Magnitude Estimation for Earthquake and Tsunami Early Warning Systems

In this study, different magnitude estimation methods were investigated for application to earthquake early warning (EEW) and tsunami early warning systems. This integrated study is divided into two main parts. First, I used strong motion accelerograms recorded by borehole and surface stations from the Kiban Kyoshin network (KiK-net) for Japanese earthquakes with moment magnitude (M) ≥ 5.0 in order to develop ground motion prediction equations (GMPEs). I developed new GMPEs for peak ground acceleration (PGA) and peak ground velocity (PGV) using two different catalogs. The first catalog included earthquakes with 5.0 ≤ M ≤ 8.1 from 1998-2010. In order to improve the determination of attenuation parameters and magnitude scaling, the second catalog included earthquakes with 5.0 ≤ M ≤ 9.0 from 1998-2011, which increased the time period by only one year but added approximately twice as much data to the first catalog. The GMPEs were used to estimate the magnitude from PGA values (Mpga) and from PGV values (Mpgv) for those events in the borehole and surface databases with at least 20 available records. The results confirmed that Mpga and Mpgv strongly correlate with the moment magnitude of the event. In addition, I studied the site effect terms in the GMPEs using the shear wave velocity in the uppermost 30 meters (VS30). It was found that correcting for VS30 improved the accuracy of magnitude estimates from surface recordings, particularly for Mpgv. Incorporation of this parameter into the GMPEs can provide a more accurate estimate of the earthquake magnitude in EEW systems. The GMPEs also were used to estimate the magnitude of the M9.0 Tohoku event and those estimates were compared with the magnitude estimates provided by the existing EEW system in Japan. I demonstrate that, unlike the estimates provided by the existing EEW system in Japan, the magnitude estimates from GMPEs do not saturate. The results demonstrate that Mpgv from borehole recordings had the smallest standard deviation among the estimated magnitudes and produced more stable and robust magnitude estimates. Based on this observation, I propose the incorporation of borehole recordings into EEW systems. This method can improve the existing EEW system in Japan or other regions that have a dense seismic network. In the second part of this thesis, the displacement spectra of the strong ground motion recordings were used to directly estimate the magnitude of Japanese earthquakes with 4.5 ≤ M ≤ 9.0, 2000 to 2011, using the first available data provided by the KiK-net and Kyoshin network stations. The source parameters were determined using the inversion of displacement spectra for available P- and S-waves windows assuming the Brune source model. I tested the application of a fixed low-cut filter, and found that it decreases the accuracy of magnitude estimation for large events (M \u3e 7.0). As a result, instead of a fixed low-cut filter I applied a frequency bandwidth cutoff based on a signal-to-noise ratio criterion. The results showed that magnitude estimation using the strong motion recordings from the closest station to the source of the event provides a good early estimate for the final size of the event, which can reduce the time required to calculate final magnitude and hence provides a longer warning time (from a few seconds to a few minutes). The results also indicated that the predicted magnitude based on the P-wave window (MP) provides a longer warning time, but with a larger uncertainty, in comparison to the estimation based on the S-wave window (MS). The magnitude estimate based on inversion of the displacement spectra is independent of magnitude scaling relationships, as is the case with magnitude vs. early P-wave parameter relationships or GMPEs, because it determines the moment magnitude from the estimated source parameters directly from the displacement spectra. Therefore, this method can be used in regions with sparse seismic networks where historic recordings of strong ground motion from potentially damaging earthquakes are not available to develop an empirical relationship, such as the Cascadia region of North America

Generalized Multigroup Method

Treatment of energy in the solution of the transport equation has been dominated by the multigroup method (MG). The multigroup method has the advantages of being simple and mathematically robust. However, it suffers from two disadvantages. When the multigroup transport equation is solved to find the group flux coefficients, the assumed spectrum becomes discontinuous at the energy boundaries, and the assumed spectrum maintains its original shape within the group. These characteristics are in contradiction with actual spectrum behavior. These disadvantages reduce the accuracy of the multigroup method, requiring a greater number of energy groups to converge to a solution with the desired accuracy. These deficiencies are caused by the use of histogram basis functions to define group membership. These basis functions are orthogonal to each other and have only one degree of freedom. Hence, the calculated group flux coefficients shift the spectrum vertically to give the optimal balance between the sources and sinks in the transport problem. To mitigate these inefficiencies of the multigroup method, a generalized multigroup method is proposed. In this method, an arbitrary set of basis functions is defined. By utilizing more appropriate basis functions, the spectrum is able to adapt within each energy group and be continuous at the boundaries. Improvement in the calculation of the spectrum will result in a more accurate solution of the equation. In addition to defining the generalized multigroup method, this research also implements the hat basis function to allow the spectrum to adapt linearly within each energy group and be continuous at the boundaries. The hat basis function implementation is called the Linear Multigroup Method (LMG). The LMG is then tested using two gamma ray spectrum calculation problems in an infinite oxygen medium. The results of these sample problems for the LMG are compared to the conventional MG method. This comparison shows that the LMG is superior to the MG in energy regions in which the flux spectrum is continuous, but less so for regions of discontinuous spectrum (e.g., near the 511 keV pair production spike or near discrete source energies). To deal with these special cases a hybrid LMG/MG method is developed and shown to give more accurate results

Anisotropic eta-substrate conical-beam leaky-wave antenna

A broadband and low beam squint anisotropic magneto-dielectric 2D leaky-wave antenna excited by a vertical electric source is presented. A comparison of the TM dis- persion behavior of the structure for Drude/Lorentz dispersive anisotropic and an isotropic non-dispersive grounded slabs is performed. The isotropic slab is restricted to leaky-wave pointing angles near endfire with very low radiation performance due to the inherent endfire radiation null caused by the slab. As a result, its radiation is dominated by the space-wave, which leads to low directivity and beam scanning incapability. In contrast, the anisotropic meta-substrate provides a highly directive and efficient 2D leaky-wave radiation with great design flexibility. At its lower frequencies, it provides narrow-band full-space conical-beam scanning while at higher frequencies, it enables a designable angle fixed-beam with low-beam squint radiation. This antenna may find applications in broadband point-to-point communication and radar systems.Ministerio de Educación y Ciencia, Ref. TEC2007-67630-C03-02. Fundación Séneca, Ref. 08833/PI/08

Broadband and Low Beam Squint Leaky-Wave Radiation from a Uniaxially Anisotropic Grounded Slab

The behavior of leaky and surface modes in uniaxially anisotropic grounded slabs is investigated. First, a transverse magnetic and transverse electric modal parametric analysis of the structure is performed, based on dispersion relations, comparing the non-dispersive and Drude/Lorentz dispersive anisotropic slabs with an isotropic non-dispersive slab. This analysis reveals that in the case of the isotropic slab, the leaky wave pointing angle is restricted to the end-fire region. In contrast, it is shown, for the first time, that the proposed anisotropic dispersive grounded slab structure provides efficient (in particular highly directive) leaky wave radiation with a high design flexibility. Toward its lower frequencies, the dominant leaky mode provides full-space conical-beam scanning. At higher frequencies, it provides fixed-beam radiation (at a designable angle) with very low beam squint. A vertical dipole source is placed inside the slab to excite the relevant leaky wave mode. The radiation characteristics obtained for this structure confirms the novel low-beam squint and high-directivity operation of the dominant leaky mode. Further validation is included using the commercial software tool CST. The structure could be used to conceive antennas either for conical beam scanning (lower-frequency range) or for point-to-point communication and radar systems (higher-frequency range).Ministerio de Educación y Ciencia, Ref. TEC2010-21520-C04-0

Analysis of the radiation properties of a point source on a uniaxially anisotropic meta-substrate and the application to a high-efficiency antenna

The radiation efficiency of a point electric source on a loss-less uniaxially anisotropic meta-substrate is computed by the mixed potential integral equation technique. For this purpose, the multilayered Green's functions of the structure are derived from the spectral domain transmission line model of the medium. The efficiency of the antenna is compared for different permittivities and permeabilities of the meta-substrate with fixed TE and TM wave numbers. It is shown that at certain frequencies the radiation efficiency is enhanced as the ratio of the permeability over permittivity is increased. This suggests that an antenna on a mushroom type meta-substrate or a meta-substrate which is constructed from the stacked split ring resonators (SRR) in the plane of the substrate may exhibit a high radiation efficiency close to the resonant frequencies of the metallic loops, as compared to a conventional substrate.Ministerio de Educación y Ciencia, Ref. TEC2007-67630-C03-02. Fundación Séneca, Ref. 08833/PI/08

Bandwidth enhancement and beam squint reduction of leaky modes in a uniaxially anisotropic meta-substrate

This paper presents a rigorous spectral TL approach analysis of meta-substrates, modeled by anisotropic mediums with constitutive parameters built from tensors.Ministerio de Educación y Ciencia, Ref. TEC2007-67630-C03-02. Fundación Séneca, Ref. 08833/PI/08

Enquête séro-épidémiologique sur les principales maladies caprines au Liban

Cette enquête séro-épidémiologique menée au Liban étudie la répartition de six pathologies caprines : la peste des petits ruminants, la pleuropneumonie contagieuse caprine, le syndrome CAEV (arthrite encéphalite caprine virale), la fièvre Q, la paratuberculose caprine, et la brucellose caprine. De manière générale, les régions géographiques les plus touchées sont la Bekaa et le Mont-Liban. Par ailleurs, le mode d'élevage mixte ovin-caprin se traduit pour une majorité d'affections par des séroprévalences supérieures à celles rencontrées lors d'élevages caprins purs'. Malheureusement, l'élevage caprin au Liban subit d'autres contraintes, politiques et économiques, aussi bien importantes que le problème des maladies contagieuses

Optimizing the Performance of Text Classification Models by Improving the Isotropy of the Embeddings using a Joint Loss Function

Recent studies show that the spatial distribution of the sentence representations generated from pre-trained language models is highly anisotropic, meaning that the representations are not uniformly distributed among the directions of the embedding space. Thus, the expressiveness of the embedding space is limited, as the embeddings are less distinguishable and less diverse. This results in a degradation in the performance of the models on the downstream task. Most methods that define the state-of-the-art in this area proceed by improving the isotropy of the sentence embeddings by refining the corresponding contextual word representations, then deriving the sentence embeddings from these refined representations. In this thesis, we propose to improve the quality and distribution of the sentence embeddings extracted from the [CLS] token of the pre-trained language models by improving the isotropy of the embeddings. We add one feed-forward layer, referred to as the Isotropy Layer, between the model and the downstream task layers. We train this layer using a novel joint loss function that optimizes an isotropy quality measure and the downstream task loss. This joint loss pushes the embeddings outputted by the Isotropy Layer to be more isotropic, and it also retains the semantics needed to perform the downstream task. The proposed approach results in transformed embeddings with better isotropy, that generalize better on the downstream task. Furthermore, the approach requires training one feed-forward layer, instead of retraining the whole network. We quantify and evaluate the isotropy through multiple metrics, mainly the Explained Variance and the IsoScore. Experimental results on 3 GLUE datasets with classification as the downstream task show that our proposed method is on par with the state-of-the-art, as it achieves performance gains of around 2-3% on the downstream tasks compared to the baseline. We also present a case study on one language abuse detection dataset, then interpret some of the findings in light of the results