Stochastic Local Interaction Model: An Alternative to Kriging for Massive Datasets

Mathematical Geosciences - Classical geostatistical methods face serious computational challenges if they are confronted with large spatial datasets. The stochastic local interaction (SLI) approach...     

MARLI: a mobile application for regional landslide inventories in Ecuador

The regions of Central and South America most susceptible to the occurrence of landslides will become even more vulnerable in the context of climate change. The Josefina disaster, in 1993, demonstrated both the vulnerability of local infrastructures and communities in the Paute River basin (Ecuador). Since this natural phenomena, several landslide inventories and susceptibility studies were developed, revealing the vulnerability of the Paute River basin to unstable terrain and the need for further studies throughout the basin. Despite this, no studies have been done since then to update the information generated. This paper describes a Mobile Application for Regional Landslide Inventories (MARLI), a simple but efficient open-access platform to report landslide events using the Open Data Kit system. Its design makes reporting fast, simple and cost-effective with an added benefit, and a specialized knowledge is not required for its use. MARLI was tested for the collection of landslides in Cuenca (Ecuador). From the data taken in the field, it was possible to analyze the performance and suitability of collected data and compare the results with regional inventories in the same area. Additionally, these results can be used for the elaboration and update of large-scale inventories or the training of automatic identification systems of landslides and later evaluation of their precision in a small-medium scale. Likewise, this product constitutes a fundamental input for the formulation of mitigation strategies, to formulate the appropriate response and in time, also the elaboration of reconstruction plans before the increase in the occurrence of such phenomena.

     

Early Jurassic palaeoenvironments in the Surat Basin,Australia – marine incursion into eastern Gondwana

Interpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two-dimensional and three-dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third-order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub-basins, with rivers flowing in different orientations in each sub-basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas.     

Formulation of a unified constitutive model for clays and sands

This paper presents a new generalized effective stress model, referred to as MIT-S1, which is capable of predicting the rate independent, effective stress–strain–strength behaviour of uncemented soils over a wide range of confining pressures and densities. Freshly deposited sand specimens compressed from different initial formation densities approach a unique condition at high stress levels, referred to as the limiting compression curve (LCC), which is linear in a double logarithmic void ratio, e, mean effective stress space, p′. The model describes irrecoverable, plastic strains which develop throughout first loading using a simple four-parameter elasto-plastic model. The shear stiffness and strength properties of sands in the LCC regime can be normalized by the effective confining pressure and hence can be unified qualitatively, with the well-known behaviour of clays that are normally consolidated from a slurry condition along the virgin consolidation line (VCL). At lower confining pressures, the model characterizes the effects of formation density and fabric on the shear behaviour of sands through a number of key features: (a) void ratio is treated as a separate state variable in the incrementally linearized elasto-plastic formulation: (b) kinematic hardening describing the evolution of anisotropic stress–strain properties: (c) an aperture hardening function controls dilation as a function of ‘formation density’; and (d) the use of a single lemniscate-shaped yield surface with non-associated flow. These features enable the model to describe characteristic transitions from dilative to contractive shear response of sands as the confining pressure increases. This paper summarizes the procedures used to select input parameters for clays and sands, while a companion paper compares model predictions with measured data to illustrate the model capability for describing the shear behaviour of clays and sands. Copyright © 1999 John Wiley & Sons, Ltd.     

Notes on late Cenomanian and Turonianammonites from Touraine,Western France

Recent collecting in the type area of the Turonian stage and adjacent parts of Touraine in western France provides new geographic and stratigraphic records as well as additional systematic information on species of the ammonite genera Puzosia, Watinoceras, Metoicoceras, Mammites, Prohauericeras, Collignoniceras, Lecointriceras, Subprionocyclus and Sciponoceras.     

Al,Si ordering in cordierite using “magic angle spinning” NMR

A method of determining the number of Al-O-Al bonds per unit cell from ²⁹Si nuclear magnetic resonance (NMR) data of synthetic cordierites with increasing Si, Al order is described. The number of Al-O-Al bonds is found to vary linearly with the logarithm of the annealing time. This may be correlated with previously published heat of solution data on similar samples (Carpenter et al. 1983) to determine the enthalpy change Δh, associated with a single Al?Si interchange in cordierite. Δh is found to be 8.1 kcal/mole. The NMR data show that the short range Al, Si order cannot be described in terms of twin domains of ordered orthorhombic cordierite. An ordering model derived from group theoretical constraints on possible Al, Si distributions within the hexagonal symmetry of the cordierite is found to provide a better fit to the NMR data.     

Xe in glacial ice and the atmospheric inventory of noble gases

We report noble gas abundance data for four Antarctic glacial ice samples which were selected to test the hypothesis that the apparent Xe deficiency in the earth's atmosphere relative to meteoritic abundance is due to incorporation of Xe in glacial ice. Our measurements indicate that the concentrations of Xe in glacial ice fall far short (~10⁴) of what the hypothesis requires. The present results complete the survey of all significant atmospheric reservoirs and show that the “missing Xe” is not contained in any of them. It must either be in the solid earth in yet unsampled reservoirs, or else it simply does not exist and the noble gas abundance pattern of the earth is dissimilar to that in meteorites.     

Ultra-rapid landscape response and sediment yield following glacier retreat, Icy Bay, southern Alaska

The páramo is a neotropical alpine ecosystem that covers more than 75,000 km² of the northern Andes of Colombia, Ecuador, Venezuela, and Peru. It provides important environmental services: more than 10 million people in the Andean highlands benefit from the water supply and regulation function, which is attributed to the volcanic soils that underlie the ecosystem. The soils are also major carbon sinks of global significance. Severe land use changes and soil degradation threaten both the hydrology and carbon sink function. Nevertheless, soil genesis and properties in the páramo is rather poorly understood, nor are their ecological functions well documented. The impact of the geomorphology of the páramo on soil genesis was studied in the rio Paute basin, south Ecuador. Two toposequences were described and analysed. In each toposequence, four pedons were selected representing summit, backslope, undrained plain situation, and valley bottom positions in the landscape. The soils are classified as Hydric Andosols in the World Reference Base for Soil Resources and Epiaquands or Hydrudands in Soil Taxonomy. They are very acidic and have a high organic matter content, high P deficiency, and Al toxicity. Their water content ranges from 2.64 g g^− 1 at saturation, down to 1.24 g g^− 1 at wilting point, resulting in a large water storage capacity. Two major soil forming processes are identified: (1) volcanic ash deposition and (2) accumulation of organic carbon. Volcanic ash deposits may vary in depth as a result of regional geomorphological factors such as parent material, orientation, slope, and altitude. Organic carbon accumulation is an interaction of both waterlogging, which depends on the position in the landscape, and the formation of organometallic complexes with Al and Fe released during volcanic ash breakdown. Despite the high variability in parent material and topography, the soil is characterised by a notable homogeneity in physico-chemical properties. Statistical analysis reveals that only topographic location has a slight but significant influence on soil pH as well as the organic matter content, saturated conductivity and water retention at high pressure. Finally, the exceptional properties of these soils provide useful insights to improve classification of the Andosols reference group of the FAO World reference Base for Soil Resources.