Browsing by Subject "Earthquakes"
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Item A study of earthquake P phases reflected and diffracted from the earth's outer core(Texas Tech University, 1966-08) Lillard, Douglas RayNot availableItem A study of the earthquake phases Pa and Sa(Texas Tech University, 1968-08) LeTourneau, Nelson JosephNot availableItem Adaptive capacity & resilience to natural disasters in Latin America : a case study on the 2007 Ica, Peru earthquake(2011-05) Zegarra-Coronado, Aurea Gabriela; Dietz, Henry A.; Wilson, Patricia AnnThe purpose of this study is to explore, compare, and analyze the process of learning and the importance of adaptation and resilience in a continuously evolving environment amidst natural disasters as seen in two earthquake-prone communities located in southern Peru. The framework of complex adaptive systems offers insight into understanding human limitations to control an environment that is constantly far from equilibrium. Complexity science theory supports the study and the self-organization of communities in the process of coping with a disaster. Reports generated from informal interviews and participatory techniques further support all evidential findings. The co-evolution process given by the participation of diverse agents may include the collaboration and involvement of victims as well as local, state, and national organizations. Results from the co-evolution process may derive from previous experiences, preparedness, education, the development of previous relationships, and the capacity of improvisation. Furthermore, solidarity, self-organization and adaptation of agents in a community may further influence the ability to deal effectively with unexpected adversity.Item Assessment of Interplate and Intraplate Earthquakes(2012-10-19) Bellam, Srigiri ShankarThe earth was shown in the last century to have a surface layer composed of large plates. Plate tectonics is the study of the movement and stresses in the individual plates that make up the complete surface of the world's sphere. Two types of earthquakes are observed in the surface plates, interplate and intraplate earthquakes, which are classified, based on the location of the origin of an earthquake either between two plates or within the plate respectively. Limited work has been completed on the definition of the boundary region between the plates from which interplate earthquakes originate, other than the recent work on the Mid Atlantic Ridge, defined at two degrees and the subsequent work to look at the applicability of this degree based definition. Others suggested an alternative view of a constant width for the interplate region in recent work at Texas A&M University. The objective of the paper is to determine whether the assumption of a linear width of the region along the tectonic plate boundaries to classify earthquakes as interplate and intraplate earthquakes using accepted statistical criteria provides a better fit to the data than the constant degree definition. There are three types of interplate boundaries defined by the relative movement of the two plates to each other, which further complicates this study. The study used a nonrandom analysis of regions of the different types of boundary to compare the rate and decay of the intraplate earthquakes from a notional centerline for the known boundaries. The study used GIS software and EXCEL for the statistical analysis component of the research work. The results show that a constant width definition provides a number of advantages in determining the relative definition of interplate and intraplate earthquakes when compared to the constant degree definition developed for work on the Mid Atlantic Ridge. Further research is suggested on a randomly selected set of study sites to improve the reliability and quality of the statistical work for each type of the boundary of the tectonic plates.Item A comparison of methodologies used to predict earthquake-induced landslides(2011-05) Dreyfus, Daniel Kenoyer; Rathje, Ellen M.; Gilbert, Robert B.The rigid sliding-block analysis introduced by Newmark in 1965 has become a popular method for assessing the stability of slopes during earthquakes. Estimates of sliding displacement calculated using this methodology serve as an index of seismic performance and are used for mapping seismic landslide hazard potential. The original approach of rigorously integrating ground acceleration time-histories to compute estimates of sliding displacement has been replaced by the use of simple, empirical models that predict displacement as a function of a slope's yield acceleration and one or more measures of ground shaking. To be useful the results of these models must be compared with observations of landslides from previous earthquakes. Seven different empirical models were evaluated by comparing predicted displacements with an inventory of observed landslides from the 1994 Northridge, California earthquake. Using a comprehensive set of ground motion data and shear strength properties from the Northridge earthquake, sliding displacements were calculated within a geographic information system (GIS) and the accuracy of each model was computed. The influence of factors such as landslide size, geologic unit, slope angle, and material strength on the prediction of landslides was also evaluated. The results were used to show that the accuracy of the predictive models depends less on the model used and more on the uncertainty in the model parameters, specifically the assigned shear strength values. Because current approaches do not take into account the spatial variability of strength within individual geologic units, the accuracy of the predictive models is controlled by the distribution of slope angles within observed and predicted landslide cells. Assigning overly conservative (low) shear strength values results in a higher percentage of landslides accurately identified, but also results in a large over-estimation of the seismic landslide hazard.Item Comparison of seismic site response analysis and downhole array recordings for stiff soil sites(2014-05) Faker, Jeremy Stuart; Rathje, Ellen M.Accurately predicting surface ground motions is critical for many earthquake engineering applications. Equivalent-linear (EQL) site response analysis is a numerical technique used to compute surface ground motions from input motions at bedrock using the site-specific dynamic soil properties. The purpose of this study was to investigate the accuracy of EQL site response analysis for stiff soil sites by comparing computed and observed transfer functions and response spectral amplification. The Kiban Kyoshin network (KiK-net) in Japan is a seismograph network consisting of downhole array sites with strong-motion accelerometers located at the ground surface and at depth. Recorded motions and shear wave velocity profiles are available for most sites. Observed transfer functions and response spectral amplification were computed for 930 individual seismic recordings at 11 stiff soil KiK-net sites. Computed transfer functions and response spectral amplification were calculated from EQL site response analysis by specifying the KiK-net base sensor motion as the input motion. Sites were characterized using the measured shear wave velocity profiles and nonlinear soil properties estimated from empirical models. Computed and observed transfer functions and response spectral amplification were compared at different levels of strain for each site. The average difference between the observed and computed response spectral amplification across the 11 sites were compared at different levels of strain. Overall, there is reasonable agreement between the computed and observed transfer functions and response spectral amplification. There is agreement between the computed and observed site periods, but with over-prediction of the computed response at the observed site periods. Higher modes often computed by the theoretical model were not always observed by the recordings. There is very good agreement between the computed and observed transfer functions and response spectral amplification for periods larger than the site periods. There is less agreement between the computed and observed transfer functions and response spectral amplification for periods less than the site periods. There is mostly over-prediction of the response spectral amplification at these periods, although some under-prediction also occurred. Across all 11 sites the predicted spectral amplification is within +/-20% at shear strains less than 0.01%. At shear strains between approximately 0.01 and 0.03%, the spectral amplification is over-predicted for these sites, in some instances by as little as 5% and in other instances by a factor of 2 or more.Item Impact of input ground motions and site variability on seismic site response(2006-08) Kottke, Albert R. (Albert Richard); Rathje, Ellen M.Seismic site response analysis allows an engineer to assess the effect of local soil conditions on the ground motions expected during an earthquake. In seismic site response analysis, an input ground motion on rock is propagated through a site specific soil column. The computed response at the surface is dependent on both the input ground motion and the soil properties that characterize the site. However, there is uncertainty in both the input ground motion and the soil properties, as well as natural variability in the soil properties across a site. To account for the uncertainty in the input ground motions, engineers use a suite of motions that are selected and scaled to fit a scenario input motion. This study introduces a semi-automated method to select and scale the input motions to fit a target input motion and its variability. The proposed method is intended to replace tedious trials of combinations by hand with combinations performed by a computer. However, as in the traditional selection methods, the final selection of the combination is done by the engineer.The effect of the selected ground motion combination on the computed surface response spectrum from the site response analysis, and its variability, was investigated in this study. The results show by using a combination with as few as five motions, the median surface response spectrum can be predicted with an error of 10%. Additionally, the manner used to scale the input motions does not impact the accuracy of the median surface response spectrum, as long as the median response spectrum of the input combination agrees with the target input response spectrum. However, if the standard deviation of the surface response spectrum is to be considered (e.g., to develop median plus one standard deviation spectra), a input combination of at least 20 motions is recommended and the combination must be scaled such that the standard deviation of the input combination matches the standard deviation of the input target spectrum. Monte Carlo simulations were used to assess the impact of soil property variability on surface spectra computed by seismic site response. The results from this study indicate that by accounting for the variability of the shear-wave velocity profile of a site can cause a significant decrease in the median surface response spectrum, as well as a slight increase in the standard deviation of the surface response spectrum at periods less than the site period. By considering the variability of the nonlinear properties (shear modulus reduction and damping ratio) the median response spectrum decreased only slightly, but the standard deviation increased in a manner similar to the increase observed when considering the variability of the shear-wave velocity profile. Simultaneously considering the variability of the shear-wave velocity profile and nonlinear properties resulted in a median surface response spectrumsimilar to the median surface response spectrumcomputed with considering the variability of the shear-wave velocity alone. However, the standard deviation of the surface response spectrum was larger than the standard deviation computed by independent consideration of the variability of the shear-wave velocity or nonlinear properties.Item Microgrid availability during natural disasters(2014-08) Krishnamurthy, Vaidyanathan; Kwasinski, AlexisA common issue with the power grid during natural disasters is low availability. Many critical applications that are required during and after natural disasters, for rescue and logistical operations require highly available power supplies. Microgrids with distributed generation resources along with the grid provide promising solutions in order to improve the availability of power supply during natural disasters. However, distributed generators (DGs) such as diesel gensets depend on lifelines such as transportation networks whose behavior during disasters affects the genset fuel delivery systems and as a result affect the availability. Renewable sources depend on natural phenomena that have both deterministic as well as stochastic aspects to their behavior, which usually results in high variability in the output. Therefore DGs require energy storage in order to make them dispatchable sources. The microgrids availability depends on the availability characteristics of its distributed generators and energy storage and their dependent infrastructure, the distribution architecture and the power electronic interfaces. This dissertation presents models to evaluate the availability of power supply from the various distributed energy resources of a microgrid during natural disasters. The stochastic behavior of the distributed generators, storage and interfaces are modeled using Markov processes and the effect of the distribution network on availability is also considered. The presented models supported by empirical data can be hence used for microgrid planning.Item Microphysical Controls on the Strength and Transport Properties of Fault Zones(2014-10-07) French, Melodie Ellen LyndsTwo studies on the mechanical properties of smectite-rich fault gouge collected from the Central Deforming Zone (CDZ) of the San Andreas Fault (SAF) in the San Andreas Fault Observatory at Depth (SAFOD) are presented. Rotary shear experiments were conducted at co-seismic slip rates (0.1 to 1 m/s). Displacement and dynamic weakening result from slip along clay-foliation assisted by shear-heating pressurization of pore fluid in wet gouge and additional grain-size reduction and possible clay dehydration in dry gouge. The results of a stability analysis show that microseismic patches within the CDZ should arrest at in-situ deformation conditions despite the documented weakening of the gouge. In some cases, however, weakening may be sufficient to sustain propagation of a rupture that nucleates within the adjacent locked segment into the CDZ. Stress-relaxation tests were also conducted on the CDZ gouge, and achieved strain-rates within an order of magnitude of in-situ creep (~ 10^-10 s^-1). The gouge is frictionally weak (< 0:15) at all conditions tested, and exhibits a change in the rate-determining mechanism at strain-rates below 10^-8 s^-1. A microphysical model for deformation of the CDZ gouge is hypothesized; the strength of the CDZ gouge is consistent with intergranular sliding whereby geometric obstacles deform by fracture/delamination and dislocation glide operating as parallel-concurrent mechanisms. At strain-rates greater than 10^-8 s^-1, fracture/delamination are the rate-controlling processes, and at lower rates, dislocation glide is rate-controlling. To understand the effects of stress and deformation on fluid flow through faulted rock, the permeability of faulted, damaged, and intact sandstone, was measured and mapped with respect to effective mean stress (15 to 100 MPa), differential stress (0 to 140 MPa), and proximity to frictional failure. The permeability and porosity of intact and faulted Punchbowl Formation Sandstone, a low-porosity (7 %) low-permeability (10^-18 m^2) altered arkosic sandstone, are strongly correlated with mean stress and insensitive to differential stress and proximity to the failure envelope. The fault core is a conduit with enhanced permeability. Porosity-permeability relations indicate that the microphysical controls of the stress-dependence are the same for intact and faulted rock despite higher microfracture densities and a localized fluid conduit.Item Modeling household adoption of earthquake hazard adjustments: a longitudinal panel study of Southern California and Western Washington residents(Texas A&M University, 2006-10-30) Arlikatti, Sudha SThis research, aimed at advancing the theory of environmental hazard adjustment processes by contrasting households from three cities in a high seismic hazard area with households from three other cities in a moderate seismic hazard area. It identified seven types of stakeholders namely, the risk area residents and their families (primary group), the news media, employers, and friends (secondary group), and federal, state, and local governments (tertiary group), and explained why they are relevant to the adoption of seismic hazard adjustments. It also addressed three key attributes?????? knowledge, trustworthiness, and responsibility for protection??????ascribed to these multiple stakeholders and the relationships of these stakeholder attributes with risk perception, hazard intrusiveness, hazard experience, gender, resource adequacy, fatalism and hazard adjustment adoption. It was specifically concerned with the effects of nested interactions due to trust and power differentials among the seven stakeholders, with the self reported adoption of 16 earthquake protective measures at two points in time (1997 and 1999). Some of the key findings indicate that risk perception, gender, fatalism, city activity in earthquake management and demographic characteristics did not significantly predict hazard adjustment adoption. However, all stakeholder characteristics had significant positive correlations with risk perception and hazard adjustment, implying a peripheral route for social influence. Hazard intrusiveness, hazard experience, and stakeholder knowledge, trustworthiness, and responsibility affected the increased adoption of hazard adjustments by households. Particularly important are the peer groups?????? (employers, friends and family) knowledge, trustworthiness and responsibility. These findings suggest, hazard managers cannot count only on the federal, state, and local government advisories put out through the news media to affect community decisions and thereby households?????? decisions to take protective actions. Instead, hazard managers need to shift focus and work through peer group networks such as service organizations, industry groups, trade unions, neighborhood organizations, community emergency response teams, faith-based organizations, and educational institutions to increase the knowledge, trustworthiness and responsibility of all in the peer group. This will assure higher household hazard adjustment adoption levels, thus facilitating a reduction in post disaster losses and recovery time.Item Off-fault Damage Associated with a Localized Bend in the North Branch San Gabriel Fault, California(2012-08-15) Becker, Andrew 1987-Structures within very large displacement, mature fault zones, such as the North Branch San Gabriel Fault (NBSGF), are the product of a complex combination of processes. Off-fault damage within a damage zone and first-order geometric asperities, such as bends and steps, are thought to affect earthquake rupture propagation and energy radiation, but the effects are not completely understood. We hypothesize that the rate of accumulation of new damage decreases as fault maturity increases, and damage magnitude saturates in very large displacement faults. Nonetheless, geometric irregularities in the fault surface may modify damage zone characteristics. Accordingly, we seek to investigate the orientation, kinematics, and density of features at a range of scales within the damage zone adjacent to an abrupt 13 degree bend over 425 m in the NBSGF in order to constrain the relative role of the initiation of new damage versus the reactivation of preexisting damage adjacent to a bend. Field investigation and microstructural study focused on structural domains before, within, and after the fault bend on both sides of the fault. Subsidiary fault fabrics are similar in all domains outside the bend, which suggests a steady state fracture density and orientation distribution is established on the straight segments before and after the bend. The density of fractures within and outside the bend is similar; however, subsidiary fault orientations and kinematics are different within the bend relative to the straight segments. These observations are best explained by relatively low rates of damage generation relative to rates of fault reactivation during the later stages of faulting on the NBSGF, and that damage zone kinematics is reset as the host rock moves into the bend and again upon exiting the bend. Consequently, significant energy released during earthquake unloading can be dissipated by reactivation and slip on existing fractures in the damage zone, particularly adjacent to mesoscale faults. Thus, areas of heightened reactivation of damage, such as adjacent to geometric irregularities in the fault surface, could affect earthquake rupture dynamics.Item Pounding and impact of base isolated buildings due to earthquakes(Texas A&M University, 2005-08-29) Agarwal, Vivek KumarAs the cost of land in cities increases, the need to build multistory buildings in close proximity to each other also increases. Sometimes, construction materials, other objects and any projections from a building may also decrease the spacing provided between the buildings. This leads to the problem of pounding of these closely placed buildings when responding to earthquake ground motion. The recent advent of base isolation systems and their use as an efficient earthquake force resisting mechanism has led to their increased use in civil engineering structures. At the same time, building codes that reflect best design practice are also evolving. The movement of these base isolated buildings can also result in building pounding. Since base isolation is itself a relatively new technique, pounding phenomenon in base isolated buildings have not been adequately investigated to date. This study looks at the base isolated response of a single two story building and adjacent two story building systems. Four earthquakes with increasing intensity were used in this study. It was found that it is difficult to anticipate the response of the adjacent buildings due to non- linear behavior of pounding and base isolation. The worst case for pounding was found to occur when a fixed base and base isolated buildings were adjacent to each other.Item Seismic fragility estimates and sensitivity analyses for corroding reinforced concrete bridges(2009-05-15) Choe, Do-EunThe objective of this study is to develop methodologies to estimate and predict the fragility of deteriorating reinforced concrete (RC) bridges, and to identify the effect of design and construction parameters on the reliability of RC bridges over time to assist in the design and construction process. To accurately estimate the fragility of deteriorating bridge, probabilistic capacity and demand models are developed. In addition, to simplify the calculation cost maintaining accuracy, fragility increment functions are developed. The proposed fragilities account for model uncertainties in the structural capacity, demand models, corrosion models. Furthermore, proper account is made of the uncertainties in the environmental conditions, material properties, and structural geometry. To identify the effect of design and construction parameters on the reliability of RC bridges, a sensitivity and importance analysis is conducted. Sensitivity analysis for an example bridge subject to corrosion is carried out to identify which parameters have the largest impact on the reliability over time. This dissertation considers different combinations of chloride exposure condition, environmental oxygen availability, water-to-cement ratios, and curing conditions, which affect the reliability of bridges over time. The developed models are applicable to both existing and new RC bridges and may be employed for the prediction of service-life and life-cycle cost analysis of RC bridges.Item Stopper-Bearing System ? A Solution to Displacement Control of Bridge Decks(2010-10-12) Tsai, Yi-TeBridges play an important role in society, especially during the post-earthquake period that enables emergency vehicles and traffic for safe egress and ingress to minimize the loss of property and life. However, some past earthquakes have resulted in large horizontal displacements on the superstructure that have lead to unseating of bridge spans and unexpected pounding forces that damaged critical components such as bearings and anchor bolts. To this end, a new bearing system, referred to as a stopperbearing system (SBS), is proposed as one solution to address the vulnerability of bridge bearings and other components. The horizontal displacement of a deck can be limited to a desired range using the SBS. The nonlinear load-deformation behavior of the SBS is obtained from ABAQUS and used to define the SBS within reinforced concrete analytical bridge models developed in SAP2000, which are subjected to the 1999 Chi- Chi, Taiwan earthquake ground motion (1.01g - E-W component and 0.43g - N-S component). The results from the nonlinear time history analyses show that the SBS is effective in limiting bridge deck displacements and pounding effects. Preliminary analytical modeling of the SBS shows promise as a solution to displacement control of bridge decks for overall enhancement of bridge performance during seismic events.Item