Constraint on foreland basin migration in the Zagros mountain belt using Sr isotope stratigraphy

We have constrained the time‐space migration of the Zagros foredeep basin by performing Sr isotope stratigraphy on 31 samples of marine macrofossils from Neogene sediments now exposed in the Zagros mountain belt in southwest Iran. Our results show that these deposits (represented mainly by the Mishan Formation) are strongly diachronous, with ages ranging between 17.2 ± 0.2 and 1.1 ± 0.1 Ma. These deposits are older in the west (Dezful region) and become progressively younger towards the south and the south‐east (Fars region). Our results show that the marine foredeep was replaced by a fluvial sedimentary environment between ca. 14 and 12 Ma in the western sector, while this occurred between ca. 8 and 1 Ma in the eastern sector, becoming younger towards the south. These results enable us to show that the foreland basin migrated perpendicular to the orogen at rates of between 17.5 and 50 mm year^?1 throughout the Neogene, exceeding migration rates in the Alps, Pyrenees, Apennines and Himalayan foreland basins. The sporadically elevated rates in the Zagros appear to be related to times when major widely spaced pre‐existing basement faults became reactivated. Finally, our results, when combined with published data, have enabled us to establish a new chronostratigraphic diagram for the Neogene portion of the Zagros foreland basin. Our study highlights that foreland basins are extremely dynamic settings where depocentres and palaeoenvironments may change rapidly in both time and space in relation to migrating deformation.     

Radio imaging of the Subaru/XMM–Newton Deep Field – I. The 100-μJy catalogue, optical identifications, and the nature of the faint radio source population

We describe deep radio imaging at 1.4 GHz of the 1.3-deg² Subaru/ XMM–Newton Deep Field (SXDF), made with the Very Large Array in B and C configurations. We present a radio map of the entire field, and a catalogue of 505 sources covering 0.8 deg² to a peak flux density limit of 100 μJy. Robust optical identifications are provided for 90 per cent of the sources, and suggested identifications are presented for all but 14 (of which seven are optically blank, and seven are close to bright contaminating objects). We show that the optical properties of the radio sources do not change with flux density, suggesting that active galactic nuclei (AGN) continue to contribute significantly at faint flux densities. We test this assertion by cross-correlating our radio catalogue with the X-ray source catalogue and conclude that radio-quiet AGN become a significant population at flux densities below 300 μJy, and may dominate the population responsible for the flattening of the radio source counts if a significant fraction of them are Compton-thick.     

A population of high-redshift type 2 quasars – I. Selection criteria and optical spectra

We discuss the relative merits of mid-infrared and X-ray selection of type 2 quasars. We describe the mid-infrared, near-infrared and radio selection criteria used to find a population of redshift   z ∼ 2  type 2 quasars which we previously argued suggests that most supermassive black hole growth in the Universe is obscured. We present the optical spectra obtained from the William Herschel Telescope, and we compare the narrow emission-line luminosity, radio luminosity and maximum size of jets to those of objects from radio-selected samples. This analysis suggests that these are genuine radio-quiet type 2 quasars, albeit the radio-bright end of this population. We also discuss the possibility of two different types of quasar obscuration, which could explain how the ∼2–3:1 ratio of type 2 to type 1 quasars preferred by modelling our population can be reconciled with the ∼1:1 ratio predicted by unified schemes.     

Geological note: New field evidence resolving the relationship between the Grampians group and the Rocklands Rhyolite,western Victoria

The Rocklands Rhyolite is a latest Silurian to Early Devonian sequence of silicic ignimbrite, lava, volcanic sedimentary rocks and dykes in western Victoria. These volcanic rocks lie west of the Grampians Ranges, which consist of a thick succession of quartz sandstone of presumed Silurian age called the Grampians Group. The previously unresolved stratigraphic relationship between these two sequences of rocks is clarified by an exposed contact between steeply dipping Grampians Group cut by quartz veins, and overlying undeformed rhyolite. The implications of this relationship are that the Grampians Group is older than the Rocklands Rhyolite and that parts of the sandstone succession were locally deformed prior to volcanism. Furthermore, other outlying areas of sandstone and rhyolite, previously correlated with the Grampians Group and Rocklands Rhyolite, respectively, display different timing relationships and are proposed to be significantly younger.     

Estimates of twenty-first century sea-level changes for Norway

In this work we establish a framework for estimating future regional sea-level changes for Norway. Following recently published works, we consider how different physical processes drive non-uniform sea-level changes by accounting for spatial variations in (1) ocean density and circulation (2) ice and ocean mass changes and associated gravitational effects on sea level and (3) vertical land motion arising from past surface loading change and associated gravitational effects on sea level. An important component of past and present sea-level change in Norway is glacial isostatic adjustment. Central to our study, therefore, is a reassessment of vertical land motion using a far larger set of new observations from a permanent GNSS network. Our twenty-first century sea-level estimates are split into two parts. Firstly, we show regional projections largely based on findings from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4) and dependent on the emission scenarios A2, A1B and B1. These indicate that twenty-first century relative sea-level changes in Norway will vary between ?0.2 to 0.3 m (1-sigma ± 0.13 m). Secondly, we explore a high-end scenario, in which a global atmospheric temperature rise of up to 6 °C and emerging collapse for some areas of the Antarctic ice sheets are assumed. Using this approach twenty-first century relative sea-level changes in Norway are found to vary between 0.25 and 0.85 m (min/max ± 0.45 m). We attach no likelihood to any of our projections owing to the lack of understanding of some of the processes that cause sea-level change.     

A continuous velocity field for Norway

In Norway, as in the rest of Fennoscandia, the process of Glacial Isostatic Adjustment causes ongoing crustal deformation. The vertical and horizontal movements of the Earth can be measured to a high degree of precision using GNSS. The Norwegian GNSS network has gradually been established since the early 1990s and today contains approximately 140 stations. The stations are established both for navigation purposes and for studies of geophysical processes. Only a few of these stations have been analyzed previously. We present new velocity estimates for the Norwegian GNSS network using the processing package GAMIT. We examine the relation between time-series length and precision. With approximately 3.5 years of data, we are able to reproduce the secular vertical rate with a precision of 0.5 mm/year. To establish a continuous crustal velocity field in areas where we have no GNSS receivers or the observation period is too short to obtain reliable results, either interpolation or modeling is required. We experiment with both approaches in this analysis by using (i) a statistical interpolation method called Kriging and (ii) a GIA forward model. In addition, we examine how our vertical velocity field solution is affected by the inclusion of data from repeated leveling. Results from our geophysical model give better estimates on the edge of the network, but inside the network the statistical interpolation method performs better. In general, we find that if we have less than 3.5 years of data for a GNSS station, the interpolated value is better than the velocity estimate based on a single time-series.     

A regional real-time debris-flow warning system for the District of North Vancouver, Canada

Engineered (structural) debris-flow mitigation for all creeks with elements at risk and subject to debris flows is often outside of the financial capability of the regulating government, and heavy task-specific taxation may be politically undesirable. Structural debris-flow mitigation may only be achieved over long (decadal scale) time periods. Where immediate structural mitigation is cost-prohibitive, an interim solution can be identified to manage residual risk. This can be achieved by implementing a debris-flow warning system that enables residents to reduce their personal risk for loss of life through timely evacuation. This paper describes Canada??s first real-time debris-flow warning system which has been operated for 2 years for the District of North Vancouver. The system was developed based on discriminant function analyses of 20 hydrometric input variables consisting of antecedent rainfall and storm rainfall intensities for a total of 63 storms. Of these 27 resulted in shallow landslides and subsequent debris flows, while 36 storms were sampled that did not reportedly result in debris flows. The discriminant function analysis identified as the three most significant variables: the 4-week antecedent rainfall, the 2-day antecedent rainfall, and the 48-h rainfall intensity during the landslide-triggering storm. Discriminant functions were developed and tested for robustness against a nearby rain gauge dataset. The resulting classification functions provide a measure for the likelihood of debris-flow initiation. Several system complexities were added to render the classification functions into a usable and defensible warning system. This involved the addition of various functionality criteria such as not skipping warning levels, providing sufficient warning time before debris flows would occur, and hourly adjustment of actual rainfall vs. predicted rainfall since predicted rainfall is not error-free. After numerous iterations that involved warning threshold and cancelation refinements and further model calibrations, an optimal solution was found that best matches the actual debris-flow data record. Back-calculation of the model??s 21-year record confirmed that 76% of all debris flows would have occurred during warning or severe warning levels. Adding the past 2 years of system operation, this percentage increases marginally to 77%. With respect to the District of North Vancouver boundaries, all debris flows occur during Warning and Severe Warnings emphasizing the validity of the system to the area for which it was intended. To operate the system, real-time rainfall data are obtained from a rain gauge in the District of North Vancouver. Antecedent rainfall is automatically calculated as a sliding time window for the 4-week and 2-day periods every hour. The predicted 48-h storm rainfall data are provided by the Geophysical Disaster Computational Fluid Dynamics Centre at the Earth and Ocean Science Department at the University of British Columbia and is updated every hour as rainfall is recorded during a given storm. The warning system differentiates five different stages: no watch, watch level 1 (the warning level is unlikely to be reached), watch level 2 (the warning level is likely to be reached), warning, and severe warning. The debris-flow warning system has operated from October 1, 2009 to April 30, 2010 and October 1, 2010 and April 30, 2011. Fortunately, we were able to evaluate model performance because the exact times of debris flows during November 2009 and January 2010 were recorded. In both cases, the debris flows did not only occur during the warning level but coincided with peaks in the warning graphs. Furthermore, four debris flows occurred during a warning period in November 2009 in the Metro Vancouver watershed though their exact time of day is unknown. The warning level was reached 13 times, and in four of these cases, debris flows were recorded in the study area. One debris flow was recorded during watch II level. There was no severe warning during the 2 years of operation. The current warning level during the wet season (October to April) is accessible via District of North Vancouver??s homepage (www.dnv.org) and by automated telephone message during the rainy season.     

Non-integrability of the dumbbell and point mass problem

This paper discusses a constrained gravitational three-body problem with two of the point masses separated by a massless inflexible rod to form a dumbbell. This problem is a simplification of a problem of a symmetric rigid body and a point mass, and has numerous applications in Celestial Mechanics and Astrodynamics. The non-integrability of this system is proven. This was achieved thanks to an analysis of variational equations along a certain particular solution and an investigation of their differential Galois group. Nowadays this approach is the most effective tool for study integrability of Hamiltonian and non-Hamiltonian systems.