. Our analysis indicates a long-term weakness that can explain the shape of several tectonic wedges worldwide without invoking diffuse near-lithostatic fluid overpressures.
Highlights
Hydrocarbon production reduces reservoir fluid pressure and increases the in situ stress, frequently leading to surface subsidence and induced seismicity (Geertsma, 1973; Yerkes and Castle, 1976)
We report an investigation of Slochteren Sandstone samples from the ZRP-3a well, aimed at searching for evidence of small-strain (0.1%–0.3%), inelastic deformation processes
We studied sandstones samples from the SDM-1 and ZRP-3a cores using techniques ranging from visual inspection to optical and backscattered electron (BSE) microscopy, X-ray mapping, cathodoluminescence (CL) imaging, 1Supplemental Material
Summary
Hydrocarbon production reduces reservoir fluid pressure and increases the in situ (effective) stress, frequently leading to surface subsidence and induced seismicity (Geertsma, 1973; Yerkes and Castle, 1976). Potential mechanisms of inelastic reservoir compaction include (1) fracture of grains forming the load-supporting rock framework, (2) grainscale dissolution-precipitation, and (3) processes operating within grain contacts, like asperity crushing/dissolution, clay film deformation, and slip (Spiers et al, 2017).
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