Areas of crustal extension often contain pre-existing structures that can reactivate or influence the geometry and growth of new, overlying faults. As strain accumulates, it is well know that new faults may link down-dip with pre-existing faults. Such linkage invariably leads to an increase in fault surface area, which is empirically linked to increasing seismic hazard. However, the timescales over which this linkage may occur, and its effects on throw-rate evolution and related seismic hazard, are poorly constrained. We use high-resolution 3D seismic reflection and borehole data from offshore NW Australia to investigate the growth and throw-rate evolution of two normal faults. By mapping age-constrained seismic horizons and constructing throw-length and -distance plots we show evidence of growth via dip-linkage, along all or part of their mapped length. We find that linkage did not occur simultaneously along the fault, but over a protracted period especially near fault tips. The absolute timing of fault linkage is influenced by the total throw on the pre-existing fault, throw accumulation rates during subsequent rifting, position along the fault, and the intervening stratigraphic thickness. Progressive dip-linkage increases fault surface area and is associated with an increase in throw-rate on linked segments. Given these effects on fault geometry and displacement patterns, we argue that dip-linkage should be integrated into fault growth models and considered in seismic hazard assessments in rifted regions with inherited structures.

Late Cretaceous intra-plate shortening, and inversion of the Permian to Jurassic rift system, resulted in the ~1000 km-long, S-shaped Syrian Arc Fold Belt which dominates the Levant regional topography through Egypt, Israel, Lebanon, and Syria. Subsequent Miocene folding along the same trends of the Late Cretaceous fold belt, was likely associated with the collision of Arabia and Eurasia. The kinematic model detailing how the Miocene collision initiated the observed inversion is currently unclear yet is essential to our understanding of the geological development of this tectonically complex region. We here present a borehole-constrained seismic-stratigraphic interpretation of 3D seismic reflection data from the Levant Basin that provides unparalleled imaging of these Oligocene-Miocene folds. We show that one of the structures, the NE-SW trending Tamar Anticline, formed during the Burdigalian (lower-Miocene) with no indication of a precursor phase of Late Cretaceous inversion, as previously suggested. We show how the Tamar Anticline was formed concurrent to movement on adjacent strike-slip faults and to the dissection of the anticline by NW-SE-striking normal faults. Simultaneous NW-SE-directed shortening and NE-SW-extension, related to motion along ~E-W strike-slip faults suggests the Tamar Anticline and similar structures developed during the Miocene folding phase formed due to transtension, driven by the opening of the Red-Sea. This new geodynamic model highlights that Late Cretaceous and Miocene folding associated with the Syrian Arc Fold Belt may be geometrically comparable, but stem from different geodynamic regimes.

Failed rifts are widely assumed to enter post-rift tectonic quiescence after termination of intracontinental rifting, but a comprehensive understanding of their regional morphotectonics is lacking. Our quantitative, rift-scale geomorphic analyses in the Suez Rift, an archetypal failed rift in Egypt, reveals widespread rifting after presumed rift "failure." Stacked topographic swaths document normal fault offsets in Plio-Quaternary rocks and fluvial metrics show steep gradients consistent with active faulting along the entire rift length. Quaternary shorelines uplifted along both margins constrain footwall uplift rates of up to 0.13 +/- 0.04 mm/yr on normal faults with down-dip heights of 10-15 km that were active by 3.12 +/- 0.23 and 4.44 +/- 0.2 Ma or earlier times. Pleistocene-Recent extension rates of 0.26-0.55 mm/yr are lower than rates characterising preceding rift phases, albeit compatible with those of modestly active intracontinental rifts (e.g., Basin and Range). Our evidence of active extension after rift "abandonment" supports continued but decelerated rifting, not failure, in the Suez Rift.

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.

Passively rising diapirs control flank deformation (i.e., within 1 km of the salt-sediment interface) and resultant stratigraphic architecture of syn-kinematic units. Growth strata associated with deformation at the flanks of passive diapirs are known as halokinetic sequences. Very few studies have conducted an integrated analysis of composite halokinetic sequences, CHS (stacked halokinetic sequences), and the damage occurring in host rocks during salt diapirism using seismic, petrophysical well data and core information.This study integrates a 3D seismic reflection survey, core, and petrophysical data from the Pierce Field, northern North Sea, offshore UK to examine CHS in near-diapir strata and associated deformation. We recognize three tapered CHS in Units 6, 5, and 2. Two tabular CHS are recognized in Units 3 and 4, comprising the Miocene and Oligocene-aged sediments. The tapered CHS represents a rapid sediment-accumulation rate relative to the diapir-rise rate. The tabular CHS represents slow sediment accumulation rates relative to the diapir-rise rate.Regarding near-diapir deformation, we observe large-scale fracturing associated with drape folding in the Ekofisk Formation resulting from the North and South Pierce salt movement. In the clastic successions, bedding parallel slip zones and slump folds dominate the Forties Sandstone Member and signify a destabilizing and rotational relationship of the Forties sandstone with the growing salt diapirs. Hybrid and remobilized flows interpreted from core data and lateral thickness changes support our interpretation of diapiric salt adjustment of deep-water deposition. Our study demonstrates the value of using an integrated dataset: 3D seismic reflection data and core to characterize the dynamic interaction between sediment gravity-flows and diapiric salt with North and South Pierce diapirs controlling thickness and facies distributions in the North Sea Central Graben.

Exploring how normal faults evolve is important for understanding the dynamic processes underlying the initiation and evolution of rift systems. Early-stage fault growth has been largely under-explored due to resolution limitations in seismic reflection data and the lack of three-dimensional exposures in the field. Physical analogue modelling offers a unique way to visualize and analyse early-stage fault growth. Here, we present results from an innovative analogue modelling approach that allows us to resolve fault growth in 4D through the use of a medical-grade, X-ray computed tomography (CT) scanner, as well as top-view time-lapse photography and digital image correlation (DIC) analysis. We show that faults establish their vertical height at the earliest stage of deformation and laterally grow via a cyclical growth pattern, alternating between periods of rapid lengthening associated with relay-breaching and segment linkage, and periods characterised by throw accumulation. As extension continues, strain is partitioned onto increasingly fewer, optimally spaced and orientated faults, which continue to lengthen via segment linkage; faults in stress shadows, and/or with double conjugate boundaries, become inactive. It is the first time that fault lengthening and throw have been tracked in 4D with such high-fidelity and that this style of cyclical fault growth has been resolved, representing significant advances in our understanding of normal fault growth from segment-scale to network-scale, made possible only by the innovative use of X-ray CT-scanning.

Observations of how faults lengthen and accrue displacement during the very earliest stages of their growth are limited, reflecting the fact that the early syn-kinematic sediments that record this growth are often deeply buried and difficult to image with geophysical data. Here, we use borehole and high-quality 3D seismic reflection data from SW Barents Sea, offshore Norway to quantify the lateral propagation (c. 0.38 – 3.4 mm/year) and displacement accumulation (c. 0.0062 – 0.025 mm/year) rates (averaged over 6.2 Myr) for several long (up to 43 km), moderate displacement (up to 155 m), syn-kinematic faults that we argue provide a unique, essentially ‘fossilised’ snapshot of the earliest stage of fault growth. We show that lateral propagation rates were up to 300 times faster than displacement rates during the initial ~25% of fault lifespan, suggesting that these faults lengthened much more rapidly than they accrued displacement. Our inference of rapid lengthening is also supported by geometric observations including: (i) low Dmax/Lmax (<0.01) scaling relationships, ii) high (>5) length/height aspect ratios, iii) broad, bell-shaped throw-length profiles, and iv) hangingwall depocenters forming during deposition of the first seismically detectable stratigraphic unit spanning the length of the fault. We suggest that the high ratio between lateral propagation rate and displacement rate is likely due to relative immaturity of the studied fault system, an interpretation that supports the ‘constant-length’ fault growth model. Our results highlight the need to document both displacement and lateral propagation rates to further our understanding of how faults evolve across various temporal and spatial scales.

Understanding the physical properties of fault zones is essential for various subsurface applications, including carbon capture and geologic storage, geothermal energy, and seismic hazard assessment. Despite improvements in fault imaging and visualisation, predicting the physical properties of faults and fault zones in the subsurface remains challenging, even with high-quality seismic reflection data. In this study, we use borehole and high-quality Post-Stack Depth Migrated (PSDM) seismic reflection and Full-Waveform Inversion (FWI) velocity data to investigate the characteristics of fault zones in the Samson Dome in the SW Barents Sea. We analyse the variance attribute of the PSDM and FWI volumes, revealing linear features that consistently appear in both datasets. These features correspond to locations of rapid velocity changes and seismic trace distortions, which we interpret as faults. These observations demonstrate the capability of FWI in recovering fault zone velocity structures. Our findings also reveal the natural heterogeneity and complexity of fault zones, with varying P-wave velocity anomalies within the studied fault network. We propose that these anomalies may indicate differences in fault transmissibility. Our study highlights the potential of FWI velocity models in predicting fault zone physical properties and improving subsurface interpretations. By integrating seismic reflection data and FWI models, we can enhance our understanding of fault zone architecture, which has implications for energy transition policies, carbon storage, geothermal energy development, waste disposal, and seismic hazard mitigation.

Continental extension is primarily accommodated by the evolution of normal fault networks. Rifts are shaped by complex tectonic processes and it has historically been difficult to determine the key rift controls using only observations from natural rifts. Here, we use 3D thermo-mechanical, high-resolution (<650 m) forward models of continental extension to investigate how fault network patterns vary as a function of key rift parameters, including extension rate, the magnitude of strain weakening, and the distribution and magnitude of initial crustal damage. We quantitatively compare modelled fault networks with observations of fault patterns in natural rift, finding key similarities in their along-strike variability and scaling distributions. We show that fault-accommodated strain summed across the entire 160 x 160 km study area increases linearly with time. We find that large faults do not abide by power-law scaling as they are limited by an upper finite characteristic, ω0. Fault weakening, and the spatial distribution of initial plastic strain blocks, exert a key control on fault characteristics. We show that off-fault (i.e. non-fault extracted) deformation accounts for 30-70% of the total extensional strain, depending on the rift parameters. As fault population statistics produce distinct characteristics for our investigated rift parameters, further numerical and observational data may enable the future reconstruction of key rifting parameters through observational data alone.

Supplementary Table S1: Acquisition and processing details of 2D seismic reflection surveys

Craig Magee and Chris Jackson examine how geophysical seismic reflection data can be used to study the inner workings of volcanoes and magma plumbing systems Craig Magee and Chris Jackson examine how geophysical seismic reflection data can be used to study the inner workings of volcanoes and magma plumbing systems

Rifting of the continental lithosphere is accommodated by the development of large, linked, normal fault arrays. However, the timescales over which fault arrays develop - from the interaction of small, isolated faults towards localisation of through-going fault systems, has not been well constrained from observations in natural systems. Our limited knowledge of timescales over which fault arrays develop has also resulted in the development of different and debated fault growth models. While scaling relationships between fault displacement and length have been extensively used to understand fault evolution, the scaling exponent value is still not resolved due to significant scatter in global displacement-length profiles.Here we use 3D seismic reflection and borehole data from the Exmouth Plateau, NW Shelf of Australia to investigate the timescales of faults growth within an array. The excellent quality seismic data allows for the entire Jurassic to Early Cretaceous fault array to be analysed over a large areal extent (~1200 km2), and the fault activity can be dated using biostratigraphy from wells. Our study is novel in that we reconstruct and quantify the length and throw on faults back through time to investigate how fault populations evolve. We find that the early stage of rifting was characterised by distributed faulting, where fault trace lengths were established early within the first 7.2 Myrs of rifting (out of a total rifting duration of 85.5 Myrs). By 28.5 Myrs of rifting (33% of the total rifting duration), strain localises on major west dipping faults as a fully linked system. Localisation continues on major faults until the cessation of rifting where strain is accommodated with maximum throw in the centre of faults decreasing towards its tips. Our results suggest that fault displacement and length may scale linearly, but grow in alternations of fault lengthening and fault displacement phases. The growth of active fault systems and death of inactive faults located in stress shadow zones is responsible for the scatter of data points frequently observed in global displacement-length profiles.

(1) Department of Earth Science, University of Bergen, Norway, (2) Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College London, UK, (3) Petrolia NOCO AS, Bergen, Norway, (4) Norwegian Geological Survey (NGU), Trondheim, Norway, (5) Geowissenschaftliches Zentrum der Georg-August Universität, Göttingen, Germany., (6) AkerBP, Lysaker, Norway, (7) Department of Geosciences, University of Oslo, Oslo, Norway., (8) Department of Geoscience, UiT The Arctic University of Norway, Norway.

Improvements in seismic imaging, computing capabilities, and analytical methods, as well as a number of industry deep-water wells sampling distal offshore settings, have underpinned new concepts for rifted margin evolution developed in the last two decades; these mark significant progress in our understanding of extensional systems. For example, the tectonic, sedimentary, and magmatic processes linked to the formation of rifted margins have been overhauled, giving rise to more quantitative approaches and new concepts. However, these processes cannot be understood in isolation, requiring consideration of the continuum in which inheritance and physical processes are integrated within a plate tectonic framework. The major progress and fundamental developments of past research in rifted margins have been made hand-inhand with other domains of Earth Sciences and have fundamental implications for the understanding of key geological systems such as active rifts, the ocean lithosphere, subduction zones, and collisional orogens. The "IMAGinING RIFTING" workshop, organized in Pontresina-Switzerland in September 2017, gathered researchers from all disciplines working on rifts and rifted margins, and included participants from academia and industry. This contribution summarizes the workshop discussions, in addition to outlining our state-of-the-art knowledge of rifted margins. We highlight future challenges in unraveling the processes and conditions under which these extensional systems form and, ultimately, how tectonic plates rupture and new oceans are born. Our aims here are to provide a framework for future research endeavors and to promote collaboration not only within the rift and rifted margins communities, but across other Earth Science disciplines.

Magnetic stripes have long been used to define the presence and age of oceanic crust. However, continental crust heavily intruded by magma can record magnetic reversals akin to those observed in oceanic crust. We re-evaluate the nature of the Cuvier Abyssal Plain (CAP), offshore NW Australia, which hosts magnetic stripes and has previously been defined as oceanic crust. We use magnetic, 2D seismic reflection, and geochemical data to test whether the CAP structure and composition is consistent with unambiguous oceanic crust. We show chemical data from a basalt within the CAP, previously described as displaying an enriched MORB-like signature, actually contains evidence of contamination by continental material. We also recognise seaward-dipping reflector (SDR) sequences across the CAP. Borehole data from overlying sedimentary rocks suggests these SDRs were emplaced in a shallow-water (<200 m depths) or sub-aerial environment. Our results indicate the CAP may not be unambiguous oceanic crust. Instead, we suggest the CAP could comprise a spectrum heavily intruded continental crust (akin to present-day Ethiopia) through to fully oceanic crust, recording the evolution from continental rifting to progressively magma-dominated, sub-aerial to shallow-water extension. Our work supports suggestions that magnetic reversals may not be truly diagnostic of oceanic crust.