Parametrizing surface wave tomographic models with harmonic spherical splines

We present a mathematical framework and a new methodology for the parametrization of surface wave phase-speed models, based on traveltime data. Our method is neither purely local, like block-based approaches, nor is it purely global, like those based on spherical harmonic basis functions. Rather, it combines the well-known theory and practical utility of the spherical harmonics with the spatial localization properties of spline basis functions. We derive the theoretical foundations for the application of harmonic spherical splines to surface wave tomography and summarize the results of numerous numerical tests illustrating the performance of a practical inversion scheme based upon them. Our presentation is based on the notion of reproducing-kernel Hilbert spaces, which lends itself to the parametrization of fully 3-D tomographic earth models that include body waves as well.     

Characterising the main karst aquifers of the Alvand basin, northwest of Zagros, Iran, by a hydrogeochemical approach

The Alvand River basin, situated in the northwest of the Zagros mountain range, Iran, drains carbonate aquifers through some important karst springs. The physical, chemical and isotopic characteristics of spring water were studied for two years in order to assess the origin of groundwater and determine the factors driving the geochemical composition. Principal components analysis was used to identify the main factors controlling the water chemistry. Two groups of springs were identified: (1) low mineralisation, ion concentration, especially sulphate, low temperature, light isotope composition and high elevation of the recharge area, and (2) moderate to high mineralisation, especially sulphate, higher temperature, heavy isotope composition and low altitude of the recharge area. The main factors controlling the groundwater composition and its seasonal variations are the geology, because of the presence of evaporite formations, the elevation and the rate of karst development. In both groups, the carbonate chemistry is diagnostic of the effect of karst development. The supersaturation with respect to calcite indicates CO₂ degassing, occurring either inside the aquifer in open conduits, or at the outlet in reservoirs. The undersaturation with respect to calcite shows the existence of fast flow and short residence-time conditions inside the aquifer. A PCA analysis showed that, contrary to most developed karst systems, where dilution occurs during the wet season, leaching of the gypsum-bearing Gachsaran Formation by rainwater produced higher mineralisation.

---

Resumen La cuenca del río Alvand, situada en el noreste de la cadena montañosa Zagros drena acuíferos compuestos por carbonatos a través de manantiales kársticos. Durante dos años se estudiaron las características físicas, químicas e isotópicas del agua de manantial con el objetivo de determinar el origen del agua subterránea y de los factores que controlan su composición geoquímica. Se utililizó el análisis de componentes principales para identificar los factores principales que controlan la química del agua. Se identificaron dos grupos de mantaniales: (1) de baja mineralización, concentración de iones especialmente sulfatos, y baja temperatura, composición de isotopos livianos y elevación alta del área de recarga, y (2) mineralización moderada y alta, especialmente, sulfatos, y temperatura más alta, composición de isotopos pesados y altitud más baja del agua de recarga. Los factores principales que controlan la composición del agua subterránea y sus variaciones estacionales son la geología debido a la presencia de formaciones evaporitas, la elevación y la tasa a la que se desarrolla el karst. En ambos grupos la química de los carbonatos es un diagnóstico del efecto del desarollo de la estructura kárstica. La supersaturación con respecto a la calcita indica presencia de CO₂ que está en proceso de degasificación que ocurre dentro de acuífero en conductos abiertos o a la salida en reservorios. La subsaturación en lo referente a la calcita muestra la existencia de flujo rápido y de tiempos cortos de residencia al interior del acuífero. El análisis de componentes principales muestra que a diferencia de la mayor parte de sistemas kársticos en donde la dilución ocurre durante la temporada de lluvias, la lixiviación de la formación Gachsaran que contiene yeso a causa de lluvia produce mineralizaciones más altas.

---

Résumé Le bassin de la rivière Alvand, situé dans le nord-ouest de la chaîne de montagne Zagros, draine des aquifères carbonatés par le biais dun important réseau de sources karstiques. Les caractéristiques physiques, chimiques et isotopiques de leau provenant des sources ont été étudiées pendant deux ans afin de déterminer lorigine de leau souterraine et les facteurs responsables de sa composition chimique actuelle. Lanalyse des éléments chimiques majeurs a été utilisée pour identifier les processus qui contrôlent la composition chimique de leau. Deux groupes différents de sources ont été identifiés: (1) faible minéralisation et concentration en ions, spécialement en sulfates, faible température, composition isotopique légère et haute élévation de la zone de recharge, et (2) minéralisation moyenne à élevée, particulièrement en sulfates, température élevée, composition isotopique lourde et plus basse altitude de la zone de recharge. Les facteurs principaux qui contrôlent la composition et la variation saisonnière de leau souterraine sont la géologie, en raison de la présence dévaporites, lélévation et le taux de développement des karsts. Dans les deux groupes, la teneur en carbonates est un diagnostic de leffet du développement de la structure des karsts. La sursaturation par rapport à la calcite indique un dégazage en CO₂ qui a lieu soit à lintérieur de laquifère, dans les conduits ouverts, ou à sa sortie, dans les réservoirs. La sous-saturation par rapport à la calcite indique lexistence dun écoulement rapide et un faible temps de résidence dans laquifère. Une analyse des éléments chimiques majeurs a démontré que contrairement aux systèmes de karst les mieux développés où la dilution a lieu lors de la saison humide, le lessivage du gypse de la formation de Gachsaran par leau de pluie produit une minéralisation plus élevée.

     

Phytoplankton community adaptation to changing light levels in the southern Beaufort Sea,Canadian Arctic

The chlorophyll a specific absorption coefficient of phytoplankton, a_φ^∗(λ) is an important parameter to determine for primary production models and for the estimation of phytoplankton physiological condition. Knowledge of this parameter at high latitudes where nutrient rich cold water submitted to low incident light is a common environment is almost nonexistent. To address this issue, we investigated the light absorption properties of phytoplankton as a function of irradiance, temperature, and nutrients using a large data set in the southern Beaufort Sea during the open water to ice cover transition period. The a_φ^∗(λ) tended to increase from autumn when open water still existed to early winter when sea ice cover was formed, resulting from a biological selection of smaller-size phytoplankton more efficient to absorb light. There was no significant correlation between a_φ^∗(λ) and irradiance or temperature for both seasons. However, a_φ^∗(λ) showed a significant positive correlation with NO₃ + NO₂. Implications of the results for phytoplankton community adaptation to changing light levels are discussed.     

Coupes sismiques des structures superficielles dans les petites antilles—I: Guadeloupe

Summary In 1976 and 1977, seismic profiles were carried out in Guadeloupe. Two profiles were established in the area of La Soufriére volcano and one profile through the northern part of Guadeloupe and southern part of Grande Terre. The two first profiles were occupied from 1 to 30 km and the third profile between 5 and 50 km.The interpretation shows that the superficial structures are characterized by a three-layers model: the compressional velocity is about 2.7 to 3.0 km/s down to a depth from 1 to 3 km. Below this, the velocity is between 4.0 and 4.5 km/s in a layer whose thickness varies from 1 to 2.5 km. Under this layer we find a 6.0–6.1 km/s layer which is one of the two known crustal layer under Lesser Antilles. The boundary between the old and new are which form the Lesser Antilles arc, is marked by a thicker layer of sediments on the eastern flank of recent volcanic chain.

     

地震环境噪声成像中的地形影响校正

以传统地震环境噪声面波成像方法研究地壳速度结构时,在一些极端的地形条件下,结果与真实结构会存在较大偏差.我们以地震波场三维正演模拟为基础,提出了一种地形校正方法.我们保留了传统噪声面波成像简单的两步反演法,在面波层析成像和一维速度结构反演的基础上,通过地震波场三维模拟近似估计地形和散射波场的影响,并据此校正瑞利波频散曲线,最终反演得到校正地形影响的S波速度结构.理论测试与在实际观测数据上的应用都证明了校正方法的有效性,同时也显示了地形校正的必要性.

     

Field investigation of ridge–runnel dynamics on an intertidal mudflat

Flow-parallel linear ridge–runnel (R–R) bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at Hills Flats in the Severn Estuary, UK. It is argued that the sequences of sand–mud laminae in the ridge sediments indicate strongly that R–R are depositional bedforms. Faint R–R topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth. Bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion [mechanical erosion by turbulent flows that may also carry sand and/or gravel] during Spring tidal flow ca. 60 cm/s. Differences in flow characteristics between ridges and runnel are minor. Corrasion [to erode or be eroded by abrasion] by sparse coarse sediment largely prevents net deposition in the runnels. Over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and/or sediment supply.     

A field experiment and numerical modeling of a tracer at a gravel beach in Prince William Sound,Alaska

Oil from the 1989 Exxon Valdez oil spill persists in many gravel beaches in Prince William Sound (Alaska, USA), despite great remedial efforts. A tracer study using lithium at a gravel beach on Knight Island, Prince William Sound, during the summer of 2008 is reported. The tracer injection and transport along a transect were simulated using the two-dimensional numerical model MARUN. Model results successfully reproduced the tracer concentrations observed at wells along the transect. A sensitivity analysis revealed that the estimated parameters are well determined. The simulated spatial distribution of tracer indicated that nutrients applied along the transect for bioremediation purposes would be washed to the sea very quickly (within a semi-diurnal tidal cycle) by virtue of the combination of the two-layered beach structure, the tidal fluctuation and the freshwater flow from inland. Thus, pore-water samples in the transect were found to be clean due to factors other than bioremediation. This may explain why the oil did not persist within the transect.     

Formation of the Upper Pleistocene terraces of Lake Van (Turkey)

Sedimentological and geomorphological studies of terraces around Lake Van (1647 m) provided a preliminary framework for lake‐level variations. The elevations of terraces and past lake level were measured with a differential global positioning system. A chronology is developed using ²³⁴U/²³⁰Th dating of travertines, ³⁹Ar/⁴⁰Ar dating of pyroclastites and ¹⁴C dating of organic matter. Facies and stratigraphic correlations identify four transgressions (C1′, C1″, C2′ and C2″), each followed by a regression which ended with low lake levels that caused river incision and terrace formation. Evidence of the oldest transgression (C1′) is found in the uppermost reaches of valleys up to 1755 m, an altitude higher than the present lake threshold (1736 m). This C1′ transgression may be related to pyroclastic flows which dammed an outlet located in the western part of the lake basin and which is dated to before 105 ka. After 100 ka, a second transgression (C1″) reached 1730/1735 m, possibly related to a younger ignimbrite flow, in association with high water inflow (warm and/or wetter conditions). The two younger transgressions reached 1700–1705 m. The first one (C2′) is dated to 26–24.5 cal. ka BP and the second one (C2″) to 21–20 cal. ka BP. Available data suggest that the long‐term lake‐level changes responded mainly to climate oscillations. Additional events such as river captures caused by volcanic falls filling valleys, tectonism, erosion and karstic diversion may have impacted these long‐term lake‐level changes. Copyright © 2010 John Wiley & Sons, Ltd.