Delimitation of ground failure zones due to land subsidence using gravity data and finite element modeling in the Querétaro valley, México

Sedimentary basins of arid and semiarid zones are often subject to regimes of intense ground-water withdrawal as it is normally the only source of water for development of communities. An associated phenomenon is land subsidence, which can develop to ground failures, and consequently, damage to infrastructure. Aquifer deformation can be analyzed using a stress–strain or a flux–force approach depending on the aquifer material (compact or loose) and on whether the water withdrawal forms a predominant flow direction toward a cone of depression. Geometry of the aquifer system also plays an important role as uneven thickness induces differential compaction and hence, tensional and shear stresses on the ground mass. In this work we present a stress–strain approach to analyze subsidence for an unconfined aquifer of varying thickness; this is done in two steps, namely when the aquifer is in equilibrium, and when it is totally depleted. Using this scheme in a region where ground failure is evident, a portion of the aquifer system of the Querétaro valley is analyzed. The geometry of the hydrologic basement is first modeled using gravity measurements properly correlated with wells and field data. Then a stress analysis is implemented using the finite element method in order to identify probable zones of ground weakness, which are calibrated with known ground failures. The results indicate that both, tensional and shear stress are present, which induce ground failure in the form of surface faults.     

A Method for the Ionospheric Delay Estimation and Interpolation in a Local GPS Network

To estimate ionospheric delays from the Global Positioning System (GPS) measurements, satellite and receiver equipment biases have to be modeled. This paper presents a procedure based on the least squares (LS) approach, which implicitly takes into account these equipment biases in the estimation of the ionospheric effect. The second part of this work deals with the interpolation of the ionospheric correction from a permanent GPS network to a single frequency GPS user. The results obtained show that for 10-cm position accuracy the ionospheric delay can be successfully interpolated when the GPS user is within 40 km of the GPS permanent network.     

An integrated thermodynamic mixing model for sphalerite geobarometry from 300 to 850°C and up to 1 GPa

An asymmetric, Margules-type, solid solution model was used to model the mixing behavior of Fe-Zn sphalerites. The model is based on an analysis of experimental results from fifteen independent data sources. After a careful, stepwise, analysis of the available runs, the solid solution model was constrained using a refined experimental database of 279 experiments which were simultaneously regressed to obtain the excess parameters and a general geobarometric equation. The model indicates that, when pressures are low, the value of γ_FeS^Sph, which is always greater than one, is higher at low FeS contents and an increase in temperature causes it to decline. However, for certain compositions γ_FeS^Sph values might be slightly less at low T than at high T. This behavior is corrected when pressure increases, regardless of the composition. The excess Gibbs free energy has positive values at any P&T while it is asymmetric. Pressure increases the value of the excess free energy. On the other hand, the Gibbs free energy of mixing is always negative, with a single minimum that tends to move towards Fe-poorer compositions as the pressure goes up. An increase in temperature leads to a more negative Gibbs free energy mixing function suggesting that increasingly Fe-poorer sphalerite would be expected at high temperatures and pressures. The application of the solid solution model to a selection of case-studies provided results which are consistent with independent pressure estimates. However, the pressure determinations for sphalerite + pyrite + pyrrhotite and sphalerite + pyrrhotite assemblages are very sensitive to uncertainties in the composition of the phases involved and, to a lesser extent, to temperature. The results of the application of the model to a field case (scheelite-mineralized Hercynian veins from the Central Pyrenees) were also consistent when compared with independent pressure-constraining silicate assemblages. Thus, the solid solution model described in this paper provides a workable framework with which to compute the pressures of the formation of rocks over a wide range of geological conditions.     

Etude de l''acquisition d''éléments dissous par les eaux de lessivage des roches granitiques sous climat tempéré

Using chemical potential diagrams and budget calculations, we show that the acquisition of solutes by surface water in granitic rocks under temperate climate corresponds with transformation of primary minerals into kaolinite or halloysite. This mineral controls aluminium solubility.     

Relations entre les concentrations des ions alcalins dans les eaux thermales sulfurées sodiques du Midi de la France

Alkali ion concentrations were studied in hot sulphurated springs in the south of France. Strong correlations between elements (K-Rb, K-Cs and Na-Li) are found. The element concentrations are also closely related with deep temperature as estimated by classical geothermometers. A discussion of the origin of the interelement correlations is presented. Further studies on the behaviour of trace elements during mineral dissolution are needed and can yield interesting methods of investigation in geothermal exploration.

Résumé

L'étude des concentrations des ions alcalins dissous dans les eaux thermales sulfurées du Midi de la France montrent de très nettes corrélations entre éléments (K-Rb, K-Cs et Na-Li) ainsi que des corrélations entre concentrations d'éléments et température profonde estimée à l'aide des géothermomètres classiques. Plusieurs suggestions quant à l'explication des relations observées sont présentées. Une bonne compréhension du comportement des ions en trace lors de la dissolution des minéraux par l'eau aurait certainement des retombées intéressantes en prospection géothermique.     

Constantes de formation des complexes hydroxydés de l'aluminium en solution aqueuse de 20 a 70°C

Stability constants of hydroxocomplexes of Al(III):Al(OH)²⁺ and A1(OH)₄^? have been measured in the 20–70°C temperature range by reactions involving only dissolved species. The stability constant ${}^1\text{K}{}_1$ of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. ${}^1\text{β}{}_4$ of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al³⁺ in acid medium, and between the same complex ion and A1(OH)₄^? in alkaline medium. The K values and the associated ΔH are ${}^1\text{K}{}_1\text{= 10}{}^{\mathrm{?5.00}}$ and ΔH₁ = 11.8 Kcal; ${}^1\text{β}{}_4\text{= 10}{}^{\mathrm{?22.20}}$ and ΔH₄ = 42.45 Kcal. These last results are not in agreement with the values of recent tables for $\text{ΔG}{}^0\text{?}$ and $\text{ΔH}{}^0\text{?}$ of Al³⁺ and Al(OH)₄^?. We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates.     

NIR Properties of the UCM Star-Forming Galaxies

We present results from a spectroscopic survey of Paβ & Brγ emission in a sample of T Tauri stars, mostly in the Taurus-Auriga complex. Velocity resolved spectra (Δv ∼ 15 km s^-1) show that, of the 41 stars observed in Paβ emission, 34% display IPC redshifted absorptions, while, of the 29 stars observed in Brγ emission, 21% display IPC redshifted absorptions. The lines are broad (FWHM ∼ 200 km s^-1) and lack blueshifted absorptions. These observations are consistent with the near infrared hydrogen lines forming predominantly in infalling material, as suggested by magnetospheric accretion column models. Radiative transfer calculations of the Paβ and Brγ line profiles in a very simplified, spherically symmetric situation are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A large marine ecosystem governance framework

A large marine ecosystem (LME) governance framework, developed from a need to effectively address the sustainable management of the shared living marine resources of the Caribbean, is proposed. The framework is based on four propositions and focuses on a linked examination of two well-known components of LME-level governance: the policy cycle process by which decisions are made and the multi-level nature of LMEs. It accommodates the diversity of policy cycles at multiple levels and the linkages among them required for effective governance of LMEs. The framework takes into account of factors such as context, purpose, jurisdictional scale, capacity and complexity and provides a means to identify critical areas for intervention.     

Thermal field and geothermal models of the lithosphere in the continent-ocean transition zone of northeastern Eurasia

The region under study is located in the active “transition zone” from the Eurasian continent to the Pacific Ocean. The zone occupies not only the continent-ocean border area (continental coastline, marginal seas, island arcs, and deep-sea trenches) but also the margins of intracontinental regions of the Eurasian continent with different structures and regimes of development. The transition zone is a natural buffering and damping regulator of the interaction between the Eurasian and Pacific plates and is characterized by intense orogenesis, contemporary volcanism, active seismicity, diverse geothermal regime, and highly nonuniform measured heat-flow values. Available geothermal data for the region are not sufficiently generalized. After the latest maps compiled in the 1990s, new data have been obtained and new geoinformation technologies have been developed. In the study presented in this paper, available geothermal information has been generalized and a detailed heat flow distribution map has been compiled and used to calculate Moho temperatures, to determine the thickness of the “geothermal” lithosphere, and to construct distribution maps of these parameters.     

Are fiddler crabs potentially useful ecosystem engineers in mangrove wastewater wetlands?

The effect of different organic-rich sewage concentration (0%, 20% and 60% diluted in seawater) and absence or presence of mangrove trees on the survival, bioturbation activities and burrow morphology of fiddler crabs species was assessed. After 6 months, males of both species always showed higher survival (80%) when compared to females (20%). Crabs inhabiting pristine conditions achieved higher survival (67–87%) than those living in sewage-exposed mesocosms (40–71%). At 60% sewage loading, fiddler crabs processed less sediment (34–46%) during feeding and excavated slightly more sediment (45–80%) than at pristine conditions. While percent volume of the burrow chambers increased (13–66%) at contaminated mesocosms for both vegetation conditions, burrows were shallower (33%) in bare cells loaded with sewage. The results show that fiddler crabs presented moderate mortality levels in these artificial mangrove wetlands, but mainly in sewage impacted cells. However, they still function as ecosystem engineers through bioturbation activities and burrow construction.