Thesis advisor: Alan L. Kafka / This study finds that, in most cases analyzed to date, past seismicity tends to delineate zones where future earthquakes are likely to occur. Network seismicity catalogs for the New Madrid Seismic Zone (NMSZ), Australia (AUS), California (CA), and Alaska (AK) are analyzed using modified versions of the Cellular Seismology (CS) method of Kafka (2002, 2007). The percentage of later occurring earthquakes located near earlier occurring earthquakes typically exceeds the expected percentage for randomly distributed later occurring earthquakes, and the specific percentage is influenced by several variables, including magnitude, depth, time, and tectonic setting. At 33% map area coverage, hit percents are typically 85-95% in the NMSZ, 50-60% in AUS, 75-85% in CA, and 75-85% in AK. Statistical significance testing is performed on trials analyzing the same variables so that the overall regions can be compared, although some tests are inconclusive due to the small number of earthquake sample sizes. These results offer useful insights into understanding the capabilities and limits of CS studies, which can provide guidance for improving the seismicity-based components of seismic hazard assessments. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

The Charleston Uplift (CU), a 30-km-long by 7-km-wide, N46°E-oriented subsurface geologic anomaly in the northern Mississippi embayment near Charleston, Missouri, exhibits up to 36 m of vertical relief across the Paleogene/Quaternary unconformity. Subsurface structural relief, along with the CU’s coincident boundary alignment with contemporary microseismicity and the New Madrid North Fault (NMNF), suggest a structural origin. Subsequent seismic soundings indicate vertical structural relief is present in Cretaceous and Paleozoic horizons, supporting the fault-controlled origin. The southern boundary (CU-s) had not been investigated, nor had any direct fault images been acquired. Integrated microgravity and seismic-reflection methods across the inferred CU-s establish the first image of this fault. Forward modeling indicated that the vertical variation of strata across the CU-s would induce a microgravity anomaly of 1.6 mGal. The observed microgravity anomaly survey across the southern boundary is 1.616 ± .004 mGal, and is consistent with the tectonic interpretation. A subsequently acquired seismic-reflection profile corroborates this interpretation. The imaged fault shows approximately 60, 35, and 35 meters of vertical down-to-the-south throw across the tops of Paleozoic, Cretaceous, and Tertiary horizons, respectively. This confirms the CU is not an erosional feature, but a structurally controlled extension of the NMNF.

In intraplate seismic zones (e.g. the New Madrid Seismic Zone, NMSZ, in the southcentral United States), the source of stress that drives earthquake is very complex. Data from the NMSZ indicate 3 earthquake of magnitude M~7, occurring at an approximate interval of 500 years during the last 2000 years. One hypothesis that satisfies these conditions proposes that short-lived bursts of earthquakes may result from perturbations in the local or regional stress field. This causes relaxation of a lower crustal weak zone which drive repeated earthquakes. The number of earthquakes is dependent on the geometry and rheology of the weak zone. Using finite element techniques which employ contact surfaces to model discrete faulting events and a maximum shear stress criteria evaluated at each node. We investigate the relevant parameter space, as it affects the concentration of stress at the base of the seismogenic fault and the number of earthquakes generated over a given time interval. Parameters that can be varied include earthquake stress drop, background tectonic stress, and maximum shear stress at failure. Results show that solutions are non-unique. With the addition of existing observational evidence, however, we can place bounds on the range of parameters which satisfy above observations.

Thesis (M.S.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 10, 2009 Includes bibliographical references.

Many seismic hazard source parameters such as slip rate, total displacement, strain accommodation, geographic fault location, etc. are poorly constrained in the New Madrid seismic zone (NMSZ). This is in large part due to the masking effect of the thick Mississippi embayment sediment package on seismogenic structures and features. Consequently, much of the subsurface geologic characterization needed for understanding seismic hazard sources requires geophysical imaging. Recent seismic reflection surveys 12 km NE of the Reelfoot Fault stepover arm of the NMSZ have suggested a northeast-oriented transpressional fault zone extending across the Reelfoot Fault stepover arm where its dextral displacement at seismogenic depth is unbalanced with the surface expression, the Reelfoot Scarp. New high-resolution seismic reflection surveys were acquired across the southwestern back projection of the hypothesized structure at a potential piercing point with the Reelfoot Fault near Proctor City, TN. The resultant images show steeply dipping northeast striking faults with uplifted and arched post-Paleozoic reflectors that extend into the Quaternary sediments, consistent with the findings of the previous surveys. The new imaged faults form a ~500-meter-wide positive flower structure, with vertical displacements of 16 m and 50 m at the top of the Eocene and top of the Paleozoic reflectors, respectively. Results corroborate the Axial Fault extending to the northeast, and provide geological evidence for Reelfoot Fault segmentation. Furthermore, the near-surface SH-wave seismic profiles show the through-going shear deformation has continued into the Quaternary, thus indicating seismogenic strain has not been completely transferred to the Reelfoot Fault, providing additional evidence for accommodating the strain imbalance.

In the central United States, undefined earthquake sources, long earthquake recurrence intervals and uncertain ground motion attenuation models have contributed to an overstatement of regional seismic hazard for the New Madrid Seismic Zone on the National Seismic Hazard Maps. This study examined concerns regarding scientific uncertainties, overly stringent seismic mitigation policies and depressed local economy in western Kentucky through a series of informal interviews with local businessmen, public officials, and other professionals in occupations associated with seismic mitigation. Scientific and relative economic analyses were then performed using scenario earthquake models developed with FEMA’s Hazus-MH software. Effects of the 2008 Wenchuan earthquake in central China and seismic mitigation policies in use there were considered for potential parallels and learning opportunities. Finally, suggestions for continued scientific research, additional educational opportunities for laymen and engineering professionals, and changes in the application of current earthquake science to public policy in the central United States were outlined with the goal of easing western Kentucky economic issues while maintaining acceptable public safety conditions.

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Accompanying "this dissertation is a CD-ROM, which contains site amplification and seismic hazard results for each grid point (1974 points) considered in the study. The results have prepared as .txt files. The CD-ROM also contains the maps generated from these estimated results. The maps are prepared as .png files." Title from title screen of thesis/dissertation PDF file (viewed January 28, 2008) Includes bibliographical references (p. 249-269).

A recently identified 30 km by 7.2 km subsurface stratigraphic uplift, called the Charleston uplift, exhibits 36 m offset of Paleogene-Quaternary unconformity based on shallow borehole data. Two seismic soundings demonstrated relief in Paleozoic and Cretaceous reflectors across the northern boundary of the uplift, suggesting a structural origin rather than an erosional origin. This study collected and analyzed 18 additional shallow seismic soundings to confirm Paleozoic and Cretaceous offset across the boundaries of the uplift, to better constrain the surface trace of the uplift, and to examine potential extension into western Kentucky. One ground penetrating radar profile was taken in western Kentucky to image recent deformation. Results confirm Paleozoic and Cretaceous offset along the boundaries of the uplift and indicate extension of the uplift into western Kentucky, although recent deformation was unconfirmed by the radar profile. These data support a structural origin. The N46°E trend of the uplift as well as its coincidence with contemporary microseismicity suggest that this feature may be related to the New Madrid seismic zone, specifically the New Madrid North fault, which may have implications for hazard assessment, as well as possible a reevaluation of the epicenters for the 23 January 1812 Mw ≥ 7.0 event.

The Mississippi River Valley, is hardly known as an earthquake zone, but may in fact be a natural disaster just waiting to happen. Historical records and paleoseismic investigations have shown that large magnitude earthquakes have occurred in the area and there are constantly microquakes all along the New Madrid Fault System. The inhabitants of the Midwest are living in a death trap so long society doesn’t preoperly prepare for earthquakes. The study presented here aims to prove that, as predicting earthquakes is difficult to the point of impossible, the only serious alternative is to reinforce existing buildings and infrastructure and make sure all new developments are seismically safe. The conclusion reached is, that although expensive, building earthquake safe and retrofitting existing buildings, is for the high risk areas by far cheaper than doing nothing when, not if, a new large magnitude earthquake occurs. For a city in the high risk area, the cost of retrofitting the current structures was 13 billion dollar to be compared with the 100 billion dollars in lost lives and properties of a worst case scenario.