Rotation of the Iberian arc: Palaeomagnetic results from North Spain

NRM directions measured from 32 sites in Middle Cambrian, Upper Silurian/Lower Devonian and Lower Carboniferous redbeds follow the trend of the Variscan arc in North Spain. Thermal demagnetisation does not significantly alter this pattern. Fold tests show that the NRM is earlier than the ?₁ folds which form the arc; consistency of angle between bedding and the tilt-corrected NRM inclination (22–28°), similarity of the corresponding palaeolatitudes to Carboniferous values and microscopic evidence of Variscan redistribution of hematite indicates that the magnetisation is post-Lower Carboniferous. A statistical plot of the orientation of ?₁ fold traces against angle between ?₁ fold traces and declination of NRM shows that where these folds curve through 165° the NRM has been rotated through 110°: the arc is an orocline. Restoration of this rotation, and that needed to close the Bay of Biscay, brings the calculated mean palaeomagnetic pole reasonably close to the Upper Carboniferous part of the apparent polar wander path for Europe.     

Sex offenders,housing and spatial restriction zones

Sex offenders are currently a major focus of crime control policies at the local, regional, state and federal levels throughout the United States. In part, the perceived threat of offender recidivism has motivated legislators to launch stringent community notification programs and to establish spatial restriction zones (SRZs) around schools, daycare facilities and public parks. The purpose of these restriction zones is to help protect children and minimize their exposure to convicted sex offenders living in the community. In addition to the concern that the implementation of SRZs dramatically reduces viable housing options for registered sex offenders, there are concerns that offenders will be forced to reside in socially disorganized areas that may encourage recidivism. The purpose of this paper is to explore the demographic and socioeconomic differences between areas inside and outside SRZs. Implications of these results for sex offender policies are discussed.

Sea stack formation and the role of abrasion on beach‐mantled headlands

Sea stacks are common and striking coastal landforms, but few details are known about how, how quickly, and under what conditions they form. We present numerical and analytical models of sea stack formation due to preferential erosion along a pre‐existing headland to address these basic questions. On sediment‐rich rocky coasts, as sea cliffs erode and retreat, they produce beach sediment that is distributed by alongshore sediment transport and controls future sea cliff retreat rates. Depending on their width, beaches can encourage or discourage sea cliff erosion by acting either as an abrasive tool or a protective cover that dissipates wave energy seaward of the cliff. Along the flanks of rocky headlands where pocket beaches are often curved and narrow due to wave field variability, abrasion can accelerate alongshore‐directed sea cliff erosion. Eventually, abrasion‐induced preferential erosion can cut a channel through a headland, separating it from the mainland to become a sea stack. Under a symmetrical wave climate (i.e. equal influence of waves approaching the coastline from the right and from the left), numerical and analytical model results suggest that sea stack formation time and plan‐view size are proportional to preferential erosion intensity (caused by, for example, abrasion and/or local rock weakness from joints, faults, or fractures) and initial headland aspect ratio, and that sea stack formation is discouraged when the sediment input from sea cliff retreat is too high (i.e. sea cliffs retreat quickly or are sand‐rich). When initial headland aspect ratio is too small, and the headland is ‘rounded’ (much wider in the alongshore direction at its base than at its seaward apex), the headland is less conducive to sea stack formation. On top of these geomorphic and morphologic controls, a highly asymmetrical wave climate decreases sea stack size and discourages stack formation through rock–sediment interactions. Copyright © 2014 John Wiley & Sons, Ltd.     

Evidence for ice flow prior to trough formation in the martian north polar layered deposits

The relative importance of surface mass fluxes and ice flow in shaping the north polar layered deposits (NPLD), now or in the past, remains a fundamental and open question. Motivated by observation of an apparent ice divide on Gemina Lingula (also known as Titania Lobe), we propose a two-stage evolution leading to the present-day topography on that lobe of the NPLD. Ice flow approximately balances surface mass fluxes in the first stage, but in the second stage ice flow has minimal influence and topography is modified predominantly by the formation of troughs. We focus here on evidence for the first stage, by testing the fit of topography between troughs to an ice-flow model. We find that independent model fits on distinct flow paths closely match inter-trough topography, uniformly over a broad region on Gemina Lingula, with mutually consistent and physically reasonable fitting parameters. However, our model requires ice to occupy and flow in spaces where troughs currently incise the ice. We therefore infer that the troughs (and the distribution of mass balance that caused them) post-date deposition of the inter-trough material and its modification by flow. Because trough formation has apparently altered inter-trough topography very little, we infer that trough formation must have been rapid in comparison to the (still unknown) time-scale of flow since troughs began to form. We view the evidence for past flow as strong, but we do not think that topographic evidence alone can be conclusive. Observations of englacial stratigraphy using orbital sounding radars will yield conclusive tests of our inferred mechanism for the formation of inter-trough topography.     

Near‐collapse response of existing RC building under severe pulse‐type ground motion using hybrid simulation

Column shear‐axial failure is a complex response, which lends itself to physical experimentation. Reinforced concrete structures built prior to the mid‐1970s are particularly susceptible to such failure. Shear‐axial column failure has been examined and studied at the element level, but current rehabilitation practice equates such a column failure with structural collapse, neglecting the collapse resistance of the full structural system following column failure. This system‐level response can prevent a column failure from leading to progressive collapse of the entire structure. In this study, a hybrid simulation was conducted on a representative pre‐1970s reinforced concrete frame structure under severe seismic ground motion, in which three full‐scale reinforced concrete columns were tested at the University of Illinois at Urbana Champaign. The analytical portion of the model was represented in the computer program OpenSees. Failure occurred in multiple physical specimens as a result of the ground motion, and the hybrid nature of the test allowed for observation of the system‐level response of the tested columns and the remaining structural system. The behavior of the system accounting for multiple column shear‐axial failure is discussed and characterized. Copyright © 2016 John Wiley & Sons, Ltd.     

Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin

The recent boom in shale gas development in the Marcellus Shale has increased interest in the methods to distinguish between naturally occurring methane in groundwater and stray methane associated with drilling and production operations. This study evaluates the relationship between natural methane occurrence and three principal environmental factors (groundwater redox state, water type, and topography) using two pre‐drill datasets of 132 samples from western Pennsylvania, Ohio, and West Virginia and 1417 samples from northeastern Pennsylvania. Higher natural methane concentrations in residential wells are strongly associated with reducing conditions characterized by low nitrate and low sulfate ([NO₃^?] < 0.5 mg/L; [SO₄^2?] < 2.5 mg/L). However, no significant relationship exists between methane and iron [Fe(II)], which is traditionally considered an indicator of conditions that have progressed through iron reduction. As shown in previous studies, water type is significantly correlated with natural methane concentrations, where sodium (Na) ‐rich waters exhibit significantly higher (p<0.001) natural methane concentrations than calcium (Ca)‐rich waters. For water wells exhibiting Na‐rich waters and/or low nitrate and low sulfate conditions, valley locations are associated with higher methane concentrations than upland topography. Consequently, we identify three factors (“Low NO₃^? & SO₄^2?” redox condition, Na‐rich water type, and valley location), which, in combination, offer strong predictive power regarding the natural occurrence of high methane concentrations. Samples exhibiting these three factors have a median methane concentration of 10,000 µg/L. These heuristic relationships may facilitate the design of pre‐drill monitoring programs and the subsequent evaluation of post‐drill monitoring results to help distinguish between naturally occurring methane and methane originating from anthropogenic sources or migration pathways.     

The use of selected genotoxicity assays in green-lipped mussels (Perna viridis): a validation study in Hong Kong coastal waters

In Hong Kong, discharges of domestic and industrial wastewaters and disposal of contaminated muds into coastal waters have resulted in high levels of persistent organic contaminants in the water column, biota and bottom sediments. Although the acute toxicity of effluents has been tested by government regulators using mortality-based bioassays, the sublethal effects of many of the pollutants, including environmental carcinogens, have not been well studied. The objective of the present work was to examine the efficiency and efficacy of using: (1) DNA strand breaks (comet assay and alkaline agarose gel electrophoresis assay); (2) oxidative DNA damage (levels of 8-hydroxy-2-deoxyguanosine in cellular DNA) and (3) micronuclei (MN) formation as early warning toxicological indicators of potential environmental carcinogen exposure. Green-lipped mussels (Perna viridis) were transplanted to study sites and retrieved after 4, 8, 12, 16 and 30 days. The bioaccumulation of organic pollutants, including the polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OC pesticides) and polychlorinated biphenyls (PCBs) was observed, and compared with biomarker assays. Some significant dose- and time-dependent inductions of the genotoxic biomarkers, including 8-OHdG, DNA strand breaks and micronuclei were observed. In particular, several very strong (r>0.9) and significantly positive relationships were found at all sites during days 0-12. In addition, significant strong relationships between certain organic contaminants (carcinogenic PAHs and 4 common OC pesticides) and micronuclei were detected at the polluted sites, Tsim Sha Tsui and Sai Wan Ho. The results suggest that the use of micronuclei as a biomarker is potentially effective, especially at the more polluted sites. Nonetheless, further research is required to validate their effectiveness under varying field conditions, especially to elucidate responses under lower contaminant loads, interactions between the environmental and physiological factors affecting organisms in differing coastal environments, and changes in biotransformation and DNA repair enzymes in test organisms.