Thesis advisor: John Ebel / The New Madrid Seismic Zone (NMSZ) is well known for producing some of the largest intra-cratonic earthquakes within the North American Plate. The common hypothesis for the geological structure within the NMSZ is that stress is released across three major faults: the Cottonwood Grove Fault, the New Madrid North Fault, and the Reelfoot Thrust Fault. Evidence exists that would suggest an alternative model of geologic deformation in the area: that stress is being released across more than these three faults. A geologic and geophysical investigation was done to investigate a hypothetical fault west of Dyersburg, TN to test the alternative multi-fault hypothesis. A seismically created sand blow was logged in close proximity to the fault projection. Weathering of the sand blow indicated that the age of the sand blow came from a seismic event prior to the 1811-1812 earthquakes. There was no evidence to confirm this sand blow was created by a hypothetical fault in close proximity. A seismic exploration of the area was done across four seismic lines, primarily mapping Quaternary-age Mississippi River flood plain deposits. These seismic surveys yielded no evidence to suggest the presence of an additional fault. Across all surveys no evidence was found to conclusively support any existing theory on fault movement in the NMSZ. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / 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 (February 28, 2007) Vita. Includes bibliographical references.

The Wabash Valley Seismic Zone (WVSZ) has produced three moderate sized earthquakes greater than or equal to mb 5.0 in the past 50 years. The majority of Wabash Valley faults originate near the junction of the Rough Creek and Cottage Grove faults and extend northeastward along the Wabash River. These faults extend through the Paleozoic and into the Precambrian and are believe to be associated with the Reelfoot Rift. Two of these moderate sized earthquakes have occurred north of the terminus of the Wabash Valley faults that the WVSZ is commonly associated with. This suggests that other sources of seismicity exist. The La Salle anticline, a Precambrian basement feature, is oriented NW to SE just north of the termination of these faults. The La Salle anticline creates up to a 750 meter uplift in the above Paleozoic strata. This uplift creates faults within the Paleozoic strata and within the La Salle anticline. This study uses seismometers arranged in a phased array near the southern terminus of the La Salle anticline to analyze the seismicity of the region. Analyzing the seismicity of the region over a 6-month period found 834 events. The vast majority were determined to be mine blasts or otherwise human induced. Two small earthquakes (~M 1.0) located near the La Salle anticline. These earthquakes likely occur on faults associated with the anticline. The lack of earthquakes suggested the b-value of the La Salle region could be as low as 0.56. This is lower than the typical value of 1, but consistent with other intraplate regions and previous studies of the WVSZ finding values nearer 0.7.

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. / Master of Science

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.

The New Madrid Seismic Zone is well known for its historical seismicity, most notably the 1811-12 New Madrid, MO earthquakes and to a lesser extent the 1895 Charlston, MO earthquake. It has been 124 years since an earthquake larger than M 5.1 occurred in the area. The debate of whether the New Madrid Seismic Zone is an active system or a system in decline has remained a contentious topic when interpreting the intricacies and challenges of an intraplate seismic system. This thesis focuses on an overlooked parameter in the already complex issue regarding the seismic hazard of the New Madrid Seismic Zone. In the early part of the 20th century the Little River Drainage District excavated 9.7 x 109 metric tons of overburden and drained approximately 5000 km2 from within the New Madrid Seismic Zone. Our model demonstrates that the Little River Drainage District resulted in a likely perturbation of the seismic system. The overburden removal, coupled with a reduction of the water column has moved the system away from failure when interpreted in the context of regional stress orientation in relation to the geographic orientation of the Little River Drainage District. This potentially explains the apparent lack of moderate to large events over the past century in the New Madrid Seismic Zone.

No description available.

Thesis (M.S. in C.E.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2004. Directed by Glenn J. Rix. / Includes bibliographical references (leaves 94-97).

No description available.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 29, 2009) Includes bibliographical references (p. 119-131).