Publications
137 results found
Elyamani M, John CM, Bell RE, 2021, SENSITIVITY ANALYSIS OF THE AMPLITUDE OF EARLY CRETACEOUS EUSTATIC CHANGES USING FORWARD STRATIGRAPHIC MODELLING (RESOLUTION GUYOT), Pages: 2332-2336
Multiple studies focused on eustatic changes during the Cretaceous as an example of greenhouse world. Most of these studies were performed in local areas. These sea level estimates might be derived from localised effects and therefore reflect relative sea level changes rather than eustasy. Based on that, sensitivity analysis to test the applicability of using the Cretaceous ESL curves of Rohl & ogg (1996), Sahagian et al. (1996), Hardenbol et al. (1998), and Haq (2014) is crucial to validate or refute them. To do that, forward stratigraphic modelling of one of the Mid-Pacific mountain guyots, Resolution Guyot, is performed. The study area is unique as it represents deposition of Cretaceous carbonates (growing at sea-level) on an isolated volcanic island away from the influence of continents and tectonic activity. The initial results show that Haq (2014) ESL curve wasn’t perfectly fitting some of our constraints, and some of the cycles need finer subdivision. The outcomes of this study will constrain the fluctuations of ESL in the Cretaceous and serve as a test to whether the amplitude and timing of regionally-derived eustatic curves are valid for other locations, or whether these curves are too influenced by specific local conditions in the areas.
Watkins SE, Whittaker AC, Bell RE, et al., 2020, Straight from the source's mouth: Controls on field‐constrained sediment export across the entire active Corinth Rift, central Greece, Basin Research, Vol: 32, Pages: 1600-1625, ISSN: 0950-091X
The volume and grain‐size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain‐size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain‐sizes of channel bars and full‐weighted grain‐size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain‐size increases westward along the southern coast of the Gulf of Corinth, with the coarse‐fraction grain‐sizes (84th percentile of weighted grain‐size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse‐fraction of the sieved grain‐size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain‐size export is primarily controlled by the input grain‐size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse‐fraction of the grain‐size distribution are predominantly transported in bedload; however, typical sand‐grade particles are transported as suspended load at bankfull conditions, suggesting disparate source‐to‐sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain‐size‐specific bedload discharged into the Gulf of Corinth using the grain‐size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain‐size of sediment export at the rift scale is particularly
Arai R, Kodaira S, Henrys S, et al., 2020, Three‐dimensional P wave velocity structure of the Northern Hikurangi margin from the NZ3D experiment: evidence for fault‐bound anisotropy, Journal of Geophysical Research: Solid Earth, Vol: 125, Pages: 1-20, ISSN: 2169-9313
We present a high‐resolution three‐dimensional (3‐D) anisotropic P wave velocity (Vp) model in the northern Hikurangi margin offshore Gisborne, New Zealand, constructed by tomographic inversion of over 430,000 first arrivals recorded by a dense grid of ocean bottom seismometers. Since the study area covers a region where shallow slow slip events (SSEs) occur repeatedly and the subduction of a seamount is proposed, it offers an ideal location to link our understanding of structural and hydrogeologic properties at megathrust faults to slip behavior. The Vp model reveals an ~30‐km‐wide, low‐velocity accretionary wedge at the toe of the overriding plate, where previous seismic reflection studies show a series of active thrust faults branching from the plate interface. We find some locations with significant Vp azimuthal anisotropy >5% near the branching faults and the deformation front. This finding suggests that the anisotropy is not ubiquitous and homogeneous within the overriding plate, but more localized in the vicinity of active thrust faults. The fast axes of Vp within the accretionary wedge are mostly oriented to the plate convergence direction, which is interpreted as preferentially oriented cracks in a compressional stress regime associated with plate subduction. We find that the magnitudes of anisotropy are roughly equivalent to values found at oceanic spreading centers, where the extensional stress regime is dominant and the crack density is expected to be higher than subduction zones. This consideration may indicate that additional effects such as fault foliation and clay mineral alignment also contribute to upper plate anisotropy along subduction margins.
Fazlikhani H, Aagotnes SS, Refvem MA, et al., 2020, Strain migration during multiphase extension, Stord Basin, northern North Sea rift, Basin Research, Vol: 33, Pages: 1474-1496, ISSN: 0950-091X
In regions experiencing multiple phases of extension, rift-related strain can vary along and across the basin during and between each phase, and the location of maximum extension can differ between the rift phase. Despite having a general understanding of multiphase rift kinematics, it remains unclear why the rift axis migrates between extension episodes. The role pre-existing structures play in influencing fault and basin geometries during later rifting events is also poorly understood. We study the Stord Basin, northern North Sea, a location characterised by strain migration between two rift episodes. To reveal and quantify the rift kinematics, we interpreted a dense grid of 2D seismic reflection profiles, produced time-structure and isochore (thickness) maps, collected quantitative fault kinematic data and calculated the amount of extension (β-factor). Our results show that the locations of basin-bounding fault systems were controlled by pre-existing crustal-scale shear zones. Within the basin, Permo-Triassic Rift Phase 1 (RP1) faults mainly developed orthogonal to the E-W extension direction. Rift faults control the locus of syn-RP1 deposition, whilst during the inter-rift stage, areas of clastic wedge progradation are more important in controlling sediment thickness trends. The calculated amount of RP1 extension (β-factor) for the Stord Basin is up to β = 1.55 (±10%, 55% extension). During the subsequent Middle Jurassic-Early Cretaceous Rift Phase 2 (RP2), however, strain localised to the west along the present axis of the South Viking Graben, with the Stord Basin being almost completely abandoned. Rift axis migration during RP2 is interpreted to be related to changes in lithospheric strength profile, possibly related to the ultraslow extension (<1 mm/year during RP1), the long period of tectonic quiescence (ca. 50 myr) between RP1 and RP2 and possible underplating. Our results highlight the very heterogeneous nature of temporal and lat
Cook AE, Paganoni M, Clennell MB, et al., 2020, Physical properties and gas hydrate at a near‐seafloor thrust fault, hikurangi margin, New Zealand, Geophysical Research Letters, Vol: 47, Pages: 1-11, ISSN: 0094-8276
The Pāpaku Fault Zone, drilled at International Ocean Discovery Program (IODP) Site U1518, is an active splay fault in the frontal accretionary wedge of the Hikurangi Margin. In logging‐while‐drilling data, the 33‐m‐thick fault zone exhibits mixed modes of deformation associated with a trend of downward decreasing density, P‐wave velocity, and resistivity. Methane hydrate is observed from ~30 to 585 m below seafloor (mbsf), including within and surrounding the fault zone. Hydrate accumulations are vertically discontinuous and occur throughout the entire logged section at low to moderate saturation in silty and sandy centimeter‐thick layers. We argue that the hydrate distribution implies that the methane is not sourced from fluid flow along the fault but instead by local diffusion. This, combined with geophysical observations and geochemical measurements from Site U1518, suggests that the fault is not a focused migration pathway for deeply sourced fluids and that the near‐seafloor Pāpaku Fault Zone has little to no active fluid flow.
Claringbould JS, Bell RE, Jackson CA, et al., 2020, Pre‐breakup extension in the northern North Sea defined by complex strain partitioning and heterogeneous extension rates, Tectonics, Vol: 39, Pages: 1-29, ISSN: 0278-7407
The early stages of continental rifting are accommodated by the growth of upper‐crustal normal fault systems that are distributed relatively evenly across the rift width. Numerous fault systems define fault arrays , the kinematics of which are poorly understood due to a lack of regional studies drawing on high‐quality subsurface data. Here we investigate the long‐term (~150 Myr) growth of a rift‐related fault array in the East Shetland Basin, northern North Sea, using a regionally extensive subsurface dataset comprising 2D and 3D seismic reflection surveys and 107 boreholes. We show that rift‐related strain during the pre‐Triassic‐to‐Middle Triassic was originally distributed across several sub‐basins. The Middle‐to‐Late Triassic saw a decrease in extension rate (~14 m/Myr) as strain localized in the western part of the basin. Early Jurassic strain initially migrated eastwards, before becoming more diffuse during the main, Middle‐to‐Late Jurassic rift phase. The highest extension rates (~89 m/Myr) corresponded with the main rift event in the East Shetland Basin, before focusing of strain within the rift axis and ultimate abandonment of the East Shetland Basin in the Early Cretaceous. We also demonstrate marked spatial variations in timing and magnitude of slip along‐strike of major fault systems during this protracted rift event. Our results imply that strain migration patterns and extension rates during the initial, pre‐breakup phase of continental rifting may be more complex than previously thought; this reflects temporal and spatial changes in both thermal and mechanical properties of the lithosphere, in addition to varying extension rates.
Harold L, Fagereng A, Meneghini F, et al., 2020, Mixed brittle and viscous strain localisation in pelagic sediments seaward of the Hikurangi margin, New Zealand, Tectonics, Vol: 39, ISSN: 0278-7407
Calcareous‐pelagic input sediments are present at several subduction zones and deform differently to their siliciclastic counterparts. We investigate deformation in calcareous‐pelagic sediments drilled ~20 km seaward of the Hikurangi megathrust toe at Site U1520 during IODP Expeditions 372 and 375. Clusters of normal faults and subhorizontal stylolites in the sediments indicate both brittle faulting and viscous pressure solution operated at <850 m below sea floor. Stylolite frequency and vertical shortening estimated using stylolite mass loss, porosity change, and distribution increase with carbonate content. We then use U1520 borehole data to constrain a P‐T‐t history for the sediments, and apply an experimentally‐derived pressure solution model to compare with strains calculated from stylolites. Modelled strains fail to replicate stylolite‐hosted strain distribution or magnitude, but comparison shows porosity, composition, and grain‐scale effects in diffusivity and mass transfer pathway width likely exert a strong influence on pressure solution localisation and strain rate. Stylolite and fault clusters concentrate clay in these sediments, creating weak volumes of clay within carbonates, that may localise slip where the plate interface intersects the carbonates at <5 km depth. Plate interface slip character and rheology will be influenced by the deformation of intermixed phyllosilicates and calcite, occurring by variably‐stable frictional slip and pressure solution of calcite. Pressure solution of calcite is therefore important at the shallow plate interface, waning at the base of the slow‐slipping zone because calcite solubility is low at temperatures > 150°C where frictional (possibly seismic) slip likely predominates.Plain Language SummaryThe type of sediments entering subduction zones will influence the way the plates in the subduction zone slide past one another. We looked at limestones in sediments drilled before they reach the subduction zone an
Hughes A, Bell RE, Mildon ZK, et al., 2020, Three‐dimensional structure, ground rupture hazards, and static stress models for complex non‐planar thrust faults in the Ventura basin, southern California, Journal of Geophysical Research: Solid Earth, Vol: 125, ISSN: 2169-9313
To investigate the subsurface geometry of a recently discovered, seismically‐active fault in the Ventura basin, southern California, USA, we present a series of cross sections and a new three‐dimensional fault model across the Southern San Cayetano fault (SSCF) based on integration of surface data with petroleum industry well‐log data. Additionally, the fault model for the SSCF, along with models of other regional faults extracted from the Southern California Earthquake Center three‐dimensional Community Fault Model, are incorporated in static Coulomb stress modeling to investigate static Coulomb stress transfer between thrust faults with complex geometry and to further our understanding of stress transfer in the Ventura basin. The results of the subsurface well investigation provide evidence for a low‐angle SSCF that dips ~15° north and connects with the western section of the San Cayetano fault around 1.5–3.5 km depth. We interpret the results of static Coulomb stress models to partly explain contrasting geomorphic expression between different sections of the San Cayetano fault and a potential mismatch in timings between large‐magnitude uplift events suggested by paleoseismic studies on the Pitas Point, Ventura, and San Cayetano faults. In addition to new insights into the structure and potential rupture hazard of a recently discovered active reverse fault in a highly populated area of southern California, this study provides a simple method to model static Coulomb stress transfer on complex geometry faults in fold and thrust belts.
Fazlikhani H, Aagotnes S, Refvem M, et al., 2020, Strain migration during multiphase extension, Stord Basin, northern North Sea rift, Publisher: California Digital Library (CDL)
In multirifted regions, rift-related strain varies along and across the basin during and between each extensional event, and the location of maximum extension often differs between rift phases. Despite having a general understanding of multiphase rift kinematics, it remains unclear why some parts of the rift are abandoned, with strain accumulating in previously less deformed areas, and how seismic and sub-seismic scale pre-existing structures influence fault and basin geometries. We study the Stord Basin, northern North Sea, a location characterized by strain migration between two rift episodes. To reveal and quantify the kinematics, we interpreted a dense grid of 2D seismic reflection profiles, produced time-structure and isochore maps, collected quantitative fault kinematic data and calculated the amount of extension (β-factor). Our results show that the locations of basin-bounding fault systems were controlled by pre-existing crustal-scale shear zones. Within the basin, rift faults mainly developed at high angles to the Permo-Triassic Rift Phase 1 (RP1) E-W extension. Rift faults control the locus of syn-RP1 deposition, whilst during the inter-rift stage, sedimentary processes (e.g. areas of clastic wedge progradation) are more important in controlling sediment thickness trends.The calculated amount of RP1 extension (β-factor) for the Stord Basin is up to β=1.55 (±10%, 55% extension). During Middle Jurassic-Early Cretaceous (Rift Phase 2, RP2) however, strain localises to the west along the present axis of the South Viking Graben, with the Stord Basin being almost completely abandoned. Migration of rift axis during RP2 is interpreted to be related to the changes in lithospheric strength profile and possible underplating due to the ultraslow extension (<2mm/yr during RP1) and the long period of tectonic quiescence (ca. 70 myr) between RP1 and RP2. Our results highlight the very heterogeneous nature of temporal and lateral strain migration
Barnes PM, Wallace LM, Saffer DM, et al., 2020, Slow slip source characterized by lithological and geometric heterogeneity, Science Advances, Vol: 6, ISSN: 2375-2548
Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust.
Zondervan JR, Whittaker AC, Bell RE, et al., 2020, New constraints on bedrock erodibility and landscape response times upstream of an active fault, GEOMORPHOLOGY, Vol: 351, ISSN: 0169-555X
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- Citations: 24
Phillips TB, Jackson C, Bell RE, et al., 2020, Rivers, reefs and deltas: geomorphological evolution of the Jurassic of the Farsund Basin, offshore southern Norway, Petroleum Geoscience, Vol: 26, Pages: 81-100, ISSN: 1354-0793
In many petroleum-bearing, data-poor ‘frontier’ basins, source, reservoir and seal distribution is poorly constrained, making it difficult to identify petroleum systems and play models. However, 3D seismic reflection data provide an opportunity to directly map the 3D distribution of key petroleum system elements, thereby supplementing typically sparse, 1D sedimentary facies information available from wells. Here, we examine the Farsund Basin, an underexplored basin offshore southern Norway. Despite lying in the mature North Sea Basin, the Farsund Basin contains only one well; meaning there remains a poor understanding of its hydrocarbon potential. This east-trending basin is anomalous to the north-trending basins present regionally, having experienced a different tectonic, and most likely geomorphological, evolution. We identify a series of east-flowing rivers in the Middle Jurassic, the distribution of which are controlled by salt-detached faults. In the Middle Jurassic, a series of carbonate reefs, expressed as subcircular amplitude anomalies, developed. Within the Upper Jurassic we identify numerous curvilinear features, which correspond to the downlap termination of southwards-prograding deltaic clinoforms. We show how seismic-attribute-driven analysis can determine the geomorphological development of basins, offering insights into both the local and regional tectonostratigraphic evolution of an area, and helping to determine its hydrocarbon potential.
Phillips TB, Fazlikhani H, Gawthorpe RL, et al., 2019, The influence of structural inheritance and multiphase extension on rift development, the northern North Sea, Tectonics, Vol: 38, Pages: 4099-4126, ISSN: 0278-7407
The northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn‐rift depocenters during this multiphase evolution and the mechanisms and extent to which they were influenced by preexisting structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole‐constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian‐Early Triassic (RP1) and Late Jurassic‐Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian orogeny and subsequent Devonian extension. During RP1, the location of major depocenters, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localizes along the Viking‐Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Toward the end of RP2, rift activity migrated northward as extension related to opening of the proto‐North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn‐rift depocenters of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocenters, as well as the locations, styles, and magnitude of fault activity and reactivation during subsequent events.
Bell R, Gray M, Morgan J, et al., 2019, New Zealand 3D full waveform inversion (NZ3D-FWI) 2017-2018 field acquisition report
Phillips T, Fazlikhani H, Gawthorpe R, et al., 2019, The influence of structural inheritance and multiphase extension on rift development, the northern North Sea, Publisher: EarthArXiv
The northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn‐rift depocenters during this multiphase evolution and the mechanisms and extent to which they were influenced by preexisting structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole‐constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian‐Early Triassic (RP1) and Late Jurassic‐Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian orogeny and subsequent Devonian extension. During RP1, the location of major depocenters, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localizes along the Viking‐Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Toward the end of RP2, rift activity migrated northward as extension related to opening of the proto‐North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn‐rift depocenters of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocenters, as well as the locations, styles, and magnitude of fault activity and reactivation during subsequent events.
Claringbould JS, Bell R, Jackson CA-L, et al., 2019, Pre-breakup extension in the northern North Sea defined by complex strain partitioning and heterogeneous extension rates, Publisher: EarthArXiv
The early stages of continental rifting are accommodated by the growth of upper-crustal normal fault systems that are distributed relatively evenly across the rift width. Numerous fault systems define fault arrays, the kinematics of which are poorly understood due to a lack of regional studies drawing on high-quality subsurface data. Here we investigate the long-term (~150 Myr) growth of a rift-related fault array in the East Shetland Basin, northern North Sea, using a regionally extensive subsurface dataset comprising 2D and 3D seismic reflection surveys and 107 boreholes. We show that rift-related strain during the pre-Triassic-to-Middle Triassic was originally distributed across several sub-basins. The Middle-to-Late Triassic saw a decrease in extension rate (~14 m/Myr) as strain localized in the western part of the basin. Early Jurassic strain initially migrated eastwards, before becoming more diffuse during the main, Middle-to-Late Jurassic rift phase. The highest extension rates (~89 m/Myr) corresponded with the main rift event in the East Shetland Basin, before focusing of strain within the rift axis and ultimate abandonment of the East Shetland Basin in the Early Cretaceous. We also demonstrate marked spatial variations in timing and magnitude of slip along-strike of major fault systems during this protracted rift event. Our results imply that strain migration patterns and extension rates during the initial, pre-breakup phase of continental rifting may be more complex than previously thought; this reflects temporal and spatial changes in both thermal and mechanical properties of the lithosphere, in addition to varying extension rates.
Alcalde J, Bond C, Johnson G, et al., 2019, Fault interpretation in seismic reflection data: an experiment analysing the impact of conceptual model anchoring and vertical exaggeration, Solid Earth, Vol: 10, Pages: 1651-1662, ISSN: 1869-9510
The use of conceptual models is essential in the interpretation of reflection seismic data. It allows interpreters to make geological sense of seismic data, which carries inherent uncertainty. However, conceptual models can create powerful anchors that prevent interpreters from reassessing and adapting their interpretations as part of the interpretation process, which can subsequently lead to flawed or erroneous outcomes. It is therefore critical to understand how conceptual models are generated and applied to reduce unwanted effects in interpretation results. Here we have tested how interpretation of vertically exaggerated seismic data influenced the creation and adoption of the conceptual models of 161 participants in a paper-based interpretation experiment. Participants were asked to interpret a series of faults and a horizon, offset by those faults, in a seismic section. The seismic section was randomly presented to the participants with different horizontal–vertical exaggeration (1:4 or 1:2). Statistical analysis of the results indicates that early anchoring to specific conceptual models had the most impact on interpretation outcome, with the degree of vertical exaggeration having a subdued influence. Three different conceptual models were adopted by participants, constrained by initial observations of the seismic data. Interpreted fault dip angles show no evidence of other constraints (e.g. from the application of accepted fault dip models). Our results provide evidence of biases in interpretation of uncertain geological and geophysical data, including the use of heuristics to form initial conceptual models and anchoring to these models, confirming the need for increased understanding and mitigation of these biases to improve interpretation outcomes.
Rotevatn A, Jackson CA-L, Tvedt ABM, et al., 2019, How do normal faults grow?, Journal of Structural Geology, Vol: 125, Pages: 174-184, ISSN: 0191-8141
Normal faults grow via synchronous increase in displacement and length (‘propagating fault model’, also known as the ‘isolated fault model’), or by rapid length establishment and subsequent displacement accrual (constant-length fault model). We here use time-series displacement (D) and length (L) data from natural and experimental faults to elucidate growth styles and D-L trajectories throughout fault life, and to assess the applicability of the two fault models. We show that the growth of most faults is characterized by two stages, with the first defined by fault lengthening (20–30% of fault lifespan) and the second by displacement accrual (70–80% of fault lifespan). Although broadly adhering to the constant-length model, fault growth throughout the lengthening stage, during which significant displacement (10–60% of the total end-of-life fault displacement) may also accumulate, is achieved through rapid tip propagation, relay breaching, and segment linkage, characteristics perhaps most intuitively thought to reflect growth in accordance with the propagating model. The subsequent growth stage is dominated by displacement accrual with limited lateral tip propagation, a phenomenon best described by the constant-length model. We also show that, despite being used primarily in support of the propagating model, global displacement-length (D-L) datasets are equally compatible with the constant-length model.
Gray M, Bell R, Morgan J, et al., 2019, Imaging the shallow subsurface structure of the North Hikurangi subduction zone, New Zealand, using 2-D full-waveform inversion, Journal of Geophysical Research. Solid Earth, Vol: 124, Pages: 9049-9074, ISSN: 2169-9356
The northern Hikurangi plate boundary fault hosts a range of seismic behaviors, of which the physical mechanisms controlling seismicity are poorly understood, but often related to high pore fluid pressures and conditionally stable frictional conditions. Using 2D marine seismic streamer data, we employ full-waveform inversion (FWI) to obtain a high-resolution 2D P-wave velocity model across the Hikurangi margin down to depths of ~2 km. The validity of the FWI velocity model is investigated through comparison with the pre-stack depth migrated seismic reflection image, sonic well data, and the match between observed and synthetic waveforms. Our model reveals the shallow structure of the overriding plate, including the fault plumbing system above the zone of SSEs to theoretical resolution of a half seismic wavelength. We find that the hanging walls of thrust faults often have substantially higher velocities than footwalls, consistent with higher compaction. In some cases, intra-wedge faults identified from reflection data are associated with low-velocity anomalies, which may suggest they are high-porosity zones acting as conduits for fluid flow. The continuity of velocity structure away from IODP drill site U1520 suggests that lithological variations in the incoming sedimentary stratigraphy observed at this site continue to the deformation front and are likely important in controlling seismic behavior. This investigation provides a high-resolution insight into the shallow parts of subduction zones, which shows promise for the extension of modeling to 3D using a recently-acquired, longer-offset, seismic dataset.
Collanega L, Siuda K, Jackson CA-L, et al., 2019, Normal fault growth influenced by basement fabrics: The importance of preferential nucleation from pre-existing structures, BASIN RESEARCH, Vol: 31, Pages: 659-687, ISSN: 0950-091X
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- Citations: 37
Fagereng A, Savage HM, Morgan JK, et al., 2019, Mixed deformation styles observed on a shallow subduction thrust, Hikurangi margin, New Zealand, Geology, Vol: 47, Pages: 872-876, ISSN: 0091-7613
Geophysical observations show spatial and temporal variations in fault slip style on shallow subduction thrust faults, but geological signatures and underlying deformation processes remain poorly understood. International Ocean Discovery Program (IODP) Expeditions 372 and 375 investigated New Zealand's Hikurangi margin in a region that has experienced both tsunami earthquakes and repeated slow-slip events. We report direct observations from cores that sampled the active Pāpaku splay fault at 304 m below the seafloor. This fault roots into the plate interface and comprises an 18-m-thick main fault underlain by ~30 m of less intensely deformed footwall and an ~10-m-thick subsidiary fault above undeformed footwall. Fault zone structures include breccias, folds, and asymmetric clasts within transposed and/or dismembered, relatively homogeneous, silty hemipelagic sediments. The data demonstrate that the fault has experienced both ductile and brittle deformation. This structural variation indicates that a range of local slip speeds can occur along shallow faults, and they are controlled by temporal, potentially far-field, changes in strain rate or effective stress.
Wrona T, Magee C, Fossen H, et al., 2019, 3-D seismic images of an extensive igneous sill in the lower crust, Geology, Vol: 47, Pages: 729-733, ISSN: 0091-7613
When continents rift, magmatism can produce large volumes of melt that migrate upwards from deep below the Earths surface. To understand how magmatism impacts rifting, it is critical to understand how much melt is generated and how it transits the crust. Estimating melt volumes and pathways is difficult, however, particularly in the lower crust where the resolution of geophysical techniques is limited. New broadband seismic reflection data allow us to image the three-dimensional (3-D) geometry of magma crystallized in the lower crust (17.5-22 km depth) of the northern North Sea, in an area previously considered a magma-poor rift. The sub-horizontal igneous sill is 97 km long (N-S), 62 km wide (E-W), and 180 40 m thick. We estimate that 472 161 km3of magma was emplaced within this intrusion, suggesting that the northern North Sea contains more igneous intrusions than previously thought. The signi cant areal extent of the intrusion ( 2700 km2), as well as presence of intrusive steps, indicate sills can facilitate widespread lateral magma transport in the lower crust.
Lenhart A, Jackson C, Bell RE, et al., 2019, Structural architecture and composition of crystalline basement offshore west Norway, Lithosphere, Vol: 11, Pages: 273-293, ISSN: 1941-8264
Numerous studies have investigated the geodynamic history and lithological composition of the Proterozoic basement, Caledonian nappes, and Devonian extensional basins and shear zones onshore west Norway. However, the offshore continuation of these structures, into the northern North Sea, where they are suspected to have influenced the structural evolution of the North Sea rift, is largely unknown. Existing interpretations of the offshore continuation of Caledonian and Devonian structures are based on simple map-view correlations between changes in offshore fault patterns and pronounced onshore structures, without providing evidence for the presence, nature, and geometry of offshore, basement-hosted structures.By integrating three-dimensional (3-D) seismic, borehole, and onshore geological and petrophysical data, as well as two-dimensional (2-D) forward modeling of gravity and magnetic data, we reveal the structural architecture and composition of the crystalline basement on the Måløy Slope, offshore west Norway. Based on 3-D mapping of intrabasement reflection patterns, we identified three basement units that can be correlated with the Caledonian thrust belt, and the major Devonian Nordfjord-Sogn detachment zone, located only 60 km to the east, onshore mainland Norway. Similar to that observed onshore, offshore crystalline basement of the Proterozoic basement (Western Gneiss Region) and allochthons is folded into large-scale antiforms and synforms. These units are separated by the strongly corrugated Nordfjord-Sogn detachment zone. Our analyses show that different types of crystalline basement can be distinguished by their seismic reflection character, and density and magnetic properties. We speculate that the main causes of the observed intrabasement reflectivity are lithological heterogeneities and strain-induced structures such as shear and fracture zones. Our interpretation of the architecture of crystalline basement offshore west Norway has importa
de Gelder G, Fernández-Blanco D, Melnick D, et al., 2019, Lithospheric flexure and rheology determined by climate cycle markers in the Corinth rift, Scientific Reports, Vol: 9, ISSN: 2045-2322
Geomorphic strain markers accumulating the effects of many earthquake cycles help to constrain the mechanical behaviour of continental rift systems as well as the related seismic hazards. In the Corinth Rift (Greece), the unique record of onshore and offshore markers of Pleistocene ~100-ka climate cycles provides an outstanding possibility to constrain rift mechanics over a range of timescales. Here we use high-resolution topography to analyse the 3D geometry of a sequence of Pleistocene emerged marine terraces associated with flexural rift-flank uplift. We integrate this onshore dataset with offshore seismic data to provide a synoptic view of the flexural deformation across the rift. This allows us to derive an average slip rate of 4.5–9.0 mm·yr−1 on the master fault over the past ~610 ka and an uplift/subsidence ratio of 1:1.1–2.4. We reproduce the observed flexure patterns, using 3 and 5-layered lithospheric scale finite element models. Modelling results imply that the observed elastic flexure is produced by coseismic slip along 40–60° planar normal faults in the elastic upper crust, followed by postseismic viscous relaxation occurring within the basal lower crust or upper mantle. We suggest that such a mechanism may typify rapid localised extension of continental lithosphere.
Mantilla A, Szafian P, Bell R, et al., 2019, Integrated reservoir characterization using high definition frequency decomposition, multi-attribute analysis and forward modelling. Chandon discovery, Australia, First Break, Vol: 37, Pages: 65-74, ISSN: 0263-5046
Frequency decomposition and forward modelling represent advanced seismic techniques that can be applied to assist hydrocarbon exploration. The Chandon (4TCF) and Yellowglen (net-pay column 137m) gas discoveries in the Exmouth Plateau, North Carnarvon Basin (NCB), Australia (Figure 1) offer an excellent opportunity to test and demonstrate the applicability of these techniques in the search for hydrocarbons, because of the high-quality seismic data available, the textbook-example of gas flat-spot response, the fluvial-dominated reservoir and the existing proven hydrocarbon accumulation (Geoscience Australia, 2014). This study presents a workflow for reservoir characterization based on the integration of seismic interpretation, seismic attribute analysis, core analysis, petrophysical interpretation, rock physics modelling, and synthetic seismic modelling to ultimately mitigate uncertainty. Firstly, the complex tectonostratigraphic history of the petroleum system is resolved using attribute analysis, attribute colour blends, and frequency decomposition. This analysis reveals an extensive set of reservoir features, emphasizing the structural evolution and stratigraphic architecture. Frequency decomposition represents a powerful tool for looking at band restricted frequency volumes of the seismic data, to reveal hidden geological features. The discrete frequency volumes are combined in a Red-Green-Blue (RGB) blend that shows the contribution of and interaction between different frequency bands, highlighting geological features. However, up until now frequency decomposition images have been used rather qualitatively. This study offers a different approach: it uses forward seismic modelling to compare the high definition frequency decomposition (HDFD, see Eckersley et al., 2018) responses of the original data set and the synthetic models (e.g. Han, 2018), in order to validate the model geometries and their rock and fluid property distribution. A 3D seismic cube (Chandon 3D
Hughes A, Rood DH, Whittaker AC, et al., 2018, Geomorphic evidence for the geometry and slip rate of a young, low-angle thrust fault: Implications for hazard assessment and fault interaction in complex tectonic environments, Earth and Planetary Science Letters, Vol: 504, Pages: 198-210, ISSN: 0012-821X
We present surface evidence and displacement rates for a young, active, low-angle (∼20°) reverse thrust fault in close proximity to major population centers in southern California (USA), the Southern San Cayetano fault (SSCF). Active faulting along the northern flank of the Santa Clara River Valley displaces young landforms, such as late Quaternary river terraces and alluvial fans. Geomorphic strain markers are examined using field mapping, high-resolution lidar topographic data, 10Be surface exposure dating, and subsurface well data to provide evidence for a young, active SSCF along the northern flank of the Santa Clara River Valley. Displacement rates for the SSCF are calculated over 103–104 yr timescales with maximum slip rates for the central SSCF of 1.9[Formula presented] mm yr−1 between ∼19–7 ka and minimum slip rates of 1.3[Formula presented] mm yr−1 since ∼7 ka. Uplift rates for the central SSCF have not varied significantly over the last ∼58 ka, with a maximum value of 1.7[Formula presented] mm yr−1 for the interval ∼58–19 ka, and a minimum value of 1.2±0.3 mm yr−1 since ∼7 ka. The SSCF is interpreted as a young, active structure with onset of activity at some time after ∼58 ka. The geometry for the SSCF presented here, with a ∼20° north dip in the subsurface, is the first interpretation of the SSCF based on geological field data. Our new interpretation is significantly different from the previously proposed model-derived geometry, which dips more steeply at 45–60° and intersects the surface in the middle of the Santa Clara River Valley. We suggest that the SSCF may rupture in tandem with the main San Cayetano fault. Additionally, the SSCF could potentially act as a rupture pathway between the Ventura and San Cayetano faults in large-magnitude, multi-fault earthquakes in southern California. However, given structural complexities, including significant changes
Watkins S, Whittaker A, Bell RE, et al., 2018, Are landscapes buffered to high frequency climate change? A comparison of sediment fluxes and depositional volumes in the Corinth Rift, central Greece, over the past 130 kyrs, Geological Society of America Bulletin, Vol: 131, Pages: 372-388, ISSN: 0016-7606
Sediment supply is a fundamental control on the stratigraphic record. However, a key question is the extent to which climate affects sediment fluxes in time and space. To address this question, estimates of sediment fluxes can be compared with measured sediment volumes within a closed basin with well-constrained tectonic boundary conditions and well-documented climate variability. The Corinth rift, central Greece, is one of the most actively extending basins on Earth, with modern day GPS extension rates of up to 15 mm/yr. The Gulf of Corinth forms a closed system and since ~600 ka the gulf has fluctuated between being marine and a lake. We have estimated suspended sediment fluxes for rivers draining into the Gulf of Corinth using the empirically-derived BQART method over the last interglacial-glacial-interglacial cycle (0-130 kyrs). Modern temperature and precipitation datasets, LGM reconstructions and palaeo climate proxy insights were used to constrain model inputs. Simultaneously, we exploited high-resolution 2D seismic surveys to interpret three seismic units from 130 ka to present and we used this data to derive an independent time series of basin sedimentary volumes to compare with our sediment input flux estimates. Our results predict total Holocene sediment fluxes into the Gulf of Corinth of between 19.2 km3 and 23.4 km3 with a preferred estimate of 21.3 km3. This value is a factor of 1.6 less than the measured Holocene sediment volume in the central depocentres, even without taking lithological factors into account, suggesting that the BQART method provides plausible estimates. Sediment fluxes vary spatially around the Gulf, and we use them to derive minimum catchment-averaged denudation rates of 0.18 to 0.55 mm/yr. Significantly, our time series of basin sedimentary volumes demonstrate a clear reduction in sediment accumulation rates during the last glacial period compared to the current interglacial. This implies that Holocene sediment fluxes must have in
Phillips T, Jackson C, Bell R, et al., 2018, Oblique reactivation of lithosphere-scale lineaments controls rift physiography – the upper-crustal expression of the Sorgenfrei–Tornquist Zone, offshore southern Norway, Solid Earth, Vol: 9, Pages: 403-429, ISSN: 1869-9510
Pre-existing structures within sub-crustal lithosphere may localise stresses during subsequent tectonic events, resulting in complex fault systems at upper-crustal levels. As these sub-crustal structures are difficult to resolve at great depths, the evolution of kinematically and perhaps geometrically linked upper-crustal fault populations can offer insights into their deformation history, including when and how they reactivate and accommodate stresses during later tectonic events. In this study, we use borehole-constrained 2-D and 3-D seismic reflection data to investigate the structural development of the Farsund Basin, offshore southern Norway. We use throw–length (T-x) analysis and fault displacement backstripping techniques to determine the geometric and kinematic evolution of N–S- and E–W-striking upper-crustal fault populations during the multiphase evolution of the Farsund Basin. N–S-striking faults were active during the Triassic, prior to a period of sinistral strike-slip activity along E–W-striking faults during the Early Jurassic, which represented a hitherto undocumented phase of activity in this area. These E–W-striking upper-crustal faults are later obliquely reactivated under a dextral stress regime during the Early Cretaceous, with new faults also propagating away from pre-existing ones, representing a switch to a predominantly dextral sense of motion. The E–W faults within the Farsund Basin are interpreted to extend through the crust to the Moho and link with the Sorgenfrei–Tornquist Zone, a lithosphere-scale lineament, identified within the sub-crustal lithosphere, that extends > 1000 km across central Europe. Based on this geometric linkage, we infer that the E–W-striking faults represent the upper-crustal component of the Sorgenfrei–Tornquist Zone and that the Sorgenfrei–Tornquist Zone represents a long-lived lithosphere-scale lineament that is periodically reactivated througho
Bell RE, Duclaux G, Nixon CW, et al., 2018, High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece, Geology, Vol: 46, Pages: 115-118, ISSN: 0091-7613
Low-angle normal faults (LANFs) accommodate extension during late-stage rifting and breakup, but what is more difficult to explain is the existence of LANFs in less-stretched continental rifts. A critical example is the <5 Ma Corinth Rift, central Greece, where microseismicity, the geometry of exposed fault planes, and deep seismically imaged faults have been used to argue for the presence of <30°-dipping normal faults. However, new and reinterpreted data call into question whether LANFs have been influential in controlling the observed rift geometry, which involves (1) exposed steep fault planes, (2) significant uplift of the southern rift margin, (3) time-averaged (tens of thousands to hundreds of thousands of years) uplift-to-subsidence ratios across south coast faults of 1:1–1:2, and (4) north margin subsidence. We test whether slip on a mature LANF can reproduce the long-term (tens of thousands of years) geometry and morphology of the Corinth Rift using a finite-element method, to model the uplift and subsidence fields associated with proposed fault geometries. Models involving LANFs at depth produce very minor coseismic uplift of the south margin, and post-seismic relaxation results in net subsidence. In contrast, models involving steep planar faults to the brittle-ductile transition produce displacement fields involving an uplifted south margin with uplift-to-subsidence ratios of ∼1:2–3, compatible with geological observations. We therefore propose that LANFs cannot have controlled the geometry of the Corinth Rift over time scales of tens of thousands of years. We suggest that although LANFs may become important in the transition to breakup, in areas that have undergone mild stretching, do not have significant magmatic activity, and do not have optimally oriented preexisting low-angle structures, high-angle faulting would be the dominant strain accommodation mechanism in the upper crust during early rifting.
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