High precision tilt observation at Mt. Etna Volcano,Italy

In 2007–2008, we installed on Mt. Etna two deep tilt stations using high resolution, self-leveling instruments. These installations are a result of accurate instrument tests, site selection, drilling and sensor positioning that has allowed detecting variations related to the principal diurnal and semidiurnal tides for first time on Mt. Etna using tilt data.     

Contribution of logging tools to understanding helium porewater data across the Mesozoic sequence of the East of the Paris Basin

Helium concentration measurements made on water and rock samples collected at various depths along a 2000 m depth borehole drilled in the eastern part of the Paris basin and reaching the Triassic conglomerates were used to establish a vertical profile of dissolved helium concentration throughout the entire Mesozoic sedimentary pile. Wireline logging tools were used to measure rock density, porosity and U and Th contents every 15 cm in the various formations. Samples from the deepest Muschelkalk and Buntsandstein show a very good agreement between measured and calculated ⁴He porewater contents. Shallower levels show lower and lower ⁴He concentrations compared to calculated values when going upwards. The data set obtained by wireline logging measurements was used as inputs for numerical simulations of 1D He production/diffusion throughout the 2000 m profile. Several assumptions regarding the transport properties in the various sedimentary layers were tested and all were found to yield fairly good agreement between modeled and measured He concentrations. There is no need to invoke either a transient regime or a deep crustal He flux in this “quiet” (seismically inactive) part of the Paris basin. Moreover, the modeling results suggest that the Keuper massive halite level associated with the upper Muschelkalk pre-evaporitic series efficiently isolates the overlying layers from any input from deeper formations in the Meuse/Haute Marne area.     

Projected Reorganization of Florida Bay Seagrass Communities in Response to the Increased Freshwater Inflow of Everglades Restoration

Historic changes in water-use management in the Florida Everglades have caused the quantity of freshwater inflow to Florida Bay to decline by approximately 60% while altering its timing and spatial distribution. Two consequences have been (1) increased salinity throughout the bay, including occurrences of hypersalinity, coupled with a decrease in salinity variability, and (2) change in benthic habitat structure. Restoration goals have been proposed to return the salinity climates (salinity and its variability) of Florida Bay to more estuarine conditions through changes in upstream water management, thereby returning seagrass species cover to a more historic state. To assess the potential for meeting those goals, we used two modeling approaches and long-term monitoring data. First, we applied the hydrological mass balance model FATHOM to predict salinity climate changes in sub-basins throughout the bay in response to a broad range of freshwater inflow from the Everglades. Second, because seagrass species exhibit different sensitivities to salinity climates, we used the FATHOM-modeled salinity climates as input to a statistical discriminant function model that associates eight seagrass community types with water quality variables including salinity, salinity variability, total organic carbon, total phosphorus, nitrate, and ammonium, as well as sediment depth and light reaching the benthos. Salinity climates in the western sub-basins bordering the Gulf of Mexico were insensitive to even the largest (5-fold) modeled increases in freshwater inflow. However, the north, northeastern, and eastern sub-basins were highly sensitive to freshwater inflow and responded to comparatively small increases with decreased salinity and increased salinity variability. The discriminant function model predicted increased occurrences of Halodule wrightii communities and decreased occurrences of Thalassia testudinum communities in response to the more estuarine salinity climates. The shift in community composition represents a return to the historically observed state and suggests that restoration goals for Florida Bay can be achieved through restoration of freshwater inflow from the Everglades.     

Morphotectonic and fault�Cearthquake relationships along the northern Ligurian margin (western Mediterranean) based on high resolution, multibeam bathymetry and multichannel seismic-reflection profiles

We present here new data from the MALISAR surveys that focus on two areas of the northern Ligurian margin where we reveal recent and active deformation. A set of N60°E scarps that are oblique to the margin is seen at the foot of the continental slope. These correspond to cumulated reverse-strike slip faulting that is consistent with the present-day kinematics of earthquakes. At the north-western margin, the Marcel Fault appears at the surface as a 10-km-long scarp trending N60°E. Several earthquakes of moderate magnitude (3.8 < M_L < 4.6) have focal mechanisms consistent with the geometry and the kinematics of, and have been located around, the Marcel Fault. At the north-eastern margin, offshore of Imperia, the major feature is a large promontory that is bound by a network of N60°E faults on its southern side. The structures and the deflection of the drainage network are consistent with a recent uplift of the Imperia Promontory. No surface ruptures have been identified in the epicentre area of the 1887 Ligurian earthquake (the major historical regional event: M_W ~6.5?C6.7), although the Imperia Fault network has the necessary characteristics to account for this earthquake. Therefore, from the present study, we propose that the rupture, as a reverse-strike slip faulting of a few or all of the segments belonging to the Imperia Fault network, was the source of the 1887 event. These MALISAR data have allowed identification of an 80-km-long transpressive system of Plio-Quaternary faults. The question of the potential activation of all of these faults during a single event is now of major concern, which has led to reappraisal of the regional seismic hazard as moderate to high.     

A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC)

The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories.     

The 1987–88 Alaskan Bight tsunamis: Deep ocean data and model comparisons

Excellent deep ocean records have been obtained of two tsunamis recently generated in the Alaskan Bight on 30 November 1987 and 6 March 1988, providing the best available data set to date for comparison with tsunami generation/propagation models. Simulations have been performed with SWAN, a nonlinear shallow water numerical model, using source terms estimated by a seafloor deformation model based on the rectangular fault plane formalism. The tsunami waveform obtained from the model is quite sensitive to the specific source assumed. Significant differences were found between the computations and observations of the 30 November 1987 tsunami, suggesting inadequate knowledge of the source characteristics. Fair agreement was found between the data and the model for the first few waves of the 6 March 1988 tsunami. Model estimates of the seismic moment and total slip along the fault plane are also in fair agreement with those derived from the published Harvard centroid solution for the 6 March 1988 event, implying that the computed seafloor deformation does bear some similarity to the actual source.     

Changement de faunes de bryozoaires dans le Valanginien supérieur des Alpes-de-Haute-Provence. Parallélisme avec la crise observée dans le Jura à la même époque

Dans le Valanginien supérieur (Marnes à Toxaster et Grande Lumachelle) des Alpes-de-Haute-Provence, la succession de deux faunes de bryozoaires est observée. Parmi les causes du changement de faune, le remplacement d'un fond vaseux en eau calme (Marnes à Toxaster) par un fond sableux coquillier en eau assez agitée (Grande Lumachelle) est certainement important. Cependant, ces modifications résultent elles-mêmes d'événements plus généraux.Le changement de faune peut être comparé à celui qui intervient dans le Jura au début de la zone à Trinodosum. La faune des Marnes à Toxaster (zone à Verrucosum) montre certaines des espèces caractéristiques de la “faune 1” du Jura et, de plus, les deux mêmes espèces dominantes. Le milieu de vasière des Marnes à Toxaster, opposé à celui de plate-forme carbonatée du Jura, entraîne seulement un appauvrissement spécifique. Quant à la faune de la grande Lumachelle, elle est absolument semblable à la “faune 2” récoltée dans les Marnes à bryozoaires et le Calcaire à Alectryonia du Jura.Ce parallélisme des deux faunes avec celles du Jura, malgré les différences de faciès sédimentaire, montre que le changement de faune, maintenant reconnu sur près de 400 km, résulte d'une même cause principale. Ainsi, l'hypothèse d'un refroidissement que j'ai proposée pour le Jura semble pouvoir être étendue à la Provence.The change of bryozoan fauna in the upper Valanginian of the Alpes-de-Haute-Provence. Parallelism with the crisis observed in the Jura at the same time.In the upper Valanginian (Marnes à Toxaster and Grande Lumachelle) of the Alpes-de-Haute-Provence, the succession of two bryozoan faunas is observed. Among the reasons for the change of fauna, the replacement of a muddy bottom in calm water (Marnes à Toxaster) by a sandy-shelly bottom in rather agitated water (Grande Lumachelle) is certainly important, but these modifications are the result of more general events. The change of fauna could be compared with the one that took place at the beginning of the Trinodosum Zone in the Jura. The fauna of the Marnes à Toxaster (Verrucosum Zone) shows some characteristic species of the “faune 1” of the Jura and, moreover, the same two dominating species. The muddy basin environment of the Marnes à Toxaster, unlike the carbonate platform environment in the Jura, involves only a specific impoverishment. As for the fauna of the Grande Lumachelle, it is totally identical to the “faune 2” found in the Marnes à bryozoaires and the Calcaire à Alectryonia of the Jura.This parallelism of the two faunas with those of the Jura, in spite of the differences of sedimentary facies, shows the change of the fauna now observed over about 400 km, has the same principal cause. Thus it seems possible to extend the cooling hypothesis I have proposed for the Jura, to Provence.     

Continuous monitoring of distal gas emanations at Vulcano,southern Italy

The increasing activity of Vulcano Island (Italy) since 1985 led to the initiation of continuous geochemical monitoring of the lateral soil gas emissions. On the basis both of their relative geochemical characteristics and of local considerations, three gaseous components were selected for monitoring, namely CO₂, He and ²²²Rn. Monitoring has been performed by means of specific analysers. Gases extracted from a water well located at the foot of the active cone were selected for monitoring, on the basis of their geochemical and isotopic characters that indicate their genetic link with central high temperature fumarolic gases emitted at the crater. Very strong variations of gas composition can be observed within one day (from 1 to about 94% for CO₂). Some variations display a daily character and can be correlated with that of atmospheric pressure. The three monitored gases are highly correlated, suggesting very high kinetics of gas transfer in the system. Because of these considerable variations of chemical composition, bulk concentrations obviously are not suitable for monitoring at Vulcano. However, the evolution with time of ratios such as ²²²Rn/CO₂ and He/CO₂ (the latter being corrected for atmospheric contamination) supplies numerical parameters that the expected to characterize the intensity of the degassing process. A new input of magmatic gases, that would lead to an increase in the ²²²Rn/CO₂ and He/CO₂ ratios, should therefore be detected by such a monitoring station.     

Coarse cliff-top aeolian sedimentation in northern Gaspésie,Québec (Canada)

This paper deals with the effects of wind on rockwall dynamics. On 5 and 6 January, 1988 very strong northwest winds (blizzard) were blowing onto the rockwall of Mount Saint-Pierre (alt.: 424 m), Gaspésie, Québec (Canada). The most violent recorded squall reached 99·4 km h^?1. During this event, the summit plateau received a large amount of aeolian sediments originating from the shale rockwall that forms the mountain's northwest side. In the 15 to 20 m wide by 75 m long belt located along the top of the rockwall, over a 1200 m² area, a continuous layer of debris completely covered the snow. This layer of debris had a mean thickness of 11·4 mm, which represents an accumulated volume in the order of 13 m³. Largely dominated by sand and granules (2–4 mm), the 28 samples collected for grain-size analysis also contained numerous thin shale flakes, many of which were longer than 10 mm. The largest flake measured had a width of 134 mm and a weight of 164·3 g. Six available ¹⁴C dates provide information concerning mean cliff-top aeolian sedimentation rate for the last thousand years (c. 1·8 mmyr^?1).