Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 258-282). Also available on the Internet.

Thesis (Ph.D.) -- University of New Brunswick, Dept. of Geology, 2006. / Title from PDF title page (viewed on May 25, 2010) Available through UMI ProQuest Digital Dissertations. Includes bibliographical references (leaves 299-321). Also issued in print.

Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2005. / Includes bibliographical references (p. 61-64).

Thesis (M.S.)--University of Tennessee, Knoxville, 2010. / Title from title page screen (viewed on July 20, 2010). Thesis advisor: Robert D. Hatcher, Jr. Vita. Includes bibliographical references.

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.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Thesis (M.S.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 62-69). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2005. / Includes bibliographical references (leaves 75-88).

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on Mar. 4, 2009). Includes bibliographical references (p. 50-59).

This is a study where new and old geophysical data together with information found in literature has been integrated to get a better understanding of the geological evolution of Svalbard. The purpose of the study is to acquire and integrate different geophysical data over the Central Spitsbergen Basin (CSB) and across the Billefjorden Fault Zone (BFZ). The integrated data has then been interpreted to identify locations of basins and structural heights. The main goals with this project have been to plan and conduct a field study to acquire magnetic- and gravity data over the study area to constrain basins and major fault zones. Furthermore, the goal was to integrate gravity- and magnetic data together with seismic interpretations and well data, discussing implications of geophysical data and lastly to add new data to the geodata platform Svalbox.  During 10 field days 7 gravity profiles were measured over the CSB and over parts of the BFZ, magnetic data was also collected along most of the profiles. Among these 7 profiles two key profiles were analysed more in detail. Further on Ground Penetrating Radar (GPR) data was collected over a glacier to obtain the glacier thickness. The report also includes a small case study analysing the Botneheia Dolerite dyke by measuring the magnetic susceptibility across the dyke. The borehole data was mostly used for the seismic interpretations, since they only penetrate about 2000 m, they do not provide any information about the deeper subsurface. The seismic interpretations varied some depending on who interpreted it so to make an even more qualified analyse, the gravity and magnetic data are suitable complements.  The gravity anomalies proceeded in this report vary in a similar way in comparison to older gravity data provided in the same area. Both Billefjorden Fault Zone (BFZ) and Lomfjorden Fault zone (LFZ) can be identified in the gravity data acquired from the field study. After integrating seismic interpretations and gravity data, the depth from the surface to the basement in CSB is assumed to decrease in a west-east direction. In this report the basement is defined as pre-Devonian rocks. In the eastern part of profile 5, east of Reindalspasset the gravity anomalies are steadily increasing while a seismic interpretation shows a dip of the basement, which could indicate the existence of another layer on top of the basement with a high density. To sum up, integration of several geophysical methods is a good method to identify fault zones and depth to the basement. It is important to interpret all data individually and combined to be able to identify what is causing the anomalies.  Suggestions for further studies is forward modelling and to correct the ortho height measured by the DGPS on top of the glacier of profile 3 by using the collected GPR data. The geophysical data provided in this report can be used for further investigation about CO2 sequestration and geothermal energy. / Denna studie syftar till att bidra till ökad förståelse av geologin på Svalbard genom att integrera nya och gamla geofysiska data tillsammans med information från litteratur. Detta har gjorts genom att samla in och integrera olika geofysiska data över Centrala Spitsbergen (CSB) och Billefjorden sprickzon (BFZ). Den integrerade datan har sedan analyserats för att få ökad förståelse av geologins lagerföljder och lagrens variation. Huvudmålen med detta projekt har varit att planera och utföra en fältstudie för att samla in magnetisk- och gravitationsdata för att identifiera lagerföljder, strukturer och sprickzoner, att integrera den insamlade magnetiska data och gravitationsdata tillsammans med seismiska tolkningar och borrhålsdata. Ytterligare huvudmål är att diskutera innebörden av geofysiska data samt att addera all nya data till geodata-plattformen Svalbox.  Datainsamlingen ute i fält pågick under 10 dagar och resulterade i 7 profiler med gravitationsdata över CSB och delar av BFZ. Av dessa 7 profiler valdes 2 ut som nyckelprofiler för djupare analys. I ett område användes Ground Penetrating Radar (GPR) för att mäta tjockleken av glaciären. Rapporten inkluderar även en mindre fallstudie för att undersöka en vertikal diabasgång och dess lutning genom att mäta magnetiska susceptibiliteten över området. Borrhålsdata användes framför allt till att göra de seismiska tolkningarna, eftersom de endast penetrerar ett par tusen meter ger de ingen information om hur berggrunden ser ut längre ner. De seismiska tolkningarna varierar något beroende av vem som gjort tolkningarna så för att göra ännu säkrare tolkningar är gravitationsdata tillsammans med magnetisk data ett bra komplement.  Resultatet av den färdigkorrigerade gravitationsdata visar liknande spatiala variationer som tidigare data i samma område. Både BFZ och Lomfjorden sprickzon (LFZ) kan identifieras i gravitationsdata som samlades in under fältarbetet. Efter att ha integrerat seismiska tolkningar med gravitationsdata kan djupet till urberget i CSB antas minska i en väst-östlig riktning. I den här rapporten är urberget definierat som bergarter äldre än Devon. I den östra delen av profil 5, öster om Reindalspasset visas gravitationsdata som ständigt ökande medan seismiska tolkningar ett ökande avstånd till urberget, detta skulle kunna indikera att det finns ett ytterligare lager med en hög densitet. Sammanfattningsvis är integration av flera olika geofysiska metoder en bra metod för att identifiera sprickzoner och djupet till berggrunden. Det är viktigt att tolka all data både individuellt och tillsammans för att se vad som orsakar anomalierna.  Förslag till fortsatta studier skulle vara att göra prediktionsmodeller baserat på data som har presenterats i rapporten för att estimera lagerföljder och sprickzoner. Ytterligare förslag på fortsatt studie är att korrigera topografi-data tillhörande profil 3 med hjälp av glaciärtjockleken från GPR-data. All geofysisk data i denna rapport kan användas för framtida undersökningar om koldioxidlagring och geotermisk energi.