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No description available.

No description available.

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.

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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.

<p>Denna uppsats syfte har varit att</p><ul><li>studera jordarter och morfologi</li><li>försöka bestämma om skreden i dagsläget kan betecknas som recenta eller stabiliserade. Detta bla. genom att studera vegetation; ålder och utbredning av denna.</li><li>beskriva vad människorna i området gjort efteråt.</li></ul>

In 1959, the Bureau of Reclamation proposed a channelization project through the Cibola Valley along the Lower Colorado River. The project entailed rerouting the river through a dry cut in order to lower groundwater levels in the Palo Verde Irrigation District upstream, thereby improving irrigation drainage. In conjunction with this, Cibola National Wildlife Refuge was created in 1964 to mitigate the effects of habitat loss from the channelization project. Aerial photographs of the Cibola Valley were analyzed for 1959, and vegetation community types were determined. A vegetation type map was developed for 1959 and compared with vegetation type maps for 1976 and 1986. Between 1959 and 1986, a lowering of the water-surface level in some parts of the refuge resulted in the draining of some lakes and the creation of slow-moving backwaters. Cottonwood-willow and marsh communities saw a significant reduction in area while the salt-cedar community saw rapid growth.