Now showing 1 - 4 of 4
  • Publication
    Static and dynamic connectivity in bed-scale models of faulted and unfaulted turbidites
    A range of unfaulted and faulted bed-scale models with sheet-like bed geometries have been built and analysed in terms of static bed connectivity and fractional permeability assuming permeable sands and impermeable shales. The models are built using a new method which allows amalgamation ratio to be included explicitly as model input and this property, rather than net:gross ratio, is found to be the dominant control on inter-bed connectivity. The connectivity of faulted sequences is much more complex and is dominated by interactions of variables. A comprehensive modelling suite illustrates these results and highlights the extremely rare combinations of circumstances in which faulted sequences have lower connectivities than their unfaulted sedimentological equivalents, irrespective of whether fault rock properties are included or not. In general, models containing stochastically placed shale smears associated with each faulted shale horizon are better connected than if deterministic Shale Gouge Ratio cut-offs are applied. Despite the complex interactions between geological input and bed-scale connectivity, the flow properties of a system are controlled by only three geometrical, rather than geological, variables describing connectivity, anisotropy and resolution. If two different faulted or unfaulted systems have identical values of these three variables they will have the same flow properties.
    Scopus© Citations 43  782
  • Publication
    2D distinct element modeling of the structure and growth of normal faults in multilayer sequences : 1. Model calibration, boundary conditions, and selected results
    (American Geophysical Union, 2007) ; ;
    The distinct element method is used for modeling the growth of normal faults in layered sequences. The models consist of circular particles that can be bonded together with breakable cement. Size effects of the model mechanical properties were studied for a constant average particle size and various sample widths. The study revealed that the bulk strength of the model material decreases with increasing sample size. Consequently, numerical lab tests and the associated construction of failure envelopes were performed for the specific layer width to particle diameter ratios used in the multilayer models. The normal faulting models are composed of strong layers (bonded particles) and weak layers (nonbonded particles) that are deformed in response to movement on a predefined fault at the base of the sequence. The modeling reproduces many of the geometries observed in natural faults, including (1) changes in fault dip due to different modes of failure in the strong and weak layers, (2) fault bifurcation (splaying), (3) the flexure of strong layers and the rotation of associated blocks to form normal drag, and (4) the progressive linkage of fault segments. The model fault zone geometries and their growth are compared to natural faults from Kilve foreshore (Somerset, United Kingdom). Both the model and natural faults provide support for the well-known general trend that fault zone width increases with increasing displacement.
      884Scopus© Citations 65
  • Publication
    2D distinct element modeling of the structure and growth of normal faults in multilayer sequences : 2. Impact of confining pressure and strength contrast on fault zone growth and geometry
    (American Geophysical Union, 2007) ; ;
    The growth of normal faults in periodically layered sequences with varying strength contrast and at varying confining pressure is modeled using the Distinct Element Method. The normal faulting models are comprised of strong layers (bonded particles) and weak layers (non-bonded particles) that are deformed using a predefined fault at the base of the sequence. The model results suggest that faults in sequences with high strength contrast at low confining pressure are highly segmented due to different types of failure (extension vs. shear failure) in the different layers. The degree of segmentation decreases as the strength contrast decreases and confining pressure increases. Faults at low confining pressure localize as extension (Mode I) fractures within the strong layers and are later linked via shallow dipping faults in the weak ones. This leads to initial staircase geometries that, with increasing displacement, cause space problems that are later resolved by splaying and segmentation. As confining pressure increases the modeled faults show a transition from extension to hybrid and to shear fracture and an associated decrease in fault refraction, with a consequent decrease in fault surface irregularities. Therefore the mode of fracture, which is active in the strong layers of a mechanical multilayer at a particular confining pressure, exerts an important control on the final fault geometry.
    Scopus© Citations 55  484
  • Publication
    Earthquake histories and Holocene acceleration of fault displacement rates
    (Geological Society of America, 2009-10) ; ; ;
    Displacement rates for normal and reverse faults (N = 57) are generally higher when averaged for the Holocene (~10 ka) than for the late Quaternary (~300 ka) and longer time scales. Holocene acceleration of displacement rates could be attributed to geological processes that produce increases of tectonic tempo. We propose an alternative model in which the observed rate changes arise from variability in earthquake slip and/or recurrence coupled with a sampling bias toward those faults that are best represented at the Earth’s surface and accrued displacement fastest during the Holocene. This model is consistent with displacement rates measured over time intervals of up to ~300 k.y. for 129 faults from the Taupo Rift, New Zealand. Departures of earthquake parameters and associated displacement rates from their long-term (>300 k.y.) averages are attributed to fault interactions and occur on time intervals inversely related to these long-term displacement rates and to regional strain rates.
      495