Katrin Huhn

Bio: Katrin Huhn is an academic researcher from University of Bremen. The author has contributed to research in topics: Submarine landslide & Landslide. The author has an hindex of 13, co-authored 51 publications receiving 685 citations. Previous affiliations of Katrin Huhn include University of Kiel.

Morphotectonics and mechanics of the central Makran accretionary wedge off Pakistan

Abstract: Swath bathymetry images and 3.5 kHz data acquired during RV Sonne cruise 123 in autumn 1997 are the base for analysing the morphology and deformation styles of the huge Makran accretionary wedge. The continental slope off Pakistan is characterised by three morphological provinces: (a) The lower slope is built of a sequence of imbricate thrust slices which form long and narrow accretionary ridges with flanks locally as steep as 20° and between 10° and 20° on average, while the regional slope is only 1–2°, (b) the nearly flat mid-slope terrace is present in the central east part of the margin, narrows significantly towards the east, and is absent east of 63° 45′ and (c) the upper slope up to the shelf has a regionally uniform slope as steep as about 8° and comprises a very rough topography with many gullies and canyons and evidence for mass wasting. Two meandering canyons crossing the entire margin down to the abyssal plain at about 63° 15′–63° 30′, can be correlated with onshore rivers. They have been formed by episodic erosion through turbidity flows and are characterised by erosional and depositional portions. Sinuosity of the canyons is exclusively caused by the accretionary ridges functioning as obstacles for flow to be directly downhill. Application of Coulomb rheology to the frontal part of the Makran Wedge implies that the mid-level decollement is intrinsically extraordinary weak with a great strength contrast to the overlying sediments. Comparison with Nankai, Cascadia, and the Western Mediterranean Ridge reveals new insights in the parameters controlling the shape of an accretionary wedge and the role of a mid-level decollement.

Newly identified strike-slip plate boundary in the northeastern Arabian Sea

Abstract: The first regional swath-bathymetry survey of the Makran accretionary wedge revealed a sinistral strike-slip fault, named herein the Sonne fault, obliquely crossing the wedge and continuing into the abyssal plane. This fault separates the western part of the Makran subduction zone where plate boundary events are absent from the eastern part that does show plate boundary seismicity; most events are concentrated along the Sonne fault. Little Murray Ridge (a basement high) and related magnetic anomalies are offset along the Sonne fault. Together, these observations identify the newly discovered Sonne strike-slip fault as a plate boundary that has been active ∼2 m.y. This finding suggests that what has been considered the northeasternmost part of the Arabian plate is actually a separate microplate, named herein the Ormara plate, the formation of which resulted from tearing of the Arabian plate along the Sonne fault. With this concept, the different dips of the downgoing plate below the western and eastern parts of the Makran margin and the related different distances between the trench and Quaternary arc volcanic centers can be unequivocally explained.

Influence of particle shape on the frictional strength of sediments — A numerical case study

Abstract: Numerous direct and ring shear tests supply that composition and texture of sediments are crucial for shear and frictional strength. We simulate particle interactions on a micro-scale level during shearing with a numerical shear box using the Discrete Element Method (DEM). Based on the granular model approach detailed information about slip localisation and rates, forces at particle contacts, as well as particle rotation can be quantified as function of particle shape, stress conditions, and shear rate. Our numerical experiments show that the deformation behaviour of ‘clay’ is largely controlled by their particle shape. Two key factors, sphericity and roughness, could be identified as relevant for frictional strength, shear zone development, and particle rotation with sphericity dominating over roughness. Decreasing sphericity leads to complex initial microfabrics whose breakdown with increasing strain is caused by particle rotation. Preferred particle orientation favours low friction, decreasing volume strain, and the evolution of particle domains of similar orientation. Decreasing roughness results in particle interlocking of different degrees which obstructs slip and rotation to preferred orientations so that friction is high and volume strain positive. Spatial and temporal shear zone development depends on the roughness of particles. Increasing roughness precludes shear zone development and particle domain evolution. Shear zone localisation depends on particle sphericity. Increasing sphericity leads to more localised but vertically dilated deformation.

Slope failure repetition in active margin environments: Constraints from submarine landslides in the Hellenic fore arc, eastern Mediterranean

Abstract: [1] It has been shown that submarine landslides can occur less frequently at subduction zone fore arcs despite the general expectation of extensive slope failures from high neotectonic activity in active margin settings. The Hellenic subduction zone, Greece, represents an example where modern evidence for slope failure is scarce. Taking the deeper parts of the fore-arc basin into account, however, a sequence of massive landslide deposits is found at recurrence intervals of approximately 250 ± 70 ka. Given high seismicity in the fore-arc area, this rate of slope failure appears to be low. In order to improve our understanding on the relationship between low landslide recurrence rates and the frequency and settings of the required trigger mechanism, we here assess the mechanical behavior of the slope sediment cover during instability scenarios. Seismic profiles and geotechnical measurements from cores of midsize landslides found on the northeastern Cretan midslope are used to back-analyze slope destabilization in one-dimensional, infinite slope models for static conditions as well as for the case of seismic loading. Results reveal that today only critically steepened parts of the Cretan slope can fail from high loading stresses of peak ground acceleration (PGA) of 37%g, maybe up to ≥64%g. We further deduce that long-term tectonic processes are important preconditioning factors controlling an occasional development of critically inclined slope parts. Therefore, the impact of seismic triggers is strongly limited in time and space: For an initially stable slope, the critical seismic intensity to trigger failure is being reduced with increasing tectonically controlled steepening of the slope through time, until an earthquake is sufficient to trigger a large landslide. Before that, the slope rather gets more resistant, because smaller PGA may rather result in dynamic compaction (seismic strengthening). Our findings imply that low frequencies of landslides in the Hellenic fore arc are not in conflict with high seismicity in this region, because seismic loading is only sufficient to trigger major collapses of a generally shear-resistant “cohesive” slope (increasing with time due to seismic strengthening) if long-term tectonic movement provides a critical steepening. This may explain the relatively scarce occurrence of large submarine landslides in this and similar tectonically active environments.

Submarine Mass Movements and Their Consequences : 6th International Symposium

Abstract: 6th International Symposium on Submarine Mass Movements and Their Consequences (ISSMMTC), 23-25 September 2013, Kiel, Germany.-- 686 pages, 268 figures

Evaluation of climate models using palaeoclimatic data

Abstract: There is large uncertainty about the magnitude of warming and how rainfall patterns will change in response to any given scenario of future changes in atmospheric composition and land use. The models used for future climate projections were developed and calibrated using climate observations from the past 40 years. The geologic record of environmental responses to climate changes provides a unique opportunity to test model performance outside this limited climate range. Evaluation of model simulations against palaeodata shows that models reproduce the direction and large-scale patterns of past changes in climate, but tend to underestimate the magnitude of regional changes. As part of the effort to reduce model-related uncertainty and produce more reliable estimates of twenty-first century climate, the Palaeoclimate Modelling Intercomparison Project is systematically applying palaeoevaluation techniques to simulations of the past run with the models used to make future projections. This evaluation will provide assessments of model performance, including whether a model is sufficiently sensitive to changes in atmospheric composition, as well as providing estimates of the strength of biosphere and other feedbacks that could amplify the model response to these changes and modify the characteristics of climate variability.

Classification of offshore mass movements

Abstract: More than 100 offshore mass-movement deposits have been studied in Holocene and Pleistocene sediments. The processes can be divided into three main types: slides/slumps, plastic flows, and turbidity currents, of which 13 main varieties have been recognized. The three types are differentiated mainly by motion, architecture, and shape of failure surface. For slides, the morphology of deposits can usually be linked to a process, but for plastic flows and turbidity currents, information about the motion is mainly provided by the sedimentary record. A static classification based on these features is given, and is related to a dynamic classification system to try to underline the morphological transformation of an offshore event from initiation to deposition.

Accretionary prisms in subduction earthquake cycles: The theory of dynamic Coulomb wedge

Abstract: [1] We expand the theory of critically tapered Coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles. Building on the Coulomb plasticity of the classical theory, we assume an elastic–perfectly Coulomb plastic rheology and derive exact stress solutions for stable and critical wedges. The new theory postulates that the actively deforming, most seaward part of an accretionary prism (the outer wedge) overlies the updip velocity-strengthening part of the subduction fault, and the less deformed inner wedge overlies the velocity-weakening part (the seismogenic zone). During great earthquakes, the outer wedge is pushed into a compressively critical state, with an increase in basal and internal stresses and pore fluid pressure. After the earthquake, the outer wedge returns to a stable state. The outer wedge geometry is controlled by the peak stress of the updip velocity-strengthening part of the subduction fault achieved in largest earthquakes. The inner wedge generally stays in the stable regime throughout earthquake cycles, acting as an apparent backstop and providing a stable environment for the formation of forearc basins. The new theory has important implications for the studies of the updip limit of the seismogenic zone, the evolution of accretionary prisms and forearc basins, activation of splay faults and tsunami generation, evolution of the fluid regime, and mechanics of frontal prisms at margins dominated by tectonic erosion.