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  • 1
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    Geochemical evidence for groundwater-charging of slope sediments: The Nice airport 1979 landslide and tsunami revisited (2009)
    In:  EPIC3Submarine mass movements and their consequences. / Hrsg. David Mosher; Hrsg. Craig Shipp; Hrsg. Lorena Moscardelli; Hrsg. Jason Chaytor; Hrsg. Chris Baxter; Hrsg. Homa Lee; Hrsg. Roger Urgeles Berlin : Springer. (Advances in Natural and Technological Haza, 203, ISBN: 978-90-481-3070-2
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 2
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    Constraints on fluid flow processes in the Hellenic Accretionary Complex (eastern Mediterranean Sea) from numerical modeling (2014)
    AGU
    In:  Journal of Geophysical Research: Solid Earth, 119 (4). pp. 3601-3626.
    Details
    Publication Date: 2020-07-23
    Description: The dynamics of accretionary convergent margins are severely influenced by intense deformation and fluid expulsion. To quantify the fluid pressure and fluid flow velocities in the Hellenic subduction system, we set up 2-D hydrogeological numerical models following two seismic reflection lines across the Mediterranean Ridge. These profiles bracket the along-strike variation in wedge geometry: moderate compression and a 〉4 km thick underthrust sequence in the west versus enhanced compression and 〈1 km of downgoing sediment in the center. Input parameters were obtained from preexisting geophysical data, drill cores, and new geotechnical laboratory experiments. A permeability-porosity relationship was determined by a sensitivity analysis, indicating that porosity and intrinsic permeability are small. This hampers the expulsion of fluids and leads to the build up of fluid overpressure in the deeper portion of the wedge and in the underthrust sediment. The loci of maximum fluid pressure are mainly controlled by the compactional fluid source, which generally decreases toward the backstop. However, pore pressure is still high at the decollement level at distances 〈100 km from the deformation front, either by the incorporation of low permeability evaporites or additional compaction of the wedge sediments in the two profiles. In the west, however, formation of a wide accretionary complex is facilitated by high pore pressure zones. When compared to other large accretionary complexes such as Nankai or Barbados, our results not only show broad similarities but also that near-lithostatic pore pressures may be easier to maintain in the Hellenic Arc because of accentuated collision, some underthrust evaporates, and a thicker underthrust sequence.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2013JB010405
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Fluid flow through active mud dome Mound Culebra offshore Nicoya Peninsula, Costa Rica: evidence from heat flow surveying (2004)
    Elsevier
    In:  Marine Geology, 207 . pp. 145-157.
    Details
    Publication Date: 2019-09-23
    Description: Mud extrusion is frequently observed as a dewatering phenomenon in compressional tectonic settings such as subduction zones. Along the Middle American Trench, several of these features have been recently discovered. This paper presents a heat flow study of actively venting Mound Culebra, offshore Nicoya Peninsula, and is complemented by data from geophysical surveys and coring. The mud diapir is characterised by methane emission and authigenic carbonate formation at its crest, and is composed of overconsolidated scaly clays and clast-bearing muds. Compared with the conductive background heat flow, the flux through the mud dome is elevated by 10–20 mW/m2, possibly related to advection of heat by fluids rising from greater depth. Decreased chlorinity in the pore waters from gravity cores may support a deep-seated fluid origin. Geothermal measurements across the mound and temperature measurements made with outriggers on gravity corers were corrected for the effects of thermal refraction, forced by the topography of the mound. Corrected values roughly correlate with the topography, suggesting advection of heat by fluids rising through the mound, thereby generating the prominent methane anomaly over the dome and nurturing vent biota. However, elevated values occur also to the southeast of the mound. We believe that the overconsolidated clays and carbonates on the crest form an almost impermeable lid. Fluids rising from depth underneath the dome are therefore partially channelled towards the flanks of the mound.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.margeo.2004.04.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Geotechnical characterization and strain analyses of sediment in the Mauritania Slide Complex, NW-Africa (2010)
    Elsevier
    In:  Marine and Petroleum Geology, 27 (6). pp. 1175-1189.
    Details
    Publication Date: 2017-07-26
    Description: Mass wasting processes are a common phenomenon along the continental margin of NW-Africa. Located on the high-upwelling regime off the Mauritanian coastline, the Mauritania Slide Complex (MSC) is one of the largest events known on the Atlantic margin with an affected area of not, vert, similar30 000 km2. Understanding previous failure events as well as its current hazard potential are crucial for risk assessment with respect to offshore installations and tsunamis. We present the results of geotechnical measurements and strain analyses on sediment cores taken from both the stable and the failed part of the MSC and compare them to previously published geophysical and sedimentological data. The material originates from water depths of 1500–3000 m and consists of detached slide deposits separated by undisturbed hemipelagic sediments. While the hemipelagites are characterized by normal consolidation with a downward increase in bulk density and shear strength (from 1.68 to 1.8 g/cm3, 2–10 kPa), the slid deposits of the uppermost debris flow event preserve constant bulk density values (1.75 and 1.8 g/cm3) with incisions marking different flow events. These slid sediments comprise three different matrix types, with normal consolidation at the base (OCR = 1.04), strong overconsolidation (OCR = 3.96) in the middle and normal consolidation to slight overconsolidation at the top (OCR = 0.91–1.28). However, the hemipelagic sediments underlying the debris flow units, which have been 14C dated at 〈24 ka BP, show strong to slight underconsolidation (OCR = 0.65–0.79) with low friction coefficients of μ = 0.18. Fabric analyses show deformation intensities R ≥ 4 (ratio σ1/σ3) in several of the remobilized sediments. Such high deformation is also attested by observed disintegrated clasts from the underlying unit in the youngest debrites (14C-age of 10.5–10.9 ka BP). These clasts show strong consolidation and intense deformation, implying a pre-slide origin and amalgamation into the mass transport deposits. While previous studies propose an emplacement by retrogressive failure for thick slide deposits separated by undisturbed units, our new data on geotechnical properties, strain and age infer at least two different source areas with a sequential failure mechanism as the origin for the different mass wasting events.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marpetgeo.2010.02.013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Origin and evolution of a splay fault in the Nankai accretionary wedge (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 . pp. 648-652.
    Details
    Publication Date: 2017-02-22
    Description: Subduction zones are often characterized by wedge-shaped sedimentary complexes—called accretionary prisms—that form when sediments are scraped off the subducting plate and added to the overriding plate. Large, landward-dipping thrust faults can cut through such a prism: these faults, known as 'megasplay faults'1, 2, originate near the top of the subducting plate and terminate at the shallow, landward edge of the prism1, 3, 4, 5, 6. Megasplay faults have been the subject of numerous geological and geophysical studies4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, but their initiation and evolution through time remains poorly constrained. Here we combine seismic reflection data from the Nankai accretionary wedge with geological data collected by the Integrated Ocean Drilling Program (IODP) and find that the splay fault cutting this wedge initiated approx1.95 Million years (Myr) ago in the lower part of the prism as an out-of-sequence thrust (OOST). After an initial phase of high activity, the movement along the fault slowed down, but uplift and reactivation of the fault resumed about 1.55 Myr ago. The alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/ngeo609
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Seismic potential of weak, near-surface faults revealed at plate tectonic slip rates (2017)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2017-11-23
    Description: The near-surface areas of major faults commonly contain weak, phyllosilicate minerals, which, based on laboratory friction measurements, are assumed to creep stably. However, it is now known that shallow faults can experience tens of meters of earthquake slip and also host slow and transient slip events. Laboratory experiments are generally performed at least two orders of magnitude faster than plate tectonic speeds, which are the natural driving conditions for major faults; the absence of experimental data for natural driving rates represents a critical knowledge gap. We use laboratory friction experiments on natural fault zone samples at driving rates of centimeters per year to demonstrate that there is abundant evidence of unstable slip behavior that was not previously predicted. Specifically, weak clay-rich fault samples generate slow slip events (SSEs) and have frictional properties favorable for earthquake rupture. Our work explains growing field observations of shallow SSE and surface-breaking earthquake slip, and predicts that such phenomena should be more widely expected.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Drilling reveals fluid control on architecture and rupture of the Alpine fault, New Zealand (2012)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2012-11-15
    Description: Rock damage during earthquake slip affects fluid migration within the fault core and the surrounding damage zone, and consequently coseismic and postseismic strength evolution. Results from the first two boreholes (Deep Fault Drilling Project DFDP-1) drilled through the Alpine fault, New Zealand, which is late in its 200–400 yr earthquake cycle, reveal a 〉50-m-thick "alteration zone" formed by fluid-rock interaction and mineralization above background regional levels. The alteration zone comprises cemented low-permeability cataclasite and ultramylonite dissected by clay-filled fractures, and obscures the boundary between the damage zone and fault core. The fault core contains a 〈0.5-m-thick principal slip zone (PSZ) of low electrical resistivity and high spontaneous potential within a 2-m-thick layer of gouge and ultracataclasite. A 0.53 MPa step in fluid pressure measured across this zone confirms a hydraulic seal, and is consistent with laboratory permeability measurements on the order of 10 –20 m 2 . Slug tests in the upper part of the boreholes yield a permeability within the distal damage zone of ~10 –14 m 2 , implying a six-orders-of-magnitude reduction in permeability within the alteration zone. Low permeability within 20 m of the PSZ is confirmed by a subhydrostatic pressure gradient, pressure relaxation times, and laboratory measurements. The low-permeability rocks suggest that dynamic pressurization likely promotes earthquake slip, and motivates the hypothesis that fault zones may be regional barriers to fluid flow and sites of high fluid pressure gradient. We suggest that hydrogeological processes within the alteration zone modify the permeability, strength, and seismic properties of major faults throughout their earthquake cycles.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Experimental evidence linking slip instability with seafloor lithology and topography at the Costa Rica convergent margin (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2013-07-23
    Description: Seismicity patterns offshore Costa Rica (Central America) at the Middle America Trench have led to speculation that large (moment magnitude, M w ~7.0) earthquakes are associated with subducting topographic highs. In areas of high basement topography, a regionally extensive nannofossil chalk unit is exposed at the seafloor on the incoming plate, whereas in regions of low basement topography, hemipelagic clay-rich sediment is exposed. Because the entire sediment section is subducted at this margin, lithologic variation in the uppermost subducting sediments may control plate boundary fault behavior. Our laboratory experiments reveal that the chalk is frictionally strong (µ = 0.71–0.88) and characterized by velocity-weakening and stick-slip behavior, notably at elevated temperature. In contrast, the hemipelagic sediment is weak (µ = 0.22–0.35) and in many cases velocity strengthening. We suggest that the presence of frictionally unstable carbonates at bathymetric highs may play a key, previously unrecognized, role in governing earthquake nucleation.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Recurring and triggered slow-slip events near the trench at the Nankai Trough subduction megathrust (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-06-16
    Description: The discovery of slow earthquakes has revolutionized the field of earthquake seismology. Defining the locations of these events and the conditions that favor their occurrence provides important insights into the slip behavior of tectonic faults. We report on a family of recurring slow-slip events (SSEs) on the plate interface immediately seaward of repeated historical moment magnitude ( M w ) 8 earthquake rupture areas offshore of Japan. The SSEs continue for days to several weeks, include both spontaneous and triggered slip, recur every 8 to 15 months, and are accompanied by swarms of low-frequency tremors. We can explain the SSEs with 1 to 4 centimeters of slip along the megathrust, centered 25 to 35 kilometers (km) from the trench (4 to 10 km depth). The SSEs accommodate 30 to 55% of the plate motion, indicating frequent release of accumulated strain near the trench.
    Keywords: Geochemistry, Geophysics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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