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Baillieux P.,University of Neuchatel | Schill E.,GEIE Exploitation Miniere de la Chaleur | Edel J.-B.,Ecole et Observatoire des science de la Terre | Mauri G.,University of Neuchatel
International Geology Review | Year: 2013

The European Cenozoic Rift System hosts major temperature anomalies in Central Europe. In its central segment, the Upper Rhine Graben (URG), temperatures range from 75°C to nearly 150°C at a depth of 2000 m. Different hypotheses have been suggested to explain the localization of these anomalies. Our review and comprehensive interpretation of gravimetric and magnetic data, as well as neotectonic activity patterns, suggests that low-density, mostly magnetic and fractured granitic basement is systematically associated with major temperature anomalies. Further analyses provide insight into different heat transport processes contributing to the localization of these anomalies. Magnetic and gravity anomalies are known to represent lithological variations associated with the pre-Permian.We show their spatial relationship with positive temperature anomalies in the URG. Correlation between magnetics and temperature reveal a mean contribution of heat production to the temperature anomaly of about 10-15°C. A slightly higher mean value is obtained from correlation between gravity and temperature, which may be attributed to effects resulting from fracture porosity. The spatial relationship between temperature anomalies and neotectonic patterns indicates compressional shear and uplift regime for the major anomalies of the central segment of the URG. This is in agreement with different numerical models indicating free convection on fracture zones linked to faults. Our findings show that about 15-25% of the temperature anomaly can be attributed to variation in heat production. Hydrothermal circulation convection along faults, activated by the tectonic context, may explain the remaining 75-85% of the temperature anomalies. © 2013 Taylor & Francis. Source

Bouche E.,CNRS Paris Institute of Global Physics | Vergniolle S.,CNRS Paris Institute of Global Physics | Staudacher T.,CNRS Paris Institute of Global Physics | Nercessian A.,CNRS Paris Institute of Global Physics | And 4 more authors.
Earth and Planetary Science Letters | Year: 2010

The activity at the surface of the lava lake on Erta 'Ale volcano (Ethiopia) shows that large bubbles are regularly breaking at a fixed position on the lava lake. This is also where the small lava fountains are sometimes produced. Since this location is likely to be directly above the volcanic conduit feeding the lava lake, we have done continuous measurements between March 22 and 26, 2003 to understand the degassing of a volcano in permanent activity. The bubble size has been first estimated from videos, which once combined with the acoustic pressure, can constrain the source of the sound. The gas volume and overpressure stayed roughly constant, between 36-700m3 and 4×103-1.8×104Pa, respectively. Simultaneous thermal measurements showed regular peaks, which occurred when the crust was broken by a large bubble, hence gave a direct indication on the typical return time between the bubbles (1h). These spherical cap bubbles had a high Reynolds number, 4600-20000, therefore a wake, periodically unstable, formed and detached from the bubble bottom. The bubbly wake, if the detachment occurs close to the surface, can explain the duration of lava fountains, measured on the videos. The periodic arrival of bubbly wakes, which mostly detach from the driving spherical cap within the lava lake, could explain the absence of cooling at Erta 'Ale, Erebus (Antartica), Villarica (Chile) and Nyiragongo (Democratic Republic of Congo) without invoking a convective downflow of magma in the conduit, as previously done. © 2010 Elsevier B.V. Source

Kopp J.-B.,ICube | Schmittbuhl J.,Ecole et Observatoire des science de la Terre | Lin J.,ICube | Fond C.,ICube
13th International Conference on Fracture 2013, ICF 2013 | Year: 2013

For rapid crack propagations, two kinds of material behavior have been observed. Typically, most materials show an increase of the fracture energy with the crack tip velocity. However, there do exist a few materials for which the fracture energy tends to decrease with the velocity [1, 2]. They are viscoplastic blend materials like polymers such as rubber toughened polymethylmethacrylate (RT-PMMA). For these materials, crack tips are seen to propagate at the same velocity whatever the loading rate is (or strain energy release rate). This critical velocity has been shown to be the crack branching velocity, at least at a macroscopic scale. Our study shows that the classical approach which considers that the amount of created surface during the propagation can be approximated as the sample thickness multiplied by the crack length is not appropriate. Indeed, this study shows that the exact fracture surface roughness has to be included in the amount of created surface in order to establish an intrinsic material fracture energy GID. As the fracture surface roughness depends on the scale at which the sample is observed, a self-affine model widely used for fracture surfaces is introduced [3, 4]. This statistical geometrical model of the fracture surface with two parameters, a Hurst exponent and a topothesy is shown to be effective and provides a better estimate of the intrinsic surface fracture energy. Copyright © (2013) by International Conference on Fracture. Source

Hofstetter A.,Geophysical Institute of Israel | Dorbath C.,Ecole et Observatoire des science de la Terre
Journal of Geophysical Research B: Solid Earth | Year: 2014

New findings of the structure of the Dead Sea sedimentary basin and its eastern and western bordering regions are obtained by P and PKP wave relative traveltime residuals of 644 teleseisms, as recorded by the Dead Sea Integrated Research portable seismic network in the Dead Sea basin and its neighboring regions. The Lisan Peninsula is characterized by relatively small teleseismic traveltime residuals of about 0.14 s, in the latitude range of 31.22°-31.37° and at the longitude of 35.50°, slowly decreasing toward the west. The largest teleseismic traveltime residuals are in the southern Dead Sea basin, south of the Lisan Peninsula in the latitude range of 31.05°-31.15° and along longitude 35.45° and continuing southward toward the Amaziahu Fault, reaching values of 0.4-0.5 s. There is a small positive residual at the Amaziahu Fault and a small negative residual south of it probably marking the southern end of the Dead Sea basin. East and west of the Dead Sea basin the mean teleseismic traveltime residuals are negative with overall averages of -0.35 s and -0.45 s, respectively. Using the teleseismic residuals, we estimate the horizontal dimensions of the Lisan salt diapir to be 23 km × 13 km at its widest and a maximal thickness of about 7.2 km. The thickness of the Mount Sodom salt diapir is estimated as 6.2 km. ©2014. American Geophysical Union. All Rights Reserved. Source

Deparis V.,77 Clos le Pastoral | Legros H.,Ecole et Observatoire des science de la Terre | Souchay J.,Paris Observatory
Lecture Notes in Physics | Year: 2013

Tidal phenomena along the coasts were known since the prehistoric era, but a long journey of investigations through the centuries was necessary from the Greco-Roman Antiquity to the modern era to unravel in a quasi-definitive way many secrets of the ebb and flow. These investigations occupied the great scholars from Aristotle to Galileo, Newton, Euler, d'Alembert, Laplace, and the list could go on. We will review the historical steps which contributed to an increasing understanding of the tides. © Springer-Verlag 2013. Source

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