Seismic hazard analysis is concerned with estimating risk to human populations due to earthquakes and the other natural disasters that they cause. In many parts of the world, earthquake-generated tsunamis are especially dangerous. Assessing the risk for seismic disasters relies on historical data that indicate which fault zones are capable of supporting significant earthquakes. Due to the nature of geologic time scales, the era of seismological data collection with modern instruments has captured only a part of the Earth's seismic hot zones. However, non-instrumental records, such as anecdotal accounts in newspapers, personal journals, or oral tradition, provide limited information on earthquakes that occurred before the modern era. Here, we introduce a method for reconstructing the source earthquakes of historical tsunamis based on anecdotal accounts. We frame the reconstruction task as a Bayesian inference problem by making a probabilistic interpretation of the anecdotal records. Utilizing robust models for simulating earthquakes and tsunamis provided by the software package GeoClaw, we implement a Metropolis-Hastings sampler for the posterior distribution on source earthquake parameters. In this work, we present our analysis of the 1852 Banda Arc earthquake and tsunami as a case study for the method. Our method is implemented as a Python package, which we call tsunamibayes. It is available, open-source, on GitHub: https://github.com/jwp37/tsunamibayes.

No description available.

No description available.

The understanding of the impact of site effects on ground motions is crucial for improving the assessment of seismic hazards. Site response analyses (SRA) can numerically accommodate the mechanics behind the wave propagation phenomena near the surface as well as the variability associated with the input motion and soil properties. As a result, SRA constitute a key component of the assessment of site-specific seismic hazards within the probabilistic seismic hazard analysis framework. This work focuses on limitations in SRA, namely, the definition of the elastic half-space (EHS) boundary condition, the selection of input ground motions so that they are compatible with the assumed EHS properties, and the proper consideration of near-surface attenuation effects. Input motions are commonly selected based on similarities between the shear wave velocity (Vs) at the recording station and the materials below the reference depth at the study site (among other aspects such as the intensity of the expected ground motion, distance to rupture, type of source, etc.). This traditional approach disregards the influence of the attenuation in the shallow crust and the degree to which it can alter the estimates of site response. A Vs-κ correction framework for input motions is proposed to render them compatible with the properties of the assumed EHS at the site. An ideal EHS must satisfy the conditions of linearity and homogeneity. It is usually defined at a horizon where no strong impedance contrast will be found below that depth (typically the top of bedrock). However, engineers face challenges when dealing with sites where this strong impedance contrast takes place far beyond the depth of typical Vs measurements. Case studies are presented to illustrate potential issues associated with the selection of the EHS boundary in SRA. Additionally, the relationship between damping values as considered in geotechnical laboratory-based models, and as implied by seismological attenuation parameters measured using ground motions recorded in the field is investigated to propose alternative damping models that can match more closely the attenuation of seismic waves in the field. / Ph. D.

Properly accounting for the uncertainties in predicting ground motion parameters is critical for Probabilistic Seismic Hazard Analyses (PSHA). This is particularly important for critical facilities that are designed for long return period motions. Non-ergodic PSHA is a framework that allows for this proper accounting of uncertainties. This, in turn, allows for more informed decisions by designers, owners and regulating agencies. The ergodic assumption implies that the standard deviation applicable to a specific source-path-site combination is equal to the standard deviation estimated using a database with multiple source-path-site combinations. The removal of the ergodic assumption requires dense instrumental networks operating in seismically active zones so that a sufficient number of recordings are made. Only recently, with the advent of networks such as the Japanese KiK-net network has this become possible. This study contributes to the state of the art in earthquake engineering and engineering seismology in general and in non-ergodic seismic hazard analysis in particular. The study is divided in for parts. First, an automated protocol was developed and implemented to process a large database of strong ground motions for GMPE development. A comparison was conducted between the common records in the database processed within this study and other studies. The comparison showed the viability of using the automated algorithm to process strong ground motions. On the other hand, the automated algorithm resulted in narrower usable frequency bandwidths because of the strict criteria adopted for processing the data. Second, an approach to include path-specific attenuation rates in GMPEs was proposed. This approach was applied to a subset of the KiK-net database. The attenuation rates across regions that contains volcanoes was found to be higher than other regions which is in line with the observations of other researchers. Moreover, accounting for the path-specific attenuation rates reduced the aleatoric variability associated with predicting pseudo-spectral accelerations. Third, two GMPEs were developed for active crustal earthquakes in Japan. The two GMPEs followed the ergodic and site-specific formulations, respectively. Finally, a comprehensive residual analysis was conducted to find potential biases in the residuals and propose models to predict some components of variability as a function of some input parameters. / Ph. D.

Ground motions from earthquakes are known to be affected by earth's surface topography. Topographic effects are a result of several physical phenomena such as the focusing or defocusing of seismic waves reflected from a topographic feature and the interference between direct and diffracted seismic waves. This typically causes an amplification of ground motion on convex features such as hills and ridges and a de-amplification on concave features such as valleys and canyons. Topographic effects are known to be frequency dependent and the spectral accelerations can sometimes reach high values causing significant damages to the structures located on the feature. Topographically correlated damage pattern have been observed in several earthquakes and topographic amplifications have also been observed in several recorded ground motions. This phenomenon has also been extensively studied through numerical analyses. Even though different studies agree on the nature of topographic effects, quantifying these effects have been challenging. The current literature has no consensus on how to predict topographic effects at a site. With population centers growing around regions of high seismicity and prominent topographic relief, such as California, and Japan, the quantitative estimation of the effects have become very important. In this dissertation, we address this shortcoming by developing empirical models that predict topographic effects at a site. These models are developed through an extensive empirical study of recorded ground motions from two large strong-motion datasets namely the California small to medium magnitude earthquake dataset and the global NGA-West2 datasets, and propose topographic modification factors that quantify expected amplification or deamplification at a site. To develop these models, we required a parameterization of topography. We developed two types of topographic parameters at each recording stations. The first type of parameter is developed using the elevation data around the stations, and comprise of parameters such as smoothed slope, smoothed curvature, and relative elevation. The second type of parameter is developed using a series of simplistic 2D numerical analysis. These numerical analyses compute an estimate of expected 2D topographic amplification of a simple wave at a site in several different directions. These 2D amplifications are used to develop a family of parameters at each site. We study the trends in the ground motion model residuals with respect to these topographic parameters to determine if the parameters can capture topographic effects in the recorded data. We use statistical tests to determine if the trends are significant, and perform mixed effects regression on the residuals to develop functional forms that can be used to predict topographic effect at a site. Finally, we compare the two types of parameters, and their topographic predictive power. / Ph. D.

Seismic hazard calculations for sites in eastern North America have traditionally assumed a Poisson process to describe the temporal behavior of earthquakes and have employed the Gutenberg-Richter relationship to define the frequency distribution of earthquake magnitude. For sites in areas where geological information indicates recurrent, large earthquakes, however, such data imply a rate for large events which often exceeds that predicted by the Gutenberg-Richter relationship. One way in which this discrepancy can be reconciled is to assume that the larger events occur as a time-dependent, or renewal, process and possess a "characteristic earthquake" magnitude distribution. The main purpose of this study is to make a quantitative comparison of seismic hazard estimates for Charleston of the influences of 1) the Poisson temporal model assuming the Gutenberg-Richter and characteristic earthquake magnitude recurrence relationships with 2) the renewal temporal model assuming the characteristic magnitude recurrence relationship. Other issues that are examined are the sensitivity of uncertainties of hazard model parameters such as maximum magnitude and seismic source delineation. Probabilistic seismic hazard calculations for the next 50 years were performed at Charleston for all potential seismic sources. The highest estimate of seismic hazard was obtained with the Poisson temporal model and characteristic earthquake recurrence relationship. The lowest hazard was obtained with the renewal temporal model and characteristic magnitude recurrence relationship. The results of this study are in good agreement with hazard estimates for Charleston in the most recent national seismic hazard maps. / Master of Science

The northern part of Algeria is located in the border zone between the African and Eurasian plates. The collision between the two plates is expressed by a moderate to high seismicity, generally localized at the margins of the Neogene basins. The Middle-Chelif Basin is located in the northwestern part of Algeria, between the northern and southern Tellian Atlas mountain belts. The seismic activity is mainly generated by the El-Asnam fault, a 40 km long reverse fault located on the western edge of the basin. The 1980 El-Asnam earthquake caused significant damage in the cities of the basin. In particular, the cities of Oued-Fodda, El-Attaf and El-Abadia were heavily affected. In the western part of the alluvial plain of the Middle-Chelif, phenomena of cracks, settlements, landslides and liquefaction, have also occurred following the earthquake. This research aims to quantify dynamic properties of the soils of the Middle-Chelif Basin in terms of shear-wave velocity (Vs), fundamental frequency or vulnerability index (Kg) for the estimation of liquefaction potential. The calculation of dynamic soil properties allows a better assessment of the seismic hazard in the region. We have focused more on the characterization of the Vs structure of the superficial sedimentary layers in the entire Middle-Chelif Plain because of the role it plays in the amplification of the seismic waves during an earthquake. Secondly, these same soil parameters allow the creation of microzonation maps classifying the surface soil according to the criteria of NEHRP (National Earthquake Hazard Reduction Program). For this purpose, techniques based on single-station and array ambient vibration measurements are applied. Ambient vibrations were recorded at 323 sites using single-station, and at 18 sites using array measurements. The measurements were densified within urban areas. This thesis is divided into three main parts; the first one consists in a seismic microzonation of the city of Oued-Fodda, located at 1-2 km from the El-Asnam fault. The Horizontal-to-Vertical Spectral Ratio (HVSR) method was applied on ambient vibration records measured at 103 sites in the city and its surroundings. Maps of the variation of soil resonance frequencies, as well as their amplitudes, were provided. Inversion of the HVSR curves allowed obtaining 1D Vs models at each site. The 2D velocity profiles were used to image the shape of the sedimentary layers and the bedrock outcrop in the central part of the city. The second part aims to characterize the sedimentary deposits in the basin. The HVSR method was applied on ambient noise records measured at 164 sites and aligned on 20 NW-SE profiles. The Frequency-Wavenumber (F-K) technique was applied on array measurements at 7 sites. The 2D velocity profiles imaged the synclinal shape of the sedimentary deposits. A bedrock model was also provided. The third and last part consists of a more complete seismic microzonation in the three other main cities of the basin; Ain-Defla, El-Attaf and El-Abadia. Ambient vibrations were measured using a single-station at 56 sites and using arrays at 11 sites. As a result, maps of resonance frequency variation, Vs variation over the first 30 meters of the soil (Vs30) and soil classification were proposed in addition to a prediction equation for Vs30 in the region.

Northern Central America is a tectonically complex zone defined by its borders with Cocos and North America plates. The Middle America subduction zone and the strike-slip motion along the North America-Caribbean plate boundary, in that order, control most of its deformation. The interaction between the different elements of the studied area is evident from the high seismicity in the region, especially along plate boundaries. Also in the interior of the region, seismicity shows that deformation takes place, though in lesser degree. In a time window of 30 years, three earthquakes with moment magnitude larger than 7 struck northern Central America evincing the need to estimate the seismic hazard for the zone. To tackle the problem, we compiled a catalogue of hypocenters commencing in 1964, defined seismogenic sources and described the evolution of earthquake activity through a Poisson model. Probabilistic seismic hazard (PSH) calculations for the next 50 years were performed. The highest estimate of seismic hazard was obtained for the zone adjacent to the subduction zone. Because of the fundamental importance of demarcating seismogenic sources in the PSH analysis, i.e. defining the seismotectonic model, we extended the catalogue to cover 102 years for the whole northern Central America. We have studied the North America-Caribbean plate boundary in order to refine the fault representation. Different techniques were used, like that of body-waveform modeling, allowing us to limit the extent of depth of faulting to 20 km. The seismic moment tensor was used to estimate the deformation velocities on known tectonic structures, including those of the Honduras depression and borderland faults. Finally, we made use of the Coulomb stress criterion to determine the relation between earthquake occurrence and static stress changes following major earthquakes.

<p>Northern Central America is a tectonically complex zone defined by its borders with Cocos and North America plates. The Middle America subduction zone and the strike-slip motion along the North America-Caribbean plate boundary, in that order, control most of its deformation. The interaction between the different elements of the studied area is evident from the high seismicity in the region, especially along plate boundaries. Also in the interior of the region, seismicity shows that deformation takes place, though in lesser degree. In a time window of 30 years, three earthquakes with moment magnitude larger than 7 struck northern Central America evincing the need to estimate the seismic hazard for the zone. To tackle the problem, we compiled a catalogue of hypocenters commencing in 1964, defined seismogenic sources and described the evolution of earthquake activity through a Poisson model. Probabilistic seismic hazard (PSH) calculations for the next 50 years were performed. The highest estimate of seismic hazard was obtained for the zone adjacent to the subduction zone. Because of the fundamental importance of demarcating seismogenic sources in the PSH analysis, i.e. defining the seismotectonic model, we extended the catalogue to cover 102 years for the whole northern Central America. We have studied the North America-Caribbean plate boundary in order to refine the fault representation. Different techniques were used, like that of body-waveform modeling, allowing us to limit the extent of depth of faulting to 20 km. The seismic moment tensor was used to estimate the deformation velocities on known tectonic structures, including those of the Honduras depression and borderland faults. Finally, we made use of the Coulomb stress criterion to determine the relation between earthquake occurrence and static stress changes following major earthquakes.</p>