Imperial College London

DrRebeccaBell

Faculty of EngineeringDepartment of Earth Science & Engineering

Senior Lecturer
 
 
 
//

Contact

 

+44 (0)20 7594 0903rebecca.bell

 
 
//

Location

 

2.37aRoyal School of MinesSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

109 results found

Davy R, Frahm L, Bell R, Arai R, Barker D, Henrys S, Bangs N, Morgan J, Warner Met al., 2021, Generating high‐fidelity reflection images directly from full‐waveform inversion: Hikurangi Subduction Zone case study, Geophysical Research Letters, Vol: 48, Pages: 1-10, ISSN: 0094-8276

Full-waveform inversion (FWI) can resolve subsurface physical properties to high resolutions, yet high-performance computing resources have only recently made it practical to invert for high frequencies. A benefit of high-frequency FWI is that recovered velocity models can be differentiated in space to produce high-quality depth images (FWI images) of a comparable resolution to conventional reflection images.Here, we demonstrate the generation of high-fidelity reflection images directly from the FWI process. We applied FWI up to 38 Hz to seismic data across the Hikurangi subduction margin. The resulting velocity models and FWI images reveal a complex faulting system, sediment deformation, and bottom-simulating reflectors within the shallow accretionary prism. Our FWI images agree with conventional reflection images and better resolve horizons around the Pāpaku thrust fault. Thus, FWI imaging has the potential to replace conventional reflection imaging whilst also providing physical property models that assist geological interpretations.

Journal article

Pan S, Bell RE, Jackson CA-L, Naliboff Jet al., 2021, Evolution of normal fault displacement and length as continental lithosphere stretches, BASIN RESEARCH, ISSN: 0950-091X

Journal article

Shmela AK, Paton DA, Collier RE, Bell REet al., 2021, Normal fault growth in continental rifting: insights from changes in displacement and length fault populations due to increasing extension in the Central Kenya Rift, Tectonophysics, Vol: 814, ISSN: 0040-1951

This study examines the scaling relationship between fault length and displacement for the purpose of gaining a better understanding of the evolution of normal faults within the central Kenya Rift. 620 normal faults were manually mapped from a digital elevation model (DEM), with 30 m2 resolution and an estimated maximum displacement of ~40–~6030 m and fault lengths of 1270 ‐ 60,600 m. To assess the contribution of fault populations to the strain accommodation from south to north, the study area has been divided into three zones of fault populations based upon their average fault orientations; zone 1 in the north is dominated by NNE striking faults, zone 2 in the centre of the rift is characterised by NNW to NNE fault trends, whereas zone 3 in the south is characterised by NNW striking fault systems. Extensional strain was estimated by summing fault heaves across six transects along the rift, which showed a progressive increase of strain from south to north. The fault length and displacement data in the three zones fit to a power law distribution. The cumulative distributions of fault length populations showed similar fractal dimension (D) in the three zones. The cumulative displacement distributions for the three zones showed a decrease in the Power-law fractal dimension with increasing strain, which implies that the strain is increasingly localized onto larger faults as the fault system becomes more evolved from south to north. Increasing displacement with increasing strain while the fault length remains almost constant may indicate that the fault system could be evolving in accordance with a constant length fault growth model, where faults lengthen quickly and then accrue displacement. Results of this study suggest that the process of progressively increasing fault system maturity and strain localization onto large faults can be observed even over a relatively small area (240 × 150 km) within the rift system. It is also suggested that patterns of fault

Journal article

Merry T, Bastow I, Kounoudis R, Ogden C, Bell R, Jones Let al., 2021, The influence of the North Anatolian Fault and a fragmenting slab architecture on upper mantle seismic anisotropy in the eastern Mediterranean, G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, Vol: 22, Pages: 1-26, ISSN: 1525-2027

The eastern Mediterranean hosts, within the span of a few hundred kilometers, extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Slab roll-back, toroidal flow, and lithospheric dripping/delamination processes are also believed to be operating. Associated asthenospheric flow and lithospheric de formation are expected to manifest as seismic anisotropy, measurable via study of SKS shear wave splitting. Surprisingly, previous SKS splitting investigations have resolved only long wavelength patterns of anisotropy in the region, interpreting them as large scale asthenospheric flow; moreover, no anisotropic signature has been associated with the North Anatolian Fault (NAF), unlike other major strike-slip plate boundaries world wide. We present a 29-year record of SKS splitting observations, revealing hitherto unrecognized short-length-scale variations in anisotropy, and backazimuthal variations of splitting parameters that attest to multi-layered anisotropy. Lithospheric anisotropy beneath the NAF exhibits fast directions either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low strained transcurrent mantle shear zone. Elsewhere, anisotropy is consistent with as thenospheric flow through tomographically-imaged slab gaps, and driven by Hellenic trench retreat. Evidence for westward flow of asthenosphere driving Anatolian plate motion is lacking. Shorter splitting delay times and nulls in central Anatolia suggest weaker azimuthal anisotropy in the asthenosphere, supporting models that invoke ver tical mantle flow patterns (lithospheric dripping/asthenospheric upwelling). Thus, we conclude that the signal of mantle anisotropy more closely reflects the lithospheric de formation, complex slab architecture and geodynamic diversity of the region than pre36 viously recognized.

Journal article

Hughes A, Rood D, DeVecchio DE, Whittaker AC, Bell RE, Wilcken KM, Corbett LB, Bierman PR, Swanson BJ, Rockwell TKet al., 2021, Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, quantified using cosmogenic isotopes and topographic analyses, Geological Society of America Bulletin, ISSN: 0016-7606

The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/-0.22 Ma to 1.06 +0.23/-0.26 Ma and our burial ages near the base of shallow marine deposits, which underlie the Saugus Formation, increase eastwards from 0.55 +0.08/-0.07 Ma to 3.30 +0.30/-0.42 Ma. Our geochronology is used the calculate a rapid long-term fault throw rate of 4.7–6.3 mm yr-1 since ~1.5 Ma for the San Cayetano fault and a slip rate of 1.3–3.0 mm yr-1 since ~1.5 Ma for the Oak Ridge fault, both of which agree with contemporary reverse slip rates derived from GPS data. We also calculate total cosmogenic nuclide (TCN)-derived catchment-averaged erosion rates that range from 0.18–2.21mm yr-1 and discuss the applicability of TCN-derived catchment-averaged erosion rates in rapidly-uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly-uplifting mountain belts, catchments may attain a quasi-steady state on timescales <105 years, even if catchment-averaged erosion rates are still 34 adjusting to tectonic forcing.

Journal article

Wrona T, Pan I, Bell RE, Gawthorpe RL, Fossen H, Brune Set al., 2021, 3D seismic interpretation with deep learning: A brief introduction, The Leading Edge, Vol: 40, Pages: 524-532, ISSN: 1070-485X

Understanding the internal structure of our planet is a fundamental goal of the earth sciences. As direct observations are restricted to surface outcrops and borehole cores, we rely on geophysical data to study the earth's interior. In particular, seismic reflection data showing acoustic images of the subsurface provide us with critical insights into sedimentary, tectonic, and magmatic systems. However, interpretations of these large 2D grids or 3D seismic volumes are time-consuming, even for a well-trained person or team. Here, we demonstrate how to automate and accelerate the analysis of these increasingly large seismic data sets with machine learning. We are able to perform typical seismic interpretation tasks such as mapping tectonic faults, salt bodies, and sedimentary horizons at high accuracy using deep convolutional neural networks. We share our workflows and scripts, encouraging users to apply our methods to similar problems. Our methodology is generic and flexible, allowing an easy adaptation without major changes. Once trained, these models can analyze large volumes of data within seconds, opening a new pathway to study the processes shaping the internal structure of our planet.

Journal article

Lathrop BA, Jackson CA-L, Bell RE, Rotevatn Aet al., 2021, Normal Fault Kinematics and the Role of Lateral Tip Retreat: An Example From Offshore NW Australia, TECTONICS, Vol: 40, ISSN: 0278-7407

Journal article

Reeve MT, Magee C, Bastow ID, McDermott C, Jackson CA-L, Bell RE, Prytulak Jet al., 2021, Nature of the cuvier abyssal plain crust, offshore NW Australia, Journal of the Geological Society, Vol: 178, Pages: 1-17, ISSN: 0016-7649

Magnetic stripes have long been assumed to be indicative of oceanic crust. However, continental crust heavily intruded by magma can also record magnetic stripes. 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 show that chemical data from a basalt within the CAP, previously described as an enriched mid-ocean ridge basalt, could equally be interpreted to contain evidence of contamination by continental material. We also recognize seaward-dipping reflector sequences in seismic reflection data across the CAP. Borehole data from overlying sedimentary rocks suggests that these seaward-dipping reflectors were emplaced in a shallow water (<200 m depth) or subaerial environment. Our results indicate that the CAP may not be unambiguous oceanic crust, but may instead consist of a spectrum of heavily intruded continental crust through to fully oceanic crust. If the CAP represents such a continent–ocean transition zone, then the adjacent unambiguous oceanic crust would be located >500 km further offshore NW Australia than currently thought. This would impact plate tectonic reconstructions, as well as heat flow and basin modelling studies. Our work also supports the growing consensus that magnetic stripes cannot, by themselves, be used to determine crustal affinity.

Journal article

Watkins SE, Whittaker AC, Bell RE, Brooke SAS, Ganti V, Gawthorpe RL, McNeill LC, Nixon CWet 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

Journal article

Arai R, Kodaira S, Henrys S, Bangs N, Obana K, Fujie G, Miura S, Barker D, Bassett D, Bell R, Mochizuki K, Kellett R, Stucker V, Fry Bet 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.

Journal article

Fazlikhani H, Aagotnes SS, Refvem MA, Hamilton-Wright J, Bell RE, Fossen H, Gawthorpe RL, Jackson CA-L, Rotevatn Aet 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

Journal article

Cook AE, Paganoni M, Clennell MB, McNamara DD, Nole M, Wang X, Han S, Bell RE, Solomon EA, Saffer DM, Barnes PM, Pecher IA, Wallace LM, LeVay LJ, Petronotis KEet 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.

Journal article

Claringbould JS, Bell RE, Jackson CA, Gawthorpe RL, Odinsen Tet 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.

Journal article

Harold L, Fagereng A, Meneghini F, Morgan J, Savage H, Wang M, Bell R, Ikari Met 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

Journal article

Hughes A, Bell RE, Mildon ZK, Rood DH, Whittaker AC, Rockwell TK, Levy Y, DeVecchio DE, Marshall ST, Nicholson Cet 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.

Journal article

Fazlikhani H, Aagotnes S, Refvem M, Hamilton-wright J, Bell R, Fossen H, Gawthorpe R, Jackson C, Rotevatn Aet 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

Working paper

Barnes PM, Wallace LM, Saffer DM, Bell RE, Underwood MB, Fagereng A, Meneghini F, Savage HM, Rabinowitz HS, Morgan JK, Kitajima H, Kutterolf S, Hashimoto Y, Engelmann de Oliveira CH, Noda A, Crundwell MP, Shepherd CL, Woodhouse AD, Harris RN, Wang M, Henrys S, Barker DHN, Petronotis KE, Bourlange SM, Clennell MB, Cook AE, Dugan BE, Elger J, Fulton PM, Gamboa D, Greve A, Han S, Hüpers A, Ikari MJ, Ito Y, Kim GY, Koge H, Lee H, Li X, Luo M, Malie PR, Moore GF, Mountjoy JJ, McNamara DD, Paganoni M, Screaton EJ, Shankar U, Shreedharan S, Solomon EA, Wang X, Wu H-Y, Pecher IA, LeVay LJ, IODP Expedition 372 Scientistset 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.

Journal article

Zondervan JR, Whittaker AC, Bell RE, Watkins SE, Brooke SAS, Hann MGet al., 2020, New constraints on bedrock erodibility and landscape response times upstream of an active fault, GEOMORPHOLOGY, Vol: 351, ISSN: 0169-555X

Journal article

Phillips TB, Jackson C, Bell RE, Valencia Aet 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.

Journal article

Bell R, Gray M, Morgan J, Warner M, Fagereng A, McNeill L, Jacobs K, Henrys S, Fry B, Watkins S, Lacey H, Black J, Victoria L, Daly D, Lindsay D, Bangs N, Arai R, Kodaira S, and the NZ3D teamet al., 2019, New Zealand 3D full waveform inversion (NZ3D-FWI) 2017-2018 field acquisition report

Report

Phillips TB, Fazlikhani H, Gawthorpe RL, Fossen H, Jackson CA-L, Bell RE, Faleide JI, Rotevatn Aet 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.

Journal article

Phillips T, Fazlikhani H, Gawthorpe R, Fossen H, Jackson CA-L, Bell R, Faleide JI, Rotevatn Aet 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.

Working paper

Claringbould JS, Bell R, Jackson CA-L, Gawthorpe R, Odinsen Tet 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.

Working paper

Alcalde J, Bond C, Johnson G, Kloppenburg A, Ferrer O, Bell R, Ayarza Pet 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.

Journal article

Rotevatn A, Jackson CA-L, Tvedt ABM, Bell RE, Blækkan Iet 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.

Journal article

Collanega L, Siuda K, Jackson CA-L, Bell RE, Coleman AJ, Lenhart A, Magee C, Breda Aet 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

Journal article

Gray M, Bell R, Morgan J, Henrys S, Barker D, IODP Expedition 372 scientists, IODP Expedition 375 scientistset 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.

Journal article

Fagereng A, Savage HM, Morgan JK, Wang M, Meneghini F, Barnes PM, Bell RE, Kitajima H, McNamara DD, Saffer DM, Wallace LM, Petronotis K, LeVay L, IODP Expedition 372375 scientistset 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.

Journal article

Wrona T, Magee C, Fossen H, Gawthorpe RL, Bell RE, Jackson C, Faleide JIet 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.

Journal article

Lenhart A, Jackson C, Bell RE, Duffy OB, Gawthorpe RL, Fossen Het 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

Journal article

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=00674641&limit=30&person=true