An Update of Seismic Monitoring and Research in the Vicinity of the Paducah Gaseous Diffusion Plant: January 2013–December 2017

From January 2013 to December 2017, the Kentucky Geological Survey monitored earthquakes and conducted research on seismic hazards in the vicinity of the Paducah Gaseous Diffusion Plant, a former uranium enrichment facility, in western Kentucky. Fifteen earthquakes with magnitude greater than 3.0 occurred in the area during this period, and data were collected from the Central U.S. Seismic Observatory and the vertical seismic array at the gaseous diffusion plant. This monitoring improved our understanding of seismic-wave propagation through thick sediments and ground-motion site effects, as well as fault locations in the New Madrid Seismic Zone, ground-motion attenuation, and seismic-hazard assessment. Results have been communicated through publications and presentations at workshops and conferences. The data will contribute to the development of design ground motions for western Kentucky, and specifically for buildings and facilities at the Paducah Gaseous Diffusion Plant

An Update of Seismic Monitoring and Research in the Vicinity of the Paducah Gaseous Diffusion Plant: January 2018–December 2019

From January 2018 to December 2019, the Kentucky Geological Survey monitored earthquakes and conducted research on seismic hazards in the vicinity of the Paducah Gaseous Diffusion Plant, a former uranium enrichment facility, in McCracken County, western Kentucky. Six hundred forty-four earthquakes with magnitude between 0.5 and 3.7 were recorded in the area during this period. Research focused on the influence of the thick sediments on earthquake ground motion, the so-called site response, through theoretical and data analysis of borehole seismic records. Our research has shown that the National Earthquake Hazards Reduction Program site classification, which is based on Vs30, and correction factors currently being used in earthquake engineering design and other safety evaluations are not appropriate to account for site response in the area

The \u3cem\u3eM\u3c/em\u3e\u3csub\u3ew\u3c/sub\u3e 4.2 Perry County, Kentucky, Earthquake of 10 November 2012: Evidence of the Eastern Tennessee Seismic Zone in Southeastern Kentucky

The 10 November 2012 Mw 4.2 Perry County earthquake may represent a continuation of the seismically active Eastern Tennessee seismic zone (ETSZ) farther north than previously recognized into southeastern Kentucky. The mainshock and aftershock data from regional seismic networks and EarthScope’s Transportable Array stations allowed high‐quality determinations of the source parameters. The focal mechanism, depth, and proximity of the mainshock to the New York–Alabama magnetic lineament, a subsurface, crustal‐scale structure that spatially correlates with central ETSZ seismicity, suggest that this earthquake may share the same type of causal geologic structures as the more‐active ETSZ region to the south

Site Characteristics, Instrumentation, and Recordings of the Central United States Seismic Observatory

The Central United States Seismic Observatory is a vertical seismic array in southwestern Kentucky within the New Madrid Seismic Zone. It is intended to record the effects of local geology, including thick sediment overburden, on seismic-wave propagation, particularly strong ground motion. The three-borehole array is composed of seismic sensors placed on the surface, in the bedrock, and at various depths within the 585-m-thick sediment overburden. The array\u27s deep borehole also provides a unique opportunity to describe the geology and geophysically measure the complete Late Cretaceous through Quaternary stratigraphy in the northern Mississippi Embayment. Based on the surface and borehole geophysical measurements, the thick sediment overburden and its complex heterogeneous stratigraphy have been partitioned into a seven-layer sediment velocity model overlying a bedrock half-space. The S- and P-wave sediment velocities range between 160 and 875 m/s, and 1,000 and 2,300 m/s, respectively, and bedrock velocities between 1,452 and 3,775 m/s, respectively. In addition, high-resolution seismic-reflection profiles acquired within a 1-km radius of the array have imaged a complex geologic model, including steeply dipping N30°E-striking faults that have uplifted and arched post-Paleozoic sediments in a manner consistent with a dextral transpression component of displacement. The subparallel fault strands have been traced 1.4 km between reflection profiles and are adjacent to the array. The fault deformation extends above Paleozoic bedrock, affecting the Late Cretaceous and Eocene Mississippi Embayment sediments, as well as the base of the Quaternary. The Paleozoic and Cretaceous horizons show as much as 75 and 50 m of relief, respectively, with the middle Eocene and basal Quaternary disrupted 25 and 15 m, respectively. The differential fault offsets suggest episodic activity during the post-Paleozoic, and represent the first indications of Quaternary neotectonics in this part of Kentucky. More important, these faults may be the first evidence for a hypothesized northeast extension of the strike-slip Axial Fault Zone from a through-going intersection with the left-stepover Reelfoot Fault (i.e., thrust). Seismometers and accelerometers were both installed at the surface, 30 m, 259 m, and 526 m depths, and at 2 m into bedrock in three separate boreholes. The instrumentation elevation in the boreholes was determined by the major impedance boundaries within the stratigraphic section. Although the array operation has been frequently interrupted by the large hydrostatic pressures on the deeper instrumentation, the full array has recorded weak motions from 95 earthquakes at local, regional, and teleseismic distances. Initial observations reveal a complex spectral mix of amplification and deamplification across the array, indicating the site effect in this deep-sediment setting is not simply generated by the shallowest layers. Preliminary horizontal-to-vertical spectral ratio (HV) experiments show the bedrock vertical and horizontal amplitudes are not equal, violating a required assumption for site characterization. Furthermore, there are marked differences between spectral ratios from the directly measure transfer function (HH) and HV for particular earthquakes. On average, however, the HH and HV methods yield similar results within a narrow band of frequencies ranging between 0.35 and 1.1 Hz

Linear site-response characteristics at central and eastern U.S. seismic stations

Earthquake S waves can become trapped, or resonate, between the free surface and high-impedance basal layers, strongly contributing to site response at specific frequencies. Strong S-wave resonances have been observed in the central and eastern U.S., where many sites sit on unlithified sediments underlain by stiff bedrock. To evaluate S-wave resonances in this region, we calculated 1D linear site-responses at 89 seismic stations with developed S-wave velocity profiles into bedrock. We found that S-wave resonances at the fundamental and strongest (peak) modes occur across large ranges of frequencies, each spanning more than two orders of magnitude — 0.21–54.0 Hz and 0.29–71.5 Hz, respectively. Amplifications of ∼5 and ∼6 are common at the fundamental frequency and peak modes, respectively; the largest amplification calculated was 13.2. Using simple regression analyses, we evaluated the skills of six proxies derived from the S-wave velocity profiles to predict the frequencies and corresponding amplifications of the fundamental and peak modes. We found that the depths to the 1.0 km/s and 2.5 km/s horizons, consistent with other studies, and to the maximum impedance contrasts strongly correlate with the resonance frequencies and that the fundamental-mode and peak amplifications correlate with the maximum impedance ratios. Correlations improved for data subsets based on the number and magnitude of impedance ratios underlying the sites and are the strongest at sites underlain by a single impedance ratio of 3.0 or greater. Finally, we calculated the S-wave horizontal-to-vertical spectral ratios (HVSR) at each possible seismic station and found, consistent with other studies, that the first peak can be used to estimate fundamental-mode frequencies and the corresponding amplifications. Thus, S-wave HVSR, can provide useful estimates of the fundamental-mode linear site response parameters at sites lacking S-wave velocity profiles. Furthermore, S-wave HVSR curves appear to be useful to broadly categorize impedance-ratio profiles

Ground Motions Induced by the March 11, 2018, Implosion of the Capital Plaza Tower, Frankfort, Kentucky

The demolition by implosion of the Capital Plaza Tower in downtown Frankfort provided an opportunity to record seismic waves from a known source of seismic energy in order to observe local ground-motion amplification and resonance within the underlying unconsolidated sediment. The Kentucky Geological Survey deployed three strong-motion accelerographs at approximately equal distances around the tower to record ground motions induced by its collapse. The KGS instruments were installed at sites with different underlying geology: one on bedrock and two on Kentucky River Valley unconsolidated sediments. Using images captured by a high-speed video camera, with timing synchronized with the clock of one of the strong-motion accelerographs, the sequence of ground-motion-inducing events from the tower demolition (blast explosions and the collapsing tower’s impact with the ground) was identified in the ground-motion time histories recorded at the rock site. This allowed the ground motions from the tower collapse recorded at all stations deployed for the event to be isolated and analyzed. The ground motions from the tower collapse recorded at the observation sites were weak and were likely imperceptible to humans. The detected motions, which had modified Mercalli intensities of only I to II at the rock and soil sites, respectively, were unlikely to have caused any damage there. Seismic-wave resonance within the Kentucky River Valley sediment was identified from the analysis of these recordings. The resonance frequencies were similar at all KGS soil sites, and also were similar to those observed on seismographs deployed by the Energy and Environment Cabinet’s Explosives and Blasting Branch. These observations indicate that in the unlikely event of a nearby strong earthquake, shaking is expected to be amplified within the unconsolidated Kentucky River Valley sediments underlying downtown Frankfort

Seismic Monitoring and Baseline Microseismicity in the Rome Trough, Eastern Kentucky

In the central and eastern United States, felt earthquakes likely triggered by fluid injection from oil and gas production or wastewater disposal have dramatically increased in frequency since the onset of the unconventional shale gas and oil boom. In the Rome Trough of eastern Kentucky, fracture stimulations and wastewater injection are ongoing and occur near areas of historical seismic activity. Unlike in surrounding and nearby states (Ohio, West Virginia, and Arkansas), in Kentucky, no seismic events related to subsurface fluid injections have been reported as felt or detected by regional seismic networks, including the Kentucky Seismic and Strong-Motion Network. Oil and gas development of the deep Cambrian Rogersville Shale in the Rome Trough is in a very early stage, and will require horizontal drilling and high-volume hydraulic fracturing. To characterize natural seismicity rates and the conditions that might lead to induced or triggered events, the Kentucky Geological Survey is conducting a collaborative study, the Eastern Kentucky Microseismic Monitoring Project, prior to large-scale oil and gas production and wastewater injection. A temporary network of broadband seismographs was deployed near dense clusters of Class II wastewater-injection wells and near the locations of new, deep oil and gas test wells in eastern Kentucky. Network installation began in mid-2015 and by November 2015, 12 stations were operating, with data acquired in real time and jointly with regional network data. Additional stations were installed between June 2016 and October 2017 in targeted locations. The network improved the monitoring sensitivity near wastewater-injection wells and deep oil and gas test wells by approximately an entire unit of magnitude: With the temporary network, the detectable magnitudes range from 0.7 to 1.0, and without it, the detectable magnitudes range from 1.5 to 1.9. Using the real-time recordings of this network in tandem with the recordings of other temporary and permanent regional seismic stations, we generated a catalog of local seismicity and developed a calibrated magnitude scale. At the time this report was prepared, 151 earthquakes had been detected and located, 38 of which were in the project area, defined as the region bounded by 37.1°N to 38.7°N latitude and 84.5°W to 82.0°W longitude. Only six earthquakes occurred in the Rome Trough of eastern Kentucky, none of which were reported in regional monitoring agency catalogs, and none of which appear to be associated with the deep Rogersville Shale test wells that were completed during the time the network was in operation or with wastewater-injection wells

Evidence for low-angle normal faulting in the Pumqu-Xianza Rift, Tibet

Low-angle normal faulting is widely discussed as a possible mechanism for continental extension, however, unambiguous evidence for seismogenic low-angle normal faulting is lacking. Here, we investigate seismicity along a short segment of the Pumqu-Xianza Rift (PXR) in southern Tibet, where the HiCLIMB seismic array recorded over 500 earthquakes between 2004 July and 2005 August. Hypocentres of the 40 best recorded earthquakes are approximately 20–25 km west of the rift and tightly clustered at about 10 km depth, consistent with moment tensor depths of the 11 largest (3.4 ≤M[subscript w]≤ 4.5) earthquakes. Events in this group have N–S striking normal faulting mechanisms with low-angle (29°) west dipping fault planes. Rupture along a west dipping, low-angle, planar normal fault (the eastern PXR boundary fault) is consistent with event hypocentres, fault dip from moment tensors, and prominent surface morphology. The dip of 29° is at the low end of physically possible values assuming normal frictional behaviour and state of stress. We suggest it is possible for a planar, low-angle fault to nucleate seismically at a low angle at depth in the presence of basal shear and work its way aseismically through the brittle crust to the surface with the aid of lubricating minerals.This is the publisher’s final pdf. The article is copyrighted by the Royal Astronomical Society and published by John Wiley & Sons, Inc. It can be found at: http://www.blackwellpublishing.com/journal.asp?ref=0956-540x.Keywords: Dynamics and mechanics of faulting, extensional, Seismicity and tectonics, Continental tectonicsKeywords: Dynamics and mechanics of faulting, extensional, Seismicity and tectonics, Continental tectonic

Patterns of care in older patients with squamous cell carcinoma of the head and neck: A Surveillance, Epidemiology, and End Results-Medicare analysis

There is growing evidence in the literature that older patients may not benefit from more intensive therapy for Head and Neck Squamous Cell Carcinoma (HNSCC). A growing number of patients with Head and Neck Squamous Cell Carcinoma (HNSCC) are age 65 and older; however, much of the evidence base informing treatment decisions is based on substantially younger and healthier clinical trial populations. The purpose of this study was to assess the patterns of care of older HNSCC patients to better understand how age is associated with treatment decision