Mining induced seismicity can lead to bumps which cause problems at many mines within the United States and around the world. This seismicity, often referred to as bumps or bursts, can result in injuries, fatalities, and expensive capital damage and production interruptions. There are many factors that contribute to mining induced seismicity but there is still no concrete method to forecast future seismic activity around a mine. One of the main precursors to large seismic events is an increase in situ stress. One way to find areas within geological strata that are highly stressed is to measure p-wave propagation velocities. High p-wave propagation velocities are associated with high in-situ stress levels. By using tomography programs a three-dimensional velocity model can be constructed. When seismic activity is present the event arrival times at each geophone, the locations of each geophone, and the three dimensional velocity model are used in conjunction with one another to locate the seismic events. This research compares the locations of seismic events from a deep coal mine longwall panel in the western United States with the associated p-wave propagation velocities from the previous 24 hours. The aim of this comparison is to provide a link between high velocities and seismic activity that could potentially be used to forecast future seismic activity. The comparison is completed both qualitatively through the use of a visual analysis, and quantitatively using various numerical and correlation comparisons on the seismic and velocity data. The qualitative comparison is completed using the event locations from the tomography program SIMULPS. The quantitative comparison is completed twice using two different tomography programs, SIMULPS and TomoDD, which use different methods for locating the seismic events. Before these comparisons were completed the stresses around the longwall panel were first modeled using the boundary element modeling program LAMODEL to study the effects of three backfilled cross panel entries which were located ahead of the mining face. The modeling showed similar vertical stress distributions as a panel without cross panel entries but higher stress magnitudes. The qualitative analysis involved comparing tomograms created with SIMULPS with seismicity plots from the following day. One noticeable feature of these tomograms is the presence of a stressed area directly ahead of the face. This stressed area represents the forward abutment. The results of this qualitative analysis illustrate a correlation between high p-wave velocities and seismic activity 24 hours later for several of the days studied. The other days showed little to no correlation. Additionally, not all high p-wave velocity regions resulted in seismic activity. Due to these inconsistencies visually analyzing velocity plots obtained from the program SIMULPS is not a reliable way to forecast the locations of seismic activity 24 hours later. The result of the quantitative comparisons completed with the programs SIMULPS and TomoDD further highlighted inconsistencies in the correlation between high p-wave velocities and associated seismic activity 24 hours later. TomoDD provided better correlation values than SIMULPS and generally showed that as the level of seismicity increased the p-wave propagation velocities 24 hours prior also increased. Although TomoDD provided good correlations for some of the data pairs studied, the overall inconsistencies prompt the need for further study in this area using TomoDD to find the optimal forecasting time period. / Master of Science

A recent concern is the cause and effect of global climate change. Many institutions give credit for these changes to the increased levels of greenhouse gases in the atmosphere, in particular the increase in the amount of carbon dioxide present. There is a growing interest in carbon capture and storage (CCS) as a means to reduce the global impact of CO₂ on the climate as a greenhouse gas. Carbon capture is the process of removing CO₂ from the atmosphere as well as preventing it from entering the atmosphere by means of exhaust. The captured carbon is stored underground in reservoirs. These reservoirs have the storage space to handle the volume of CO₂ injected as well as a caprock layer preventing the injection fluid from returning to the surface. Additionally, CO₂ can be used for enhanced oil recovery (EOR). To monitor the injection sites used for the CO₂ storage or EOR process, the integrity of the caprock as well as the surrounding rock formations are the locations of interest. Knowing when a joint or a fracture is going to slip is necessary to prevent major failures within geologic strata. It is necessary to prevent these slips from occurring to retain the integrity of the caprock, which is keeping the fluid within the reservoirs. Passive acoustic emissions monitoring was used to determine how effectively failure locations could be located in three unique tests. Coupled with double difference tomography, the failure of a Berea Sandstone sample and Marcellus Shale sample were calculated to determine how well the stress redistribution within the sample could be mapped using the recorded data. For the main indenter tests two samples were tested, a piece of Berea Sandstone and a piece of Marcellus Shale. The secondary test was a transform shear test using sandstone, and the third test for caprock upheaval test attempted to recreate the failure of caprock due to injection pressure. For all tests, the samples were monitored using acoustic emissions software until failure or it was deduced that the test would not produce failure. The secondary tests did not progress through the data analysis as far as the indentation tests, however valuable information was gathered from these tests. The shear test demonstrated the effectiveness of the passive acoustic emissions monitoring system to record shear failure. This test provides confidence in this technology to record and located events that are not occurring in compression. The caprock upheaval tests were not successful in causing failure in the caprock, however during the testing the passive acoustic emissions monitoring system was able record and locate events that occurred within the sample around the boundary on the reservoir. At the reservoir boundaries there was evidence of fluid flowing through the reservoir, and the events align with these locations. This positive result shows that the monitoring system is able to locate events induced by fluid injection. The results of these tests provide confidence in the passive acoustic emissions monitoring system to record accurate data for the caprock integrity monitoring. The tomograms created from the recorded data accurately imaged the areas of interest within the rock samples. From these results, passive acoustic emissions monitoring systems coupled with double difference tomography has proven capable of monitoring homogeneous samples within a laboratory environment. With further testing, this technology could possibly be a viable option for monitoring carbon sequestration sites. / Master of Science

Reservoir level and discharge data were collected for three Tennessee Valley Authority (TVA) dams (Chickamauga, Watts Bar and Douglas) on the Tennessee river in the Eastern Tennessee Seismic Zone (ETSZ). Earthquake catalog data was also collected for the ETSZ from 1980-2018. Well levels from 2 U.S. Geological Survey groundwater monitoring wells were also collected. Rainfall data were collected for the ETSZ. Reservoir, well and rainfall data were examined for correlation with earthquake occurrence rates. High Pearson correlation and anti-correlation coefficients (.7-.9) were obtained for the reservoir level and dam discharge volume rates vs monthly earthquake counts. Pearson correlation coefficients for rainfall and well level vs. monthly earthquake counts were small (.0-.2). A large difference in earthquake rates between the months of February (low rate) and April (high rate) over the 39 year study period was observed. The difference in earthquakes rates for February and April are statistically significant at the 95% confidence interval using the two sample Poisson rate test. The high correlations for the reservoir level and flow discharge vs. earthquake counts provides strong evidence of hydro-seismicity occurring in the ETSZ from seasonal fluctuations in reservoir level and discharge flow. / Master of Science / Reservoir level and discharge data were collected for three Tennessee Valley Authority (TVA) dams (Chickamauga, Watts Bar and Douglas) on the Tennessee river in the Eastern Tennessee Seismic Zone (ETSZ). Reservoir discharge and level data was collected for the three reservoirs. Also collected were rainfall data for the study area. This was provided by the TVA. Earthquake and well level data was collected from the USGS. High Pearson correlations for dam discharge and reservoir level vs. earthquake counts provided strong evidence of hydro-seismicity in the ETSZ.

The Charleston earthquake of 1886 was one of the largest shocks to occur on the eastern coast of North America. The geological cause has long been a controversial issue and a variety of source models have been proposed. Previous potential field modeling and reinterpretation of seismic reflection and well data collected in the early 1980s indicate that the crust between approximately 1 and 4.5 km depth is comprised primarily of Mesozoic mafic rocks, with extensive faulting that is spatially coincident with modern seismicity in the epicentral area (Chapman and Beale, 2010). This thesis proposes a new and testable hypothesis concerning the fault source of the 1886 shock that is very different from all previous interpretations. It is based on data collected during 2011-2012 from a local seismic network deployment in the immediate epicentral area. The 8-station temporary network was designed to better constrain earthquake hypocenter locations and focal mechanisms. Hypocenter locations of 134 earthquakes indicate a south-striking, west-dipping seismogenic zone in the upper 12 km of the crust. Over 40% of the 66 well-constrained focal mechanisms show reverse faulting on approximately north-south trending nodal planes, consistent with the orientation of the tabular hypocenter distribution. I offer the following hypothesis: The 1886 shock occurred by compressional reactivation of a major, south-striking, west-dipping early Mesozoic extensional fault. The modern seismicity can be regarded as a long-term aftershock sequence that is outlining the 1886 damage zone. Variability of shallow focal mechanisms is due to the complex early Mesozoic fault structure in the upper 4-5 km. / Master of Science

No description available.

During the late or post Weichselian glacial periods, about 9500 years ago, several faulting associated with large scale earthquakes were triggered in northern Fennoscandia. The end- or post-glacial scarps have a range of the lengths c. 3 to 155 km and the heights 0 to 30 m while most of them are reverse faults trending NE-SW with SE dips. In this literature study, I try to compile the estimated history and cause of seismicity in northern Sweden, and predict the future activity. The result indicates that although the timing of these faulting might not be in the same phase of deglaciation, the upheaval induced by glacial retreating is considered as the major factor of these paleoseismicity. Since the strain from glaciers has been mostly released, the main cause of recent earthquakes in this region is tectonic stress accumulation. Accompanied by the progress of observing techniques such as drilling and grand penetrating radar detection especially in this decade, the geometry of these glacially induced faults and recent micro-seismicity in the vicinity of these scarps have been detected better and better. According to the results, the recorded epicenters form clusters in the east side of the faults’ zone. It implies the correlation between recent seismicity and end- or post-glacial faults. However, there is still insufficient data of the faults’ structure and previous seismicity in order to clarify the faults’ geometry, the age of main movements and estimate their future activity. More investigations are expected to take place in this region.

The work in this thesis concentrates on Katla volcano in southern Iceland. This is one of Europe’s most active volcanoes and its history tells us that it poses many threats to society, both locally (Iceland) and on a broader scale (Europe). Its geological setting is complex, where the effects of a melting anomaly in the mantle and a changing rift geometry, perturb the classical setting of volcanism in a rifting setting. The work has focused on two aspects. The first is the varying distribution of physical properties in the subsurface around the volcano. The second is the distribution of microearthquakes around the volcano. The physical properties that we study are the speeds of seismic waves that reflect variations of temperature, composition and fracturing of the rocks. These can, therefore, help us learn about long-term processes in the volcano. The seismicity gives shorter-term information about deformation associated with current processes. I have applied two tomographic techniques to study Katla’s subsurface to a depth of 5-10 km, namely local-earthquake and ambient-noise tomography. The former makes use of the timing of waves generated by local earthquakes to constrain the earthquakes’ locations and the distribution of wave speed. Here I have concentrated on compressional waves or P waves with a typical frequency content around 10 Hz. With the latter, surface waves are extracted from microseismic noise that is generated far away at sea and their timing is measured to constrain their wave-speed distribution, which then is used to map shear-wave velocity variations. This is done at a typical frequency of 0.3 Hz. I find that the volcano contains rocks of higher velocity than its surroundings, that Katla’s caldera is underlain by low velocities at shallow depth that may be explained by hot or partially molten rocks and that beneath the caldera lies a volume of particularly high velocities that may constitute differentiated cumulates. But, I also find that it is not simple to compare results from such different wave types and discuss a number of complications in that regard. In addition to the well-known microearthquake distribution in the caldera region of Katla and to its west, we have discovered two additional areas of microearthquake activity on the volcano’s flanks, south and east of the caldera. These point to current activity and are, therefore, of interest from a hazard point of view. However, it is difficult to pinpoint their underlying process. Speculation about possible interpretation leads me to hydrothermal processes or small pockets of melt ascending due to their buoyancy or locally enhancing fluid pressure, thereby lowering the effective stress.

In the present thesis we perform modeling of earthquake source using laboratory derive rate-and-state laws of friction. We have developed a code in Fortran 90 for modeling a planar, two-dimensional fault with general dip and heterogeneous distribution of frictional parameters. We use a quasi-dynamic approximation and assume that the fault is submnerged in an infinite elastic half-space. We performed an extensive number of numerical experiments to study the effect of fricitonal parameters distribution on the spatio-temporal complexity of slip on fault. We also study the effect of the so called Coulomb stress changed on clock advance and clock delay of events. For this purpose we use both a homogeneous model and a model of random frictional parameteres which exhibits the Gutenberg-Richter frequency- size dependence in the range of two magnitudes. We find that the effect of Couloumb stress change is nontrivial and depends on factors such as the domain of stress load and the slip velocity on it. Powered by TCPDF (www.tcpdf.org)

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.

This dissertation details work aimed at better understanding topographic effects in earthquake ground motions. The experiment, conducted in Central-Eastern Utah, used frequent and predictable seismicity produced by underground longwall coal mining as a source of low-intensity ground motions. Locally-dense arrays of seismometers deployed over various topographic features were used to passively monitor seismic energy produced by mining-induced implosions and/or stress redistribution in the subsurface. The research consisted of two separate studies: an initial feasibility experiment (Phase I) followed by a larger-scale main study (Phase II). Over 50 distinct, small-magnitude (M[subscript 'L'] < 1.6) seismic events were identified in each phase. These events were analyzed for topographic effects in the time domain using the Peak Ground Velocity (PGV), and in the frequency domain using the Standard Spectral Ratio (SSR) method, the Median Reference Method (MRM), and the Horizontal-to-Vertical Spectral Ratio (HVSR) method. The polarities of the horizontal ground motions were also visualized using directional analyses. The various analysis methods were compared to assess their ability to estimate amplification factors and determine the topographic frequencies of interest for each feature instrumented. The MRM was found to provide the most consistent, and presumably accurate, estimates of the amplification factor and frequency range for topographic effects. Results from this study clearly indicated that topographic amplification of ground motions does in fact occur. These amplifications were very frequency dependent, and the frequency range was correctly estimated in many, but not all, cases using simplified, analytical methods based on the geotechnical and geometrical properties of the topography. Amplifications in this study were found to generally range from 2 to 3 times a reference/baseline site condition, with some complex 3D features experiencing amplifications as high as 10. Maximum amplifications occurred near the crest of topographic features with slope angles greater than approximately 15 degrees, and the amplifications were generally oriented in the direction of steepest topographic relief, with some dependency on wave propagation direction. / text