Imperial College London

DrRebeccaBell

Faculty of EngineeringDepartment of Earth Science & Engineering

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 0903rebecca.bell

 
 
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Location

 

2.37aRoyal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

96 results found

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, 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

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, 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

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

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

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

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

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 2D 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

de Gelder G, Fernández-Blanco D, Melnick D, Duclaux G, Bell RE, Jara-Muñoz J, Armijo R, Lacassin Ret 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.

Journal article

Mantilla A, Szafian P, Bell R, Han Cet 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

Journal article

Hughes A, Rood DH, Whittaker AC, Bell RE, Rockwell TK, Levy Y, Wilcken KM, Corbett LB, Bierman PR, DeVecchio DE, Marshall ST, Gurrola LD, Nicholson Cet 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

Journal article

Watkins S, Whittaker A, Bell RE, McNeill L, Gawthorpe R, Brooke S, Nixon Cet 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

Journal article

Phillips T, Jackson C, Bell R, Duffy Oet 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

Journal article

Rodriguez CR, Jackson CA-L, Bell RE, Rotevatn A, Francis Met al., Dual tectonic-climatic controls on salt giant deposition in the Santos Basin, Offshore Brazil, Geosphere, ISSN: 1553-040X

Journal article

Phillips TB, Magee C, Jackson CA-L, Bell REet al., 2017, Determining the three-dimensional geometry of a dike swarm and its impact on later rift geometry using seismic reflection data, Geology, Vol: 46, Pages: 119-122, ISSN: 0091-7613

Dike swarm emplacement accommodates extension during rifting and large igneous province (LIP) formation, with ancient dike swarms serving to localize strain during later tectonic events. Deciphering three-dimensional (3-D) dike swarm geometry is critical to accurately calculating magma volumes and magma-assisted crustal extension, allowing syn-emplacement mantle and tectonic processes to be interrogated. It is also important for quantifying the influence of ancient dike swarms on post-emplacement faulting. However, the essentially 2-D nature of Earth's surface, combined with the difficulties in imaging subvertical dikes in seismic reflection data and the relatively low resolution of geophysical data in areas of active diking, means our understanding of dike swarm geometry at depth is limited. We examine an ~25-km-wide, >100-km-long, west-southwest–trending dike swarm imaged, due to post-emplacement rotation to shallower dips, in high-quality 2-D and 3-D seismic reflection data offshore southern Norway. Tuned reflection packages correspond to thin (<75 m thick), closely spaced dikes. These data provide a unique opportunity to image and map an ancient dike swarm at variable structural levels. Crosscutting relationships indicate emplacement occurred in the Late Carboniferous–Early Permian, and was linked to the formation of the ca. 300 Ma Skagerrak-centered LIP. Dike swarm width increases with depth, suggesting that magma volume and crustal extension calculations based on surface exposures are dependent on the level of erosion. During the Mesozoic, rift-related faults localized above and exploited mechanical anisotropies within the dike swarm. We demonstrate that seismic reflection data are a powerful tool in understanding dike swarm geometry and the control of dikes on subsequent faulting.

Journal article

Bell RE, Duclaux G, Nixon CW, Gawthorpe RL, McNeill LCet al., 2017, 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.

Journal article

Claringbould JS, Bell RE, Jackson CAL, Gawthorpe RL, Odinsen Tet al., 2017, Pre-existing normal faults have limited control on the rift geometry of the northern North Sea, Earth and Planetary Science Letters, Vol: 475, Pages: 190-206, ISSN: 0012-821X

Many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first-phase normal faults and rift-related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts. However, many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data, making it difficult to test these models. Here we integrate recent 3D seismic reflection and borehole data across the entire East Shetland Basin, northern North Sea, to constrain the long-term, regional development of this multiphase rift. We document the following key stages of basin development: (i) pre-Triassic to earliest Triassic development of multiple sub-basins controlled by widely distributed, NNW- to NE-trending, east- and west-dipping faults; (ii) Triassic activity on a single major, NE-trending, west-dipping fault located near the basins western margin, and formation of a large half-graben; and (iii) Jurassic development of a large, E-dipping, N- to NE-trending half-graben near the eastern margin of the basin, which was associated with rift narrowing and strain focusing in the Viking Graben. In contrast to previous studies, which argue for two discrete periods of rifting during the Permian–Triassic and Late Jurassic–Early Cretaceous, we find that rifting in the East Shetland Basin was protracted from pre-Triassic to Cretaceous. We find that, during the Jurassic, most pre-Jurassic normal faults were buried and in some cases cross-cut by newly formed faults, with only a few being reactivated. Previously developed faults thus had only a limited control on the evolution and geometry of the later rift. We instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere, an interpretation supporting the predictions of lithosphere-scale numerical models. Our study indicates that additional regional studie

Journal article

Olakunle O, Chapman M, Bell RE, Lynn Het al., Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA, Pure and Applied Geophysics

Journal article

Bell RE, Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA, Pure and Applied Geophysics, ISSN: 1420-9136

Journal article

Fazli Khani H, Fossen H, Gawthorpe RL, Faleide JL, Bell REet al., 2017, Basement structure and its influence on the structural configuration of the northern North Sea, Tectonics, Vol: 36, Pages: 1151-1171, ISSN: 1944-9194

The northern North Sea rift basin developed on a heterogeneous crust comprising structures inherited from the Caledonian orogeny and Devonian postorogenic extension. Integrating two-dimensional regional seismic reflection data and information from basement wells, we investigate the prerift structural configuration in the northern North Sea rift. Three seismic facies have been defined below the base rift surface: (1) relatively low-amplitude and low-frequency reflections, interpreted as pre-Caledonian metasediments, Caledonian nappes, and/or Devonian clastic sediments; (2) packages of high-amplitude dipping reflections (>500 ms thick), interpreted as basement shear zones; and (3) medium-amplitude and high-frequency reflections interpreted as less sheared crystalline basement of Proterozoic and Paleozoic (Caledonian) origin. Some zones of Seismic Facies 2 can be linked to onshore Devonian shear zones, whereas others are restricted to the offshore rift area. Interpreted offshore shear zones dip S, ESE, and WNW in contrast to W to NW dipping shear zones onshore West Norway. Our results indicate that Devonian strain and ductile deformation was distributed throughout the Caledonian orogenic belt from central South Norway to the Shetland Platform. Most of the Devonian basins related to this extension are, however, removed by erosion during subsequent exhumation. Basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters, e.g., in the Stord and East Shetland basins. Prerift structures with present-day dips >15° were reactivated, although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction.

Journal article

Al-Maghlouth M, Szafian P, Bell RE, 2017, Characterising carbonate facies using high definition frequency decomposition: case study from northwest Australia, Interpretation, Vol: 5, Pages: SJ49-SJ59, ISSN: 0020-9635

Carbonate facies identification is difficult using conventional seismic attributes due to subtle lithologic changes that cannot be easily recognized. Therefore, there is a need to develop new methodologies to study their evolution and their associated sedimentary processes, which will eventually lead to better prediction for reservoir-quality rocks. New insights into the Cenozoic carbonates in North West Australia have been captured with the application of a high-definition seismic attribute workflow. The workflow starts with conditioning of the seismic volume using structurally oriented noise attenuation filters to remove any random and coherent noise from the input data. It also benefits from a high-definition frequency decomposition that matches the original seismic resolution without smearing interfaces using a “matching pursuit” algorithm. A color blend of multigeometric attributes, such as semblance and conformance, has also been used in the workflow to define edges and discontinuities present in the data within carbonate deposits that are attributed to depositional geometries, such as barrier reefs. Our workflow has been developed to investigate the geomorphology and the sedimentary processes affecting Cenozoic successions in the Northern Carnarvon Basin in North West Australia. Geomorphological and sedimentological observations have been documented such as an Eocene rounded carbonate ramp with evidence of slump blocks and scarps, Middle Miocene accretions generated due to longshore drift, and the presence of Pliocene-Pleistocene patch and barrier reefs. These observations were extracted as geobodies to allow for visualization, and they can be used in an automated seismically based facies classification scheme. The new appreciations are not only useful for understanding the carbonate evolution but can also be used to identify geohazards such as slumps ahead of future drilling.

Journal article

Jackson, Rotevatn A, Tvedt BM, Bell Ret al., 2017, The role of gravitational collapse in controlling the evolution of crestal faults systems (Espirito Santo Basin, SE Brazil) - Discussion, Journal of Structural Geology, Vol: 98, Pages: 95-97, ISSN: 0191-8141

Journal article

Jackson CA-L, Bell RE, Rotevatn A, Tvedt ABMet al., Techniques to determine the kinematics of synsedimentary normal faults and implications for fault growth models, Geometry and Growth of Normal Faults

Conference paper

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