Publications

Journal article

Potter RWK, Kring DA, Collins GS, 2015,

Scaling of basin-sized impacts and the influence of target temperature

, Geological Society of America Special Papers, Vol: 518, Pages: 99-113, ISSN: 0072-1077

We produce a set of scaling laws for basin-sized impacts using data from a suiteof lunar basin numerical models. The results demonstrate the importance of preimpacttarget temperature and thermal gradient, which are shown to greatly infl uencethe modifi cation phase of the impact cratering process. Impacts into targets withcontrasting thermal properties also produce very different crustal and topographicprofi les for impacts of the same energy. Thermal conditions do not, however, signifi -cantly infl uence the excavation stage of the cratering process; results demonstrate,as a consequence of gravity-dominated growth, that transient crater radii are generallywithin 5% of each other over a wide range of thermal gradients. Excavationdepth-to-diameter ratios for the basin models (~0.12) agree well with experimental,geological, and geophysical estimates, suggesting basins follow proportional scaling.This is further demonstrated by an agreement between the basin models andPi- scaling laws based upon fi rst principles and experimental data. The results of thiswork should also be applicable to basin-scale impacts on other silicate bodies, includingthe Hadean Earth.

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Conference paper

Colombero R, Kontoe S, Foti S, Potts DMet al., 2015,

Numerical modelling of wave attenuation through soil

, XVI ECSMGE Geotechnical Engineering for Infrastructure and Development

Conference paper

Summersgill FC, Kontoe S, Potts DM, 2015,

Finite element investigation of vertical stabilisation piles in a stiff clay excavated slope using a nonlocal strain softening model

, XVI ECSMGE Geotechnical Engineering for Infrastructure and Development

Conference paper

Mason PJ, Ghail RC, Bischoff C, Skipper JAet al., 2015,

Detecting and monitoring small-scale discrete ground movements across London, using Persistent Scatterer InSAR (PSI)

, XVI ECSMGE, Publisher: ICE Publishing

The geology of London is surprisingly poorly understood and, until recently, has been accepted as that of an unfaulted subsidingintraplate basin. The detection of deformation in such quiescent intraplate regions is, however, rather difficult since the movementrates are at least an order of magnitude less than those at plate margins. Growing evidence from across the capital indicates that London'sground conditions are considerably more complex than expected and that faulting is almost always involved.PSInSAR is a developing technique widely used to detect and monitor ground subsidence, especially in urban settings, the movements ofwhich may be up to tens of millimetres. This work focuses on the detection of smaller scale ground movements (of a few millimetres),which we believe are caused by fault-controlled intraplate adjustments, using PSInSAR.The London PSInSAR dataset derives from an imaging SAR archive spanning 18 years (1992 - 2000 and 2001 to 2010). Our preliminaryfindings have revealed systematic patterns of both vertical and horizontal ground displacement. These displacements appear to be faultconstrained and fit the predicted framework of Caledonian, Variscan/Alpine structures known to exist across southern Britain. More detailedanalysis has revealed some surprising patterns, which hint at discrete movements rather than continuous 'creep' over the 18 year period;we believe these are driven by basement faults beneath an inverting London basin.

Conference paper

Ghail RC, Mason PJ, Skipper JA, 2015,

The geological context and evidence for incipient inversion of the London Basin

, XVI ECSMGE 2015, Pages: 3523-3528

A reappraisal of ground investigation data across London reveal that a range of unexpected ground conditions, encountered in engineering works since Victorian times, may result from the effects of ongoing inversion of the London Basin. Site investigation borehole data and the distribution of river terrace deposits of the Thames and its tributaries reveal a complex pattern of block movements, tilting and dextral transcurrent displacement. Significant displacements (~10 m) observed in Thames terrace gravels in borehole TQ38SE1565 at the Lower Lea Crossing, showing that movement has occurred within the last ~100 ka. Restraining bends on reactivated transcurrent faults may ex-plain the occurrence of drift filled hollows, previously identified as fluvially scoured pingos, by faulting and upward migration of water on a flower structure under periglacial conditions. Mapping the location of these features constrains the location of active transcurrent faults and so helps predict the likelihood of encountering hazardous ground conditions during tunnelling and ground engineering.

Journal article

Sun T, Liu JG, Shi Y, Chen W, Qin Q, Zhang Zet al., 2015,

Computational imaging from non-uniform degradation of staggered TDI thermal infrared imager

, Optics Express, Vol: 23, Pages: 24572-24586, ISSN: 1094-4087

For the Time Delay Integration (TDI) staggered line-scanningthermal infrared imager, a Computational Imaging (CI) approach isdeveloped to achieve higher spatial resolution images. After a thoroughanalysis of the causes of non-uniform image displacement and degradationfor multi-channel staggered TDI arrays, the study aims to approach onedimensional(1D) sub-pixel displacement estimation and superposition ofimages from time-division multiplexing scanning lines. Under theassumption that a thermal image is 2D piecewise C2 smooth, a sparse-andsmoothdeconvolution algorithm with L1-norm regularization termscombining the first and second order derivative operators is proposed torestore high frequency components and to suppress aliasing simultaneously.It is theoretically and experimentally demonstrated, with simulation andairborne thermal infrared images, that this is a state-of-the-art practical CImethod to reconstruct clear images with higher frequency components fromraw thermal images that are subject to instantaneous distortion and blurring.

Journal article

Stevenson CJ, Jackson CA-L, Hodgson DM, Hubbard SM, Eggenhuisen JTet al., 2015,

Deep-water sediment bypass

, Journal of Sedimentary Research, Vol: 85, Pages: 1058-1081, ISSN: 1527-1404

Submarine gravity flows are a key process for transporting large volumes of sediment from the continents to the deep sea. The location, volume, and character of the sediment bypassed by these flows dictates the areal extent and thickness of the associated deposits. Despite its importance, sediment bypass is poorly understood in terms of flow processes and the associated stratigraphic expression. We first examine the relationships between the physical parameters that govern bypass in flows, before assessing the variable stratigraphic expression of bypass from modern seafloor, outcrop, and subsurface datasets. Theoretical and numerical approaches distinguish grain size, slope, flow size, and sediment concentration as parameters that exert major controls on flow bypass. From field data, a suite of criteria are established to recognize bypass in the geological record. We identify four bypass-dominated zones, each of which is associated with a set of diagnostic criteria: slope-channel bypass, slope-bypass from mass wasting events, base-of-slope bypass, and basin-floor bypass. As the expression of bypass varies spatially and is dependent on the scale of observation, a range of scale-dependent criteria are required for robust interpretation of these zones in the field or subsurface. This synthesis of deep-water sediment bypass highlights the challenge in quantitatively linking process with product. The establishment of criteria to recognize sediment bypass, qualitatively linked with flow processes, is an important step towards improving our understanding of submarine flow dynamics and resultant stratigraphic architecture.

Journal article

Duffy OB, Bell RE, Jackson CA-L, Gawthorpe RL, Whipp PSet al., 2015,

Fault Growth and Interactions in a Multiphase Rift Fault Network: Horda Platform, Norwegian North Sea

, Journal of Structural Geology, Vol: 80, Pages: 99-119, ISSN: 0191-8141

Physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non-colinear normal fault sets. Furthermore, multiphase rifts will display a greater frequency and range of styles of fault interactions than single-phase rifts. Although these physical models have yielded useful information on the evolution of fault networks in map view, the true 3D geometry of the faults and associated interactions are poorly understood. Here, we use an integrated 3D seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern Horda Platform, northern North Sea. In particular we aim to: i) determine the range of styles of fault interaction that occur between non-colinear faults; ii) examine the typical geometries and throw patterns associated with each of these different styles; and iii) highlight the differences between single-phase and multiphase rift fault networks. Our study focuses on a ca. 350 km2 region around the >60 km long, N-S-striking Tusse Fault, a normal fault system that was active in the Permian-Triassic and again in the Late Jurassic-to-Early Cretaceous. The Tusse Fault is one of a series of large (>1500 m throw) N-S-striking faults forming part of the northern Horda Platform fault network, which includes numerous smaller (2-10 km long), lower throw (<100 m), predominantly NW-SE-striking faults that were only active during the Late Jurassic to Early Cretaceous. We examine how the 2nd-stage NW-SE-striking faults grew, interacted and linked with the N-S-striking Tusse Fault, documenting a range of interaction styles including mechanical and kinematic isolation, abutment, retardation and reactivated relays. Our results demonstrate that: i) isolated, non-interacting and abutting interactions are the most common fault interaction styles in the northern Horda Platform; ii) pre-existing faults can act as

Journal article

Lewis MM, Jackson CA, Gawthorpe RL, 2015,

Tectono-sedimentary development of early syn-rift deposits: the Abura Graben, Suez Rift, Egypt

, Basin Research

The thickness and distribution of early syn-rift deposits record the evolution of structures accommodating the earliest phases of continental extension. However, our understanding of the detailed tectono-sedimentary evolution of these deposits is poor, because in the subsurface, they are often deeply buried and below seismic resolution and sparsely sampled by borehole data. Furthermore, early syn-rift deposits are typically poorly exposed in the field, being buried beneath thick, late syn-rift and post-rift deposits. To improve our understanding of the tectono-sedimentary development of early syn-rift strata during the initial stages of rifting, we examined quasi-3D exposures in the Abura Graben, Suez Rift, Egypt. During the earliest stage of extension, forced folding above blind normal fault segments, rather than half-graben formation adjacent to surface-breaking faults, controlled rift physiography, accommodation development and the stratigraphic architecture of non-marine, early syn-rift deposits. Fluvial systems incised into underlying pre-rift deposits and were structurally focused in the axis of the embryonic depocentre, which, at this time, was characterized by a fold-bound syncline rather than a fault-bound half graben. During this earliest phase of extension, sediment was sourced from the rift shoulder some 3 km to the NE of the depocentre, rather than from the crests of the flanking, intra-basin extensional forced folds. Fault-driven subsidence, perhaps augmented by a eustatic sea-level rise, resulted in basin deepening and the deposition of a series of fluvial-dominated mouth bars, which, like the preceding fluvial systems, were structurally pinned within the axis of the growing depocentre, which was still bound by extensional forced folds rather than faults. The extensional forced folds were eventually locally breached by surface-breaking faults, resulting in the establishment of a half graben, basin deepening and the deposition of shallow marine sandsto

Journal article

Wilson P, Elliott GM, Gawthorpe RL, Jackson CA-L, Sharp IRet al., 2015,

Lateral variation in structural style along an evaporite-influenced rift fault system in the Halten Terrace, Norway: the influence of basement structure and evaporite facies

, Journal of Structural Geology, Vol: 79, Pages: 110-123, ISSN: 0191-8141

The Halten Terrace is underlain by a Triassic evaporitic package, resulting in vertically decoupled normal fault systems following subsequent extension. Four structural domains are identified along the eastern margin of the Halten Terrace, characterised by: i) thick-skinned normal faults affecting both sub-salt and supra-salt cover, ii) basement-restricted normal faults associated with fault-propagation folds, iii) thick-skinned, distributed normal faults, and iv) thick-skinned, localised normal faults. A fault domain boundary associated with an NE–SW striking basement fault corresponds to an abrupt change in style in the north of the Halten Terrace. Summed throw and estimated strain measurements show that throw and strain accommodated by the fault system increase southward, corresponding to a transition from distributed to localised faulting. The evaporite package is variable in thickness, but those variations do not correspond spatially to variations in structural style. Wells that penetrate the evaporite package, and volume attribute analysis of 3D seismic data, suggest variable evaporite facies. A change in seismic attributes from high-amplitude, low variance to low-amplitude, high variance corresponds to a change from decoupled to thick-skinned faulting. The sub-evaporite fault template, amount of strain accommodated across the fault system, and facies variations in the evaporite package are key influences on structural style.

Journal article

Shanks RP, Ascough PL, Dougans A, Gallacher P, Gulliver P, Rood DH, Xu S, Freeman SPHTet al., 2015,

Performance of the rebuilt SUERC single-stage accelerator mass spectrometer

, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, Vol: 361, Pages: 76-79, ISSN: 0168-583X

The SUERC bipolar single-stage accelerator mass spectrometer (SSAMS) has been dismantled and rebuilt to accommodate an additional rotatable pre-accelerator electrostatic spherical analyser (ESA) and a second ion source injector. This is for the attachment of an experimental positive-ion electron cyclotron resonance (ECR) ion source in addition to a Cs-sputter source. The ESA significantly suppresses oxygen interference to radiocarbon detection, and remaining measurement interference is now thought to be from 13C injected as 13CH molecule scattering off the plates of a second original pre-detector ESA.

Journal article

Vinogradov J, Jackson MD, 2015,

Zeta potential in intact natural sandstones at elevated temperatures

, Geophysical Research Letters, Vol: 42, Pages: 6287-6294, ISSN: 1944-8007

We report measurements of the zeta potential of natural sandstones saturated with NaCl electrolytes of varying ionic strengths at temperatures up to 150°C. The zeta potential is always negative but decreases in magnitude with increasing temperature at low ionic strength (0.01 M) and is independent of temperature at high ionic strength (0.5 M). The pH also decreases with increasing temperature at low ionic strength but remains constant at high ionic strength. The temperature dependence of the zeta potential can be explained by the temperature dependence of the pH. Our findings are consistent with published models of the zeta potential, so long as the temperature dependence of the pH at low ionic strength is accounted for and can explain the hitherto contradictory results reported in previous studies.

Journal article

Gold PO, Behr WM, Rood D, Sharp WD, Rockwell TK, Kendrick K, Salin Aet al., 2015,

Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California

, Journal of Geophysical Research. Solid Earth, Vol: 120, Pages: 5639-5663, ISSN: 2169-9313

Northwest directed slip from the southern San Andreas Fault is transferred to the Mission Creek, Banning, and Garnet Hill fault strands in the northwestern Coachella Valley. How slip is partitioned between these three faults is critical to southern California seismic hazard estimates but is poorly understood. In this paper, we report the first slip rate measured for the Banning fault strand. We constrain the depositional age of an alluvial fan offset 25 ± 5 m from its source by the Banning strand to between 5.1 ± 0.4 ka (95% confidence interval (CI)) and 6.4 + 3.7/−2.1 ka (95% CI) using U-series dating of pedogenic carbonate clast coatings and 10Be cosmogenic nuclide exposure dating of surface clasts. We calculate a Holocene geologic slip rate for the Banning strand of 3.9 + 2.3/−1.6 mm/yr (median, 95% CI) to 4.9 + 1.0/−0.9 mm/yr (median, 95% CI). This rate represents only 25–35% of the total slip accommodated by this section of the southern San Andreas Fault, suggesting a model in which slip is less concentrated on the Banning strand than previously thought. In rejecting the possibility that the Banning strand is the dominant structure, our results highlight an even greater need for slip rate and paleoseismic measurements along faults in the northwestern Coachella Valley in order to test the validity of current earthquake hazard models. In addition, our comparison of ages measured with U-series and 10Be exposure dating demonstrates the importance of using multiple geochronometers when estimating the depositional age of alluvial landforms.

Journal article

Civiero C, Hammond J, Goes S, Fishwick S, Ahmed A, Ayele A, Doubre C, Goitom B, Keir D, Kendall M, Leroy S, Ogubazghi G, Rumpker G, Stuart Get al., 2015,

Multiple mantle upwellings in the transition zone beneath the Northern East-African Rift System from relative P-wave travel-time tomography

, Geochemistry Geophysics Geosystems, Vol: 16, Pages: 2949-2968, ISSN: 1525-2027

Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated dataset allows us to image structures of ∼100 km length scale down to depths of 700-800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100±50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper-mantle upwellings.

Journal article

Dejong BD, Bierman PR, Newell WL, Rittenour TM, Mahan SA, Balco G, Rood DHet al., 2015,

Pleistocene relative sea levels in the Chesapeake Bay region and their implications for the next century

, GSA Today, Vol: 25, Pages: 4-10, ISSN: 1052-5173

Today, relative sea-level rise (3.4 mm/yr) is faster in the Chesapeake Bay region than any other location on the Atlantic coast of North America, and twice the global average eustatic rate (1.7 mm/yr). Dated interglacial deposits suggest that relative sea levels in the Chesapeake Bay region deviate from global trends over a range of timescales. Glacio-isostatic adjustment of the land surface from loading and unloading of continental ice is likely responsible for these deviations, but our understanding of the scale and timeframe over which isostatic response operates in this region remains incomplete because dated sea-level proxies are mostly limited to the Holocene and to deposits 80 ka or older. To better understand glacio-isostatic control over past and present relative sea level, we applied a suite of dating methods to the stratigraphy of the Blackwater National Wildlife Refuge, one of the most rapidly subsiding and lowest-elevation surfaces bordering Chesapeake Bay. Data indicate that the region was submerged at least for portions of marine isotope stage (MIS) 3 (ca. 60-30 ka), although multiple proxies suggest that global sea level was 40-80 m lower than present. Today MIS 3 deposits are above sea level because they were raised by the Last Glacial Maximum forebulge, but decay of that same forebulge is causing ongoing subsidence. These results suggest that glacio-isostasy controlled relative sea level in the mid-Atlantic region for tens of thousands of years following retreat of the Laurentide Ice Sheet and continues to influence relative sea level in the region. Thus, isostatically driven subsidence of the Chesapeake Bay region will continue for millennia, exacerbating the effects of global sea-level rise and impacting the region's large population centers and valuable coastal natural resources.

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Citations: 22

Conference paper

Muxworthy AR, Bland PA, Collins G, Moore Jet al., 2015,

MAGNETIC FABRICS IN ALLENDE: IMPLICATIONS FOR MAGNETIC REMANENCE ACQUISITION.

, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379

Conference paper

Forman LV, Bland PA, Timms NE, Daly L, Collins GS, Davison TM, Trimby PW, Ringer SPet al., 2015,

RECOVERING THE PRIMORDIAL IMPACT HISTORY OF CHONDRITES IN UNPRECEDENTED DETAIL USING MASSIVE EBSD DATASETS

, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379

Journal article

Bora SS, Scherbaum F, Kuehn N, Stafford P, Edwards Bet al., 2015,

Development of a Response Spectral Ground-Motion Prediction Equation (GMPE) for Seismic-Hazard Analysis from Empirical Fourier Spectral and Duration Models

, Bulletin of the Seismological Society of America, Vol: 105, Pages: 2192-2218, ISSN: 1943-3573

Empirical ground-motion prediction equations (GMPEs) require adjustmentto make them appropriate for site-specific scenarios. However, the process ofmaking such adjustments remains a challenge. This article presents a holistic frameworkfor the development of a response spectral GMPE that is easily adjustable todifferent seismological conditions and does not suffer from the practical problemsassociated with adjustments in the response spectral domain. The approach for developinga response spectral GMPE is unique, because it combines the predictions ofempirical models for the two model components that characterize the spectral andtemporal behavior of the ground motion. Essentially, as described in its initial formby Bora et al. (2014), the approach consists of an empirical model for the Fourieramplitude spectrum (FAS) and a model for the ground-motion duration. These twocomponents are combined within the random vibration theory framework to obtainpredictions of response spectral ordinates. In addition, FAS corresponding to individualacceleration records are extrapolated beyond the useable frequencies using thestochastic FAS model, obtained by inversion as described in Edwards and Fäh (2013a).To that end, a (oscillator) frequency-dependent duration model, consistent with theempirical FAS model, is also derived. This makes it possible to generate a responsespectral model that is easily adjustable to different sets of seismological parameters,such as the stress parameter Δσ, quality factor Q, and kappa κ0. The dataset used inBora et al. (2014), a subset of the RESORCE-2012 database, is considered for thepresent analysis. Based upon the range of the predictor variables in the selected dataset,the present response spectral GMPE should be considered applicable over the magnituderange of 4 ≤ Mw ≤ 7:6 at distances ≤200 km.

Conference paper

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2015,

Numerical investigation of the effect of the irregular nature of seismic loading on the liquefaction resistance of saturated sand deposits

, SECED 2015 Conference: Earthquake Risk and Engineering towards a Resilient World

Journal article

Colombero R, Kontoe S, Foti S, Potts DMet al., 2015,

Numerical modelling of drop load tests

, Soil Dynamics and Earthquake Engineering, Vol: 77, Pages: 279-289, ISSN: 1879-341X

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Detecting and monitoring small-scale discrete ground movements across London, using Persistent Scatterer InSAR (PSI)

MAGNETIC FABRICS IN ALLENDE: IMPLICATIONS FOR MAGNETIC REMANENCE ACQUISITION.

RECOVERING THE PRIMORDIAL IMPACT HISTORY OF CHONDRITES IN UNPRECEDENTED DETAIL USING MASSIVE EBSD DATASETS

Numerical investigation of the effect of the irregular nature of seismic loading on the liquefaction resistance of saturated sand deposits