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Maouche S.,CRAAG | Maouche S.,University of Science and Technology Houari Boumediene | Meghraoui M.,Institute Of Physique Du Globe | Morhange C.,CEREGE | And 3 more authors.
Tectonophysics | Year: 2011

Major uplifts of late Quaternary marine terraces are visible along the coastline of the Tell Atlas of Algeria located along the Africa-Eurasia convergent plate boundary. The active tectonics of this region is associated with large shallow earthquakes (M ≥ 6.5), numerous thrust mechanisms and surface fault-related fold. We conducted a detailed levelling survey of late Pleistocene and Holocene marine notches in the Algiers region that experienced 0.50. m coastal uplift during the 2003 Zemmouri earthquake (Mw 6.8). East of Algiers, Holocene marine indicators show three pre-2003 main notch levels formed in the last 21.9. ka. West of Algiers on the Sahel anticline, the levelling of uplifted marine terraces shows a distinct staircase morphology with successive notches that document the incremental folding uplift during the late Pleistocene and Holocene. The timing of successive uplifts related to past coseismic movements along this coastal region indicates episodic activity during the late Holocene. Modelling of surface deformation in the Zemmouri earthquake area implies a 50-km-long, 20-km-wide, NE-SW trending, SE dipping fault rupture and an average 1.3 m coseismic slip at depth. Further west, the 70-km-long Sahel fold is subdivided in 3 sub-segments and shows ~0.84-1.2 mm/yr uplift rate in the last 120-140. ka. The homogeneous Holocene uplift of marine terraces and the anticline dimensions imply the possible occurrence of large earthquakes with Mw ≥ 7 in the past. The surface deformation and related successive uplifts are modelled to infer the size and characteristics of probable future earthquakes and their seismic hazard implications for the Algiers region. © 2011 Elsevier B.V.

Gasperini L.,CNR Institute of Neuroscience | Polonia A.,CNR Institute of Neuroscience | Bortoluzzi G.,CNR Institute of Neuroscience | Henry P.,CEREGE | And 4 more authors.
Tectonics | Year: 2011

An open problem concerning the Mw 7.4, 1999 İzmit earthquake along the North Anatolian Fault (NAF) system is the apparent conflict between estimates of strike-slip deformation based on field and remote sensing data. This is due to the fact that the main strand of the NAF west of the epicenter lies below the Sea of Marmara. Seismological evidence and models based on synthetic aperture radar interferometry suggest that coseismic and early postseismic displacement accumulated after the earthquake could have reached the western end of the İzmit Gulf and possibly the southern edge of the Çinarcik Basin, tapering off along the northern coast of the Armutlu Peninsula, more than 60 km from the epicenter. This scenario is not confirmed by onshore field observations that point toward a termination of the surface rupture around 30 km to the east. These discrepancies convey high uncertainties in the estimate of the tectonic load produced by the İzmit earthquake on the adjacent fault segment toward Istanbul. We analyzed data from different sources, including high-resolution marine geophysical surveys and two Nautile dives along the fault-controlled canyon that connects İzmit Çinarcik basins. Our observations suggest that the surface rupture of the 1999 İzmit earthquake propagated through the shallow Gulf but did not reach the deep Marmara basins. In fact, along the slope between Çinarcik and the western end of the İzmit Gulf, we do not observe fault-related ruptures affecting the seafloor but rather a series of active gas seeps and "black patches" that mark the presence of known active faults. Our findings have implications for seismic risk assessment in the highly populated region of Istanbul, both for the estimate of tectonic load transferred to the next fault segments and the location of the next earthquake. Copyright 2011 by the American Geophysical Union.

Swingedouw D.,French Climate and Environment Sciences Laboratory | Terray L.,European Center for Research and Advanced Training in Scientific Computation | Servonnat J.,French Climate and Environment Sciences Laboratory | Guiot J.,CEREGE
Climate of the Past | Year: 2012

A simulation of the last millennium is compared to a recent spatio-temporal reconstruction of summer temperature over Europe. The focus is on the response to solar forcing over the pre-industrial era. Although the correlation between solar forcing and the reconstruction remains small, the spatial regression over solar forcing shows statistically significant regions. The meridional pattern of this regression is found to be similar in the model and in the reconstruction. This pattern exhibits a large warming over Northern and Mediterranean Europe and a lesser amplitude response over Central and Eastern Europe. The mechanisms explaining this pattern in the simulation are mainly related to evapotranspiration fluxes. It is shown that the evapotranspiration is larger in summer over Central and Eastern Europe when solar forcing increases, while it decreases over the Mediterranean area. The explanation for the evapotranspiration increase over Central and Eastern Europe is found in the increase of winter precipitation there, leading to a soil moisture increase in spring. As a consequence, the evapotranspiration is larger in summer, which leads to an increase in cloud cover over this region, reducing the surface shortwave flux there and leading to less warming. Over the Mediterranean area, the surface shortwave flux increases with solar forcing, the soil becomes dryer and the evapotranspiration is reduced in summer leading to a larger increase in temperature. This effect appears to be overestimated in the model as compared to the reconstruction. Finally, the warming of Northern Europe is related to the albedo feedback due to sea-ice cover retreat with increasing solar forcing. © 2012 Author(s).

Codo J.M.,Total S.A. | Fournier F.,CEREGE
3rd EAGE/SBGf Workshop 2016: Quantitative Seismic Interpretation of Lacustrine Carbonates | Year: 2016

The acoustic properties of carbonate reservoirs are strongly controlled by pore space architecture resulting from both depositional and diagenetic processes. As a consequence seismic inversion in highly diagenetized sedimentary systems such pre-salt non-marine carbonates requires first a quantification of the mineralogic, pore volume, pore geometry and fluid effects on acoustic impedance. In addition such a poroelastic modelling approach must be coupled with the characterization and quantification of the diagenetic processes controlling the pore space architecture and mineralogy in order to constrain the seismic inversion and to compute geologically realistic models of carbonate reservoirs in 3D.

News Article | March 1, 2017
Site: www.newscientist.com

Like tiny skydivers, particles of space dust use water to “parachute” safely to Earth. This helps wet particles withstand the plunge to Earth better than dry ones, meaning we may be overestimating the wetness of nearby asteroids. The area around Earth is full of cosmic dust particles, so Earth is full of them too. “Cosmic dust is everywhere: it is on our streets, it’s in our homes, and it’s quite possibly on our clothes as well,” says Matthew Genge at Imperial College London, who has studied these micrometeorites for decades. “You’re probably no more than a few feet away from a cosmic dust particle that parachuted through the atmosphere.” In his latest study, Genge ran simulations showing that as it hurtles through the atmosphere, cosmic dust can reach temperatures in excess of 1000°C. Any water in the particles will boil, forming bubbles in the rock. “They are really sort of dramatic little particles,” says Genge. “They contain so many bubbles, they’re basically magma foams.” These bubbles cause the dust to become bigger and less dense, slowing its descent through the atmosphere. “As it gets hot, popcorn pops and opens. It becomes bigger and less dense, and due to this, it will slow down in the air like a feather and will not burn,” says Tomas Kohout at the University of Helsinki in Finland. “The same thing happens with the micrometeorites.” Genge’s study found that hydrated dust particles that go through this popcorn-like process are twice as likely to survive as their drier counterparts, which melt or are incinerated in the atmosphere. This explains why most of the unmelted micrometeorites that we find on the ground come from asteroids with water on them. “It is clear this effect skews our sampling of micrometeorites,” says Pierre Rochette at the European Centre for Research and Education in Environmental Geosciences (CEREGE). So when researchers use micrometeorites to study asteroids near Earth, they will have to keep in mind that more wet dust doesn’t necessarily mean more wet asteroids.

Carpena J.,CEREGE | Lacout J.-L.,ENSIACET
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010

Synthetic analogues of poor-silicated natural apatites have been doped with uranium. These minerals have been irradiated with a thermal neutron dose in the aim to induce the 235U fission and to obtain a fission track population. Thermal annealing experiments have been performed on the fission track population and allow us to compare the ability of the synthetic minerals to anneal such nuclear damages with their natural analogues. The thermal of the fission tracks in the synthetic minerals need more time and/or higher temperature to reach the same annealing rate as in the natural analogues. The alpha damage present in the natural analogues seems to enhance the thermal annealing of fission tracks. © 2010 Elsevier B.V. All rights reserved.

Rood D.H.,University of California at Santa Barbara | Rood D.H.,Lawrence Livermore National Laboratory | Burbank D.W.,University of California at Santa Barbara | Finkel R.C.,CEREGE | Finkel R.C.,University of California at Berkeley
Earth and Planetary Science Letters | Year: 2011

Patterns in fault slip rates through time and space are examined across the transition from the Sierra Nevada to the Eastern California Shear Zone-Walker Lane belt. At each of four sites along the eastern Sierra Nevada frontal fault zone between 38 and 39° N latitude, geomorphic markers, such as glacial moraines and outwash terraces, are displaced by a suite of range-front normal faults. Using geomorphic mapping, surveying, and 10Be surface exposure dating, mean fault slip rates are defined, and by utilizing markers of different ages (generally, ~20ka and ~150ka), rates through time and interactions among multiple faults are examined over 104-105year timescales. At each site for which data are available for the last ~150ky, mean slip rates across the Sierra Nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval (~20ky and ~150ky timescales): 0.3±0.1mm year-1 (mode and 95% CI) at both Buckeye Creek in the Bridgeport basin and Sonora Junction; and 0.4 +0.3/-0.1mm year-1 along the West Fork of the Carson River at Woodfords. Data permit rates that are relatively constant over the time scales examined. In contrast, slip rates are highly variable in space over the last ~20ky. Slip rates decrease by a factor of 3-5 northward over a distance of ~20km between the northern Mono Basin (1.3 +0.6/-0.3mm year-1 at Lundy Canyon site) to the Bridgeport Basin (0.3±0.1mm year-1). The 3-fold decrease in the slip rate on the Sierra Nevada frontal fault zone northward from Mono Basin is indicative of a change in the character of faulting north of the Mina Deflection as extension is transferred eastward onto normal faults between the Sierra Nevada and Walker Lane belt. A compilation of regional deformation rates reveals that the spatial pattern of extension rates changes along strike of the Eastern California Shear Zone-Walker Lane belt. South of the Mina Deflection, extension is accommodated within a diffuse zone of normal and oblique faults, with extension rates increasing northward on the Fish Lake Valley fault. Where faults of the Eastern California Shear Zone terminate northward into the Mina Deflection, extension rates increase northward along the Sierra Nevada frontal fault zone to ~0.7mm year-1 in northern Mono Basin. This spatial pattern suggests that extension is transferred from more easterly fault systems, e.g., Fish Lake Valley fault, and localized on the Sierra Nevada frontal fault zone as the Eastern California Shear Zone-Walker Lane belt faulting is transferred through the Mina Deflection. © 2010 Elsevier B.V.

Rood D.H.,University of California at Santa Barbara | Rood D.H.,Lawrence Livermore National Laboratory | Burbank D.W.,University of California at Santa Barbara | Finkel R.C.,CEREGE | Finkel R.C.,University of California at Berkeley
Quaternary Science Reviews | Year: 2011

We use 10Be surface exposure dating to construct a high-resolution chronology of glacial fluctuations in the Sierra Nevada, California. Most previous studies focused on individual glaciated valleys, whereas our study compares chronologies developed throughout the range to identify regional patterns in the timing of glacier response to major climate changes. Sites throughout the range indicate Last Glacial Maximum retreat at 18.8 ± 1.9 ka (2σ) that suggests rather consistent changes in atmospheric variables, e.g., temperature and precipitation, throughout the range. The penultimate glacial retreat occurred at ca 145 ka. Our data suggest that the Sierra Nevada landscape is dominated by glacial features deposited during marine isotope stage (MIS) 2 and MIS 6. Deposits of previously recognized glaciations between circa 25 and 140 ka, e.g., MIS 4, Tenaya, early Tahoe, cannot be unequivocally identified. The timing of Sierra Nevada glacial retreat correlates well with other regional paleoclimate proxies in the Sierra Nevada, but differs significantly from paleoclimate proxies in other regions. Our dating results indicate that the onset of LGM retreat occurred several thousand years earlier in the Sierra Nevada than some glacial records in the western US. © 2010 Elsevier Ltd.

Tisnerat-Laborde N.,French Climate and Environment Sciences Laboratory | Paterne M.,French Climate and Environment Sciences Laboratory | Metivier B.,French Natural History Museum | Arnold M.,CEREGE | And 3 more authors.
Quaternary Science Reviews | Year: 2010

We compiled new 14C analyses of mollusc shells (bivalves and gastropods) of known age from the collection of the Muséum National d'Histoire Naturelle de Paris and previously published data to investigate changes in the sea surface Δ14C and reservoir age in the northeast Atlantic sector (NEA) between 1823 and 1952 AD. The mollusc shells are mainly located off the Atlantic margin between 45°N and 60°N downstream of the North Atlantic Current (NAC). We show that the temporal variability of the NEA Δ14C is independent of the mollusc species, depth habitat, diet and latitudinal distribution. The quasi-null difference between mollusc Δ14C and the marine model indicate that the mollusc Δ14C reflects the Δ14C values of open marine conditions. Between 1823 and 1850 AD, the pre-anthropogenic mean of Δ14C is -45 ± 5‰, corresponding to a reservoir age of 380 ± 60 years and a ΔR value of -7 ± 50 years, in agreement with previous estimates. The Δ14C values show a significant long-term decrease of ∼12‰ from 1823 to 1952 AD attributed to changes in 14C production between 1823 and 1900 AD and the Suess effect between 1900 and 1952 AD.Between 1885 and 1950 AD, Δ14C fluctuations of ∼10‰ up to 18‰ occurred in the northeast Atlantic, corresponding to reservoir age variations of ∼90 years up to 170 years. These fluctuations are very similar to changes of Δ14C in the southern Norwegian Sea. Spectral analyses of the NEA Δ14C exhibit quasi-periodic cycles of about 7.4 years, almost equivalent to the quasi-periodic cycles of the winter index of the North Atlantic Oscillation (NAO) with a period around 6.5 years. We find that changes of NEA Δ14C cannot be attributed to changes in river runoff or the precipitation/evaporation budget. The Δ14C lows (or high reservoir ages) correspond to the more intense phase of the winter NAO, with a time lag of ∼1-3 years. Such a time lag may reflect the eastward transit time of upstream changes originating in the Labrador Sea, then entrained within the NAC along with the subpolar gyre into the northeast Atlantic sector. During these events, we estimate that about 70% of the total transport in the NAC was due to water originating in the Labrador Sea. © 2010 Elsevier Ltd.

Alexandre A.,CEREGE | Crespin J.,CEREGE | Sylvestre F.,CEREGE | Sonzogni C.,CEREGE | And 2 more authors.
Climate of the Past | Year: 2012

Phytoliths are micrometric particles of amorphous silica that form inside or between the cells of higher plant tissues throughout the life of a plant. With plant decay, phytoliths are either incorporated into soils or exported to sediments via regional watersheds. Phytolith morphological assemblages are increasingly used as proxy of grassland diversity and tree cover density in inter-tropical areas. Here, we investigate whether, along altitudinal gradients in northeast Queensland (Australia), changes in the δ18O signature of soil top phytolith assemblages reflect changes in mean annual temperature (MAT) and in the oxygen isotopic composition of precipitation (δ18Oprecipitation), as predicted by equilibrium temperature coefficients previously published for silica. Oxygen isotopic analyses were performed on 16 phytolith samples, after controlled isotopic exchange (CIE), using the IR Laser-Heating Fluorination Technique. Long-term mean annual precipitation (MAP) and MAT values at the sampled sites were calculated by the ANUCLIM software. δ18Oprecipitation estimates were calculated using the Bowen and Wilkinson (2002) model, slightly modified. An empirical temperature-dependant relationship was obtained: δ18Owood phytolith-precipitation (‰ vs. VSMOW) -0.4 (±0.2) τ (°C) + 46 (±3) (R 2 = 0.4, p < 0.05; n = 12). Despite the various unknowns introduced when estimating δ18Oprecipitation values and the large uncertainties on δ18Owood phytolith values, the temperature coefficient (-0.4 ± 0.2‰ °C-1) is in the range of values previously obtained for natural quartz, fresh and sedimentary diatoms and harvested grass phytoliths (from -0.2 to -0.5‰ °C-1). The consistency supports the reliability of δ18Owood phytolith signatures for recording relative changes in mean annual δ18Osoil water values (which are assumed to be equivalent to the weighted annual δ18O precipitation values in rainforests environments) and MAT, provided these changes were several ‰ and/or several °C in magnitude. © Author(s) 2012.

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