Geosciences Azur

Valbonne, France

Geosciences Azur

Valbonne, France
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Jiang G.-J.,Eastern Taiwan Study Association | Angelier J.,Geosciences Azur | Lee J.C.,Academia Sinica, Taiwan | Chu H.-T.,Central Geological Survey | And 3 more authors.
Terrestrial, Atmospheric and Oceanic Sciences | Year: 2011

Field investigations following the 2003 Mw = 6.8 Chengkung earthquake in eastern Taiwan revealed some interesting observations of surface geological processes closely related to the co-seismic deformation. We discovered that the Tama Fault, which is about 15 km east of the causative Chihshang Fault, underwent shortening of about 15.5 mm locally in 2001 - 2006, particularly during the 2003 earthquake. This shows that ESE-WNW compression affects the upper crust of the Coastal Range and produces significant shortening in addition to that of the major Chihshang Fault. On the hanging wall of the Chihshang Fault, we also found vigorous activities of the two major mud volcanoes during the main shock, lasting several days. To the north, the Luoshan Mud Volcano, a large mud basin, erupted noisily with water and gases during the earthquake. To the south, in the Leikunghuo Mud Volcano, two sets of fractures, one aligned with the N 16°E right-lateral fault and the other with the N80°E left-lateral fault, occurred during the earthquake. This conjugate system revealed a strike-slip stress regime with NESW compression and NW-SE extension. We interpret it to be the result of local stress permutation rather than regional tectonic stress. We conclude that deformation did occur inside of the Coastal Range, especially during the co-seismic event. Therefore, a better understanding of the internal deformation of the Coastal Range is an important target for future studies, particularly across three mapped faults: the Yungfeng, Tuluanshan and Tama faults. We also want to draw attention to the stress analysis in the mud volcanoes area, where the local stress perturbation plays an important role.

Parsons T.,U.S. Geological Survey | Segou M.,Geosciences Azur | Sevilgen V., | Milner K.,University of Southern California | And 3 more authors.
Geophysical Research Letters | Year: 2014

We calculate stress changes resulting from the M = 6.0 West Napa earthquake on north San Francisco Bay area faults. The earthquake ruptured within a series of long faults that pose significant hazard to the Bay area, and we are thus concerned with potential increases in the probability of a large earthquake through stress transfer. We conduct this exercise as a prospective test because the skill of stress-based aftershock forecasting methodology is inconclusive. We apply three methods: (1) generalized mapping of regional Coulomb stress change, (2) stress changes resolved on Uniform California Earthquake Rupture Forecast faults, and (3) a mapped rate/state aftershock forecast. All calculations were completed within 24 h after the main shock and were made without benefit of known aftershocks, which will be used to evaluative the prospective forecast. All methods suggest that we should expect heightened seismicity on parts of the southern Rodgers Creek, northern Hayward, and Green Valley faults. Key Points The West Napa earthquake changed stress on Bay Area faultsRapid stress-based earthquake forecasts for evaluating methodsForecasts will be evaluated against the actual aftershock patterns ©2014. American Geophysical Union. All Rights Reserved.

Magny M.,French National Center for Scientific Research | Arnaud F.,University of Savoy | Holzhauser H.,Ahornstrasse 38 | Chapron E.,CNRS Earth Sciences Institute of Orléans | And 6 more authors.
Quaternary Research | Year: 2010

This paper presents a lake-level record established for the last millennium at Lake Saint-Point in the French Jura Mountains. A comparison of this lake-level record with a solar irradiance record supports the hypothesis of a solar forcing of variations in the hydrological cycle linked to climatic oscillations over the last millennium in west-central Europe, with higher lake levels during the solar minimums of Oort (around AD 1060), Wolf (around AD 1320), Spörer (around AD 1450), Maunder (around AD 1690), and Dalton (around AD 1820). Further comparisons of the Saint-Point record with the fluctuations of the Great Aletsch Glacier (Swiss Alps) and a record of Rhône River floods from Lake Bourget (French Alps) give evidence of possible imprints of proxy sensitivity on reconstructed paleohydrological records. In particular, the Great Aletsch record shows an increasing glacier mass from AD 1350 to 1850, suggesting a cumulative effect of the Little Ice Age cooling and/or a possible reflection of a millennial-scale general cooling until the mid-19th century in the Northern Hemisphere. In contrast, the Saint-Point and Bourget records show a general trend toward a decrease in lake levels and in flood magnitude anti-correlated with generally increasing solar irradiance. © 2009 University of Washington.

Loncke L.,University of Perpignan | Vendeville B.C.,Lille University of Science and Technology | Gaullier V.,University of Perpignan | Mascle J.,Geosciences Azur
Basin Research | Year: 2010

In the Nile deep-sea fan, thin-skinned deformation detaching on a layer of Messinian salt has generated an upslope to downslope progression from growth faults, to polygonal minibasins bounded by salt ridges, to buckle folds. Such progression is common in salt-bearing passive margins, where gravity spreading of the salt-sediment system causes proximal thin-skinned extension on the shelf and upper slope, and distal contraction along and in front of the lower slope. In the Eastern Nile deep-sea fan, this structural progression seems to be restricted to a corridor bounded by NW-SE-trending lineaments more than 200 km in length. These are associated with salt ridges and record strike-slip movements. In the absence of a large grid of deep-penetrating seismic data accurately imaging the basement, different likely hypotheses have been advanced about the origin of this corridor: (1) it may result from possible deep-seated tectonics related to the Rift of Suez, combined with salt-related deformation or, (2) by complex interaction between the overburden's gravity spreading and pre-existing pre-Messinian paleo-topographic features, particularly the possible buttressing effect of a seamount located North of the eastern Nile deep-sea fan. In order to understand how this corridor could have been generated, we used a series of physical experiments to test the effect on three-dimensional spreading of a sediment lobe of the following parameters: (1) active, crustal, oblique extension, (2) a dormant subsalt graben, (3) a passive buttress, such as a seamount and (4) complex paleo-topographic features along the Egyptian margin affecting initial salt distribution. These experiments show that the presence of a distal buttress, combined with a complex Messinian topography best explain the complex deformational pattern observed in the eastern Nile deep-sea fan. © 2009 The Authors. Journal Compilation © Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

Saillet E.,Geosciences Azur | Wibberley C.A.J.,Total S.A.
Journal of Structural Geology | Year: 2010

Cataclastic deformation structures in Cretaceous high-porosity sands in the Bassin du Sud-Est, SE France were surveyed by scan-lines to examine: (i) the role of tectonic loading path on cataclastic deformation band (CDB) network development, and (ii) the development of larger ultracataclastic faults as strain increases. Deformation during Pyrenean-Provençal shortening resulted in a persistent high density (∼10/m2) of conjugate reverse-sense CDB zones (displacements up to ∼30cm), with no generation of larger faults. High-low-density undulations occur for each pair of the conjugate set in an alternating manner, suggestive of network hardening, with a wavelength of several tens of metres being in the order of mechanical bed thickness. For two study areas which experienced significant Oligocene-Miocene extension, a moderate, undulating background density (∼4/m2) of normal-offset CDBs was recorded, which became focussed in places into clusters (∼50/m2) a few metres wide. Thus tectonic loading path may strongly influence strain distribution. CDB zones develop by the addition of successive bands at the edges until, at a thickness of around 5cm, new bands tend to stray further away from the zone edges. Coarser sands have thicker CDB zones, suggesting that host grain size, along with mechanical bed thickness, could be an important contributor to the scale limit in CDB zone growth. Larger ultracataclastic faults and discrete slip zones localised within or at the edges of some clusters of CDB zones, post-date cluster development rather than inducing it. This stage of deformation evolution is only reached in extension, not in shortening, suggesting the infeasibility of achieving the critical state line during horizontal compression. © 2010 Elsevier Ltd.

Giresse P.,University of Perpignan | Loncke L.,University of Perpignan | Huguen C.,Total S.A. | Muller C.,6 bis | Mascle J.,Geosciences Azur
Sedimentary Geology | Year: 2010

During the last 10. years several marine geological/geophysical surveys conducted on the Nile deep-sea fan have provided much new information about the large fluid seepage phenomenon, which characterizes this passive margin segment. Among the data, more than 60 sediment cores have been recovered in this area. Rock clasts were collected from eight of them as well as during deep-sea dives, notably in the area of Isis, Osiris and Amon mud volcanoes. In few areas, especially in the Western and the North-eastern provinces of the Nile fan, some clasts consist of crust fragments resulting from cementation of muddy sediment by precipitation of high-Mg calcite. These clasts correspond to a simple cementation of the mud by precipitation of high-Mg calcite: as a consequence no obvious textural or faunal difference with the ambient matrix mud can be observed. These clasts are made of autochthonous crusts derived from microbial anaerobic oxidation of methane and release of bicarbonate and sulphide in the surrounding pore water. These clasts also lack aragonite. In most of the other cases (Menes caldera, Isis, Osiris, and Amon mud volcanoes), allochthonous clasts characterized by low-Mg calcite cement, siderite or dolomite mixed with expelled mud outcrop on the seafloor. Nannofossils have allowed us to date some of these clasts. Most of the ages range from Pliocene to Pleistocene; one clast is Lower Cretaceous in age. The lithological facies often indicate coastal or deltaic environments. Some clasts are closely linked to an evaporite-rich environment (halite, gypsum, and analcime); they all provide useful information on the nature of buried sedimentary series covering the margin. Their presence on the seafloor is due to the expulsion of a pressurized mixture of sediment, water, and gas. This process is believed to have used pre-existing tectonic conduits. © 2010 Elsevier B.V.

Obayashi M.,Japan Agency for Marine - Earth Science and Technology | Yoshimitsu J.,Japan Agency for Marine - Earth Science and Technology | Nolet G.,Geosciences Azur | Fukao Y.,Japan Agency for Marine - Earth Science and Technology | And 4 more authors.
Geophysical Research Letters | Year: 2013

We present a new whole mantle P wave tomographic model GAP-P4. We used two data groups; short-period data of more than 10 million picked-up onset times and long-period data of more than 20 thousand differential travel times measured by waveform cross correlation. Finite frequency kernels were calculated at the corresponding frequency bands for both long- and short-period data. With respect to an earlier model GAP-P2, we find important improvements especially in the transition zone and uppermost lower mantle beneath the South China Sea and the southern Philippine Sea owing to broadband ocean bottom seismometers (BBOBSs) deployed in the western Pacific Ocean where station coverage is poor. This new model is different from a model in which the full data set is interpreted with classical ray theory. BBOBS observations should be more useful to sharpen images of subducted slabs than expected from simple raypath coverage arguments. Key Points We did a global P tomography using travel times including those from seafloors All data were analyzed using finite frequency kernels We revealed a stagnant slab in the MTZ detached from the downgoing Mariana slab ©2013. American Geophysical Union. All Rights Reserved.

Tari G.,OMV Austria Exploration and Production GmbH | Kohazy R.,OMV Austria Exploration and Production GmbH | Hannke K.,OMV Austria Exploration and Production GmbH | Hussein H.,OMV | And 2 more authors.
Leading Edge | Year: 2012

Numerous deep-water play types have been identified along the transform margin of NW Egypt. A large segment of the offshore Matruh Basin has play types related to a prominent shale décollement within the Matruh Canyon. The footwalls of the growth faults associated with the shale detachment provide fault-controlled three-way closures very similar to the well-known rafts in the Lower Congo Basin in West Africa. As updip extension transitions to downdip contraction, some thin-skinned toe-thrust imbrications can be found in the ultradeep-water part of Matruh Basin. Another important play type in the deep-water offshore Matruh Basin is related to the prominent syn-rift "hinge zone" of an interpreted transform margin of the eastern Mediterranean. This play type could serve as a play opener along the transform margin of NW Egypt and NE Libya. The offshore Matruh and Herodotus basins of NW Egypt represent an underexplored region of the Mediterranean, with only one deep-water well drilled along the margin to date. © 2012 Society of Exploration Geophysicists.

Parsons T.,U.S. Geological Survey | Segou M.,Geosciences Azur | Marzocchi W.,Italian National Institute of Geophysics and Volcanology
Tectonophysics | Year: 2014

The aftershock zone of each large (M≥. 7) earthquake extends throughout the shallows of planet Earth. Most aftershocks cluster near the mainshock rupture, but earthquakes send out shivers in the form of seismic waves, and these temporary distortions are large enough to trigger other earthquakes at global range. The aftershocks that happen at great distance from their mainshock are often superposed onto already seismically active regions, making them difficult to detect and understand. From a hazard perspective we are concerned that this dynamic process might encourage other high magnitude earthquakes, and wonder if a global alarm state is warranted after every large mainshock. From an earthquake process perspective we are curious about the physics of earthquake triggering across the magnitude spectrum. In this review we build upon past studies that examined the combined global response to mainshocks. Such compilations demonstrate significant rate increases during, and immediately after (~. 45. min) M>. 7.0 mainshocks in all tectonic settings and ranges. However, it is difficult to find strong evidence for M>. 5 rate increases during the passage of surface waves in combined global catalogs. On the other hand, recently published studies of individual large mainshocks associate M>. 5 triggering at global range that is delayed by hours to days after surface wave arrivals. The longer the delay between mainshock and global aftershock, the more difficult it is to establish causation. To address these questions, we review the response to 260 M≥. 7.0 shallow (Z≤. 50. km) mainshocks in 21 global regions with local seismograph networks. In this way we can examine the detailed temporal and spatial response, or lack thereof, during passing seismic waves, and over the 24. h period after their passing. We see an array of responses that can involve immediate and widespread seismicity outbreaks, delayed and localized earthquake clusters, to no response at all. About 50% of the catalogs that we studied showed possible (localized delayed) remote triggering, and ~. 20% showed probable (instantaneous broadly distributed) remote triggering. However, in any given region, at most only about 2-3% of global mainshocks caused significant local earthquake rate increases. These rate increases are mostly composed of small magnitude events, and we do not find significant evidence of dynamically triggered M>. 5 earthquakes. If we assume that the few observed M>. 5 events are triggered, we find that they are not directly associated with surface wave passage, with first incidences being 9-10. h later. We note that mainshock magnitude, relative proximity, amplitude spectra, peak ground motion, and mainshock focal mechanisms are not reliable determining factors as to whether a mainshock will cause remote triggering. By elimination, azimuth, and polarization of surface waves with respect to receiver faults may be more important factors. © 2014.

Dupre S.,VU University Amsterdam | Dupre S.,French Research Institute for Exploitation of the Sea | Woodside J.,VU University Amsterdam | Klaucke I.,Leibniz Institute of Marine Science | And 2 more authors.
Marine Geology | Year: 2010

Fluid escape structures on the Nile Deep Sea Fan were investigated during the MEDIFLUX MIMES expedition in 2004. Mud volcanoes, pockmarks and authigenic carbonate structures were surveyed for the first time with a high-resolution deep-towed 75. kHz sidescan sonar and a 2-8. kHz Chirp sediment echosounder. In combination with existing multibeam bathymetry and detailed seafloor in situ geological observations, these new data allowed detailed seep analyses. About 60 gas flares were detected acoustically in the water column from the sidescan sonar raw data at water depths from 770 to 1700. m. These gas flares coincide at the seabed with 1) the centres of the mud volcanoes where mud is also extruded, 2) the borders of the mud volcanoes where the emitted gases contribute to the precipitation of authigenic carbonates, and 3) to the edges of broad sheets of authigenic carbonates. Subsurface sediments are commonly disturbed by ascending fluids throughout the delta, with an abundance of seep-related carbonate structures on the seafloor. The feeder channels below mud volcanoes, similar to the gas conduits below the widespread carbonate crust structures and pockmarks, are relatively narrow and, for the vast majority of them, do not exceed a few metres in diameter. The seeps on the Nile Deep Sea Fan clearly follow lineations on the seafloor that we can relate to faults. © 2010 Elsevier B.V.

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