Thesis (Ph. D.)--State University of New York at Binghamton, Department of Geological Sciences and Environmental Studies, 2007. / Includes bibliographical references (leaves 308-314).

We are concerned with the quantum inverse scattering problem. The corresponding Marchenko integral equation is solved by using the collocation method together with piece-wise polynomials, namely, Hermite splines. The scarcity of experimental data and the lack of phase information necessitate the generation of the input reflection coefficient by choosing a specific profile and then applying our method to reconstruct it. Various aspects of the single and coupled channels inverse problem and details about the numerical techniques employed are discussed. We proceed to apply our approach to synthetic seismic reflection data. The transformation of the classical one-dimensional wave equation for elastic displacement into a Schr¨odinger-like equation is presented. As an application of our method, we consider the synthetic reflection travel-time data for a layered substrate from which we recover the seismic impedance of the medium. We also apply our approach to experimental seismic reflection data collected from a deep water location in the North sea. The reflectivity sequence and the relevant seismic wavelet are extracted from the seismic reflection data by applying the statistical estimation procedure known as Markov Chain Monte Carlo method to the problem of blind deconvolution. In order to implement the Marchenko inversion method, the pure spike trains have been replaced by amplitudes having a narrow bell-shaped form to facilitate the numerical solution of the Marchenko integral equation from which the underlying seismic impedance profile of the medium is obtained. / Physics / D.Phil.(Physics)

Electrical substations perform a key role in electrical transmission and distribution; the ability for a substation to remain functional during and after a seismic event contributes significantly to the resilience of the clients supplied. Many legacy components currently installed in the main grid substations were designed with minimal consideration of lateral loads and are not qualified per IEEE693. One of the more critical high-voltage substation components that are vulnerable to earthquake damage is the 500kV freestanding current transformer (CT). The CT is particularly vulnerable due to the slenderness and mass distribution of the component. Current transformers are typically constructed from a combination of aluminum and brittle porcelain. Two novel retrofit measures were investigated utilizing base rocking and supplemental damping to reduce the seismic amplification in the CT while also potentially providing post-earthquake self-centering capability. The retrofit measures utilize both shift in system frequency and energy dissipation through supplemental damping to reduce seismic demands on the CT. The purpose of the research was to conceptually develop, detail design, analyze and experimentally validate the retrofit measures. A desired feature of the retrofit measures was for minimal or no residual displacement following the seismic event, which was implemented in the retrofit through a preloaded centering mechanism. Based on the analyses and experiments, the proposed retrofit measures exhibited significantly decreased demands on the CT and true self-centering.

Naturally fractured reservoirs have attracted an increased interest of exploration and production geophysics in recent years. In many instances, natural fractures control the permeability of the reservoir, and hence the ability to find and characterize fractured areas of the reservoir represents a major challenge for seismic investigations. In fractured and porous reservoirs the fluid affects elastic anisotropy of the rock and also causes significant frequency dependent attenuation and dispersion. In this study we develop a mathematical model for seismic wave attenuation and dispersion in a porous medium in a porous medium with aligned fractured, caused by wave induced fluid flow between pores and fractures. In this work fractures in the porous rock are modelled as very thin and highly porous layers in a porous background. Dry highly porous materials have low elastic moduli; thus dry skeleton of our system contains thin and soft layers, and is described by linear slip theory. The fluid saturated rock with high-porasity layers is described by equations of poroelasticity with periodically varying coefficients. These equations are analyzed using propagator matrix approach commonly used to study effective properties of layered system. This yields a dispersion equation for a periodically layered saturated porous medium taking into account fluid communication between pore spaces of the layers. Taking in this dispersion equation a limit of small thickness for high-porosity layers gives the velocity and attenuation as a function of frequency and fracture parameters. The results of this analysis show that porous saturated rock with aligned fractures exhibits significant attenuation and velocity dispersion due to wave induced fluid flow between pores and fractures. / At low frequencies the material properties are equal to those obtained by anisotropic Gassmann theory applied to a porous material with linear-slip, interfaces. At high frequencies the results are equivalent to those for fractures with vanishingly small normal slip in a solid (non-porous) background. The characteristic frequency of the attenuation and dispersion depends on the background permeability, fluid viscosity, as well as fracture density and spacing. The wave induced fluid flow between pores and fractures considered in this work has exactly the same physical nature as so-called squirt flow, which is widely believed to by a major cause of seismic attenuation. Hence, the present model can be viewed as a new model of squirt-flow attenuation, consistent with Biot’s theory of poroelasticity. The theoretical results of this work are also limited by the assumption of periodic distribution of fractures. In reality fractures may be distributed in a random fashion. Sensitivity of our results to the violation of the periodicity assumption was examined numerically using reflectivity modelling for layered poroelastic media. Numerical experiments for a random distribution of fractures of the same thickness still show surprisingly good agreement with theoretical results obtained for periodic fractures. However this agreement may break down if fracture properties are allowed to vary from fracture to fracture. The results of this thesis show how to compute frequency dependences of attenuation and velocity caused by wave induced fluid flow between pores and fractures. These results can be used to obtain important parameters of fractured reservoirs, such as permeability and fracture weakness, from attenuation measurements. The major requirement for the success of such an approach is that measurements must be made in over a relatively broad frequency range.

On November 6, 1988, two strong earthquakes (Mw: 7.0 and 6.8) separated by about 13 minutes occurred in Yunnan Province, China. The aftershocks located by Kunming Telemetered Seismic Network form a lineament approximately 120 km long and 20 km wide with the long dimension oriented approximately N30°W. The epicenter of the first event lies about 30 km from the southern terminus of the aftershock zone while the epicenter of the second event is 60 km further to the northwest. Field investigations indicate that the surface fault ruptures associated with the first and second shock and a variety of ground deformations. We analyze teleseismic data recorded by the GDSN network to determine the rupture process of these two mainshocks (referred to as Ml and M2) and the two largest aftershocks (referred to as Al and A2). Inversion of long-period body waves gives the following centroid source parameters for Ml: strike 154°±4°, dip 86°±1°, slip 181°±1°, centroid depth shallower than 15 km (least-misfit centroid depth 12 km), and seismic moment 4.5-4.9 X 10²⁶ dyn cm (least-misfit seismic moment 4.6 X 10²⁶ dyn cm). The source time function, further constrained by broadband seismograms, indicates that the source duration for this event is 12 seconds. Due to signal interference with Ml, body wave inversion techniques cannot be applied to M2. The Rayleigh waves provide a better look at this event. In order to identify the energy contributions from the two events, group velocity analysis was performed on the surface wave trains. The energy from the individual events was then isolated based on their dispersion patterns. The amplitude spectra in the period range of 100 to 66 s were inverted for the source parameters. The inversion constrains the strike of M2 precisely (155°±3°), however, dip and slip angles were not well resolved by the inversion. Similar Rayleigh wave amplitude spectra and radiation patterns of Ml and M2, however, suggest that they had very similar mechanisms and centroid depths. On the average, the amplitude spectra of M2 are smaller than those of Ml by a factor of 2.2, indicating the seismic moment of M2 is 2.1 X 10²⁶ dyn cm. The two largest aftershocks, Al (Mw 6.1) and A2 (Mw 5.3), which occurred at the southern terminus of the aftershock zone, were analyzed by modeling teleseismic and strong ground motion data. Teleseismic body wave inversion gives source orientation of Al: strike 165°±2.5°, dip 90°±1.5°, slip 178°±0.5°, centroid depth shallower than 12 km (least-misfit centroid depth 7 km from broadband waveform inversion), and seismic moment 1.5-1.6 X 10²⁵ dyn cm. The inversion of A2 gives the source orientation and centroid depth very similar to those of Al. The seismic moment for this event is 1.3-1.6 X 10²⁴ dyn cm. Modeling of strong ground motion seismograms adds more constraints on centroid depths and source time functions of Al and A2. To minimize the effect of scattering caused by upper crustal heterogeneity, we confined our analysis to frequencies lower than 1 Hz. A crustal model, with a low velocity sedimentary layer, was found that predicts common features of observed strong ground motion seismograms for both events. Derived source orientation is consistent with that found from teleseismic body wave inversion. The centroid depths of Al and A2 were constrained to be between 4 and 12 km. A source duration of 7 s and 2 s was obtained for Al and A2, respectively. Derived rupture parameters of Ml and M2, aftershock distribution, field investigations, geological information and concepts of geometrical barriers and fault asperities, indicate that the preexisting fault intersections played the key role in rupture terminations and initiations. The 12 s source duration of Ml and about 60 km long zone of ground deformation along the strike suggest that Ml rupture was bilateral. The rupture initiated near a fault intersection and propagated to NNW and SSE along the strike. The SSE propagating rupture was terminated by a preexisting fault which intersects the ruptured fault 30 km to the south. The aftershock Al and A2 as well as a dense group of small aftershocks were associated with the termination of the SSE segment. The NNW propagating rupture was also terminated by a NE striking preexisting fault on which several of the largest aftershocks appear to have occurred. This NE striking fault right-laterally offsets the fault on which Ml and M2 occurred forming a geometrical barrier for the rupture. M2 presumably nucleated near this barrier and unilaterally ruptured about 25 km toward NNW where it was terminated by a well documented preexisting fault. / Graduation date: 1992

It is well known that direct surface waves of large earthquakes are capable of triggering shallow earthquakes and deep tremor at long-range distances. Recent studies have shown that multiple surface waves circling the earth could also remotely trigger microearthquakes. However, it is still not clear whether multiple surface waves returning back to the main shock epicenters could also trigger/modulate aftershock behavior. Here we conduct a study to search for evidence of such triggering by systematically examining aftershock patterns of earthquakes with magnitude ≥ 8 since 1990 that produce observable surface waves circling the globe repeatedly. We specifically examine the 2011 M9 Tohoku-Oki event using a composite catalog of JMA, HiNet and newly detected events obtained by waveform cross correlation. We compute the magnitude of completeness for each sequence, and stack all the sequences together to compute the seismicity and moment rates by sliding data windows. The sequences are also shuffled randomly and these rates are compared to the actual data as well as synthetic aftershock sequences to estimate the statistical significance of the results. Our results suggest that there is some moderate increase of early aftershock activity after a few hours when the surface waves return to the epicentral region. However, we could not completely rule out the possibility that such an increase is purely due to random fluctuations of aftershocks or caused by missing aftershocks in the first few hours after the mainshock.

The large number of bridge collapses that have occurred in recent earthquakes has exposed the vulnerabilities in existing bridges. One of the emerging tools for protecting bridges from the damaging effects of earthquakes is the use of isolation systems. Seismic isolation is achieved via inserting flexible isolator elements into the bridge that shift the vibration period and increase energy dissipation. To date, the structural performance of bridges incorporating sliding seismic isolation is not well-understood, in part due to the lack of adequate models that can account for the complex behavior of the isolators. This study investigates and makes recommendations on the structural performance of bridges utilizing sliding type seismic isolators, based on the development of state-of-the-art analytical models. Unlike previous models, these models can account simultaneously for the variation in the normal force and friction coefficient, large deformation effects, and the coupling of the vertical and horizontal response during motion. The intention is to provide support for seismic risk mitigation and insight for the analysis and design of seismically isolated bridges by quantifying response characteristics. The level of accuracy required for isolator analytical models used in typical highway bridges are assessed. The comparative viability of the two main isolator types (i.e. sliding and elastomeric) for bridges is investigated. The influence of bridge and sliding isolator design parameters on the system s seismic response is illustrated.

My dissertation focuses primarily on the following three aspects associated with passing seismic waves in the field of earthquake seismology: temporal changes of fault zone properties, nonlinear site response, and dynamic triggering. Quantifying the temporal changes of material properties within and around active fault zones (FZ) is important for better understanding of rock rheology and estimating the strong ground motion that can be generated by large earthquakes. As high-amplitude seismic waves propagate through damaged FZ rocks and/or shallow surface layers, they may produce additional damage leading to nonlinear wave propagation effects and temporal changes of material properties (e.g., seismic velocity, attenuation). Previous studies have found several types of temporal changes in material properties with time scales of tens of seconds to several years. Here I systematically analyze temporal changes of fault zone (FZ) site response along the Karadere-Düzce branch of the North Anatolian fault that ruptured during the 1999 İzmit and Düzce earthquake sequences. The coseismic changes are on the order of 20-40%, and are followed by a logarithmic recovery over an apparent time scale of ~1 day. These results provide a bridge between the large-amplitude near-instantaneous changes and the lower-amplitude longer-duration variations observed in previous studies. The temporal changes measured from this high-resolution spectral ratio analysis also provide a refinement for the beginning of the longer more gradual process typically observed by analyzing repeating earthquakes. An improved knowledge on nonlinear site response is critical for better understanding strong ground motions and predicting shaking induced damages. I use the same sliding-window spectral ratio technique to analyze temporal changes in site response associated with the strong ground motion of the Mw6.6 2004 Mid-Niigata earthquake sequence recorded by the borehole stations in Japanese Digital Strong-Motion Seismograph Network (KiK-Net). The coseismic peak frequency drop, peak spectral ratio drop, and the postseismic recovery time roughly scale with the input ground motions when the peak ground velocity (PGV) is larger than ~5 cm/s, or the peak ground acceleration (PGA) is larger than ~100 Gal. The results suggest that at a given site the input ground motion plays an important role in controlling both the coseismic change and postseismic recovery in site response. In a follow-up study, I apply the same sliding-window spectral ratio technique to surface and borehole strong motion records at 6 KiK-Net sites, and stack results associated with different earthquakes that produce similar PGAs. In some cases I observe a weak coseismic drop in the peak frequency when the PGA is as small as ~20-30 Gal, and near instantaneous recovery after the passage of the direct S waves. The percentage of drop in the peak frequency starts to increase with increasing PGA values. A coseismic drop in the peak spectral ratio is also observed at 2 sites. When the PGA is larger than ~60 Gal to more than 100 Gal, considerably stronger coseismic drops of the peak frequencies are observed, followed by a logarithmic recovery with time. The observed weak reductions of peak frequencies with near instantaneous recovery likely reflect nonlinear response with essentially fixed level of damage, while the larger drops followed by logarithmic recovery reflect the generation (and then recovery) of additional rock damage. The results indicate clearly that nonlinear site response may occur during medium-size earthquakes, and that the PGA threshold for in situ nonlinear site response is lower than the previously thought value of ~100-200 Gal. The recent Mw9.0 off the Pacific coast of Tohoku earthquake and its aftershocks generated widespread strong shakings as large as ~3000 Gal along the east coast of Japan. I systematically analyze temporal changes of material properties and nonlinear site response in the shallow crust associated with the Tohoku main shock, using seismic data recorded by the Japanese Strong Motion Network KIK-Net. I compute the spectral ratios of windowed records from a pair of surface and borehole stations, and then use the sliding-window spectral ratios to track the temporal changes in the site response of various sites at different levels of PGA The preliminary results show clear drop of resonant frequency of up to 70% during the Tohoku main shock at 6 sites with PGA from 600 to 1300 Gal. In the site MYGH04 where two distinct groups of strong ground motions were recorded, the resonant frequency briefly recovers in between, and then followed by an apparent logarithmic recovery. I investigate the percentage drop of peak frequency and peak spectral ratio during the Tohoku main shock at different PGA levels, and find that at most sites they are correlated. The third part of my thesis mostly focuses on how seismic waves trigger additional earthquakes at long-range distance, also known as dynamic triggering. Previous studies have shown that dynamic triggering in intraplate regions is typically not as common as at plate-boundary regions. Here I perform a comprehensive analysis of dynamic triggering around the Babaoshan and Huangzhuang-Gaoliying faults southwest of Beijing, China. The triggered earthquakes are identified as impulsive seismic arrivals with clear P- and S-waves in 5 Hz high-pass-filtered three-component velocity seismograms during the passage of large amplitude body and surface waves of large teleseismic earthquakes. I find that this region was repeatedly triggered by at least four earthquakes in East Asia, including the 2001 Mw7.8 Kunlun, 2003 Mw8.3 Tokachi-oki, 2004 Mw9.2 Sumatra, and 2008 Mw7.9 Wenchuan earthquakes. In most instances, the microearthquakes coincide with the first few cycles of the Love waves, and more are triggered during the large-amplitude Rayleigh waves. Such an instantaneous triggering by both the Love and Rayleigh waves is similar to recent observations of remotely triggered 'non-volcanic' tremor along major plate-boundary faults, and can be explained by a simple Coulomb failure criterion. Five earthquakes triggered by the Kunlun and Tokachi-oki earthquakes were recorded by multiple stations and could be located. These events occurred at shallow depth (< 5 km) above the background seismicity near the boundary between NW-striking Babaoshan and Huangzhuang-Gaoliying faults and the Fangshan Pluton. These results suggest that triggered earthquakes in this region likely occur near the transition between the velocity strengthening and weakening zones in the top few kms of the crust, and are likely driven by relatively large dynamic stresses on the order of few tens of KPa.

Thesis (Doctoral)--Universität Karlsruhe, 2000. / Abstract in German. Includes bibliographical references (p. 107-111). Also available via the World Wide Web. Also available via the World Wide Web. http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2000/physik/1 http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=/2000/physik/2

Thesis (Doctoral)--Universität Karlsruhe, 2000. / Hochschulschrift = Thèse/Mémoire. Also available via the World Wide Web. http://www.ubka.uni-karlsruhe.de/cgi-bin/psview?document=2001/physik/2