Seismic plastic deformation in the free-field

An analytical solution for the free-field seismic elastoplastic deformation of granular dry soil is developed. This solution is possible since the stress field solution from pseudostatic analysis is known at any acceleration level. A plastic potential function with two plastic material parameters is suggested to model the soil. This model can describe both the volume dilation and contraction of soil under shearing. Closed-form deformation solutions are derived for two special cases and the results from a numerical evaluation of the solution are compared with those measured from shaking table tests. From the deformation solution the shape of the horizontal plastic displacement distribution with depth is identical to that for the elastic deformation since both depend only on the distribution of the elastic shear modulus. Copyright © 1999 John Wiley & Sons, Ltd.     

The influence of basement faults on local extension directions: Insights from potential field geophysics and field observations

Complex arrays of faults in extensional basins are potentially influenced by pre‐existing zones of weakness in the underlying basement, such as faults, shear zones, foliation, and terrane boundaries. Separating the influence of such basement heterogeneities from far‐field tectonics proves to be challenging, especially when the timing and character of deformation cannot be interpreted from seismic reflection data. Here we aim to determine the influence of basement heterogeneities on fault patterns in overlying cover rocks using interpretations of potential field geophysical data and outcrop‐scale observations. We mapped >1 km to meter scale fractures in the western onshore Gippsland Basin of southeast Australia and its underlying basement. Overprinting relationships between fractures and mafic intrusions are used to determine the sequence of faulting and reactivation, beginning with initial Early Cretaceous rifting. Our interpretations are constrained by a new Early Cretaceous U‐Pb zircon isotope dilution thermal ionization mass spectrometry age (116.04 ± 0.15 Ma) for an outcropping subvertical, NNW‐SSE striking dolerite dike hosted in Lower Cretaceous Strzelecki Group sandstone. NW‐SE to NNW‐SSE striking dikes may have signaled the onset of Early Cretaceous rifting along the East Gondwana margin at ca. 105–100 Ma. Our results show that rift faults can be oblique to their expected orientation when pre‐existing basement heterogeneities are present, and they are orthogonal to the extension direction where basement structures are less influential or absent. NE‐SW to ENE‐WSW trending Early Cretaceous rift‐related normal faults traced on unmanned aerial vehicle orthophotos and digital aerial images of outcrops are strongly oblique to the inferred Early Cretaceous N‐S to NNE‐SSW regional extension direction. However, previously mapped rift‐related faults in the offshore Gippsland Basin (to the east of the study area) trend E‐W to WNW‐ESE, consistent with the inferred regional extension direction. This discrepancy is attributed to the influence of NNE‐SSW trending basement faults underneath the onshore part of the basin, which caused local re‐orientation of the Early Cretaceous far‐field stress above the basement during rifting. Two possible mechanisms for inheritance are discussed—reactivation of pre‐existing basement faults or local re‐orientation of extension vectors. Multiple stages of extension with rotated extension vectors are not required to achieve non‐parallel fault sets observed at the rift basin scale. Our findings demonstrate the importance of (1) using integrated, multi‐scale datasets to map faults and (2) mapping basement geology when investigating the structural evolution of an overlying sedimentary basin.     

Contrasting Pliocene fluvial depositional systems within the rapidly subsiding South Caspian Basin; a case study of the palaeo-Volga and palaeo-Kura river systems in the Surakhany Suite,Upper Productive Series,onshore Azerbaijan

The South Caspian Basin contains major hydrocarbon reservoirs within the largely Early Pliocene Productive Series. This paper describes and contrasts outcrops of the uppermost ∼500 m of the series (the Surakhany Suite) deposited by two of the main fluvial systems that supplied the Azeri margin of the basin. Sedimentary facies and, for the first time from the Productive Series, palynological analyses document fluvial channel belt complexes, sheetflood overbank and flood plain to flood plain lake environments. The Productive Series on the Apsheron Peninsula, Azerbaijan, was supplied predominantly from the north by the palaeo-Volga river system. It displays an overall fining-upward trend, such that the Surakhany Suite at Lokbatan is dominated by mudstone. Siltstone and coarser-grained sediments make up 28% of the section. Channel bodies are on average 1.5 m thick and form 13% of the succession. In the sub-surface of the Apsheron Peninsula, ratty wireline log responses also indicate that siltstone and sandstone bodies are predominantly thin bedded, with SP-derived net-to-gross sand ratios of ∼0.35–0.40. The succession in the Kura Basin was sourced predominantly from the west by the palaeo-Kura river system. It displays a coarsening-upward trend, such that in the middle and upper Surakhany Suite at Babazanan siltstone and coarser sediments make up 52% of the section. It is characterised by numerous stacked and laterally continuous channel sandstone bodies that are on average 5.8 m thick and comprise 42% of the outcrop. In the sub-surface of the Kura Basin, wireline log responses of the Surakhany Suite have a blocky character and indicate SP-derived net-to-gross sand ratios of 0.26–0.38. These values are similar to calculated sandstone volumes at outcrop (44%). The palynological data, including multivariate analyses, show that the main controls on palynomorph distribution are the degree of fluvial or lacustrine influence, subaerial exposure and salinity. Despite their more lithic nature, Surakhany Suite sandstones derived from the palaeo-Kura river system along the Kurovdag-Babazanan-Neftchala trend have similar or better petrophysical properties than those derived from the palaeo-Volga river on the Apsheron Peninsula and its offshore continuation. This is probably due to their coarser-grain size. This, combined with their greater sandstone body thickness, would suggest that the axis of the Kura Basin forms the most promising part of the Azeri sector of the South Caspian Basin for exploration within the uppermost part of the Productive Series.     

Managed realignment as compensation for the loss of intertidal mudflat: A short term solution to a long term problem?

Intertidal mudflats are critical to the functional ecology of estuaries yet large areas are being lost as a result of land claim, erosion and coastal squeeze. This study examines whether managed realignment (at Paull Holme Strays, Humber estuary) can realistically achieve compensation for the loss of intertidal mudflat in the long term. Typical estuarine species quickly colonised the site with the total number of species recorded from the site as a whole being almost equal to that in the reference area within one year. Comparable biomass between the two areas was achieved after 2 years. However, organism abundance remains an order of magnitude lower within the realignment site compared to outside. Community structure within the realignment has changed from one characterised by terrestrial/freshwater organisms and early colonising species to one composed of typically estuarine species. However, the developing benthic communities only represent those typical of the estuary in areas of low elevation and high inundation frequency. Rapid accretion has favoured saltmarsh colonisation in much of the realignment site and this is expected to increase as accretion proceeds with invertebrate colonisation being inhibited by increasing elevation. Hence, realignment to restore intertidal mudflats can only be a short term solution in sites of high tidal elevation and in a dynamic and turbid estuary with high natural accretion rates, such as the Humber.     

Contemporary initiatives on the future of the International Whaling Commission

In his term as Chairman of the International Whaling Commission between 2006 and 2009, Dr BillHogarth championed a process for finding a way forward for the IWC. In parallel with, and in places intertwined with the Hogarth Initiative, a number of other initiatives attempting to move the IWC forward have been proposed by a range of stakeholders; both governments and NGOs. This paper traces the more important suggestions, commenting on their likelihood of success.     

Mitigating systematic error in topographic models for geomorphic change detection: accuracy,precision and considerations beyond off-nadir imagery

Unmanned aerial vehicles (UAVs) and structure-from-motion photogrammetry enable detailed quantification of geomorphic change. However, rigorous precision-based change detection can be compromised by survey accuracy problems producing systematic topographic error (e.g. ‘doming’), with error magnitudes greatly exceeding precision estimates. Here, we assess survey sensitivity to systematic error, directly correcting topographic data so that error magnitudes align more closely with precision estimates. By simulating conventional grid-style photogrammetric aerial surveys, we quantify the underlying relationships between survey accuracy, camera model parameters, camera inclination, tie point matching precision and topographic relief, and demonstrate a relative insensitivity to image overlap. We show that a current doming-mitigation strategy of using a gently inclined (<15°) camera can reduce accuracy by promoting a previously unconsidered correlation between decentring camera lens distortion parameters and the radial terms known to be responsible for systematic topographic error. This issue is particularly relevant for the wide-angle cameras often integrated into current-generation, accessible UAV systems, frequently used in geomorphic research. Such systems usually perform on-board image pre-processing, including applying generic lens distortion corrections, that subsequently alter parameter interrelationships in photogrammetric processing (e.g. partially correcting radial distortion, which increases the relative importance of decentring distortion in output images). Surveys from two proglacial forefields (Arolla region, Switzerland) showed that results from lower-relief topography with a 10°-inclined camera developed vertical systematic doming errors > 0·3 m, representing accuracy issues an order of magnitude greater than precision-based error estimates. For higher-relief topography, and for nadir-imaging surveys of the lower-relief topography, systematic error was < 0·09 m. Modelling and subtracting the systematic error directly from the topographic data successfully reduced error magnitudes to values consistent with twice the estimated precision. Thus, topographic correction can provide a more robust approach to uncertainty-based detection of event-scale geomorphic change than designing surveys with small off-nadir camera inclinations and, furthermore, can substantially reduce ground control requirements. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Morphologic adjustments of actively evolving highly curved neck cutoffs

Neck cutoffs and their resultant oxbow lakes are important and prominent features of riverine landscapes. Detailed field-based research focusing on the morphologic evolution of neck cutoffs is currently insufficient to fully characterize cutoff evolution. High-resolution bathymetric data were collected over 3 years for the purpose of determining channel morphology and morphologic change on three actively evolving neck cutoffs. Results indicate the following general trends in morphologic adjustment: (1) a longitudinal bar in the upstream meander limb that develops near the entrance to the abandoned bend; (2) a deep scour hole in the downstream meander limb immediately downstream of the cutoff channel; (3) erosion of the bank opposite the cutoff in the downstream meander limb; (4) a cutoff bar in the downstream meander limb at the junction corner of the cutoff channel and the downstream meander limb; and (5) perching of the exit of the abandoned bend above the cutoff channel due to channel bed incision. The results presented herein were used to develop a conceptual model that depicts the morphologic evolution of highly curving neck cutoffs. The findings of this research are combined with recent analyses of the three-dimensional flow structure through neck cutoffs to provide a mechanistic explanation for the morphodynamics of neck cutoffs. © 2019 John Wiley & Sons, Ltd.     

Fear of crime: testing alternative hypotheses

This paper examines the spatial and social distribution of the fear of crime and the relationships of such fear with aspects of the environment. Through an analysis of a questionnaire survey conducted in a variety of areas in Stoke-on-Trent in the English Midlands, it considers both the causes of the fear of crime and the associations that have been identified with other dimensions shaping vulnerability. It concludes by offering some guidance on how to address the differences between those populations who fear crime most and those who are most vulnerable.