@phdthesis{Olen2016,
  author    = {Olen, Stephanie M.},
  title     = {Understanding Himalayan denudation at the catchment and orogen scale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-91423},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 174},
  year      = {2016},
  abstract  = {Understanding the rates and processes of denudation is key to unraveling the dynamic processes that shape active orogens. This includes decoding the roles of tectonic and climate-driven processes in the long-term evolution of high- mountain landscapes in regions with pronounced tectonic activity and steep climatic and surface-process gradients. Well-constrained denudation rates can be used to address a wide range of geologic problems. In steady-state landscapes, denudation rates are argued to be proportional to tectonic or isostatic uplift rates and provide valuable insight into the tectonic regimes underlying surface denudation. The use of denudation rates based on terrestrial cosmogenic nuclide (TCN) such as 10Beryllium has become a widely-used method to quantify catchment-mean denudation rates. Because such measurements are averaged over timescales of 102 to 105 years, they are not as susceptible to stochastic changes as shorter-term denudation rate estimates (e.g., from suspended sediment measurements) and are therefore considered more reliable for a comparison to long-term processes that operate on geologic timescales. However, the impact of various climatic, biotic, and surface processes on 10Be concentrations and the resultant denudation rates remains unclear and is subject to ongoing discussion. In this thesis, I explore the interaction of climate, the biosphere, topography, and geology in forcing and modulating denudation rates on catchment to orogen scales. There are many processes in highly dynamic active orogens that may effect 10Be concentrations in modern river sands and therefore impact 10Be-derived denudation rates. The calculation of denudation rates from 10Be concentrations, however, requires a suite of simplifying assumptions that may not be valid or applicable in many orogens. I investigate how these processes affect 10Be concentrations in the Arun Valley of Eastern Nepal using 34 new 10Be measurements from the main stem Arun River and its tributaries. The Arun Valley is characterized by steep gradients in climate and topography, with elevations ranging from <100 m asl in the foreland basin to >8,000 asl in the high sectors to the north. This is coupled with a five-fold increase in mean annual rainfall across strike of the orogen. Denudation rates from tributary samples increase toward the core of the orogen, from <0.2 to >5 mm/yr from the Lesser to Higher Himalaya. Very high denudation rates (>2 mm/yr), however, are likely the result of 10Be TCN dilution by surface and climatic processes, such as large landsliding and glaciation, and thus may not be representative of long-term denudation rates. Mainstem Arun denudation rates increase downstream from ~0.2 mm/yr at the border with Tibet to 0.91 mm/yr at its outlet into the Sapt Kosi. However, the downstream 10Be concentrations may not be representative of the entire upstream catchment. Instead, I document evidence for downstream fining of grains from the Tibetan Plateau, resulting in an order-of-magnitude apparent decrease in the measured 10Be concentration. In the Arun Valley and across the Himalaya, topography, climate, and vegetation are strongly interrelated. The observed increase in denudation rates at the transition from the Lesser to Higher Himalaya corresponds to abrupt increases in elevation, hillslope gradient, and mean annual rainfall. Thus, across strike (N-S), it is difficult to decipher the potential impacts of climate and vegetation cover on denudation rates. To further evaluate these relationships I instead took advantage of an along-strike west-to-east increase of mean annual rainfall and vegetation density in the Himalaya. An analysis of 136 published 10Be denudation rates from along strike of the revealed that median denudation rates do not vary considerably along strike of the Himalaya, ~1500 km E-W. However, the range of denudation rates generally decreases from west to east, with more variable denudation rates in the northwestern regions of the orogen than in the eastern regions. This denudation rate variability decreases as vegetation density increases (R=- 0.90), and increases proportionately to the annual seasonality of vegetation (R=0.99). Moreover, rainfall and vegetation modulate the relationship between topographic steepness and denudation rates such that in the wet, densely vegetated regions of the Himalaya, topography responds more linearly to changes in denudation rates than in dry, sparsely vegetated regions, where the response of topographic steepness to denudation rates is highly nonlinear. Understanding the relationships between denudation rates, topography, and climate is also critical for interpreting sedimentary archives. However, there is a lack of understanding of how terrestrial organic matter is transported out of orogens and into sedimentary archives. Plant wax lipid biomarkers derived from terrestrial and marine sedimentary records are commonly used as paleo- hydrologic proxy to help elucidate these problems. I address the issue of how to interpret the biomarker record by using the plant wax isotopic composition of modern suspended and riverbank organic matter to identify and quantify organic matter source regions in the Arun Valley. Topographic and geomorphic analysis, provided by the 10Be catchment-mean denudation rates, reveals that a combination of topographic steepness (as a proxy for denudation) and vegetation density is required to capture organic matter sourcing in the Arun River. My studies highlight the importance of a rigorous and careful interpretation of denudation rates in tectonically active orogens that are furthermore characterized by strong climatic and biotic gradients. Unambiguous information about these issues is critical for correctly decoding and interpreting the possible tectonic and climatic forces that drive erosion and denudation, and the manifestation of the erosion products in sedimentary archives.},
  language  = {en}
}
@phdthesis{JaraMunoz2016,
  author    = {Jara Mu{\~n}oz, Julius},
  title     = {Quantifying forearc deformation patterns using coastal geomorphic markers},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-102652},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XXV, 213},
  year      = {2016},
  abstract  = {Rapidly uplifting coastlines are frequently associated with convergent tectonic boundaries, like subduction zones, which are repeatedly breached by giant megathrust earthquakes. The coastal relief along tectonically active realms is shaped by the effect of sea-level variations and heterogeneous patterns of permanent tectonic deformation, which are accumulated through several cycles of megathrust earthquakes. However, the correlation between earthquake deformation patterns and the sustained long-term segmentation of forearcs, particularly in Chile, remains poorly understood. Furthermore, the methods used to estimate permanent deformation from geomorphic markers, like marine terraces, have remained qualitative and are based on unrepeatable methods. This contrasts with the increasing resolution of digital elevation models, such as Light Detection and Ranging (LiDAR) and high-resolution bathymetric surveys. Throughout this thesis I study permanent deformation in a holistic manner: from the methods to assess deformation rates, to the processes involved in its accumulation. My research focuses particularly on two aspects: Developing methodologies to assess permanent deformation using marine terraces, and comparing permanent deformation with seismic cycle deformation patterns under different spatial scales along the M8.8 Maule earthquake (2010) rupture zone. Two methods are developed to determine deformation rates from wave-built and wave-cut terraces respectively. I selected an archetypal example of a wave-built terrace at Santa Maria Island studying its stratigraphy and recognizing sequences of reoccupation events tied with eleven radiocarbon sample ages (14C ages). I developed a method to link patterns of reoccupation with sea-level proxies by iterating relative sea level curves for a range of uplift rates. I find the best fit between relative sea-level and the stratigraphic patterns for an uplift rate of 1.5 +- 0.3 m/ka. A Graphical User Interface named TerraceM® was developed in Matlab®. This novel software tool determines shoreline angles in wave-cut terraces under different geomorphic scenarios. To validate the methods, I select test sites in areas of available high-resolution LiDAR topography along the Maule earthquake rupture zone and in California, USA. The software allows determining the 3D location of the shoreline angle, which is a proxy for the estimation of permanent deformation rates. The method is based on linear interpolations to define the paleo platform and cliff on swath profiles. The shoreline angle is then located by intersecting these interpolations. The accuracy and precision of TerraceM® was tested by comparing its results with previous assessments, and through an experiment with students in a computer lab setting at the University of Potsdam. I combined the methods developed to analyze wave-built and wave-cut terraces to assess regional patterns of permanent deformation along the (2010) Maule earthquake rupture. Wave-built terraces are tied using 12 Infra Red Stimulated luminescence ages (IRSL ages) and shoreline angles in wave-cut terraces are estimated from 170 aligned swath profiles. The comparison of coseismic slip, interseismic coupling, and permanent deformation, leads to three areas of high permanent uplift, terrace warping, and sharp fault offsets. These three areas correlate with regions of high slip and low coupling, as well as with the spatial limit of at least eight historical megathrust ruptures (M8-9.5). I propose that the zones of upwarping at Arauco and Topocalma reflect changes in frictional properties of the megathrust, which result in discrete boundaries for the propagation of mega earthquakes. To explore the application of geomorphic markers and quantitative morphology in offshore areas I performed a local study of patterns of permanent deformation inferred from hitherto unrecognized drowned shorelines at the Arauco Bay, at the southern part of the (2010) Maule earthquake rupture zone. A multidisciplinary approach, including morphometry, sedimentology, paleontology, 3D morphoscopy, and a landscape Evolution Model is used to recognize, map, and assess local rates and patterns of permanent deformation in submarine environments. Permanent deformation patterns are then reproduced using elastic models to assess deformation rates of an active submarine splay fault defined as Santa Maria Fault System. The best fit suggests a reverse structure with a slip rate of 3.7 m/ka for the last 30 ka. The register of land level changes during the earthquake cycle at Santa Maria Island suggest that most of the deformation may be accrued through splay fault reactivation during mega earthquakes, like the (2010) Maule event. Considering a recurrence time of 150 to 200 years, as determined from historical and geological observations, slip between 0.3 and 0.7 m per event would be required to account for the 3.7 m/ka millennial slip rate. However, if the SMFS slips only every ~1000 years, representing a few megathrust earthquakes, then a slip of ~3.5 m per event would be required to account for the long- term rate. Such event would be equivalent to a magnitude ~6.7 earthquake capable to generate a local tsunami. The results of this thesis provide novel and fundamental information regarding the amount of permanent deformation accrued in the crust, and the mechanisms responsible for this accumulation at millennial time-scales along the M8.8 Maule earthquake (2010) rupture zone. Furthermore, the results of this thesis highlight the application of quantitative geomorphology and the use of repeatable methods to determine permanent deformation, improve the accuracy of marine terrace assessments, and estimates of vertical deformation rates in tectonically active coastal areas. This is vital information for adequate coastal-hazard assessments and to anticipate realistic earthquake and tsunami scenarios.},
  language  = {en}
}