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Relocation of Eastern Tennessee Earthquakes Using hypoDD

Type of Document Master's Thesis
Author Dunn, Meredith M.
URN etd-08162004-152254
Title Relocation of Eastern Tennessee Earthquakes Using hypoDD
Degree Master of Science
Department Geosciences
Advisory Committee Advisor Name Title
Martin Chapman Committee Chair
J. Arthur Snoke Committee Member
John Hole Committee Member

Keywords Hypocenter Relocations
Eastern Tenneessee Seismic Zone
Earthquakes

Date of Defense 2004-08-02
Availability unrestricted
Abstract
Relocation of Eastern Tennessee Earthquakes Using hypoDD

by

Meredith M. Dunn

(Abstract)

The double difference earthquake location algorithm, implemented in the program HYPODD, was used to relocate a data set of approximately 1000 earthquakes in the eastern Tennessee seismic zone (ETSZ), using a recently developed velocity model. The double difference algorithm is used to calculate accurate relative hypocenter locations by removing the effects of un-modeled velocity structure. The study examines the earthquake hypocenter relocations in an effort to resolve fault orientations and thereby gain insights into the tectonics of the seismic zone. The analysis involves visual comparison of three-dimensional perspective plots of the hypocenter relocations oriented according to focal mechanism nodal planes derived from events within several, dense clusters of earthquakes.

The northwestern boundary of the seismic zone corresponds to the steep magnetic gradient of the New York-Alabama lineament. The double-difference relocations reinforced previous interpretations of a vertical boundary between seismic and relatively aseismic crust at that location. Areas at the northeastern and southwestern ends of the ETSZ exhibit northwest trending hypocenter alignments, which are perpendicular to the overall northeastern trend of the seismic zone. These alignments agree with focal mechanism nodal plane orientations and are interpreted as seismogenic faults. In the central, most seismically active portion of the ETSZ, relocations appear to indicate a diffuse zone of hypocenters that are west-striking and north-dipping. The orientation of this zone of earthquake hypocenters is consistent with an existing seismic reflection profile that images mid to upper crustal reflectors with apparent dips of approximately 35 degrees to the north.

The interpreted fault planes are all consistent with an east-northeast oriented, sub-horizontal maximum regional compressive stress, consistent with findings in previous studies.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-08162004-152254/unrestricted/MDunnthesis.pdf

Disaggregated Seismic Hazard and the Elastic Input Energy Spectrum: An Approach to Design Earthquake Selection

Type of Document Dissertation
Author Chapman, Martin Colby
Author's Email Address Chapman@vtso.geol.vt.edu
URN etd-6198-10207
Title Disaggregated Seismic Hazard and the Elastic Input Energy Spectrum: An Approach to Design Earthquake Selection
Degree Doctor of Philosophy
Department Geological Sciences
Advisory Committee Advisor Name Title
Arthur Snoke Committee Chair
Edwin S. Robinson Committee Member
Gilbert A. Bollinger Committee Member
J. Arthur Snoke Committee Member
James R. Martin Committee Member
Mahendra P. Singh Committee Member

Keywords Seismic Hazard
Strong Motion
Design Earthquakes
Input Energy

Date of Defense 1998-06-25
Availability unrestricted
Abstract
The design earthquake selection problem is fundamentally probabilistic. Disaggregation of a probabilistic model of the seismic hazard offers a rational and objective approach that can identify the most likely earthquake scenario(s) contributing to hazard. An ensemble of time series can be selected on the basis of the modal earthquakes derived from the disaggregation. This gives a useful time-domain realization of the seismic hazard, to the extent that a single motion parameter captures the important time-domain characteristics. A possible limitation to this approach arises because most currently available motion prediction models for peak ground motion or oscillator response are essentially independent of duration, and modal events derived using the peak motions for the analysis may not represent the optimal characterization of the hazard.

The elastic input energy spectrum is an alternative to the elastic response spectrum for these types of analyses. The input energy combines the elements of amplitude and duration into a single parameter description of the ground motion that can be readily incorporated into standard probabilistic seismic hazard analysis methodology. This use of the elastic input energy spectrum is examined. Regression analysis is performed using strong motion data from Western North America and consistent data processing procedures for both the absolute input energy equivalent velocity, (Vea), and the elastic pseudo-relative velocity response (PSV) in the frequency range 0.5 to 10 Hz. The results show that the two parameters can be successfully fit with identical functional forms. The dependence of Vea and PSV upon (NEHRP) site classification is virtually identical. The variance of Vea is uniformly less than that of PSV, indicating that Vea can be predicted with slightly less uncertainty as a function of magnitude, distance and site classification. The effects of site class are important at frequencies less than a few Hertz. The regression modeling does not resolve significant effects due to site class at frequencies greater than approximately 5 Hz.

Disaggregation of general seismic hazard models using Vea indicates that the modal magnitudes for the higher frequency oscillators tend to be larger, and vary less with oscillator frequency, than those derived using PSV. Insofar as the elastic input energy may be a better parameter for quantifying the damage potential of ground motion, its use in probabilistic seismic hazard analysis could provide an improved means for selecting earthquake scenarios and establishing design earthquakes for many types of engineering analyses.
لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-6198-10207/unrestricted/dissertation-mcc.pdf

Performance of Improved Ground and Reinforced Soil Structures during Earthquakes – Case Studies and Numerical Analyses

Type of Document Dissertation
Author Olgun, Celal Guney
Author's Email Address olgun@vt.edu
URN etd-01162004-154238
Title Performance of Improved Ground and Reinforced Soil Structures during Earthquakes – Case Studies and Numerical Analyses
Degree PhD
Department Civil Engineering
Advisory Committee Advisor Name Title
James R. Martin II Committee Chair
J. Michael Duncan Committee Member
James K. Mitchell Committee Member
Mahendra P. Singh Committee Member
Marte S. Gutierrez Committee Member
Martin C. Chapman Committee Member

Keywords numerical analysis
finite element analysis
soil improvement
soil-structure interaction
earthquakes
reinforced soil strustures

Date of Defense 2003-12-12
Availability unrestricted
Abstract
The 1999 Kocaeli Earthquake (M=7.4) struck northwestern Turkey on August 17, 1999 and caused significant damage in urban areas located along Izmit Bay. The sites that suffered the greatest damages were located primarily in areas of poorest soil conditions, typically containing soft clays and silts and/or loose, liquefiable sands. Because the affected region is heavily developed with infrastructure and there is a preponderance of poor soils, a wide range of soil improvement measures had been used to mitigate anticipated earthquake damages throughout the region. Following the earthquake and significant aftershocks, Virginia Tech researchers traveled to Turkey to investigate the affected area to document geotechnical field performance. Primary focus of the Virginia tech team was given to investigating the performance of improved soil sites and reinforced soil structures. The sites were subjected to ground motions ranging from about 0.10g to 0.35g. The site locations ranged from 0 to 35 km from the zone of energy release. This dissertation presents in detail, the findings from the two most instructive sites. The investigation of these sties involved field reconnaissance, field and laboratory testing of soils, seismic analysis, numerical modeling, and other analytical work
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Development of Computational Tools for Characterization, Evaluation, and Modification of Strong Ground Motions within a Performance-Based Seismic Design Framework

Type of Document Master's Thesis
Author Syed, Riaz
Author's Email Address rsyed@vt.edu
URN etd-12242003-112654
Title Development of Computational Tools for Characterization, Evaluation, and Modification of Strong Ground Motions within a Performance-Based Seismic Design Framework
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Finley A. Charney Committee Chair
James R. Martin Committee Member
Raymond H. Plaut Committee Member

Keywords Fourier Amplitude Spectrum
Attenuation Relationships
Site Response
EQTools
NONLIN
Ground Motion Histories
Amplitude Parameters
Duration Parameters
Ground Motions
Response Spectrum
Groound Motion Database
Performance-Based Seismic Design
Probabilistic Seismic Hazard Analysis

Date of Defense 2003-12-09
Availability unrestricted
Abstract
One of the most difficult tasks towards designing earthquake resistant structures is the determination of critical earthquakes. Conceptually, these are the ground motions that would induce the critical response in the structures being designed. The quantification of this concept, however, is not easy. Unlike the linear response of a structure, which can often be obtained by using a single spectrally modified ground acceleration history, the nonlinear response is strongly dependent on the phasing of ground motion and the detailed shape of its spectrum. This necessitates the use of a suite (bin) of ground acceleration histories having phasing and spectral shapes appropriate for the characteristics of the earthquake source, wave propagation path, and site conditions that control the design spectrum. Further, these suites of records may have to be scaled to match the design spectrum over a period range of interest, rotated into strike-normal and strike-parallel directions for near-fault effects, and modified for local site conditions before they can be input into time-domain nonlinear analysis of structures. The generation of these acceleration histories is cumbersome and daunting. This is especially so due to the sheer magnitude of the data processing involved.

The purpose of this thesis is the development and documentation of PC-based computational tools (hereinafter called EQTools) to provide a rapid and consistent means towards systematic assembly of representative strong ground motions and their characterization, evaluation, and modification within a performance-based seismic design framework. The application is graphics-intensive and every effort has been made to make it as user-friendly as possible. The application seeks to provide processed data which will help the user address the problem of determination of the critical earthquakes. The various computational tools developed in EQTools facilitate the identification of severity and damage potential of more than 700 components of recorded earthquake ground motions. The application also includes computational tools to estimate the ground motion parameters for different geographical and tectonic environments, and perform one-dimensional linear/nonlinear site response analysis as a means to predict ground surface motions at sites where soft soils overlay the bedrock.

While EQTools may be used for professional practice or academic research, the fundamental purpose behind the development of the software is to make available a classroom/laboratory tool that provides a visual basis for learning the principles behind the selection of ground motion histories and their scaling/modification for input into time domain nonlinear (or linear) analysis of structures. EQTools, in association with NONLIN, a Microsoft Windows based application for the dynamic analysis of single- and multi-degree-of-freedom structural systems (Charney, 2003), may be used for learning the concepts of earthquake engineering, particularly as related to structural dynamics, damping, ductility, and energy dissipation.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-12242003-112654/unrestricted/Thesis-EQTools.pdf

Understanding Time-Variant Stress-Strain in Turkey: A Numerical Modeling Approach

Type of Document Dissertation
Author Nowak, Stephanie Beth
URN etd-01302005-161019
Title Understanding Time-Variant Stress-Strain in Turkey: A Numerical Modeling Approach
Degree PhD
Department Geosciences
Advisory Committee Advisor Name Title
Cahit Coruh Committee Chair
Jim Spotila Committee Member
Martin Chapman Committee Member
Ron Kriz Committee Member
Sam Peavy Committee Member

Keywords Stress Transfer
Finite Element Modeling
Rupture Probability Analysis
North Anatolian Fault Zone
Turkey

Date of Defense 2004-11-23
Availability unrestricted
Abstract
Over the past century, a series of large (> 6.5) magnitude earthquakes have struck along the North Anatolian Fault Zone (NAFZ) in Turkey in a roughly East to West progression. The progression of this earthquake sequence began in 1939 with the Ms 8.0 earthquake near the town of Erzincan and continued westward, with two of the most recent ruptures occurring near the Sea of Marmara in 1999. The sequential nature of ruptures along this fault zone implies that there is a connection between the location of the previous rupture and that of the future rupture zones. This study focuses on understanding how previous rupture events and tectonic influences affect the stress regime of the NAFZ and how these stress changes affect the probability of future rupture along any unbroken segments of the fault zone using a two dimensional finite element modeling program.

In this study, stress changes due to an earthquake are estimated using the slip history of the event, estimations of rock and fault properties along the fault zone (elastic parameters), and the far-field tectonic influence due to plate motions. Stress changes are not measured directly. The stress regime is then used to calculate the probability of rupture along another segment of the fault zone.

This study found that when improper estimates of rock properties are utilized, the stress changes may be under- or over- estimated by as much as 350% or more. Because these calculated stress changes are used in probability calculations, the estimates of probability can be off by as much as 20%. A two dimensional model was built to reflect the interpreted geophysical and geological variations in elastic parameters and the 1939 through 1999 rupture sequence was modeled. The far-field tectonic influence due to plate motions contributed between 1 and 4 bars of stress to the unbroken segments of the fault zone while earthquake events transferred up to 50 bars of stress to the adjacent portions of the fault zone.

The 1999 rupture events near Izmit and Düzce have increased the probability of rupture during the next ten years along faults in the Marmara Sea to 38% while decreasing the probability of rupture along the faults near the city of Bursa by ~6%. Large amounts of strain accumulation are interpreted along faults in the Marmara Sea, further compounding the case for a large rupture event occurring in that area in the future.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-01302005-161019/unrestricted/SNowakDissertation1.pdf

A NUMERICAL INVESTIGATION OF THE SEISMIC RESPONSE OF THE AGGREGATE PIER FOUNDATION SYSTEM
Type of Document Master's Thesis
Author Girsang, Christian Hariady
URN etd-12212001-133242
Title A NUMERICAL INVESTIGATION OF THE SEISMIC RESPONSE OF THE AGGREGATE PIER FOUNDATION SYSTEM
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Dr. Marte S. Gutierrez Committee Chair
Dr. James K. Mitchell Committee Member
Dr. James R. Martin Committee Member

Keywords liquefaction
aggregate pier
ground improvement
numerical modeling
earthquake
mitigation

Date of Defense 2001-12-20
Availability unrestricted
Abstract
The response of an aggregate pier foundation system during seismic loading was investigated. The factors and phenomena governing the performance of the aggregate pier and the improved ground were identified and clarified. The key factors affecting the performance of the aggregate pier include soil density, stiffness modulus, and drainage capacity. The improved ground is influenced by soil stratification, soil properties, pore pressure dissipation, and earthquake time history.

Comprehensive numerical modeling using FLAC were performed. The focus of the study in this research was divided into three parts: the studies of the ground acceleration, the excess pore water pressure ratio and the shear stress in soil matrix generated during seismic loading. Two earthquake time histories scaled to different peak acceleration were used in the numerical modeling: the 1989 Loma Prieta earthquake (pga = 0.45g) and the 1988 Saguenay earthquake (pga = 0.05g).

The main results of the simulation showed the following effects of aggregate pier on liquefiable soil deposits: 1) The aggregate pier amplifies the peak horizontal acceleration on the ground surface (amax), 2) The aggregate pier reduces the liquefaction potential up to depth where it is installed, 3) Pore pressures are generally lower for soils reinforced with aggregate pier than unreinforced soils except for very strong earthquake, 4) The maximum shear stresses in soil are much smaller for reinforced soils than unreinforced soils.

The excess pore water pressure ratio and the shear stress in the soil matrix calculated by FLAC were generally lower than those predicted by available procedures.

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Seismic design of energy dissipation systems for optimal structural perfromance

Type of Document Dissertation
Author Moreschi, Luis M.
URN etd-07132000-16010022
Title Seismic design of energy dissipation systems for optimal structural perfromance
Degree PhD
Department Engineering Mechanics
Advisory Committee Advisor Name Title
Mahendra P. Singh Committee Chair
David Y. Gao Committee Member
Muhammad R. Hajj Committee Member
Romesh C. Batra Committee Member
Scott L. Hendricks Committee Member

Keywords passive control
genetic algorithms
structural optimization
seismic design

Date of Defense 2000-07-10
Availability unrestricted
Abstract
The usefulness of supplementary energy dissipation devices is now quite well-known in the earthquake structural engineering community for reducing the earthquake-induced response of structural systems. However, systematic design procedures for optimal sizing and placement of these protective systems in structural systems are needed and are not yet available. The main objective of this study is, therefore, to formulate a general framework for the optimal design of passive energy dissipation systems for seismic structural applications. The following four types passive energy dissipation systems have been examined in the study: (1) viscous fluid dampers, (2) viscoelastic dampers, (3) yielding metallic dampers and, (4) friction dampers. For each type of energy dissipation system, the study presents the (a) formulation of the optimal design problem, (b) consideration of several meaningful performance indices, (c) analytical and numerical procedures for seismic response and performance indices calculations, (d) procedures for obtaining the optimal design by an appropriate optimization scheme and, (e) numerical results demonstrating the effectiveness of the procedures and the optimization-based design approach.
For building structures incorporating linear damping devices, such as fluid and solid viscoelastic dampers, the seismic response and performance evaluations are done by a random vibration approach for a stochastic characterization of the earthquake induced ground motion. Both the gradient projection technique and genetic algorithm approach can be conveniently employed to determine the required amount of damping material and its optimal distribution within a building structure to achieve a desired performance criterion. An approach to evaluate the sensitivity of the optimum solution and the performance function with respect to the problem parameters is also described. Several sets of numerical results for different structural configurations and for different performance indices are presented to demonstrate the effectiveness and applicability of the approach.

For buildings installed with nonlinear hysteretic devices, such as yielding metallic elements or friction dampers, the computation of the seismic structural response and performance must be performed by time history analysis. For such energy dissipation devices, the genetic algorithm is more convenient to solve the optimal design problem. It avoids the convergence to a local optimal solution. To formulate the optimization problem within the framework of the genetic algorithm, the study presents the discretization procedures for various parameters of these nonlinear energy dissipation devices. To include the uncertainty about the seismic input motion in the search for optimal design, an ensemble of artificially generated earthquake excitations are considered. The similarities of the optimal design procedure with yielding metallic devices and friction devices are clearly established. Numerical results are presented to illustrate the applicability of the proposed optimization-based approach for different forms of performance indices and types of building structures.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-07132000-16010022/unrestricted/etd.pdf

An Experimental Study of the Dynamic Behavior of Slickensided Surfaces

Type of Document Dissertation
Author Meehan, Christopher Lee
Author's Email Address cmeehan@vt.edu
URN etd-01302006-101603
Title An Experimental Study of the Dynamic Behavior of Slickensided Surfaces
Degree PhD
Department Civil Engineering
Advisory Committee Advisor Name Title
J. Michael Duncan Committee Chair
James R. Martin II Committee Member
Marte S. Gutierrez Committee Member
Rakesh K. Kapania Committee Member
Thomas L. Brandon Committee Member

Keywords Earthquakes
Cyclic Loading
Shear Strength
Residual Strength
Clay
Slope Stability

Date of Defense 2006-01-25
Availability unrestricted
Abstract
When a clay soil is sheared, clay particles along the shear plane become aligned in the direction of shear, forming “slickensided” surfaces. Slickensided surfaces are often observed along the sliding plane in field landslides. Because the clay particles along a slickensided surface are already aligned in the direction of shear, the available shear resistance is significantly less than that of the surrounding soil.
During an earthquake, ground shaking often causes landslide movement. For existing landslides or repaired landslides that contain slickensided rupture surfaces, it is reasonable to expect that the movement will occur along the existing slickensided surfaces, because they are weaker than the surrounding soil. The amount of movement that occurs is controlled by the dynamic resistance that can be mobilized along the slickensided surfaces.

The objective of this study was to investigate, through laboratory strength tests and centrifuge model tests, the shearing resistance that can be mobilized on slickensided rupture surfaces in clay slopes during earthquakes. A method was developed for preparing slickensided rupture surfaces in the laboratory, and a series of ring shear tests, direct shear tests, and triaxial tests was conducted to study the static and cyclic shear resistance of slickensided surfaces. Two dynamic centrifuge tests were also performed to study the dynamic shear behavior of slickensided clay slopes. Newmark’s method was used to back-calculate cyclic strengths from the centrifuge data.

Test results show that the cyclic shear resistance that can be mobilized along slickensided surfaces is higher than the drained shear resistance that is applicable for static loading conditions. These results, coupled with a review of existing literature, provide justification for using cyclic strengths that are at least 20% larger than the drained residual shear strength for analyses of seismic stability of slickensided clay slopes. This represents a departure from the current state of practice, which is to use the drained residual shear strength as a “first-order approximation of the residual strength friction angle under undrained and rapid loading conditions” (Blake et al., 2002).

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An Examination of Site Response in Columbia, South Carolina: Sensitivity of Site Response to "Rock" Input Motion and the Utility of Vs(30)

Type of Document Master's Thesis
Author Lester, Alanna Paige
Author's Email Address alester@vt.edu
URN etd-06072005-163816
Title An Examination of Site Response in Columbia, South Carolina: Sensitivity of Site Response to "Rock" Input Motion and the Utility of Vs(30)
Degree Master of Science
Department Geosciences
Advisory Committee Advisor Name Title
Martin Chapman Committee Chair
Gordon Matheson Committee Member
J. Arthur Snoke Committee Member
J. R. Martin Committee Member

Keywords Earthquake Hazard Analysis
Strong Motion
Site Response
Columbia
South Carolina
IBC 2000

Date of Defense 2005-06-01
Availability unrestricted
Abstract
This study examines the sensitivity of calculated site response in connection with alternative assumptions regarding input motions and procedures prescribed in the IBC 2000 building code, particularly the use of average shear wave velocity in the upper 30 meters as an index for engineering design response spectra. Site specific subsurface models are developed for four sites in and near Columbia, South Carolina using shear wave velocity measurements from cone penetrometer tests. The four sites are underlain by thin coastal plain sedimentary deposits, overlying high velocity Paleozoic crystalline rock. An equivalent-linear algorithm is used to estimate site response for vertically incident shear waves in a horizontally layered Earth model. Non-linear mechanical behavior of the soils is analyzed using previously published strain-dependent shear modulus and damping degradation models.

Two models for material beneath the investigated near-surface deposits are used: B-C outcrop conditions and hard rock outcrop conditions. The rock outcrop model is considered a geologically realistic model where a velocity gradient, representing a transition zone of partially weathered rock and fractured rock, overlies a rock half-space. Synthetic earthquake input motions are generated using the deaggregations from the 2002 National Seismic Hazard Maps, representing the characteristic Charleston source. The U. S. Geological Survey (2002) uniform hazard spectra are used to develop 2% in 50 year probability of exceedance input ground motions for both B-C boundary and hard rock outcrop conditions. An initial analysis was made for all sites using an 8 meter thick velocity gradient for the rock input model. Sensitivity of the models to uncertainty of the weathered zone thickness was assessed by randomizing the thickness of the velocity gradient. The effect of the velocity gradient representing the weathered rock zone increases site response at high frequencies.

Both models (B-C outcrop conditions and rock outcrop conditions) are compared with the International Building Code (IBC 2000) maximum credible earthquake spectra. The results for both models exceed the IBC 2000 spectra at some frequencies, between 3 and 10 Hz at all four sites. However, site 2, which classifies as a C site and is therefore assumed to be the most competent of the four sites according to IBC 2000 design procedures, has the highest calculated spectral acceleration of the four sites analyzed. Site 2 has the highest response because a low velocity zone exists at the bottom of the geotechnical profile in immediate contact with the higher velocity rock material, producing a very large impedance contrast. An important shortcoming of the IBC 2000 building code results from the fact that it does not account for cases in which there is a strong rock-soil velocity contrast at depth less than 30 meters. It is suggested that other site-specific parameters, specifically, depth to bedrock and near-surface impedance ratio, should be included in the IBC design procedures.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-06072005-163816/unrestricted/lesterrevised_mcc.pdf