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Examining fault activity over several earthquake cycles is necessary for long term modeling of the faults strain budget and stress state. While this requires knowledge of coseismic slip distributions for successive earthquakes along the fault, these exist only for the most recent events. However, overlying the Sunda Trench, sparsely distributed coral microatolls are sensitive to tectonically induced changes in relative sea levels and provide a century spanning paleo geodetic and paleoseismic record. This thesis presents a new technique called the Genetic Algorithm Slip Estimator (GASE) to constrain slip distributions from observed surface deformations of corals. A suite of models consistent with the observations is identified and from them an ensemble estimate of the causative slip is computed. The technique is systematically tested using synthetic data. Applying the technique to observed coral displacements for the 2005 Nias-Simeulue earthquake and 2007 Mentawai sequence, modeled solutions reproduce features of slip (i.e. along strike extent, magnitude of slip and the presence of asperities), present in previously published inversions such as the magnitude and location of slip asperities. From the displacement data available for the 1797 and 1833 Mentawai earthquakes, slip estimates are presented that reproduce observed displacements. The areas of highest modeled slip in the paleoearthquakes are non-overlapping and our solutions appear to tile the plate interface, complementing one another. Using the slip estimated produced by the GASE technique the total stress field of the Sumatran section of the Sunda megathrust is modeled. Combining the coseismic stresses produced by the GASE models of the 1797 and 1833 paleo earthquake and by 25 other M >7.0 events that have occurred along the megathrust, along with the cumulative interseismic stressing since 1796, the evolving stress field of the Sunda megathrust is investigated. The use of GASE slip distributions for the 1797 and 1833 paleoearthquakes resolve some inconsistencies between the prestress state of the fault and coseismic slip reported by Nalbant et al. [2013]. However, further work is required to explore the sensitivity of the stress field to variation in slip. While this thesis describes the development and testing of the GASE technique for use with the coral displacement data along the Sunda Megathrust, it may be possible to adapt the algorithm to examine paleoseismic records elsewhere. Application of the technique to alternative sources of paleoseismic data may yield insight into the details of pre-instrumental earthquakes in other regions. In tum, more robust modeling of the past seismicity in these areas may allow better constraints on the future risks posed by earthquakes to at risk communities.

Since tidal forces deform the Earth's crust with completely predictable stresses, the role of the Earth tides in triggering seismicity has long been investigated. The results of these investigations have, however, been inconclusive. Tidal triggering has been found to be non-existent or small (still not statistically significant) for strike-slip faults. On the other hand, a tide-earthquake has been observed in hydrothermal or magmaaffected areas and for reverse faults in the oceanic settings where the amplitude of tidal stresses is the largest. Here, we examine the effect of tidal stresses on earthquake occurrence in Southern California using three novel approaches. First, we analyse the difference in seismicity rates at times of positive and negative tidal Coulomb stresses/stress rates; for that, we resolve the tidal stresses/stress rates on failure planes assumed to be controlled by the orientation of their nearest geological structures. We find the earthquake behaviour with respect to tidal influence statistically non-random only in close proximity to tidal extremes. A particularly strong tidal signal is observed for reverse fault type events. Along with the significant increase in earthquake rates around tidal Coulomb stress maxima, we observe that the strength of the tidal correlation is closely related to the amplitude of the tidal stresses. Second, we look at the response of aftershocks to tidal stresses. Based on the 1992 Mw 7.3 Landers and 1999 Mw 7.1 aftershock activity, we demonstrate that the probability of a fault failure due to tidal oscillations is strongly affected by earthquake-induced static stress changes. Accordingly, earthquakes in regions of increased static stresses are more consistent with tidal triggering than events in areas of static stress decrease. Third, we examine the relationship between the effect of tidal maximum compressional stresses on earthquake timing and the orientation of regional tectonic stress.

Geophysical motions can occur over a broad temporal spectrum, from high frequency seismic movements to very long period tectonic deformation. The Aegean region is tectonically one of the most active areas on Earth. There have, over the past 15 years, been a range of campaign style GPS studies which have looked to increase our knowledge of the area and better define the geodynamic processes involved. In 2002 the Center for the Observation and Modelling of Earthquakes and Tectonics (COMET) established a network of continuously operating GPS receivers (CGPS) throughout the region in order to add to the knowledge gained from previous studies. This thesis focuses on which tectonic motions can be observed using the COMET continuous GPS network. Approaches for the precise analytical estimation of subtle tectonic motion are presented. Daily coordinate estimates of COMET sites and a number of ITRF (International Terrestrial Reference Frame) sites around Europe were calculated using a precise point positioning strategy and ambiguity resolution using NASA’s GIPSY – OASIS II processing software and IGS (International GPS Service) precise products. Time series produced showed post fit standard deviations of 2-3 mm in the horizontal and 6-8 mm in the vertical. Significant annual periodic variation is observed in the time series. The coordinate time series studies were further refined using a selection of filters. Firstly, gross and sigma filters were applied to remove outliers, the data then had a range of regional filters applied looking to best define and remove the common mode error in the area. These filters produced mixed results with time series improvement occurring on a site by site basis. In some cases noise was reduced by a factor of 2 whilst in other cases there was little or no improvement. This combined with a lack of knowledge of the individual site movements led to the use of a filtered baseline method, whereby common mode error was removed purely on a site by site basis. This method revealed expansion across the Hellenic arc of the order of a few millimetres per year and sub millimetre north-south compaction behind the arc. It also revealed first evidence of transient motion at a number of sites parallel to the Hellenic arc. The transient signals occurred every 12 months ±1.5 and lasting for 40 – 100 days. These signals were not so much a reversal of tectonic motion akin to the silent earthquakes observed in Cascadia, Japan and Mexico, instead they appeared more as a pause in the otherwise consistent movement of the Aegean microplate overriding the subducting African lithosphere. In addition to the observed tectonic signals, the effects and implications of the two post processing strategies are analysed and discussed. Higher temporal frequency positioning is carried out on seismic events (Mw 6.7 earthquake Kithera, Mw 8.1 and Mw 6.7 earthquakes, Macquarie island) using instantaneous positioning followed by “sidereal filtering” whereby integer-cycle phase ambiguities are resolved using only single epochs of dual frequency phase and pseudorange data. These positions are then siderealy stacked to reduce the effects of geometry related error. The technique reduces geometry related noise by a factor ≈2 using epoch by epoch 30 second data. The feasibility of the technique for observing pre, co and post seismic signals is demonstrated. A visualisation tool was developed to allow the simultaneous observation of the tectonic motion of a CGPS network data over any spatial and temporal regimes.

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The increased demand for non-destructive evaluation of the shear wave profiling, condition monitoring and performance assessment of soils and roads in a dynamic state has made seismic methods the most desirable and effective non-destructive techniques. Surface wave methods have gained popularity over the last decades since they monitor the propagation of the surface wave with non-invasive transducers working from the surface. Nonetheless, their use is restricted by resolution problems and their ability to assess the actual dispersive behaviour of Rayleigh wave. Non-destructive, in-situ methods for characterizing existing infrastructures require the ability to detect structural damage and features such as cracking and discontinuities. The proper assessment of the location and of the extension of such discontinuities is crucial for the determination of the level of deterioration of an infrastructure and for planning the maintenance interventions. Damage in a pavement structure is usually initiated in the asphalt layers, making the Rayleigh wave ideally suited for the detection of shallow surface defects. Nonetheless, the practical application of crack detection methods in asphalt is hampered due to the heterogeneous and dispersive nature of the material tested. This thesis describes new signal processing methods and the novel application of existing methods to tackle the problems that hinder the non-destructive surface wave methods. The spectral convolution method proposed in this thesis, based on the simultaneous exploitation of the vertical and the horizontal components of a seismic event, improved the resolution and the overall accuracy of the spectral image in the frequency-wavenumber (f-k) domain. Hence, it led to more accurate seismic inversion by reducing the amount of uncertainty coming from a seismic survey. This research investigated the use of this new proposed method in soils and asphalts for the measurement of surface wave dispersion through conceptual analysis and numerical investigation alongside experimental investigation on soil and asphalt. The application of spectral wave methods and the transformation of the wave field into the frequency wave number domain allowed the identification of the position and the extension of vertical defects. The joint use of the Multichannel Analysis of Surface Waves and the Multiple Impact of Surface Waves methods in numerical and experimental investigations presented in this thesis proved to be effective for crack detection and sizing. Moreover, the space-normalised seismogram helped in the interpretation of f-k spectra for cracks detection. Here, the wave decomposition method for crack interrogation consisted of a signal processing algorithm capable of computing the direct and reflected waves’ amplitudes and phase angles from the signals of a deployment of sensors. It solved linear systems with a number of measurements much bigger than the number of unknowns. It tackled the measurement errors naturally present in experimental data by finding a least square approximate solution with the help of the pseudo-inverse matrix for over determined systems. The results coming from numerical simulations and experimental investigations showed the effectiveness of the wave decomposition method for the assessment of the location and of the depth of surface-breaking cracks in the half-space and in layered systems. Contrary to other techniques, it was able to cope with the heterogeneities and the dispersive nature of layered system, thus making possible to detect and assess the depth of surface-breaking cracks in roads.

The thick and seismically fast Precambrian continental remnants (cratons) provide fundamental clues about the tectonic processes that operated on the early Earth. Eastern Canada is a natural laboratory to study such processes: its geological record spans more than 3 Ga of Earth history, including the assembly of the largest Archean craton in the world, the Superior craton, which is surrounded by global scale Proterozoic and Phanerozoic orogenic belts. To investigate the crustal and lithospheric structure of eastern Canada, earthquake data recorded at a new broadband seismic network were analysed, in conjunction with other permanent and temporary networks. The QM-III (Quebec-Maine Across Three Sutures) network was deployed across the main tectonic boundaries in eastern Canada, extending from Hudson Bay to the Atlantic Ocean. Using Hk stacking and probabilistic inversion of receiver functions, bulk crustal composition (Vp/Vs ratio), crustal thickness and shear wavespeed (Vs) were estimated beneath seismic stations. Post- Archean crust is thicker ( ~40 km), faster (dVs ~ 0.2 km/s), more heterogenous and more ma c (Vp/Vs ~1.76), suggesting increased crustal growth efficiency, possibly stimulated by mafic underplating. Lack of correlation between Moho topography, elevation and gravity anomalies in Proterozoic terranes indicate isostatic imbalance, best explained by strong mantle buoyant support. An anisotropic seismic model of the Precambrian lithosphere was constructed using fundamental mode Rayleigh waves. Phase velocity heterogeneity and azimuthal anisotropy patterns reveal multiple lithospheric layers within the Superior craton, with distinct tectonic origins. The upper lithosphere is seismically fast ( ~2%) and preserves Archean fossil anisotropy ( ~1%), implying that plate-scale deformation occured during the Archean. This layer partially extends beneath the adjacent Proterozoic belt and survived subsequent metasomatism. The lower lithosphere is fast ( ~2%), more homogenous and weakly anisotropic ( < 0.5%), documenting post assembly lithospheric growth in a slow convection regime. Cratonization processes may be episodic and are not exclusively an Archean phenomenon.

Earthquake, the natural phenomena, is conceived by the movement of the tectonic plates that induce shocks and impulse of devastating magnitude at ground level. Reducing losses during an earthquake has always been one of the most critical concerns of humans in earthquake prone areas. The main goal has been always to attenuate the shocks induced by ground motions on man-made structures. Two approaches have been conducted; increasing the earthquake resistant capacity of a structure, and reducing the seismic demands on a structure. With regard to the concept of reducing seismic demands on a structures, seismic base isolation is considered as an efficient method in mitigation of earthquake damages. A proper base isolation framework offers a structure great dynamic performance and in this way, the structure will be able to remain in elastic mode during an earthquake. On the other hand, not all isolation systems can provide the target structure with efficient seismic performance. The majority of currently available isolation systems still have some practical limitations. These limitations affect the functionality of a structural system and impose some restrictions to its proper use and protection level, causing it not to achieve anticipated level of performances. In this dissertation, an innovative seismic isolation system is proposed and investigated via laboratory tests and computer simulation to introduce a practical and effective seismic isolation system. The proposed system has aimed to modify some drawbacks of current seismic isolation system whilst at the same time keeping their advantages. The innovative isolation system in this study incorporates air-bearing benefits together with roller bearings and bungee cords in a complex system for horizontal base isolation. An experimental study was carried out to test a scale structure model (1/10th in length) as a case study for this research, to observe the behaviour of the structure with and without isolation system and to extract the dynamic characteristics of the structure by measuring fundamental frequencies and damping through a free vibration test. Computer simulation was conducted to simulate the dynamic behaviour of the structure when it is subjected to three different types of earthquakes; and with different base vi configurations (fixed base and base isolated). The simulation was performed to gain an insight into the performance of the proposed isolation system under the given structure. Results from computer simulation were compared and validated with findings from experimental tests. It was confirmed that the present isolation system offers a significant reduction in acceleration demand in the structure leading to the reduction of base shear and consequently the level of damage to the structure. Results revealed that the proposed isolation system is able to mitigate the seismic responses under different ground motion excitations while exhibiting robust performance for the given structure. Furthermore, the system can also be used to isolate sensitive equipment or hardware in buildings affected by seismic shocks.

Analyses of deformations associated with earthquakes are calculated in terms of plate motions and co-seismic stress changes, which assume the crust responds as an elastic medium. However, the lower crust and region of ductile mantle behaves viscoealastically over much longer time scales. In other words, lithospheric stress change following earthquakes is time dependent process. In order to draw a complete picture of total deformation over a seismic cycle, we cannot ignore the considerable influence of the viscoelastic relaxation processes. The objective of this thesis is to assess the role of post-seismic viscoelastic relaxation processes following earthquakes. First, I investigate the post-seismic viscoelastic flow in the lower crust and upper mantle of large earthquakes in eastern Turkey, during the 19th and 20th century. Using three possible rheological models, the viscoelastic, post-seismic deformation is analysed to assess the extent to which these events influence the velocity fields at GPS sites in the region. Models show that the post-seismic signal currently contributes to the observed deformation in the eastern part of the North Anatolian fault and northern and middle parts of the East Anatolian Fault Zone, primarily due to the long-lasting effect of the Ms 7.9 1939 earthquake. Study results identify a post-seismic signal in the region and could contribute to between 3% and 25% of the observed GPS measurements. Next, in order to assess the importance of the post-seismic viscoelastic relaxations over the last seismic cycle, I investigate stress accumulation over the East Anatolian Fault Zone by modelling the stress changes associated with 16 large (M>6.8) earthquakes that occurred in the region since 1822. Two areas of increased stress in the region are identified; the first in a fault segment that runs from the southern part of the city of Kahramanmaras to the southern part of the city of Malatya (KM Segment) and the second is the Yedisu segment at the eastern terminus of the North Anatolian Fault Zone. It is also observed that the stress accumulation associated with the post-seismic viscoelastic stress equals or larger than the co-seismic stress values in these segments. Finally, I assess the extent of time dependent viscoelastic post-seismic stress influences on the static shear stress change on the rate of triggered events that located in ± 2° after a main shock. Receiver faults that have calculated shear stress changes (on their nodal planes) between ±0.01 and ±1 MPa are considered as potentially triggered by the source earthquakes. The stress changes associated with 244 main shocks (M>7.0) from Global Centroid Moment Tensor Catalogue are modelled. A 10-year time window after the main shocks is used for the subsequent analysis to allow the numbers of aftershocks to decaying to the background seismicity rate. Regional variations in the rate of triggered aftershocks are observed ranging from 35% (Mediterranean and Tibet) to 65% (Western Pacific, Sumatra, Central and South America). When time-dependent viscoelastic post-seismic effects are incorporated into the calculations, the global rate remains unchanged. However, the total number of triggered earthquakes in areas of increased positive and negative stresses rises by up to 13% and 12% respectively. After excluding earthquakes whose Moment Tensor solutions having large uncertainties from the catalogue, the global rate of positively triggered events has increased considerably by 3%, which illustrates 63% of potentially triggered events are associated with shear stress increase due to prior events while 37% of events with shear stress decrease.