Drainage diversions as evidence of propagating active faults: example of the El Asnam and Thenia faults, Algeria

Digital elevation models and aerial photographs provide evidence of past drainage diversions associated with known and inferred active faults in Northern Algeria. The El Asnam anticline is a fault-bend fold that is growing in response to displacement on the historically active El Asnam fault. The diversion of the Fodda River and a sequence of uplifted palaeovalleys across the anticline formed in response to the active southwestward propagation of the Sidi Ada–El Ardja segment of the El Asnam anticline. Deformation associated with the 1980 El Asnam earthquake (Ms 7.3) and its effect on drainage demonstrate the occurrence of coseismic uplift of the El Asnam anticline associated with slip on the underlying thrust fault. Similar geomorphic relations are observed between the Isser River and the Thenia fault. Diversions of the Isser River and evidence for Quaternary uplift indicate that the Thenia fault, which is close to Algiers, is tectonically active and should be considered to be a source of potentially damaging earthquakes.     

Residential mobility trajectories and integration in Douala and Bafoussam,Cameroon

Abstract

This study examines how migrant households relocate their homes in two Cameroonian cities over the course of lifetimes or even generations. The central claim is that homeownership is the ultimate sign of integration into city life. Using qualitative and quantitative research methods (218 interviews, 30 focus groups and a household survey, sample size 686), the study argues that three key factors explain why people move: the quality of housing they can affords, the proximity to a workplace and the potential for homeownership. Three residential model trajectories are identified. The first describes a journey from being a new migrant who is a guest of family or friends in the city centre to being a married family with kids owning a home in the urban periphery. The second model continues that journey by returning back to the city centre in pursuit of more convenient, high-status home location (if finances permit). A third model describes moves to sites all over the city later in life as older individuals seek to maximize family income in the way they use multiple properties. Understanding residential mobility patterns has the potential to lead to a better public policies and more effective private investments in the housing sector.     

Visualizing the temporal development of thermo-radiative features on ground-based thermographs

In urban microclimate research, ground-based thermography is used to gain insight into the spatial distribution of surface temperatures of various materials. Taking snapshots over a certain time span helps experts to observe the temporal thermo-radiative behavior of the monitored surface elements and therefore supports decisions on possible optimizations, e.g., improving the thermal comfort in a neighborhood. Appropriate visualization techniques facilitate decision-making and are thus crucial in the optimization process. In this study, we present a tool that eases the extraction of thermo-radiative features from multi-temporal thermographs taken from a monitored scene. Assisted by our tool, users can identify, choose, and register thermo-radiative features for each time step according to their individual research needs. The features’ temporal development is then visualized using a directed graph that encodes topological events as well as each feature’s size and summarizing statistics. To enhance this summary, a comprehensive animated sequence emphasizes the spatiotemporal behavior of the most significant thermo-radiative features. Salient developments are visually embedded and highlighted in the original infrared images, which are blended in an animation from time step to time step. Since we enable the user to interact with the data in a flexible way, noisy and low resolution image data sets can also be processed.     

Noble gases as proxies of mean ocean temperature: sensitivity studies using a climate model of reduced complexity

Past global mean ocean temperature may be reconstructed from measurements of atmospheric noble gas concentrations in ice core bubbles. Assuming conservation of noble gases in the atmosphere-ocean system, the total concentration within the ocean mostly depends on solubility which itself is temperature dependent. Therefore, the colder the ocean, the more gas can be dissolved and the less remains in the atmosphere. Here, the characteristics of this novel paleoclimatic proxy are explored by implementing krypton, xenon, argon, and N₂ into a reduced-complexity climate model. The relationship between noble gas concentrations and global mean ocean temperature is investigated and their sensitivities to changes in ocean volume, ocean salinity, sea-level pressure and geothermal heat flux are quantified. We conclude that atmospheric noble gas concentrations are suitable proxies of global mean ocean temperature. Changes in ocean volume need to be considered when reconstructing ocean temperatures from noble gases. Calibration curves are provided to translate ice-core measurements of krypton, xenon, and argon into a global mean ocean temperature change. Simulated noble gas-to-nitrogen ratios for the last glacial maximum are δKr_atm = ?1.10‰, δXe_atm = ?3.25‰, and δAr_atm = ?0.29‰. The uncertainty of the krypton calibration curve due to uncertainties of the ocean saturation concentrations is estimated to be ±0.3 °C. An additional ±0.3 °C uncertainty must be added for the last deglaciation and up to ±0.4 °C for earlier transitions due to age-scale uncertainties in the sea-level reconstructions. Finally, the fingerprint of idealized Dansgaard-Oeschger events in the atmospheric krypton-to-nitrogen ratio is presented. A δKr_atm change of up to 0.34‰ is simulated for a 2 kyr Dansgaard-Oeschger event, and a change of up to 0.48‰ is simulated for a 4 kyr event.     

A reappraisal of the 1950 (Mw 6.9) Mondy earthquake, Siberia, and its relationship to the strain pattern at the south-western end of the Baikal rift zone

ABSTRACT The precise nature of the transition between the present-day compressional tectonics in central Mongolia and extensional deformation in the central Baikal rift has still to be determined. For that purpose we have built a comprehensive earthquake focal mechanism data base for the Mongolia – southern Siberia area, from which we map the variations of the stress field. We focus our detailed investigations on the largest seismic event in the transition zone, the 1950 (Mw 6.9) Mondy earthquake, for which several discordant focal mechanisms have been proposed. Using a new approach in source inversion, we resolve the focal mechanism (left-lateral strike slip type on a steep south-dipping fault) and depth (14 ± 3 km) of the Mondy earthquake with a satisfactory accuracy. This seismological information, combined with the geological observations, allows us to decipher the connections between the 1950 mainshock, the local stress tensor and the active faults, which strongly suggest a partitioning of the deformation between two faults, namely the Mondy and Ikhe–Ukghun faults.     

Near-IR spectral evolution of dusty starburst galaxies

We propose a multicomponent analysis of starburst galaxies, based on a model that takes into account the young and evolved stellar components and the gas emission, with their respective extinction, in the frame of a coherent dust distribution pattern. Near-IR signatures are preferentially investigated, in order to penetrate as deep as possible into the dusty starburst cores. We computed the 1.4-2.5 μm spectra of synthetic stellar populations evolving through strong, short timescale bursts of star formation (continuum and lines, R ? 500). The evolution model is specifically sensitive to cool stellar populations (AGB and red supergiant stars). It takes advantage of the stellar library of Lançon & Rocca-Volmerange (1992) [A&ASS, 96, 593], observed with the same instrument (FTS/CFHT) as the analysed galaxy sample, so that the instrumental effects are minimised. The main near-IR observable constraints are the molecular signatures of CO and H₂O and the slope of the continuum, observed over a range exceptionally broad for spectroscopic data. The H - K colour determined from the spectra measures the intrinsic stellar energy distribution but also differential extinction, which is further constrained by optical emission line ratios. Other observational constraints are the near-IR emission lines (Brγ, He I 2.06 μm, [Fe II] 1.64 μm, H₂ 2.12 μm) and the far-IR luminosity. The coherence of the results relies on the interpretation in terms of stellar populations from which all observable properties are derived, so that the link between the various wavelength ranges is secured. The luminosity L_K is used for the absolute calibration.We apply this approach to the typical spectrum of the core of NGC 1614. Consistent solutions for the starburst characteristics (star-formation rate, IMF, burst age, morphology) are found and the role of each observational constraint in deriving satisfactory models is extensively discussed. The acceptable contamination of the K band light by the underlying population amounts ≥ 15% even through a 5 arcsec aperture. The model leads to a limit on the direct absorption of Lyman continuum photons by dust situated inside the ionised areas, which in turn, with standard gas-to-dust ratios, translates into small characteristic sizes for the individual coexisting H II regions of the massive starburst area (clusters containing ∼ 10² ionising stars). We show that room is left for IMFs extending to 120 M_⊙, rather than truncated at ∼ 60 M_⊙ as most conservative studies conclude. High internal velocity dispersions (≥ 20 km s⁻¹) are then needed for the H II regions. An original feature of this work is to base the analysis of near-infrared spectral galaxy observations on a large wavelength range, using models constructed with spectral stellar data observed with the same instrument. However a broader use of this spectral evolution model on other spectral or photometric data samples is possible if the spectral resolution of the model is adapted to observations or if colours are derived from the energy distributions.Catherine J. Cesarsky     

Modeling of the nonlinear drift oscillations of moored vessels subject to non-Gaussian random sea-wave excitation

A quadratic system model based on Volterra series representation is utilized to model the nonlinear response of moored vessels subjected to random seas. The key idea is to represent the relationship between the incident sea wave (input) and corresponding sway response of the moored vessel (output) with a parallel combination of linear and quadratic transfer functions, and to estimate them by processing actual input and output data. Compared to previous approaches, we take the important step of removing the restriction that the random input must possess Gaussian statistics. The feasibility and validity of the approach is demonstrated by analyzing experimental data taken in model basin tests. We also describe some of the deleterious consequences of assuming Gaussian sea-wave excitation when in fact the excitation is non-Gaussian.     

Using luminescence dating of coarse matrix material to estimate the slip rate of the Astaneh fault,Iran

In this paper, we present optically and infrared stimulated luminescence (OSL and IRSL) ages for four samples from alluvial fan surfaces in the Astaneh Valley. This valley is located in the north-east part of the Alborz range in Iran. Our morphologic interpretations recognize at least three generations of fans in the study area, all of which have been displaced along the left-lateral strike-slip Astaneh fault. Because of the dry, loose, and sometimes complex juxtaposition of the target sediments, we collected the samples in total darkness beneath dark plastic layers placed atop the pit openings. Luminescence ages of the fans are ～55 ka, ～32 ka and ～16 ka. These ages are concurrent with periods of loess deposition and wet climatic conditions previously recorded in the Arabia-Iranian region. They allow estimation of a horizontal slip rate of ～2 mm/yr along the Astaneh fault, which is consistent with additional slip rates determined for the Holocene period along faults further west of the Astaneh fault.     

Comparaison des méthodes d'interpolation pour l'é laboration de modèles numé riques d'é lé vation de haute pré cision dans la repré sentation micro-topographique des plaines inondables

Résumé

La micro-topographie des zones inondables influence l'étendue des nappes d'eau des secteurs submergés lors des crues. Cette analyse vise à comparer des méthodes d'interpolation pour la réalisation de modèles numériques d'élévation (MNE) de haute précision représentant la micro-topographie des plaines d'inondation. Ces méthodes ont été comparées au moyen d'un système d'information géographique (SIG) afin d'identifier lesquelles apparaissent les plus efficaces dans l'élaboration de l'image micro-topographique des sites, et ce en fonction d'un nombre restreint de données d'élévation. L'efficacité de chacune des méthodes d'interpolation a été validée au moyen du calcul de l'erreur quadratique moyenne, de tests statistiques, de cartes de l'erreur et d'une évaluation visuelle en trois dimensions. Il ressort que les méthodes d'interpolation du krigeage simple, de la fonction radiale, du réseau de triangles irréguliers et du krigeage ordinaire sont celles qui représentent le plus adéquatement la micro-topographie des sites, alors que les méthodes d'interpolation de l'inverse de la distance et du krigeage universel produisent des erreurs élevées.

Citation Drouin, A. & Saint-Laurent, D. (2010) Comparaison des méthodes d'interpolation pour l'élaboration de modèles numériques d'élévation de haute précision dans la représentation micro-topographique des plaines inondables. Hydrol. Sci. J. 55(4), 526?539.