TY - JOUR A1 - Panek, Tomas A1 - Korup, Oliver A1 - Lenart, Jan A1 - Hradecky, Jan A1 - Brezny, Michal T1 - Giant landslides in the foreland of the Patagonian Ice Sheet JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Quaternary glaciations have repeatedly shaped large tracts of the Andean foreland. Its spectacular large glacial lakes, staircases of moraine ridges, and extensive outwash plains have inspired generations of scientists to reconstruct the processes, magnitude, and timing of ice build-up and decay at the mountain front. Surprisingly few of these studies noticed many dozens of giant (≥108 m3) mass-wasting deposits in the foreland. We report some of the world's largest terrestrial landslides in the eastern piedmont of the Patagonian Ice Sheet (PIS) along the traces of the former Lago Buenos Aires and Lago Puyerredón glacier lobes and lakes. More than 283 large rotational slides and lateral spreads followed by debris slides, earthflows, rotational and translational rockslides, complex slides and few large rock avalanches detached some 164 ± 56 km3 of material from the slopes of volcanic mesetas, lake-bounding moraines, and river-gorge walls. Many of these landslide deposits intersect with well-dated moraine ridges or former glacial-lake shorelines, and offer opportunities for relative dating of slope failure. We estimate that >60% of the landslide volume (∼96 km3) detached after the Last Glacial Maximum (LGM). Giant slope failures cross-cutting shorelines of a large Late Glacial to Early Holocene lake (“glacial lake PIS”) likely occurred during successive lake-level drop between ∼11.5 and 8 ka, and some of them are the largest hitherto documented landslides in moraines. We conclude that 1) large portions of terminal moraines can fail catastrophically several thousand years after emplacement; 2) slopes formed by weak bedrock or unconsolidated glacial deposits bordering glacial lakes can release extremely large landslides; and 3) landslides still occur in the piedmont, particularly along postglacial gorges cut in response to falling lake levels. KW - Quaternary KW - Landslide KW - Geomorphology KW - Relative dating KW - Glacier foreland KW - Glacial lake KW - Patagonian Ice Sheet KW - Paleogeography KW - South America Y1 - 2018 U6 - https://doi.org/10.1016/j.quascirev.2018.06.028 SN - 0277-3791 VL - 194 SP - 39 EP - 54 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Ramos, Catalina A1 - Mechie, James A1 - Stiller, Manfred T1 - Reflection seismic images and amplitude ratio modelling of the Chilean subduction zone at 38.25 degrees S JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - Active source near-vertical reflection (NVR) data from the interdisciplinary project TIPTEQ were used to image and identify structural and petrophysical properties within the Chilean subduction zone at 38.25 degrees S, where in 1960 the largest earthquake ever recorded (M-w 9.5) occurred. Reflection seismic images of the subduction zone were obtained using the post-stack depth migration technique to process the three components of the NVR data, allowing to present P- and S-stacked time sections and depth-migrated seismic reflection images. Next, the reflectivity method allowed to model traveltimes and amplitude ratios of pairs of reflections for two 1D profiles along the studied transect. The 1D seismic velocities that produced the synthetic seismograms with amplitudes and traveltimes that fit the observed ones were used to infer the rock composition of the different layers in each 1D profile. Finally, an image of the subduction zone is given. The Chilean subduction zone at 38.25 degrees S underlies a continental crust with highly reflective horizontal, as well as dipping events. Among them, the Lanalhue Fault Zone (LFZ), interpreted to be east-dipping, is imaged to very shallow depths for the first time. In terms of seismic velocities, the inferred composition of the continental crust is in agreement with field geology observations at the surface along the profile. Furthermore, no measurable amounts of fluids above the plate interface in the continental crust in this part of the Chilean subduction zone are necessary to explain the results. A large-scale anisotropy in the continental crust and upper mantle is qualitatively proposed. However, quantitative studies on this topic in the continental crust of the Chilean subduction zone at 38.25 degrees S do not exist to date. KW - Reflection seismics KW - Reflectivity method KW - Subduction zone KW - South America Y1 - 2018 U6 - https://doi.org/10.1016/j.tecto.2018.10.007 SN - 0040-1951 SN - 1879-3266 VL - 747 SP - 115 EP - 127 PB - Elsevier CY - Amsterdam ER - TY - THES A1 - Ramos, Catalina T1 - Structure and petrophysical properties of the Southern Chile subduction zone along 38.25°S from seismic data T1 - Struktur und petrophysikalische Eigenschaften der südlichen Chile-Subduktionszone bei 38.25°S anhand seismischer Daten N2 - Active and passive source data from two seismic experiments within the interdisciplinary project TIPTEQ (from The Incoming Plate to mega Thrust EarthQuake processes) were used to image and identify the structural and petrophysical properties (such as P- and S-velocities, Poisson's ratios, pore pressure, density and amount of fluids) within the Chilean seismogenic coupling zone at 38.25°S, where in 1960 the largest earthquake ever recorded (Mw 9.5) occurred. Two S-wave velocity models calculated using traveltime and noise tomography techniques were merged with an existing velocity model to obtain a 2D S-wave velocity model, which gathered the advantages of each individual model. In a following step, P- and S-reflectivity images of the subduction zone were obtained using different pre stack and post-stack depth migration techniques. Among them, the recent prestack line-drawing depth migration scheme yielded revealing results. Next, synthetic seismograms modelled using the reflectivity method allowed, through their input 1D synthetic P- and S-velocities, to infer the composition and rocks within the subduction zone. Finally, an image of the subduction zone is given, jointly interpreting the results from this work with results from other studies. The Chilean seismogenic coupling zone at 38.25°S shows a continental crust with highly reflective horizontal, as well as (steep) dipping events. Among them, the Lanalhue Fault Zone (LFZ), which is interpreted to be east-dipping, is imaged to very shallow depths. Some steep reflectors are observed for the first time, for example one near the coast, related to high seismicity and another one near the LFZ. Steep shallow reflectivity towards the volcanic arc could be related to a steep west-dipping reflector interpreted as fluids and/or melts, migrating upwards due to material recycling in the continental mantle wedge. The high resolution of the S-velocity model in the first kilometres allowed to identify several sedimentary basins, characterized by very low P- and S-velocities, high Poisson's ratios and possible steep reflectivity. Such high Poisson's ratios are also observed within the oceanic crust, which reaches the seismogenic zone hydrated due to bending-related faulting. It is interpreted to release water until reaching the coast and under the continental mantle wedge. In terms of seismic velocities, the inferred composition and rocks in the continental crust is in agreement with field geology observations at the surface along the proflle. Furthermore, there is no requirement to call on the existence of measurable amounts of present-day fluids above the plate interface in the continental crust of the Coastal Cordillera and the Central Valley in this part of the Chilean convergent margin. A large-scale anisotropy in the continental crust and upper mantle, previously proposed from magnetotelluric studies, is proposed from seismic velocities. However, quantitative studies on this topic in the continental crust of the Chilean seismogenic zone at 38.25°S do not exist to date. N2 - Innerhalb des interdisziplinären Projektes TIPTEQ (from The Incoming Plate to mega Thrust EarthQuake processes) wurden aktive und passive Quelldaten zweier seismischer Experimente verwendet, um die strukturellen und petrophysikalischen Eigenschaften (wie zum Beispiel P- und S-Geschwindigkeiten, Poissonsverh ältnisse, Porendruck, Dichte und Flüssigkeitsmenge) in der chilenischen seismogenen Kopplungszone bei 38.25°S darzustellen und zu identifizieren, wo im Jahr 1960 das stärkste je gemessene Erdbeben (Mw 9.5) stattgefunden hat. Zwei Modelle für S-Wellengeschwindigkeiten, basierend auf Techniken für Laufzeiten und Rausch-Tomographie, wurden mit einem existierenden Geschwindigkeitsmodell zu einem 2D-Modell für S-Wellengeschwindigkeiten verbunden, welches der Vorteile der einzelnen Modellkomponenten vereint. Im nächsten Schritt wurden verschiedene pre-stack und post-stack Techniken der Tiefenmigration verwendet, um Bilder der P- und S-Reflektivität zu erhalten. Von diesen Techniken hat das jüngste Schema der pre-stack Linienzug-Tiefenmigration die erkenntnisreichtsen Ergebnisse geliefert. Darauf aufbauend erlauben synthetische Seismogramme, welche die Reflektivitätsmethode verwenden, durch Eingabe der synthetischen 1-D P- und S-Geschwindigkeiten, auf die Komposition und auf Gesteine in der Subduktionszone rückzuschlie ÿen. Schlieÿlich wird ein Bild der Subduktionszone gezeigt, welche die Ergebnisse dieser Arbeit im Zusammenhang mit weiteren Studien interpretiert. Die chilenische seismogene Kopplungszone bei 38.25°S zeigt eine kontinentale Kruste mit sowohl hochgradig reflektierenden horizontalen als auch (steil) geneigten Strukturen. Unter diesen ist die Lanalhue-Bruchzone (LFZ), welche östlich abtaucht, auf sehr flache Tiefen abgebildet. Einige steile Reflektoren wurden zum ersten Mal beobachtet, zum Beispiel nahe der Küste verbunden mit hoher Seismizität, und nahe der LFZ. Steile oberflächliche Reflektivität hin zum vulkanischen Bogen konnten mit einem steilen westlich abtauchenden Reflektor verbunden werden. Dieser besteht wahrscheinlich aus Flüssigkeit oder geschmolzenem Material, welches sich durch Materialrecycling im kontinentalen Mantelkeil aufwärts bewegt. Die hohe Auflösung des S-Geschwindigkeitsmodells in den ersten Kilometern erlaubte es, mehrere sedimentäre Becken zu identifizieren, die sich durch sehr niedrige P- und S-Geschwindigkeiten, hohe Poissonsverhältinesse und mögliche steile reflektivität auszeichnen. Solch hohen Poissonverhältinesse wurden auch in der ozeanischen Kruste beobachtet, welche die seismogene Zone durch krümmungsverursachte Abbrüche hydriert erreicht. Das Wasser wird dabei an der Küste und unter dem kontinentalen Mantelkeil freigesetzt. Mit Hinsicht auf seismische Geschwindigkeiten stimmen die hergeleitete Komposition und Gesteinsverteilung in der kontinentalen Kruste mit geologischen Feldbeobachtungen an der Oberfläche des Profils überein. Des Weiteren zeigt sich keine Notwendigkeit für die Existenz von messbaren Mengen an gegenwärtigen Flüssigkeiten über der Plattengrenze in der kontinentalen Kruste der küstennahen Kordilleren und dem Zentraltal in diesem Teil der chilenischen Konvergenzspanne. Anhand der seismischen Geschwindigkeiten wird eine groÿskalige Anisotropie in der kontinentalen Kruste und im oberen Mantel vorgeschlagen, wie schon zuvor durch magnetotellurische Studien. Jedoch existieren bis heute keine Studien zu diesem Thema für die kontinentale Kruste der chilenische seismogenen Zone bei 38.25°S. KW - active source data KW - seismogenic coupling zone KW - South America KW - reflection seismics KW - seismic tomography KW - synthetic seismograms KW - aktive Quelldaten KW - seismogene Kopplungszone KW - Südamerika KW - Reflexionsseismik KW - seismische Tomographie KW - synthetische Seismogramme Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-409183 ER -