The ultimate goal of seismology is to estimate the timing, magnitude and potential spatial extent of future seismic events along pre-existing faults. Based on the rate-state friction law, several theoretical physical earthquake models have been proposed towards this goal. Tectonic loading rate and frictional properties of faults are required in these models. Modern geodetic observations, e.g. GPS and InSAR, have provided unprecedented near-field observations following large earthquakes. In theory, according to the frictional rate and state asperity earthquake model, velocity-weakening regions holding seismic motions on faults should be separated with velocity-strengthening regions within which faults slip only aseismically. However, early afterslip following the 2011 MW 9.1 Tohoku-Oki earthquake revealed from GPS measurements was largely overlaid on the historical rupture zones, which challenged the velocity weakening asperity model. Therefore, the performance of the laboratory based friction law in the natural events needs further investigation, and the factors that may affect the estimates of slip models through geodetic modelling should also be discussed systematically. In this thesis, several moderate-strong events were investigated in order to address this important issue. The best-fit co- and post-seismic slip models following the 2009 MW 6.3 Haixi, Qinghai thrust-slip earthquake determined by InSAR deformation time-series suggest that the maximum afterslip is concentrated in the same area as the coseismic slip model, which is similar to the patterns observed in the 2011 Japan earthquake. In this case, complex geometric asperity may play a vital role in the coseismic nucleation and postseismic faulting. The major early afterslip after the 2011 MW 7.1 Van mainshock, which was revealed by one COSMO-SkyMed postseismic interferogram, is found just above the coseismic slip pattern. In this event, a postseismic modelling that did not allow slip across the coseismic asperity was also tested, suggesting that the slip model without slip in the asperities can explain the postseismic observations as well as the afterslip model without constraints on slip in the asperities. In the 2011 MW 9.1 Tohoku-Oki earthquake, a joint inversion with the GRACE coseismic gravity changes and inland coseismic GPS observations was conducted to re-investigate the coseismic slip model of the mainshock. A comparison of slip models from these different datasets suggests that significant variations of slip models can be observed, particularly the locations of the maximum slips. The joint slip model shows that the maximum slip of ~42 m appears near the seafloor surface close to the Japan Trench. Meanwhile, the accumulative afterslip patterns (slip >2 m) determined in previous studies appear in spatial correlation with the Coulomb stress changes generated using the joint slip model. As a strike-slip faulting event, the 2011 MW 6.8 Yushu earthquake was also investigated through co- and post-seismic modelling with more SAR data than was used in previous study. Best slip models suggest that the major afterslip is concentrated in shallow parts of the faults and between the two major coseismic slip patterns, suggesting that the performance of the rate and state frictional asperity model is appropriate in this event. Other postseismic physical mechanisms, pore-elastic rebound and viscoelastic relaxation have also been examined, which cannot significantly affect the estimate of the shallow afterslip model in this study. It is believed that the shallow afterslip predominantly controlled the postseismic behaviour after the mainshock in this case. In comparison to another 21 earthquakes investigated using geodetic data from other studies, complementary spatial extents between co- and post-seismic slip models can be identified. The 2009 MW 6.3 Qinghai earthquake is an exceptional case, in which the faulting behaviours might be dominated by the fault structure (e.g. fault bending). In conclusion, the major contributions from this thesis include: 1) the friction law gives a first order fit in most of natural events examined in this thesis; 2) geometric asperities may play an important role in faulting during earthquake cycles; 3) significant uncertainties in co- and post-seismic slip models can appreciably bias the estimation of fault frictional properties; 4) new insights derived from each earthquake regarding their fault structures and complex faulting behaviours have been observed in this thesis; and (5) a novel package for geodetic earthquake modelling has been developed, which can handle multiple datasets including InSAR, GPS and land/space based gravity changes.

No description available.

No description available.

The Toutle-Cowlitz River system experienced dramatic landscape disturbance during the catastrophic eruption of Mount St Helens on May 18, 1980. The eruption was triggered by a 2.5 km3 debris avalanche which buried the upper 60 km2 of the North Fork Toutle River catchment to an average depth of 45 m and obliterated the surface drainage network. Subsequent channel response on the debris avalanche, dominated by incision and widening, has delivered significant quantities of sediment to downstream reaches where resultant deposition has reduced channel capacity and heightened flood risk. Estimates of future sediment yield from the upper North Fork Toutle River are therefore required to inform development of sustainable options for long-term flood risk mitigation. Previous estimates have been based on extrapolation of post-eruption trends in sediment yield and channel network evolution, but the divergent predictions reported in a number of studies have clouded effective decision-making regarding long-term sediment management. This study therefore uses a numerical, landscape evolution model (CAESAR-Lisflood) to make long-term forecasts of sediment yield based on process simulation rather than extrapolation. A suite of forecasts of cumulative catchment sediment yields up to 2100 are produced using scenario-based model runs designed to account for uncertainty associated with the hydrological impacts of climate change and the model coefficient for lateral mobility. The forecasts fall in a narrow band +/-20% of the mean that lies between two previous estimates derived from the extrapolation of post-eruption trends. Importantly, predicted trends in future annual sediment yield are predominantly linear, although some limited decay is evident for runs in which modelled channel lateral mobility is lower. Sustained sediment production in the upper North Fork Toutle River is found to result from persistent bank erosion and channel widening. These findings cast doubt on the applicability of negative exponential decay functions based on the rate law to characterise post-disturbance sediment yield when lateral rather than vertical adjustments dominate channel evolution. Moreover, forecast trends in future sediment yield suggest that it may not be possible to manage future sediment-related flood risk along the lower Cowlitz solely by retaining sediment in the upper North Fork Toutle River catchment.

The channels of the great rivers of Bangladesh are highly dynamic and their banklines change continuously, consuming large areas of floodplain and making thousands of people landless. As a result, bank erosion is a serious cause of poverty in Bangladesh. Severe bank retreat associated with net widening of the Jamuna, Padma and Lower Meghna Rivers during the last 50 years has greatly increased the suffering of the people. Changes in the width and planform patterns of these rivers indicate that they have not been operating in dynamic equilibrium. However, the causes of instability and planform metamorphosis remain contested. This is significant as identifying the causes of the observed channel adjustments would be of great interest not only to river scientists and engineers, but also to planners attempting better to manage the nation's natural and human resources. In this context, the research reported in this thesis proposes a working hypothesis that morphological changes in the Jamuna-Padma-Lower Meghna system have occurred in response to disturbance of the fluvial system by the Assam earthquake of 1950. Contemporary documents report that landslides triggered by the earthquake generated about 4.5* 1010 m3 sediment, much of which entered the Brahmaputra River in Assam either directly or via its tributaries. It is proposed that the fine fraction of this sediment (silt and clay) travelled quickly through the system, without disturbing the morphology of the channels, before settling in the Meghna Estuary and Bay of Bengal. In contrast, it is hypothesised that the coarser fraction (sand) took half a century to progress through the system, moving as a wave of bed material load, with a celerity between 10 and 32 kmy-1. Preliminary analyses of historical maps and satellite images, together with records of discharge, water level, sediment transport and cross-sectional form reveals a sequence of morphological changes in the Jamuna-Padma-Lower Meghna system with a downstream phase lag that is commensurate with the celerity of the coarse sediment wave. A conceptual process-response model has been developed to elucidate the relationship between downstream propagation of the sand wave and morphological responses, based on models previously reported in the literature and the sequence of changes observed in the Jamuna River. The model has been validated using morphological responses observed in the Padma and Lower Meghna rivers, which appear to have acted as a downstream continuation of the Jamuna River. Based on the conceptual model, a scheme has also been developed to explain and predict planform responses to changes in sediment supply to a braided river. This scheme is shown to be consistent with earlier models, the responses to increased sediment supply in the great rivers of Bangladesh and those of some very large rivers in China. Once fully validated, the conceptual model and the scheme may be used not only to explain the past behaviour of braided rivers, but also to predict the morphological responses of the large rivers of Bangladesh to future disturbance by, for example, climate change, seismic events or interventions in the fluvial system upstream in India. The capability to make such predictions would be immensely helpful in planning how to manage future channel instability and mitigate its socioeconomic impacts for the benefit of floodplain dwellers and the Nation.

This project described the vegetation of a stretch of the Parana River and investigated which natural or human-imposed factors might be controlling its characteristics, its capacity for biodiversity support and its potential to provide an economic resource. This information is of value in the planning of management strategies aiming to conserve biodiversity and develop sustainable ways in which the floodplain resources can be utilised. Central to this study were the surveys of vegetation and environmental characteristics of aquatic, terrestrial and transitional habitats of the Parana floodplain near Porto Rico. These produced extensive data sets which helped to reveal the types of vegetation-environment relationships structuring the floodplain plant communities. To complement this investigative approach, three aspects of the functioning of floodplain vegetation were chosen for closer study. These were the impacts of livestock grazing on wetland and island vegetation, competitive interactions between pairs of free-floating aquatic plant species and the role of aquatic macrophytes in contributing carbon to aquatic food webs. Three major community types were identified in the aquatic habitats of the floodplain, one which included Eichhornia azurea in mixture with several free-floating and emergent species, a second in which E. azurea was strongly dominant and a third comprised purely of submerged species. Two strongly contrasting broad vegetation communities were identified at bank and shore environments. Polygonum and Ludwigia species were important in one group and Poaceae, creepers, woody plants and ferns in the other group. Sub-groups of these communities could also be suggested, but these are less distinct. Most of the floodplain sites supported a Poaceae-creeper community type with the remaining sites supporting a community indicated by Polygonum species. The Poaceae group was comprised of a number of sub-communities in which the importance of Poaceae relative to other species varied. The aquatic vegetation communities differed structurally with contrasting community biomass, canopy height, canopy cover, species richness and stem density. They were associated with waterbodies with different water depth and pH and different sediment nitrogen and phosphorus contents. Water flow rate category and underwent light availability also differed between the sites that tended to support the different vegetation types. The two major bank and shore vegetation communities differed in canopy cover, in the soil nitrogen, phosphorus and calcium levels with which they were associated and in the steepness of the bank on which they tended to grow. Floodplain vegetation communities contrasted in species richness and differed in the soil nitrogen and calcium levels and river systems with which they were associated.

This thesis investigates the role that superglacial snowpack hydrology plays in mediating meltwater delivery to glacier systems. The movement of water through glaciers is of fundamental importance as a control on proglacial hydrograph amplitude and timing, subglacial and proglacial geomorphic processes, the hydrochemistry of glacial runoff, and glacier dynamics, and as such has been the subject of considerable research effort. Although studies in non-glacial environments have shown that meltwater waves are both dampened and delayed by passage through snow, the role of supraglacial snowcover in mediating water inputs to the rest of the glacier system ahs received limited attention in studies of glacier hydrology to date. It has been suggested, however, that the varying thickness, and ultimately removal, of the superglacial snowpack may play a role in controlling the timing and magnitude of ice velocity events. Despite this suggested importance there have been few field observations of the hydrological behaviour of supraglacial snowpacks or of the way in which this behaviour evolves during the melt season. A thorough assessment of the linkages between supraglacial snowpack conditions and glacier dynamic events has therefore not been possible. This study helps fill this gap in our knowledge by explicitly investigating the hydrological behaviour of the supraglacial snowpack at an alpine glacier and its evolution during the summer melt season. Field data was collected during two summer field seasons (2003 and 2004) at Haut Glacier d’Arolla, Valais, Switzerland. Dye tracing experiments were used as the primary method of obtaining information about water flow through the snowpack. Dye was used both qualitatively, to give a visual impression of flow patterns through the snowpack, and quantitatively, with return curves detected by fluorometer providing detailed information about rates of dye movement and dispersion through the snowpack. Physically-based modelling representations of water flow through snow also informed consideration of the characteristics of snowpack runoff. Experiments were designed to determine: i) the nature of water flow through the supraglacial snowpack; ii) if, and in what way, this evolves over the course of the melt season; and iii) what factors control water movement, and the importance of their roles. In order that links between supraglacial snowpack hydrology and other parts of the glacier system could be considered, season-long records of glacier dynamics, proglacial meltwater discharge, and water quality parameters indicating subglacial conditions were also collected.

Methodology The basis of the research was to identify those physical, chemical and geological attributes of slate which make it a good roofing material. These were often related to specific Scottish quarries in order to select those which showed the best potential for resumed production. However, as no fresh samples of Scottish slate were available, the work was based initially on slate of known and reliable quality from producing quarries elsewhere. The parameters examined were mineral composition, metamorphic grade, fabric and weathering properties. When the parameters most closely related to the quality of finished slates were established then the Scottish slate was examined for these same parameters. Mineral Composition Recent progress in the determination of the chemical formulae of the phyllosilicates of fine-grained material has enabled the mineral composition of slate to be calculated from its total oxide composition. Calculations based on representative samples from each group of quarries gave good results when taken from sites in close proximity, but application to samples from more remote sites gave a weaker correlation. Metamorphic Grade Metamorphic grade affects the crystallinity and the grain size of a material. Traditionally for sedimentary rocks both properties were evaluated by the sharpness of peaks in XRD analysis, using Full Width at Half Magnitude (FWHM) as the criterion. However, this method is not effective when applied to slate, and an alternative method of determining its crystallinity was developed, based on the intensities of peaks of the main minerals.

Eutrophication results in the loss of conservation and amenity value from shallow lakes. Efforts have been made to restore shallow lakes by reducing the external nutrient loading. Removing nutrient-rich inflows can reduce nutrient loading but may alter lake hydrology. This thesis is primarily aimed at investigating the effects of a nutrient-rich river on water chemistry and plankton by comparing six shallow (<3.5 m) lakes that are connected to and isolated from the River Erewash, in the Attenborough Nature Reserve, Nottinghamshire, U.K. Lakes that received River Erewash discharge had higher nutrient concentrations and higher phytoplankton biomass than those that were isolated from it. Turbid water was also found in a lake isolated from the River Erewash but with a nutrient-rich inflow stream. Lakes isolated from the inflows had abundant submerged macrophytes and clear water but other lakes were turbid and devoid of macrophytes. In lakes without inflows, cyanobacteria were proportionally more abundant. Lakes receiving nutrient-rich water were generally dominated by small chlorophytes and centric diatoms. Phosphorus concentrations had little effect on the phytoplankton. N and Si in the connected lakes, and zooplankton grazing and N in the isolated lakes, probably limited phytoplankton. A mesocosm experiment found chlorophyll-a concentrations were reduced by the addition of silica, and that the biovolume of dinophytes increased in the mesocosms without nitrate addition. Total zooplankton biomass did not change significantly between treatments. Summer floods reduced P concentrations in the connected lakes, suggesting that internal P loading was diluted and flushed out. Phytoplankton biomass was also lower during floods. Cryptophytes and diatoms dominated the phytoplankton and cyanobacteria were rare during flooding. A simulation of lake restoration by river diversion using mesocosms confirmed the importance of lake flushing for reducing internal loading. Diverting the River Erewash in order to reduce the nutrient loading to Attenborough Nature Reserve may be problematic in the short-term, because the lack of flushing may increase the effect of internal P loading and favour cyanobacterial growth. Reducing the external supply of N may further stimulate the dominance of cyanobacteria while P concentrations remain high.

It has become increasingly clear that river channel sediment dynamics must be taken into account within British flood risk management because changes in channel morphology resulting from sediment transfer can have an impact on channel flood capacity. It is also recognised that an understanding of catchment-scale sediment dynamics is desirable with respect to many other aspects of river management. However, despite this recognition, application of existing approaches that account for coarse sediment dynamics has been limited within British river management. Based on these considerations, this study aims to develop and substantiate a new approach that quantitatively accounts for catchment-scale coarse sediment dynamics in British rivers. These research efforts contribute to the activity of the Flood Risk Management Research Consortium (http://www.floodrisk.org.uk/) A review of the availability and accuracy of data sources useful to considerations of coarse sediment dynamics reveals that only discharge, channel slope, and channel width can be represented widely at the catchment-scale. As a result, none of the approaches currently available to account for coarse sediment dynamics were found to be both scientifically robust and practically applicable at the catchment-scale. This leads to the conclusion that the most suitable approach to account for coarse sediment dynamics at the catchment-scale in British rivers is a reach-based sediment balance model, using no more than slope, width and discharge data. A new reach-based sediment balance model, ST:REAM (Sediment Transport: Reach Equilibrium Assessment Method), is developed. It has several unique features including: representation of the entire catchment network; automatic delineation of the catchment network into functional reaches using a zonation algorithm; application of a new general formula for the prediction of bed surface material transport rate; and adoption of an assumption that makes it unnecessary to collect bed material size data. The outputs from ST:REAM are in the form of predicted Capacity Supply Ratios which compare the annual mass of sediment predicted to enter a reach with the annual mass of sediment predicted to leave it. Initial assessment of ST:REAM using two test catchments shows that it can produce a reasonable representation of observed, broad-scale sediment dynamics. The accuracy of its predictions decreases when attempting to incorporate downstream variability in bed material size into the model, and scale issues are encountered when attempting to increase the resolution at which reaches are identified by the zonation algorithm. ST:REAM has many potential applications within river management, but it is of most value when providing a broad-scale picture of predicted reach sediment balances throughout the drainage network. As well as the practical applications of ST:REAM, the research contained within this thesis has important theoretical implications, relating both to the insights it provides on catchment-scale sediment dynamics in particular and methodological and foundational developments in the field of sediment studies more generally. Online version lacks Appendices, which were submitted on CD-ROM accompanying printed version.