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Fault Growth (fault + growth)
Selected AbstractsDynamic non-planar crack rupture by a finite volume methodGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2007M. Benjemaa SUMMARY Modelling dynamic rupture for complex geometrical fault structures is performed through a finite volume method. After transformations for building up the partial differential system following explicit conservative law, we design an unstructured bi-dimensional time-domain numerical formulation of the crack problem. As a result, arbitrary non-planar faults can be explicitly represented without extra computational cost. On these complex surfaces, boundary conditions are set on stress fluxes and not on stress values. Prescribed rupture velocity gives accurate solutions with respect to analytical ones depending on the mesh refinement, while solutions for spontaneous propagation are analysed through numerical means. An example of non-planar spontaneous fault growth in heterogeneous media demonstrates the good behaviour of the proposed algorithm as well as specific difficulties of such numerical modelling. [source] The structural evolution of the Halten Terrace, offshore Mid-Norway: extensional fault growth and strain localisation in a multi-layer brittle,ductile systemBASIN RESEARCH, Issue 2 2010N. Marsh ABSTRACT Tectonic subsidence in rift basins is often characterised by an initial period of slow subsidence (,rift initiation') followed by a period of more rapid subsidence (,rift climax'). Previous work shows that the transition from rift initiation to rift climax can be explained by interactions between the stress fields of growing faults. Despite the prevalence of evaporites throughout the geological record, and the likelihood that the presence of a regionally extensive evaporite layer will introduce an important, sub-horizontal rheological heterogeneity into the upper crust, there have been few studies that document the impact of salt on the localisation of extensional strain in rift basins. Here, we use well-calibrated three-dimensional seismic reflection data to constrain the distribution and timing of fault activity during Early Jurassic,Earliest Cretaceous rifting in the Åsgard area, Halten Terrace, offshore Mid-Norway. Permo-Triassic basement rocks are overlain by a thick sequence of interbedded halite, anhydrite and mudstone. Our results show that rift initiation during the Early Jurassic was characterised by distributed deformation along blind faults within the basement, and by localised deformation along the major Smørbukk and Trestakk faults within the cover. Rift climax and the end of rifting showed continued deformation along the Smørbukk and Trestakk faults, together with initiation of new extensional faults oblique to the main basement trends. We propose that these new faults developed in response to salt movement and/or gravity sliding on the evaporite layer above the tilted basement fault blocks. Rapid strain localisation within the post-salt cover sequence at the onset of rifting is consistent with previous experimental studies that show strain localisation is favoured by the presence of a weak viscous substrate beneath a brittle overburden. [source] Investigating the surface process response to fault interaction and linkage using a numerical modelling approachBASIN RESEARCH, Issue 3 2006P.A. Cowie ABSTRACT In order to better understand the evolution of rift-related topography and sedimentation, we present the results of a numerical modelling study in which elevation changes generated by extensional fault propagation, interaction and linkage are used to drive a landscape evolution model. Drainage network development, landsliding and sediment accumulation in response to faulting are calculated using CASCADE, a numerical model developed by Braun and Sambridge, and the results are compared with field examples. We first show theoretically how the ,fluvial length scale', Lf, in the fluvial incision algorithm can be related to the erodibility of the substrate and can be varied to mimic a range of river behaviour between detachment-limited (DL) and transport-limited (TL) end-member models for river incision. We also present new hydraulic geometry data from an extensional setting which show that channel width does not scale with drainage area where a channel incises through an area of active footwall uplift. We include this information in the coupled model, initially for a single value of Lf, and use it to demonstrate how fault interaction controls the location of the main drainage divide and thus the size of the footwall catchments that develop along an evolving basin-bounding normal fault. We show how erosion by landsliding and fluvial incision varies as the footwall area grows and quantify the volume, source area, and timing of sediment input to the hanging-wall basin through time. We also demonstrate how fault growth imposes a geometrical control on the scaling of river discharge with downstream distance within the footwall catchments, thus influencing the incision rate of rivers that drain into the hanging-wall basin. Whether these rivers continue to flow into the basin after the basin-bounding fault becomes fully linked strongly depends on the value of Lf. We show that such rivers are more likely to maintain their course if they are close to the TL end member (small Lf); as a river becomes progressively more under supplied, i.e. the DL end member (large Lf), it is more likely to be deflected or dammed by the growing fault. These model results are compared quantitatively with real drainage networks from mainland Greece, the Italian Apennines and eastern California. Finally, we infer the calibre of sediments entering the hanging-wall basin by integrating measurements of erosion rate across the growing footwall with the variation in surface processes in space and time. Combining this information with the observed structural control of sediment entry points into individual hanging-wall depocentres we develop a greater understanding of facies changes associated with the rift-initiation to rift-climax transition previously recognised in syn-rift stratigraphy. [source] The role of evaporite mobility in modifying subsidence patterns during normal fault growth and linkage, Halten Terrace, Mid-NorwayBASIN RESEARCH, Issue 2 2005Nick J. Richardson Well-calibrated seismic interpretation in the Halten Terrace of Mid-Norway demonstrates the important role that structural feedback between normal fault growth and evaporite mobility has for depocentre development during syn-rift deposition of the Jurassic,Early Cretaceous Viking and Fangst Groups. While the main rift phase reactivated pre-existing structural trends, and initiated new extensional structures, a Triassic evaporite interval decouples the supra-salt cover strata from the underlying basement, causing the development of two separate fault populations, one in the cover and the other confined to the pre-salt basement. Detailed displacement,length analyses of both cover and basement fault arrays, combined with mapping of the component parts of the syn-rift interval, have been used to reveal the spatial and temporal evolution of normal fault segments and sediment depocentres within the Halten Terrace area. Significantly, the results highlight important differences with traditional models of normal fault-controlled subsidence, including those from parts of the North Sea where salt is absent. It can now be shown that evaporite mobility is intimately linked to the along-strike displacement variations of these cover and basement faults. The evaporites passively move beneath the cover in response to the extension, such that the evaporite thickness becomes greatest adjacent to regions of high fault displacement. The consequent evaporite swells can become large enough to have pronounced palaeobathymetric relief in hangingwall locations, associated with fault displacement maxima, the exact opposite situation to that predicted by traditional models of normal fault growth. Evaporite movement from previous extension also affects the displacement,length relationships of subsequently nucleated or reactivated faults. Evaporite withdrawal, on the other hand, tends to be a later-stage feature associated with the high stress regions around the propagating tips of normal faults or their coeval hangingwall release faults. The results indicate the important effect of, and structural feedback caused by, syn-rift evaporite mobility in heavily modifying subsidence patterns produced by normal fault array evolution. Despite their departure from published models, the results provide a new, generic framework within which to interpret extensional fault and depocentre development and evolution in areas in which mobile evaporites exist. [source] Normal fault growth and early syn-rift sedimentology and sequence stratigraphy: Thal Fault, Suez Rift, EgyptBASIN RESEARCH, Issue 4 2003Mike J. Young This paper investigates the tectono-stratigraphic development of a major, segmented rift border fault (Thal Fault) during ca. 6 Myr of initial rifting in the Suez Rift, Egypt. The Thal Fault is interpreted to have evolved by the progressive linkage of at least four fault segments. We focus on two contrasting structural settings in its hangingwall: Gushea, towards the northern tip of the fault, and Musaba Salaama, ca. 20 km along-strike to the south, towards the centre of the fault. The early syn-rift stratigraphic succession passes upwards from continental facies, through a condensed marginal marine shell-rich facies, into fully marine shoreface sandstone and offshore mudstone. Regionally correlatable stratal surfaces within this succession define time-equivalent stratal units that exhibit considerable along-strike variability in thickness and facies architecture. During the initial ca. 6 Myr of rifting, the thickest stratigraphy developed towards the centre of the array of fault segments that subsequently hard linked to form the Thal Fault. Thus, a displacement gradient existed between fault segments at the centre and tip of the fault array, suggesting that the fault segments interacted, and a fixed length was established for the fault array, at an early stage in rifting. Towards the centre of the Thal Fault the early syn-rift succession shows pronounced thickening away from the fault and towards a series of intra-block antithetic faults that were active for up to ca. 6 Myr. This indicates that a large proportion of fault-controlled subsidence during the initial ca. 6 Myr of rifting occurred in the hangingwalls of antithetic intra-block faults, and not the present-day Thal Fault. The antithetic faults progressively switched off during rifting such that after ca. 6 Myr of rifting, fault-activity had localised on the Thal Fault enabling it to accrue to the present-day high level of displacement. Aspects of the development of the Thal Fault appear to be in contrast to many models of fault evolution that predict large-displacement rift-climax faults to have always had the greatest displacement during fault population evolution. This study has implications for tectono-stratigraphic development during early rift basin evolution. In particular, we stress that caution must be taken when relating final rift-climax fault structure to the early tectono-stratigraphy, as these may differ considerably. [source] Tectono-sedimentary evolution of active extensional basinsBASIN RESEARCH, Issue 3-4 2000R. L. Gawthorpe We present conceptual models for the tectono-sedimentary evolution of rift basins. Basin architecture depends upon a complex interaction between the three-dimensional evolution of basin linkage through fault propagation, the evolution of drainage and drainage catchments and the effects of changes in climate and sea/lake level. In particular, the processes of fault propagation, growth, linkage and death are major tectonic controls on basin architecture. Current theoretical and experimental models of fault linkage and the direction of fault growth can be tested using observational evidence from the earliest stages of rift development. Basin linkage by burial or breaching of crossover basement ridges is the dominant process whereby hydrologically closed rifts evolve into open ones. Nontectonic effects arising from climate, sea or lake level change are responsible for major changes in basin-scale sedimentation patterns. Major gaps in our understanding of rift basins remain because of current inadequacies in sediment, fault and landscape dating. [source] | ||||||||||