No description available.

A new method using a machine learning technique is applied to event classification and detection at seismic networks. This method is applicable to a variety of network sizes and settings. The algorithm makes use of a small catalogue of known observations across the entire network. Two attributes, the polarization and frequency content, are used as input to regression. These attributes are extracted at predicted arrival times for P and S waves using only an approximate velocity model, as attributes are calculated over large time spans. This method of waveform characterization is shown to be able to distinguish between blasts and earthquakes with 99 percent accuracy using a network of 13 stations located in Southern California. The combination of machine learning with generalized waveform features is further applied to event detection in Oklahoma, United States. The event detection algorithm makes use of a pair of unique seismic phases to locate events, with a precision directly related to the sampling rate of the generalized waveform features. Over a week of data from 30 stations in Oklahoma, United States are used to automatically detect 25 times more events than the catalogue of the local geological survey, with a false detection rate of less than 2 per cent. This method provides a highly confident way of detecting and locating events. Furthermore, a large number of seismic events can be automatically detected with low false alarm, allowing for a larger automatic event catalogue with a high degree of trust.

A comprehensive seismotectonic model is developed to explain the seismicity of British Columbia. In order to do this extensive revisions are made to location and magnitude parameters in the Canadian Earthquake Data File. Fault plane solutions are calculated for all earthquakes possible and all mechanisms previously calculated are examined and upgraded where necessary. It is proposed that the subcrustal suite of earthquakes in the Puget Sound and southern Vancouver Island region are a result of strain caused by phase changes in the descending oceanic lithosphere of the subducting Juan de Fuca plate. The crustal earthquakes above the deeper seismicity can be explained with an oblique subduction model. The distribution of seismicity, the amount of seismicity and the focal mechanisms support these interpretations. The large earthquakes of central Vancouver Island are probably a result of the interaction of the Explorer Plate with the overriding America Plate. In the southern Queen Charlotte Islands thrusting components in the fault plane solutions confirm there is an element of convergence across the pacific/America boundary in this region. The distribution of seismicity suggests all relative plate motion is presently occurring along the Queen Charlotte fault. The Quaternary volcanoes of British Columbia show little correlation with the seismicity pattern except for the eastern end of the Anahim volcanic belt. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Karhunen-Loève transform, which optimally extracts coherent information from multichannel data, has been applied to several problems in reflection seismic data processing. The transform is derived by a least-squares construction of an orthogonal set of principal components and eigenvectors, with corresponding eigenvalues. Data are reconstructed as a linear combination of the principal components. The mathematical properties of the Karhunen-Loève transform which render it applicable to problems in seismic data processing are reviewed, and a number of new algorithms developed. Most algorithms are tested on synthetic and real data examples, and 'production-line' industrially viable versions of some of the programs have been developed. A new signal-to-noise ratio enhancement technique, based on reconstruction of stacked seismic sections, has proved to be successful on real data. Reconstruction of less coherent information to emphasize anomalous features in stacked seismic data ("misfit" reconstruction) shows some promise. Diffraction hyperbolae isolated by misfit reconstruction are used to estimate residual migration velocities with some success. And, the ability of the transform to segregate coherent information is used successfully as the basis of a new multiple suppression technique. An anomaly identification scheme, based on cluster analysis of the eigenvectors of the transform, works well on the synthetic data used, and gives promising results when applied to real data. A new velocity analysis method, utilizing a ratio of the eigenvalues, works well for good data at early travel times, and offers a potential for high resolution velocity inversion studies. Use of the eigenvalues in evaluation of a constant phase approximation to dispersion for synthetic data provides promising results, leading to quantification of dispersion in terms of relative phase shifts. As part of this development, an analysis of the effect of dispersion on Vibroseis© data acquisition, which represents an original investigation, is presented. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

During July 1974, two reversed deep seismic sounding (DSS) profiles extending about 75 km were recorded in the Explorer Ridge region of the northeastern Pacific, one parallel and the other perpendicular to the ridge. A two-ship operation was used to record near-vertical incidence to wide-angle reflected waves and refracted waves with penetration from the ocean bottom to the upper mantle. Signals from six individual hydrophones suspended at 45 m depth from a 600 m cable trailed behind the receiving ship were recorded in digital form. The shooting ship detonated charges ranging from 2.3 kg to 280 kg and recorded the direct arrival plus the WWVB time code. Processing of the data recorded at distances beyond 4 km included demultiplexing, stacking, and filtering. Before the data were presented in record section form, traveltime corrections were made for topography and shot distance, and amplitude corrections were made for amplifier gain, charge size, and spherical spreading. The interpretation procedure consisted of two steps. A homogeneous, layered velocity-depth model was initially constructed from first arrival traveltime data. The p-A curve corresponding to this model was then altered until an amplitude fit was obtained using synthetic seismograms. Weichert-Herglotz integration of the resultant p-A curve produced the final velocity-depth model. This traveltime and amplitude interpretation required the introduction of velocity gradients into the model. The profile run across the ridge showed no anomalous behaviour as the ridge was crossed; the profile on the Juan de Fuca plate, paralleling the ridge, exhibited traveltime branch offsets and delays. These have been interpreted as due to faulting with a. vertical component of offset of about 5 km. The reversed upper mantle velocities are 7.8 and 7.3 km/s in directions perpendicular and parallel to the ridge. Anisotropy is proposed to explain these different velocities. Compared with crustal sections from other ridge areas, the data require a thick "layer 3" (up to 7 km) near the ridge crest. The total depth to the base of the oceanic crust varies between 10 and 12 km except in the faulted region. The results of this study favor the hypothesis that Explorer Ridge is presently an inactive spreading center. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Our knowledge of Earth's structure and dynamics is owed, in large part, to techniques that allow us to infer the physical properties of rocks based on observations made near the surface. In particular, passive seismic imaging relies on natural sources of elastic wave energy (typically earthquakes) to illuminate Earth's interior. The frequency-dependent dispersive characteristics of surface waves from earthquakes provides a valuable constraint on the depth heterogeneity beneath the surface, which can be used to infer structure of the lithosphere (i.e., tectonics). The first part of this thesis develops novel tools for passive seismic imaging considering surface-wave dispersion. Specifically, Bayesian (probabilistic) methods are developed that provide rigorous uncertainty quantification. The ability to estimate the directional dependence of surface-wave speeds (i.e., seismic anisotropy) is demonstrated. Furthermore, a general approach for considering circular (wrapped) data, such as surface-wave phase measurements, is developed and applied to estimate the average dispersion between pairs of seismic stations. These ideas are applied to data recorded at seismic stations over British Columbia, Canada, to produce a large volume of data products that will help improve our understanding of the tectonics throughout the region. The second part of this thesis investigates the structural and mechanical conditions in subduction zones, where tectonic plates collide and one plate is thrust beneath the other. Specifically, a type of passive seismic imaging based on recordings of body waves from distant earthquakes (known as receiver functions) is used to infer subduction zone structure in relation to the coupling between tectonic plates. Receiver function data calculated for stations over the Cascadia subduction zone (southwestern Canada) suggest that episodes of slow slip on the plate interface occur in tandem with changes in mechanical conditions. Receiver function data calculated for stations over the Hikurangi subduction zone (New Zealand) suggest that stress and deformation along the margin are spatially linked to plate coupling. These results improve our understanding of the dynamics of these tectonic systems, including the seismic hazards that they pose.

I apply a suite of seismic techniques to investigate iceberg calving at large glaciers around Greenland. Iceberg calving accounts for up to half of the Greenland Ice Sheet's annual mass loss, which makes understanding the physics of the calving process vital to gaining a clear picture of current behavior and future evolution of the Greenland Ice Sheet. However, the varied and complex modes of calving behavior at individual glaciers, paired with the challenges to data collection presented by an actively calving glacier, mean that much remains unknown about the dynamics of calving at marine-terminating glaciers. Seismic data offer a unique opportunity to study this active phenomenon, by allowing remote observation of calving events and quantification of the forces active during calving. Using seismic data collected during the most productive three years of buoyancy-driven calving on record, I estimate the forces active during iceberg calving at 13 glaciers around Greenland. My waveform-modeling results highlight the large number of buoyancy-driven calving events currently occurring at Jakobshavn Isbrae and other glaciers in west Greenland. I demonstrate that a glacier's grounded state exerts control on the production or cessation of rotational calving events and investigate the dynamics of calving at individual glaciers. I pair seismic results with terminus imagery to identify the location of individual calving events within calving sequences that occur over days to weeks at a single glacier terminus. By applying a new cross-correlation technique to seismic data collected within 100 km of three of Greenland's largest glaciers, I identify the occurrence of buoyancy-driven calving events with iceberg volumes up to two orders of magnitude smaller than previously observed. These small calving events frequently occur within ~30 minutes of a larger calving event. In between calving sequences, a glacier terminus changes little, suggesting that the majority of ice lost from marine-terminating glaciers occurs through these sequences. I estimate that these small events may contribute up to 30% more to dynamic mass loss than previously thought (up to 15 Gt/yr). I find no evidence of the cliff failure predicted by the marine-ice-cliff-instability hypothesis, in which catastrophic failure occurs when an ice cliff reaches a theoretical maximum-height limit, despite the three glaciers I investigate in detail having some of the tallest ice cliffs in the world. I use independent constraints on iceberg size from high-quality terminus imagery to present the first demonstration of an empirical relationship between glacial-earthquake magnitude and iceberg size. I investigate this relationship further by considering additional metrics of glacial-earthquake magnitude, and find advantages to using maximum force, rather than the more commonly employed mass-distance product Mcsf, as a measure of glacial-earthquake size. Through a detailed investigation into the character of the glacial-earthquake source, I identify key characteristics of the source function that generates the glacial-earthquake signal. I use experiments on both synthetic and observed waveforms to demonstrate that more-accurate estimates of glacial-earthquake size can be retrieved using source models constructed using a representation of the force history that is more sophisticated than that captured by the simple boxcar model. I confirm the presence of a correlation between iceberg volume and glacial-earthquake size, which moves us closer to having the ability to use remotely recorded seismic signals to quantify mass loss at Greenland glaciers. This work presents testable hypotheses for future model development.

New Insights on the Uncertainties in Finite-Fault Earthquake Source Inversion Hoby Njara Tendrisoa Razafindrakoto Earthquake source inversion is a non-linear problem that leads to non-unique solutions. The aim of this dissertation is to understand the uncertainty and reliability in earthquake source inversion, as well as to quantify variability in earthquake rupture models. The source inversion is performed using a Bayesian inference. This technique augments optimization approaches through its ability to image the entire solution space which is consistent with the data and prior information. In this study, the uncertainty related to the choice of source-time function and crustal structure is investigated. Three predefined analytical source-time functions are analyzed; isosceles triangle, Yoffe with acceleration time of 0.1 and 0.3 s. The use of the isosceles triangle as source-time function is found to bias the finite-fault source inversion results. It accelerates the rupture to propagate faster compared to that of the Yoffe function. Moreover, it generates an artificial linear correlation between parameters that does not exist for the Yoffe source-time functions. The effect of inadequate knowledge of Earth’s crustal structure in earthquake rupture models is subsequently investigated. The results show that one-dimensional structure variability leads to parameters resolution changes, with a broadening of the posterior 5 PDFs and shifts in the peak location. These changes in the PDFs of kinematic parameters are associated with the blurring effect of using incorrect Earth structure. As an application to real earthquake, finite-fault source models for the 2009 L’Aquila earthquake are examined using one- and three-dimensional crustal structures. One- dimensional structure is found to degrade the data fitting. However, there is no significant effect on the rupture parameters aside from differences in the spatial slip extension. Stable features are maintained for both structures. In the last part of this work, a multidimensional scaling method is presented to compare and classify earthquake slip distributions. A similarity scale to rank them are thus formulated. Dissimilarities among slip models (from various parameterizations) are computed using two different distance metrics, normalized squared and gray-scale metrics. Multidimensional scaling is then used to visualize the differences among the models. The analyzes are done for 2 case studies; one based on artificial scenarios with a known answer and another one based on the published rupture models of the 2011 Tohoku earthquake.

Legio is the base of the Roman II Triana and the VI Ferrata Legion, occupied from the early 2nd century to the early 4th century CE. It is the first of its kind to be excavated in the Eastern Roman Empire. Today the site sprawls beneath 30 hectares of pasture with slopes up to 15 degrees. Rapid, dense ground penetrating radar (GPR) survey with an antenna array would be ideal, but so far logistically impractical. The survey has proceeded since 2013 with a single 400 MHz antenna using parallel transects 0.5m apart for 5.85 ha to date. Like most Roman bases, Legio includes an extensive network of buildings and streets enclosed by rectangular fortifications. Unlike most Roman bases, however, it was constructed on a hillside with architectural components built by a combination of bedrock incision and above-ground construction. In addition, much of the site’s stonework has been robbed. These aspects demand topographic correction and interpretation using reflection profiles, depth slices, and 3D models. This paper presents data processing and results for the principia (central headquarters). Previous investigations were conducted at Legio and surrounding area by Tel Aviv University from 1998 to 2010. GPR and excavations since 2013 have been conducted as part of the Jezreel Valley Regional Project (JVRP)in association with the W.F. Albright Institute of Archaeological Research.

No description available.