Writing Analytic Element Programs in Python

The analytic element method is a mesh-free approach for modeling ground water flow at both the local and the regional scale. With the advent of the Python object-oriented programming language, it has become relatively easy to write analytic element programs. In this article, an introduction is given of the basic principles of the analytic element method and of the Python programming language. A simple, yet flexible, object-oriented design is presented for analytic element codes using multiple inheritance. New types of analytic elements may be added without the need for any changes in the existing part of the code. The presented code may be used to model flow to wells (with either a specified discharge or drawdown) and streams (with a specified head). The code may be extended by any hydrogeologist with a healthy appetite for writing computer code to solve more complicated ground water flow problems.     

Quantification of seismic potential failure modes in concrete dams

A comprehensive framework for potential failure modes (PFM) identification and quantification of concrete dams subjected to seismic excitation is presented. A quantifiable indicator of PFM is presented in the context of both linear and nonlinear analyses. As an illustrative example, a thin arch dam subjected to a set of ground motions at different seismic intensity levels is investigated and corresponding PFM quantified. An outcome of this analysis is the probabilistic‐based correlation between linear and nonlinear analyses and identification of the optimal intensity measure parameter. This study, is an adaptation and extension of well‐accepted procedures defined by the performance‐based earthquake engineering paradigm in buildings. Copyright © 2015 John Wiley & Sons, Ltd.     

Holocene flood histories in south‐western USA

River basins in south‐western USA are some of the most extensively studied arid land fluvial systems in the world. Since the early 1960s their hydro‐climatic histories have been reconstructed from the analysis of alluvial cut‐and‐fill cycles, while from the late 1970s there have been investigations of slackwater deposits and palaeostage indicators for large floods in stable‐boundary bedrock reaches. However, no studies have regionally integrated Holocene fluvial histories from these two different types of fluvial environments. The current study combines the alluvial archive with flood records from bedrock reaches to generate a probability‐based 12,000 year record of flooding in south‐western USA. Using more than 700 ¹⁴C‐dated fluvial units, the analysis produces a high resolution (centennial) flood record. Seven episodes of increased flooding occurred at 11,250–10,400, 8800–8350, 8230–7600, 6700–5700, 5600–4820, 4550–3320 and 2000–0 cal. BP. Bedrock reaches are found to record more frequent floods during the middle to late Holocene, while in alluvial rivers more flood units are dated to the early and middle Holocene. These differences are primarily the result of selective preservation with alluvial reaches tending to erode during periods characterised by very large floods. Episodes of major Holocene flooding recorded in slackwater deposits within bedrock systems correspond with periods of increased precipitation in the region and lower temperatures. In contrast, within alluvial rivers above‐average flooding probabilities, as well as regionally extensive channel entrenchment episodes, match with reduced annual precipitation and lower temperatures. The results of this study clearly demonstrate the value of the Holocene fluvial archive for reconstructing regional, short‐term hydro‐climatic change in south‐western USA. Copyright © 2010 John Wiley & Sons, Ltd.     

(137)Cs baseline levels in the Mediterranean and Black Sea: a cross-basin survey of the CIESM Mediterranean Mussel Watch programme

The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify (137)Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured (137)Cs levels were found to be very low (usually < 1 Bq kg(-1) wet wt) (137)Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.     

Morpho-tectonic analysis of the Azores Volcanic Plateau from a new bathymetric compilation of the area

The existing studies of the Azores triple junction, although based on specific geological or geophysical data, largely rely upon morphological considerations. However, there is no systematic bathymetric coverage of this area, and the quality of the available bathymetric charts does not allow consistent morpho-structural analysis.In this work we present a new bathymetric grid elaborated with all the available data sources in an area comprised between 24° W to 32° W and 36° N to 41° N. The basic data set corresponds to the merge of NGDC data with new swath profiles. This new map, included as an Appendix, combined with other results from seismology and neotectonics, is the basis for the study of the morpho-structural pattern of the Azores area, the present day stress field and its implications on the current view of the Azores geodynamics.As a major result, we conclude that the Azores region is controlled by two sets of conjugated faults with 120° and 150° strikes that establish the framework for the onset of volcanism, expressing as linear volcanic ridges or as point source volcanism. This interaction develops what can be considered as the morphological signature of the Azores Spreading axis segmentation. We argue that the Azores domain, presently in a broad transtensional regime, is acting simultaneously as a ultra slow spreading centre and as a transfer zone between the MAR and the dextral Gloria Fault, as it accommodates the differential shear movement between the Eurasian and African plates.     

Étude de quelques palynomorphes du crétace supérieur du bassin offshore de Côte d'Ivoire: implications biostratigraphiques et paléoenvironnementales

The palynological analysis of the core samples from the interval 1722–1777 m of well IVCO-25, located in the Abidjan margin, has revealed a rich microflora composed of Pteridophyta and Chlorophyta spores combined with Palmaceae and Proteaceae pollen grains. This palynoflora suggests a vegetation developed under a hot and humid tropical climate, suggestive of estuarine conditions. The microplankton, composed of various species of dinocysts, were indicative of a Campanian age for the studied interval.     

A numerical solution for lageos thermal thrust: The rapid-spin case

We report the results of detailed numerical calculations of the thermal thrust on the rapidly-spinning LAGEOS spacecraft. This thrust results from anisotropic emission of thermal radiation from its surface. LAGEOS is a good test case for such calculations because of its relatively simple structure and because precise orbit determinations based on laser ranging give observed thrust effects for comparison.The numerical integration includes the varying heating over spacecraft-surface latitude from earth infrared radiation (for the earth-Yarkovsky force) and the varying solar heating as the spacecraft moves in and out of the earth's shadow (for the solar-Yarkovsky force). The computation allows for the poor thermal coupling between the spacecraft structure and individual surface elements (the fused-silica cube-corner reflectors and their aluminum retainer rings), and the poor conduction between structural hemispheres.A Fourier analysis of the computed force with respect to orbital longitude gives the important frequency components for the computation of long-term orbit perturbations. Empirical formulas fit to the numerical results accurately express the component amplitudes as simple functions of spin axis orbital latitude, the sun aspect angle from the spin axis, and the fraction of the orbit period spent in the earth's shadow. These results. based on first principles, are similar to those from simplified theories of the thermal thrust. but add the following new feature: The decrease in orbit-averaged satellite temperature when the orbit intersects the earth's shadow decreases the earth-Yarkovsky drag by 0.14 pm/s² from the no-eclipse value.The development of spacecraft-element thermal parameters is the most difficult part of the analysis; the paper tabulates the parameters that should be directly measured before the launch of future geodynamic satellites.     

The origin and use of basalt in Old Kingdom funerary temples

Conventional petrographic analysis suggests that basalts in Old Kingdom funerary temples are mineralogically and texturally similar to the Haddadin basalt flow of northern Egypt. To affirm that the Haddadin flow is the stone source, a total of 88 augite and 74 plagioclase electron microprobe analyses were obtained from two Abu Sir (Sahure, Fifth Dynasty) and three Giza (Khufu, Fourth Dynasty) temple paving stone samples and compared to all known, possible (unaltered), basalt units in Egypt (total of 379 augite and 265 plagioclase analyses). Cluster analysis using the averaged temple paving stone and flow unit mineral chemistry data shows that indeed the paving stones are most similar to the Haddadin flow. Discriminant analysis applied to individual augite and plagioclase analyses substantiates this conclusion. Quarrying of the Haddadin flow, probably at Gebel Qatrani, may have lasted more than 900 years, but production peaked during a 320‐year period in the Old Kingdom when funerary temples were being constructed. It is not clear why the Haddadin basalt was so popular, but ease of quarrying (because of columnar jointing), transportability, homogeneity, lack of tectonic joints, religious and symbolic traditions related to color, and resistance to wear may have all been important factors. The methods presented here are applicable to a wide variety of provenance questions involving igneous rocks. More specifically, the discriminant diagrams used to source the temple floor rocks should help in determining the origin of basalts used in other Egyptian artefacts. © 2000 John Wiley & Sons, Inc.     

Late Cryogenian glaciation in South Australia:Fluctuating ice margin and no extreme or rapid post-glacial sea-level rise

Postulated extreme sea-level rise of up to 1-1.5 km with the late Cryogenian Ghaub deglaciation in Namibia is contentious,as is the great rapidity(<104 yr)of the sea-level rise.Such extreme glacioeustatic events,if real,would have been global and affected all continents.In South Australia,up to six glacial advances and retreats during the late Cryogenian Elatina glaciation indicate a fluctuating ice margin.The latter stage of the Elatina glaciation and the immediate post-glacial environment are examined here for evidence of extreme and rapid sea-level rise.In the central Adelaide Rift Complex,diamictite with faceted and striated clasts occurs at the top of the Elatina Formation<1-2 m beneath the early Ediacaran Nuccaleena Formation’cap carbonate’.One hundred kilometres to the south,~30 m of siltstone and sandstone followed by^6 m of clast-poor diamictite with clasts 10+cm long occur between tidal rhythmites and the cap carbonate.Three hundred kilo metres further south,~70 m of siltsto ne,dolo mitic siltstone and minor dolomite separate tidal rhythmites and early Ediacaran strata.Hence the rhythmites were deposited during a high stand(interstadial or interglacial),not during post-glacial sea-level rise.Storm-generated erosional surfaces within tidal rhythmites at Warren Gorge indicate intermittent rhythmite deposition,and water depth and other palaeoenvironmental factors are uncertain,casting doubt on a published estimate of rapid sea-level rise during rhythmite deposition.The lack of late Cryogenian deeply incised valleys and thick valley-fill deposits in South Australia and central Australia argues against extreme sea-level variations.A hiatus occurred between Elatina deglaciation and deposition of the Nuccaleena cap carbonate,and three palaeomagnetic polarity chrons identified in the cap carbonate imply slow deposition spanning 10^5-10^6 yr.This is supported by independent evidence from magnetic chronostratigraphy for Ediacaran strata in South Australia and California,and by stratigraphic and sedimentological arguments for condensed deposition of cap carbonates.It is concluded that neither extreme nor rapid sea-level rise was associated with late Cryogenian deglaciation in South Australia.