Understanding how normal faults grow is key to determining the tectono-stratigraphic evolution of rifts. According to recent studies, normal faults tend to grow in two temporally distinct stages: a lengthening stage, followed by a throw/displacement accumulation stage. However, this model is still debated and not widely supported by many additional studies. Relatively few studies have investigated what happens to a fault as it becomes inactive, i.e. does it abruptly die, or does its atsurface trace-length progressively shorten by so-called tip retreat? We here use a 3D seismic reflection dataset from the Exmouth Plateau, offshore Australia to develop a three-stage fault growth model for seven normal faults of various sizes, and to show how the throw-length scaling relationship changes as a fault dies. We show that during the lengthening stage, which lasted <30% of the faults' lives, faults reached their near-maximum lengths, yet accumulated only 10-20% of their total throw. During the throw/displacement accumulation stage, which accounts for c. 30-75% of the faults' lives, throw continued to accumulate along the entire length of the faults.All of the studied faults also underwent a stage of lateral tip-retreat (last c. 25% of the faults' lives), where the active at-surface trace-length decreased by up to 25%. The results of our study may have broader implications for fault growth models, slip rate variability during fault growth, and the way in which faults die, in particular the role of lateral tip-retreat. IntroductionNormal fault growth models have been widely debated over the past c. 20 years. The propagating fault model, also referred to as the isolated fault model (Walsh et al., 2003), suggests that normal faults grow via a synchronous increase in length and displacement, i.e. that when Accepted ArticleThis article is protected by copyright. All rights reserved.faults lengthen, they also accumulate displacement. Faults can also lengthen via tip propagation and linkage of these individual segments (e.g.

Quantitative reconstruction of palaeohydrology from fluvial stratigraphy provides sophisticated insights into the response, and relative impact, of tectonic and climatic drivers on ancient fluvial landscapes. Here, field measurements and a suite of quantitative approaches are used to develop a four-dimensional (space and time) reconstruction of palaeohydrology in Late Cretaceous palaeorivers of central Utah, USAthese rivers drained the Sevier mountains to the Western Interior Seaway. Field data include grainsize and cross-set measurements and span five parallel fluvial systems, two of which include up-dip to down-dip transects, across seven stratigraphic intervals through the Blackhawk Formation, Castlegate Sandstone and Price River Formation. Reconstructed palaeohydrological parameters include fluvial morphologies (flow depths, palaeoslopes, palaeorelief and planform morphologies) and various hydrodynamic properties (flow velocities, water discharges and sediment transport modes). Results suggest that fluvial morphologies were similar in space and time; median flow depths spanned 2 to 4 m with marginally greater flow depths in southerly systems. Meanwhile palaeoslopes spanned 10 −3 to 10 −4 , decreasing downstream by an order of magnitude. The most prominent spatio-temporal change is an up to four-fold increase in palaeoslope at the Blackhawk-Castlegate transition; associated alluvial palaeorelief is tens of metres during Blackhawk deposition and >100 m during Castlegate Sandstone deposition. This study observed no change in unit water discharges at the Blackhawk-Castlegate transition, which argues against a climatically driven increase in palaeoslope and channel steepness. These findings instead point to a tectonically driven palaeoslope increase, although one limitation in this study is uncertainty in palaeochannel widths, which directly influences total water discharges. These reconstructions complement and expand on extensive previous work in this region, which enables the efficacy of quantitative reconstruction tools to be tested. Comparison of results with facies-based interpretations indicates that quantitative tools work well, but inconsistencies in more complex reconstructions (for example, planform morphologies) highlight the need for further work.

Quantitative reconstruction of palaeohydrology from fluvial stratigraphy provides sophisticated insights into the response, and relative impact, of tectonic and climatic drivers on ancient fluvial landscapes. Here, field measurements and a suite of quantitative approaches are used to develop a four-dimensional (space and time) reconstruction of palaeohydrology in Late Cretaceous palaeorivers of central Utah, USA-these rivers drained the Sevier mountains to the Western Interior Seaway. Field data include grain-size and cross-set measurements and span 5 parallel fluvial systems, 2 of which include up-dip to down-dip transects, across 7 stratigraphic intervals through the Blackhawk Formation, Castlegate Sandstone and Price River Formation. Reconstructed palaeohydrological parameters include fluvial morphologies (flow depths, palaeoslopes, palaeorelief, and planform morphologies) and various hydrodynamic properties (flow velocities, water discharges, and sediment transport modes). Results suggest that fluvial morphologies were similar in space and time; median flow depths spanned 2-4 m with marginally greater flow depths in southerly systems. Meanwhile palaeoslopes spanned 10-3 to 10-4 , decreasing downstream by an order of magnitude. The most prominent spatio-temporal change is an up to 4-fold increase in palaeoslope at the Blackhawk-Castlegate transition; associated alluvial palaeorelief is 10s of metres during Blackhawk deposition and >100 m during Castlegate Sandstone deposition. Unit water discharges do not change at the Blackhawk-Castlegate transition, which argues against a climatically driven increase in palaeoslope and channel steepness. These findings instead point to a tectonically driven palaeoslope increase, although one limitation in this study is uncertainty in palaeochannel widths, which directly influences total water discharges. These reconstructions complement and expand on extensive previous work in this region, which enables us to test the efficacy of quantitative reconstruction tools. Comparison of results with facies-based interpretations indicates that quantitative tools work well, but inconsistencies in more complex reconstructions (e.g. planform morphologies) highlight the need for further work.

The accommodation of shortening by penetrative strain is widely considered as an important process during contraction, but the distribution and magnitude of penetrative strain in a contractional system with a ductile décollement are not well understood. Penetrative strain constitutes the proportion of the total shortening across an orogen that is not accommodated by the development of macroscale structures, such as folds and thrusts. In order to create a framework for understanding penetrative strain in a brittle system above a ductile décollement, eight analog models, each with the same initial configuration, were shortened to different amounts in a deformation apparatus. Models consisted of a silicon polymer base layer overlain by three fine-grained sand layers. A grid was imprinted on the surface to track penetrative strain during shortening. As the model was shortened, a series of box fold structures developed, with a zone of penetrative strain in the foreland. Penetrative strain in the foreland decreases away from the fold belt. Restoration of the model layers to the horizontal indicates that penetrative strain accounts for 90.5%-30.8% of total shortening in a brittle system with a ductile décollement, compared to 45.2%-3.6% within a totally brittle system. Analog model geometries were consistent with the deformation styles observed in salt-floored systems, such as the Swiss Jura. Penetrative strain has not been accounted for in previous studies of salt-floored regions and estimates of this type could help resolve concerns of missing shortening highlighted by global positioning system data.

Magma emplacement is commonly accommodated by uplift of the overburden and free surface. By assuming this deformation is purely elastic, we can invert the shape and kinematics of ground deformation to model the geometry and dynamics of underlying intrusions. However, magma emplacement can be accommodated by viscoelastic and/or inelastic processes. We use 3D seismic reflection data to reconstruct how elastic bending and inelastic processes accommodated emplacement of a Late Jurassic sill offshore NW Australia. We restore syn-emplacement ground deformation and compare its relief to sill thickness, showing that: (i) where they are equal, elastic bending accommodated intrusion; but (ii) where sill thickness is greater, inversion of a pre-existing fault and overburden compaction contributed to magma accommodation. Our results support work showing inelastic processes can suppress ground deformation, and demonstrate magmatism can modify fault displacements. Reflection seismology is thus powerful tool for unravelling links between magma emplacement, ground deformation, and faulting.

The accommodation of shortening by penetrative strain is widely considered as an important process during contraction, but the distribution and magnitude of penetrative strain in a contractional system with a ductile décollement are not well understood. Penetrative strain constitutes the proportion of the total shortening across an orogen that is not accommodated by the development of macroscale structures, such as folds and thrusts. In order to create a framework for understanding penetrative strain in a brittle system above a ductile décollement, eight analog models, each with the same initial configuration, were shortened to different amounts in a deformation apparatus. Models consisted of a silicon polymer base layer overlain by three fine-grained sand layers. A grid was imprinted on the surface to track penetrative strain during shortening. As the model was shortened, a series of box fold structures developed, with a zone of penetrative strain in the foreland. Penetrative strain in the foreland decreases away from the fold belt. Restoration of the model layers to the horizontal indicates that penetrative strain accounts for 90.5%-30.8% of total shortening in a brittle system with a ductile décollement, compared to 45.2%-3.6% within a totally brittle system. Analog model geometries were consistent with the deformation styles observed in salt-floored systems, such as the Swiss Jura. Penetrative strain has not been accounted for in previous studies of salt-floored regions and estimates of this type could help resolve concerns of missing shortening highlighted by global positioning system data.

The relationship between normal fault displacement (D) and length (L) varies due to numerous factors, including fault size, maturity, basin tectonic history, and host rock lithology. Understanding how fault D and L relate is useful, given related scaling laws are often used to help refine interpretations of often incomplete, subsurface datasets, which has implications for hydrocarbon and low-carbon energy applications. Here we provide a review of D/L scaling laws for normal faults, discuss factors that could influence these relationships, including both geological factors and errors in measurement, and provide a critique of previously published D/L databases. We then present our newly assembled database of 4059 normal faults from 66 sources that include explicit information on: 1) fault length and displacement, 2) host rock lithology, 3) host basin tectonic history, and 4) maturity, as well as fault D and L through time when these data are available. We find an overall scaling law of D = 0.3L0.92, which is similar to previously published scaling equations and that varies in response to the aforementioned geological factors. Our data show that small faults (&lt;1 m length) tend to be over-displaced compared to larger faults, active faults tend to be over-displaced compared to inactive faults, and faults with stiffer host rock lithologies, like igneous and carbonate rocks, tend to be under-displaced with respect to faults within softer, more compliant host rocks, like clastic sedimentary rocks. Our dynamic D/L through time data show that faults follow the hybrid fault growth model, i.e., they initially lengthen, during which time they will appear under-displaced, before accumulating displacement. To the best of our knowledge, this is the first comprehensive, integrated, critical study of D/L scaling laws for normal faults and the factors influencing their growth. These revised relationships can now be utilized for predicting fault length or displacement when only one variable is available and provide the basis for general understanding D/L scaling laws in the context of normal fault growth. This underpinning database is open-access and is available for analysis and manipulation by the broader structural geology community.

The geomorphology and sediment systems of volcanic areas can be influenced by uplift (forced folding) related to subsurface migration and accumulation of magma. Seismic geomorphological analysis presents a unique tool to study how surface morphology and subsurface magma dynamics relate, given seismic reflection data can image buried landscapes and underlying intrusions in 3D at resolutions of only a few metres-to-decametres. However, differential compaction of the sedimentary sequence above incompressible igneous intrusions during burial modifies palaeosurface morphology. Here we use 3D seismic reflection data from offshore NW Australia to explore how the stratigraphic record of igneous intrusion and associated ground deformation can be unravelled. We focus on a forced fold that formed in the Early Cretaceous to accommodate intrusion of magma, but which was later amplified by burial-related differential compaction of the host sedimentary sequence. We show how: (1) marine channels and clinoforms may be deflected by syn-depositional intrusion-induced forced folds; and (2) differential compaction can locally change clinoform depth post-deposition, potentially leading to erroneous interpretation of shoreline trajectories. Our results demonstrate seismic geomorphological analysis can help us better understand how magma emplacement translates into ground deformation, and how this shapes the landform of volcanic regions.