Selecting a level of seismic hazard at the Paducah Gaseous Diffusion Plant for policy considerati... more Selecting a level of seismic hazard at the Paducah Gaseous Diffusion Plant for policy considerations and engineering design is not an easy task because it not only depends on seismic hazard, but also on seismic risk and other related environmental, social, and economic issues. Seismic hazard is the main focus. There is no question that there are seismic hazards at the Paducah Gaseous Diffusion Plant because of its proximity to several known seismic zones, particularly the New Madrid Seismic Zone. The issues in estimating seismic hazard are (1) the methods being used and (2) difficulty in characterizing the uncertainties of seismic sources, earthquake occurrence frequencies, and ground-motion attenuation relationships. This report summarizes how input data were derived, which methodologies were used, and what the hazard estimates at the Paducah Gaseous Diffusion Plant are.
Since the 1980s, the research associated with the UK network has been primarily strong-motion sei... more Since the 1980s, the research associated with the UK network has been primarily strong-motion seismology of engineering interest. Currently the University of Kentucky operates a strong-motion network of nine stations in the New Madrid Seismic Zone. A unique feature of the network is the inclusions of vertical strong-motion arrays, each with one or two downhole accelerometers. The deepest borehole array is 260 m below the surfaces at station VASA in Fulton County, Kentucky. A preliminary surface seismic refraction survey was conducted at the site before drilling the hole at VSAS (Woolery and Wang, 2002). The depth to the Paleozoic bedrock at the site was estimated to be approximately 595 m, and the depth to the first very stiff layer (i.e. Porters Creek Clay) was found to be about 260 m. These depths and stratigraphic interpretation correlated well with a proprietary seismic reflection line and the Ken-Ten Oil Exploration No. 1 Sanger hole (Schwalb, 1969), as well as our experience i...
Earthquakes pose a seismic hazards and risk to the Commonwealth of Kentucky. Furthermore, the sei... more Earthquakes pose a seismic hazards and risk to the Commonwealth of Kentucky. Furthermore, the seismic hazards and risk vary throughout the Commonwealth. The US Nuclear Regulatory Commission uses the seismic hazard maps developed by the US Geological Survey for seismic safety regulation for nuclear facilities. Under current US Geological Survey's seismic hazard assessment it is economically unfeasible to build a new uranium plant near Paducah relative to the Portsmouth, Ohio site. This is not to say that the facility cannot be safely engineered to withstand the present seismic load, but enormously expensive to do so. More than 20 years observations and research at UK have shown that the US Geological Survey has overestimated seismic hazards in western Kentucky, particularly in the Jackson Purchase area that includes Paducah. Furthermore, our research indicates underestimated seismic hazards in northeastern Kentucky and southeastern Ohio. Such overestimation and underestimation co...
Spectral analyses were performed on S-waves of earthquake recordings from two vertical seismic an... more Spectral analyses were performed on S-waves of earthquake recordings from two vertical seismic and strong-motion arrays in the central United States to obtain horizontal-to-vertical spectral ratios (HVSR) and transfer functions. Spectral analyses were also performed on ambient noises to obtain HVSRs at both sites. Theoretical SH-wave transfer functions were obtained using Thomson-Haskell propagation matrices and soil profiles at both sites. The results demonstrate that the S-wave HVSR is similar to the observed and theoretical SH-wave transfer functions. In other words, the S-wave HVSR could be used as an empirical SH-wave transfer function and provide in situ constraints on the shear-wave velocity structure of soils at these sites. The results also demonstrate that the ambient-noise HVSR is different from the S-wave HVSR and SH-wave transfer functions of the soils. Thus, caution should be exercised before using the ambient-noise HVSR to characterize earthquake ground-motion site-effect as well as to determine the shearwave velocity structure.
A borehole that penetrated 585 m of soil deposits and terminated 9 m into Paleozoic bedrock was c... more A borehole that penetrated 585 m of soil deposits and terminated 9 m into Paleozoic bedrock was completed near the New Madrid Seismic Zone of the central United States. A vertical array of strongmotion accelerometers and broadband seismometers-the Central United States Seismic Observatory (CUSSO) was installed. CUSSO provides a test site for verification and calibration of seismic-wave propagation analysis and near-surface seismic exploration. Preliminary results show that velocity models produced from the P-wave walkaway soundings, P-wave arrival of earthquake recordings, and downhole P-wave suspension measurements at CUSSO are comparable; however, the S-wave suspension log model underestimates the velocity compared to the models derived from S-wave walkaway soundings and S-wave arrival of earthquake recordings. Significant sediment disturbance in the borehole annulus is speculated to have affected the accuracy of the S-wave suspension log, whereas the saturated condition of the soft sediment at depth made the downhole P-wave measurements less susceptible to the sediment disturbance.
Seismic hazards in greater North China were estimated from 500 years of intensity observations. H... more Seismic hazards in greater North China were estimated from 500 years of intensity observations. Historical intensity observations were collected, the completeness of the earthquake catalog was tested, and aftershocks were deleted. The intensity data were digitized and placed in a geographic information system (GIS). Finally, the digitized intensity data were analyzed to determine the frequency-intensity relationship (i.e., seismic hazard curve). Seismic risks were also estimated, assuming a Poisson distribution for earthquake occurrence in time. The results show that greater North China faces significant seismic hazards and risks. The results also show that the current design peak ground acceleration (PGA) for greater North China might not be adequate, particularly for the Beijing, Tianjin, and Tangshan areas.
Abstract Communities need information about seismic hazards, ground-motion hazards, in particular... more Abstract Communities need information about seismic hazards, ground-motion hazards, in particular, to formulate engineering designs for buildings and other structures. Developing scientifically sound ground-motion hazard assessments and associated information in the central United States is challenging, however, because of large uncertainties in the seismic sources, earthquake recurrence intervals, and local geologic conditions. Scenario-based seismic hazard analysis (SSHA) is a viable approach to provide ground-motion hazard information, including time histories and their peak values and response accelerations, for engineering design and other applications. Some perceived advantages of SSHA include (1) resultant ground motions have a clear physical meaning, (2) ground-motion time histories, which are necessary for engineering analysis, are provided, and (3) the results are easily communicated between earth scientists, engineers, and others. We describe and summarize how SSHA has been applied to develop (1) ground-motion time histories and associated parameters and maps from natural earthquakes for engineering design and safety evaluation of bridges and highway facilities and residential buildings and other structures, and (2) potential ground-motion hazards from induced earthquake in the central United States, Kentucky in particular.
Bulletin of the Seismological Society of America, Feb 1, 2018
The work of the original article (Rong et al., 2017) also represents the results of the cooperati... more The work of the original article (Rong et al., 2017) also represents the results of the cooperative research between the
Bulletin of the Seismological Society of America, May 25, 2021
ABSTRACTV S 30 is currently used as a key proxy to parameterize site response in engineering desi... more ABSTRACTV S 30 is currently used as a key proxy to parameterize site response in engineering design and other applications. However, it has been found that VS30 is not an appropriate proxy, because it does not reliably correlate with site response. Therefore, the VS30-based National Earthquake Hazards Reduction Program site maps may not capture regional site responses. In earthquake engineering, site resonance, which can be characterized by the fundamental mode with a site period (Tf) and its associated peak amplification (A0), is the primary site-response concern. Mapping Tf and A0 is thus essential for accurate regional seismic hazard assessment. We developed a 3D shear-wave velocity model for the Jackson Purchase Region of western Kentucky, based on shear-wave velocity profiles interpreted from seismic reflections and refractions, mapped geologic units, and digital-elevation-model datasets. We generated shear-wave velocity profiles at grid points with 500 m spacing from the 3D model and performed 1D linear site-response analyses to obtain Tf and A0, which we then used to construct contour maps for the study area. Our results show that Tf and A0 maps correlate with the characteristics of regional geology in terms of sediment thicknesses and their average shear-wave velocities. We also observed a strong dependency of A0 on bedrock shear-wave velocities. The mapped Tf and A0 are consistent with those estimated from borehole transfer functions and horizontal-to-vertical spectral ratio analyses at broadband and strong-motion stations in the study area. Our analyses also demonstrate that the depth to bedrock (Zb) is correlated to Tf, and the average sediment shear-wave velocity (VS-avg) is correlated to A0. This implies that Zb and VS-avg may be considered as paired proxies to parameterize site resonance in the linear-elastic regime.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Abstract Communities need sound seismic hazard maps for formulating policies such as engineering ... more Abstract Communities need sound seismic hazard maps for formulating policies such as engineering design for buildings and other structures to reduce potential earthquake losses. However, developing scientifically sound seismic hazard maps is challenging because there are large inherent uncertainties and many unknowns (or even sheer ignorance). It is critical for any seismic hazard mapping that these uncertainties be quantified and communicated clearly to engineers, policy makers, and the public. Although probabilistic seismic hazard analysis (PSHA) has been the most widely used method for seismic hazard mapping, the hazard maps produced from PSHA are artifacts and difficult, even impossible, to understand because PSHA is a pure computer model without a sound earth science (physics) basis and its mathematics is simply wrong. The use of PSHA hazard maps has led to overly stringent engineering design and mitigation policies in the central USA, and unsafe engineering design and other mitigation policies in western China. On the other hand, the hazard maps derived from deterministic seismic hazard analysis (DSHA) or Neo-DSHA have a clear physical and statistical meaning and are easy to understand. Deterministic (or scenario) hazard maps have been proven to be effective. Thus, deterministic hazard maps are more appropriate for engineering design and other mitigation policy considerations in the central USA and western China, as well as other areas in the world.
The 10 November 2012 M w 4.2 Perry County earthquake may represent a continuation of the seismica... more The 10 November 2012 M w 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 highquality determinations of the source parameters. The focal mechanism, depth, and proximity of the mainshock to the New York-Alabama magnetic lineament, a subsurface, crustalscale 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.
Over 1.5 kilometers of high-resolution, SH-wave refraction and reflection profiles have been perf... more Over 1.5 kilometers of high-resolution, SH-wave refraction and reflection profiles have been performed in the Madrid Bend area of northwestern Tennessee, approximately 8 km north of Tiptonville, Tennessee, to establish the existence of neo-tectonic, near-surface deformation. The specific area was chosen because of the access it provided to the Tiptonville dome (a Holocene flexure) and the trend of contemporary seismicity within the New Madrid seismic zone (NMSZ). We believed the highest likelihood of near-surface deformation to be over these features. Partially reversed refraction/reflection walk-away tests and common depth point (CDP) seismic profiling, using the non-traditional SH-wave method, have traced antiformal flexure and numerous faults into the late Eocene and Holocene sediments of the Tiptonville dome province of the Lake County uplift (LCU). Vertical displacements exhibited across the faults range from approximately 3 to 30 m. These structures have been interpreted to be neo-tectonic features associated with tensional stresses across the Tiptonville dome.
Bulletin of the Seismological Society of America, Jan 21, 2020
ABSTRACT Site response at many locations in the central and eastern United States is a resonance-... more ABSTRACT Site response at many locations in the central and eastern United States is a resonance-based phenomenon, which site factors based on the VS30 proxy may not reliably capture. Alternative factors, fundamental frequency, f0, and fundamental-mode amplification, A0, calculated from simplified expressions were evaluated against 1D linear, viscoelastic SH-wave full-resonance (FR) site responses. Tests were conducted using S-wave velocity profiles to bedrock at 11 seismic stations. The results showed that simplified expressions approximate FR f0 and A0 at most stations. However, at two sites with intermediate-depth strong impedance contrasts, the simplified approach underestimates A0 by ∼40%. In addition, FR f0 and A0 were compared with weak-motion earthquake S-wave horizontal-to-vertical (H/V) spectral ratios. Measuring f0 and A0 from S-wave H/V for our comparisons required considering multiple observations at the regional scale. The first S-wave H/V peaks occurred between ∼1 and ∼3 Hz at all seven stations in the Illinois basin (IB), which is a much lower f0 than expected for five of these sites. Thus, we used the first S-wave H/V peaks at f>3 Hz at these five sites in our comparisons. The S-wave H/V peaks we evaluated indicate that S-wave H/V can approximate FR f0. However, although the A0 measured from S-wave H/V is positively correlated with theoretical A0, it overestimated FR A0 by more than 40% at all but three sites, indicating that additional study is needed to determine the appropriate use of A0 from S-wave H/V. The observed, unmodeled amplifications between ∼1 and ∼3 Hz are of similar magnitudes as those from the shallower sediment layers at most stations, which highlights the importance of collecting empirical site-response estimations. Furthermore, the amplifications indicate the need to investigate deeper velocity structures in the IB to account for site responses within the frequency band of engineering interest.
The Xianshuihe fault zone consists of left-lateral, segmented strike-slip faults, which produce s... more The Xianshuihe fault zone consists of left-lateral, segmented strike-slip faults, which produce strong and relatively frequent earthquakes, and exposes millions of people to the risk of strong motion and earthquake-induced geologic hazards in Southwest China. Seismicity in this fault zone exhibits typical features of characteristic earthquakes. The stochastic finite-fault model was used to generate time-histories and peak values of strong ground motion at near-fault locations for the characteristic earthquakes. First, the source parameters were determined and verified by comparing them with the simulated time-histories and intensity distribution and observations from the 2014 Kangding earthquake (M w 6.0). Then, scenario-based ground-motion hazard maps were produced from simulated ground motions of characteristic earthquakes. The scenario-based ground-motion hazard maps can be directly compared with historical and future earthquakes in the Xianshuihe fault zone. Scenario-based seismic hazard analysis also has other advantages. Our results show that current design ground motion for the Xianshuihe Fault area is not adequate.
Selecting a level of seismic hazard at the Paducah Gaseous Diffusion Plant for policy considerati... more Selecting a level of seismic hazard at the Paducah Gaseous Diffusion Plant for policy considerations and engineering design is not an easy task because it not only depends on seismic hazard, but also on seismic risk and other related environmental, social, and economic issues. Seismic hazard is the main focus. There is no question that there are seismic hazards at the Paducah Gaseous Diffusion Plant because of its proximity to several known seismic zones, particularly the New Madrid Seismic Zone. The issues in estimating seismic hazard are (1) the methods being used and (2) difficulty in characterizing the uncertainties of seismic sources, earthquake occurrence frequencies, and ground-motion attenuation relationships. This report summarizes how input data were derived, which methodologies were used, and what the hazard estimates at the Paducah Gaseous Diffusion Plant are.
Since the 1980s, the research associated with the UK network has been primarily strong-motion sei... more Since the 1980s, the research associated with the UK network has been primarily strong-motion seismology of engineering interest. Currently the University of Kentucky operates a strong-motion network of nine stations in the New Madrid Seismic Zone. A unique feature of the network is the inclusions of vertical strong-motion arrays, each with one or two downhole accelerometers. The deepest borehole array is 260 m below the surfaces at station VASA in Fulton County, Kentucky. A preliminary surface seismic refraction survey was conducted at the site before drilling the hole at VSAS (Woolery and Wang, 2002). The depth to the Paleozoic bedrock at the site was estimated to be approximately 595 m, and the depth to the first very stiff layer (i.e. Porters Creek Clay) was found to be about 260 m. These depths and stratigraphic interpretation correlated well with a proprietary seismic reflection line and the Ken-Ten Oil Exploration No. 1 Sanger hole (Schwalb, 1969), as well as our experience i...
Earthquakes pose a seismic hazards and risk to the Commonwealth of Kentucky. Furthermore, the sei... more Earthquakes pose a seismic hazards and risk to the Commonwealth of Kentucky. Furthermore, the seismic hazards and risk vary throughout the Commonwealth. The US Nuclear Regulatory Commission uses the seismic hazard maps developed by the US Geological Survey for seismic safety regulation for nuclear facilities. Under current US Geological Survey's seismic hazard assessment it is economically unfeasible to build a new uranium plant near Paducah relative to the Portsmouth, Ohio site. This is not to say that the facility cannot be safely engineered to withstand the present seismic load, but enormously expensive to do so. More than 20 years observations and research at UK have shown that the US Geological Survey has overestimated seismic hazards in western Kentucky, particularly in the Jackson Purchase area that includes Paducah. Furthermore, our research indicates underestimated seismic hazards in northeastern Kentucky and southeastern Ohio. Such overestimation and underestimation co...
Spectral analyses were performed on S-waves of earthquake recordings from two vertical seismic an... more Spectral analyses were performed on S-waves of earthquake recordings from two vertical seismic and strong-motion arrays in the central United States to obtain horizontal-to-vertical spectral ratios (HVSR) and transfer functions. Spectral analyses were also performed on ambient noises to obtain HVSRs at both sites. Theoretical SH-wave transfer functions were obtained using Thomson-Haskell propagation matrices and soil profiles at both sites. The results demonstrate that the S-wave HVSR is similar to the observed and theoretical SH-wave transfer functions. In other words, the S-wave HVSR could be used as an empirical SH-wave transfer function and provide in situ constraints on the shear-wave velocity structure of soils at these sites. The results also demonstrate that the ambient-noise HVSR is different from the S-wave HVSR and SH-wave transfer functions of the soils. Thus, caution should be exercised before using the ambient-noise HVSR to characterize earthquake ground-motion site-effect as well as to determine the shearwave velocity structure.
A borehole that penetrated 585 m of soil deposits and terminated 9 m into Paleozoic bedrock was c... more A borehole that penetrated 585 m of soil deposits and terminated 9 m into Paleozoic bedrock was completed near the New Madrid Seismic Zone of the central United States. A vertical array of strongmotion accelerometers and broadband seismometers-the Central United States Seismic Observatory (CUSSO) was installed. CUSSO provides a test site for verification and calibration of seismic-wave propagation analysis and near-surface seismic exploration. Preliminary results show that velocity models produced from the P-wave walkaway soundings, P-wave arrival of earthquake recordings, and downhole P-wave suspension measurements at CUSSO are comparable; however, the S-wave suspension log model underestimates the velocity compared to the models derived from S-wave walkaway soundings and S-wave arrival of earthquake recordings. Significant sediment disturbance in the borehole annulus is speculated to have affected the accuracy of the S-wave suspension log, whereas the saturated condition of the soft sediment at depth made the downhole P-wave measurements less susceptible to the sediment disturbance.
Seismic hazards in greater North China were estimated from 500 years of intensity observations. H... more Seismic hazards in greater North China were estimated from 500 years of intensity observations. Historical intensity observations were collected, the completeness of the earthquake catalog was tested, and aftershocks were deleted. The intensity data were digitized and placed in a geographic information system (GIS). Finally, the digitized intensity data were analyzed to determine the frequency-intensity relationship (i.e., seismic hazard curve). Seismic risks were also estimated, assuming a Poisson distribution for earthquake occurrence in time. The results show that greater North China faces significant seismic hazards and risks. The results also show that the current design peak ground acceleration (PGA) for greater North China might not be adequate, particularly for the Beijing, Tianjin, and Tangshan areas.
Abstract Communities need information about seismic hazards, ground-motion hazards, in particular... more Abstract Communities need information about seismic hazards, ground-motion hazards, in particular, to formulate engineering designs for buildings and other structures. Developing scientifically sound ground-motion hazard assessments and associated information in the central United States is challenging, however, because of large uncertainties in the seismic sources, earthquake recurrence intervals, and local geologic conditions. Scenario-based seismic hazard analysis (SSHA) is a viable approach to provide ground-motion hazard information, including time histories and their peak values and response accelerations, for engineering design and other applications. Some perceived advantages of SSHA include (1) resultant ground motions have a clear physical meaning, (2) ground-motion time histories, which are necessary for engineering analysis, are provided, and (3) the results are easily communicated between earth scientists, engineers, and others. We describe and summarize how SSHA has been applied to develop (1) ground-motion time histories and associated parameters and maps from natural earthquakes for engineering design and safety evaluation of bridges and highway facilities and residential buildings and other structures, and (2) potential ground-motion hazards from induced earthquake in the central United States, Kentucky in particular.
Bulletin of the Seismological Society of America, Feb 1, 2018
The work of the original article (Rong et al., 2017) also represents the results of the cooperati... more The work of the original article (Rong et al., 2017) also represents the results of the cooperative research between the
Bulletin of the Seismological Society of America, May 25, 2021
ABSTRACTV S 30 is currently used as a key proxy to parameterize site response in engineering desi... more ABSTRACTV S 30 is currently used as a key proxy to parameterize site response in engineering design and other applications. However, it has been found that VS30 is not an appropriate proxy, because it does not reliably correlate with site response. Therefore, the VS30-based National Earthquake Hazards Reduction Program site maps may not capture regional site responses. In earthquake engineering, site resonance, which can be characterized by the fundamental mode with a site period (Tf) and its associated peak amplification (A0), is the primary site-response concern. Mapping Tf and A0 is thus essential for accurate regional seismic hazard assessment. We developed a 3D shear-wave velocity model for the Jackson Purchase Region of western Kentucky, based on shear-wave velocity profiles interpreted from seismic reflections and refractions, mapped geologic units, and digital-elevation-model datasets. We generated shear-wave velocity profiles at grid points with 500 m spacing from the 3D model and performed 1D linear site-response analyses to obtain Tf and A0, which we then used to construct contour maps for the study area. Our results show that Tf and A0 maps correlate with the characteristics of regional geology in terms of sediment thicknesses and their average shear-wave velocities. We also observed a strong dependency of A0 on bedrock shear-wave velocities. The mapped Tf and A0 are consistent with those estimated from borehole transfer functions and horizontal-to-vertical spectral ratio analyses at broadband and strong-motion stations in the study area. Our analyses also demonstrate that the depth to bedrock (Zb) is correlated to Tf, and the average sediment shear-wave velocity (VS-avg) is correlated to A0. This implies that Zb and VS-avg may be considered as paired proxies to parameterize site resonance in the linear-elastic regime.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Abstract Communities need sound seismic hazard maps for formulating policies such as engineering ... more Abstract Communities need sound seismic hazard maps for formulating policies such as engineering design for buildings and other structures to reduce potential earthquake losses. However, developing scientifically sound seismic hazard maps is challenging because there are large inherent uncertainties and many unknowns (or even sheer ignorance). It is critical for any seismic hazard mapping that these uncertainties be quantified and communicated clearly to engineers, policy makers, and the public. Although probabilistic seismic hazard analysis (PSHA) has been the most widely used method for seismic hazard mapping, the hazard maps produced from PSHA are artifacts and difficult, even impossible, to understand because PSHA is a pure computer model without a sound earth science (physics) basis and its mathematics is simply wrong. The use of PSHA hazard maps has led to overly stringent engineering design and mitigation policies in the central USA, and unsafe engineering design and other mitigation policies in western China. On the other hand, the hazard maps derived from deterministic seismic hazard analysis (DSHA) or Neo-DSHA have a clear physical and statistical meaning and are easy to understand. Deterministic (or scenario) hazard maps have been proven to be effective. Thus, deterministic hazard maps are more appropriate for engineering design and other mitigation policy considerations in the central USA and western China, as well as other areas in the world.
The 10 November 2012 M w 4.2 Perry County earthquake may represent a continuation of the seismica... more The 10 November 2012 M w 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 highquality determinations of the source parameters. The focal mechanism, depth, and proximity of the mainshock to the New York-Alabama magnetic lineament, a subsurface, crustalscale 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.
Over 1.5 kilometers of high-resolution, SH-wave refraction and reflection profiles have been perf... more Over 1.5 kilometers of high-resolution, SH-wave refraction and reflection profiles have been performed in the Madrid Bend area of northwestern Tennessee, approximately 8 km north of Tiptonville, Tennessee, to establish the existence of neo-tectonic, near-surface deformation. The specific area was chosen because of the access it provided to the Tiptonville dome (a Holocene flexure) and the trend of contemporary seismicity within the New Madrid seismic zone (NMSZ). We believed the highest likelihood of near-surface deformation to be over these features. Partially reversed refraction/reflection walk-away tests and common depth point (CDP) seismic profiling, using the non-traditional SH-wave method, have traced antiformal flexure and numerous faults into the late Eocene and Holocene sediments of the Tiptonville dome province of the Lake County uplift (LCU). Vertical displacements exhibited across the faults range from approximately 3 to 30 m. These structures have been interpreted to be neo-tectonic features associated with tensional stresses across the Tiptonville dome.
Bulletin of the Seismological Society of America, Jan 21, 2020
ABSTRACT Site response at many locations in the central and eastern United States is a resonance-... more ABSTRACT Site response at many locations in the central and eastern United States is a resonance-based phenomenon, which site factors based on the VS30 proxy may not reliably capture. Alternative factors, fundamental frequency, f0, and fundamental-mode amplification, A0, calculated from simplified expressions were evaluated against 1D linear, viscoelastic SH-wave full-resonance (FR) site responses. Tests were conducted using S-wave velocity profiles to bedrock at 11 seismic stations. The results showed that simplified expressions approximate FR f0 and A0 at most stations. However, at two sites with intermediate-depth strong impedance contrasts, the simplified approach underestimates A0 by ∼40%. In addition, FR f0 and A0 were compared with weak-motion earthquake S-wave horizontal-to-vertical (H/V) spectral ratios. Measuring f0 and A0 from S-wave H/V for our comparisons required considering multiple observations at the regional scale. The first S-wave H/V peaks occurred between ∼1 and ∼3 Hz at all seven stations in the Illinois basin (IB), which is a much lower f0 than expected for five of these sites. Thus, we used the first S-wave H/V peaks at f>3 Hz at these five sites in our comparisons. The S-wave H/V peaks we evaluated indicate that S-wave H/V can approximate FR f0. However, although the A0 measured from S-wave H/V is positively correlated with theoretical A0, it overestimated FR A0 by more than 40% at all but three sites, indicating that additional study is needed to determine the appropriate use of A0 from S-wave H/V. The observed, unmodeled amplifications between ∼1 and ∼3 Hz are of similar magnitudes as those from the shallower sediment layers at most stations, which highlights the importance of collecting empirical site-response estimations. Furthermore, the amplifications indicate the need to investigate deeper velocity structures in the IB to account for site responses within the frequency band of engineering interest.
The Xianshuihe fault zone consists of left-lateral, segmented strike-slip faults, which produce s... more The Xianshuihe fault zone consists of left-lateral, segmented strike-slip faults, which produce strong and relatively frequent earthquakes, and exposes millions of people to the risk of strong motion and earthquake-induced geologic hazards in Southwest China. Seismicity in this fault zone exhibits typical features of characteristic earthquakes. The stochastic finite-fault model was used to generate time-histories and peak values of strong ground motion at near-fault locations for the characteristic earthquakes. First, the source parameters were determined and verified by comparing them with the simulated time-histories and intensity distribution and observations from the 2014 Kangding earthquake (M w 6.0). Then, scenario-based ground-motion hazard maps were produced from simulated ground motions of characteristic earthquakes. The scenario-based ground-motion hazard maps can be directly compared with historical and future earthquakes in the Xianshuihe fault zone. Scenario-based seismic hazard analysis also has other advantages. Our results show that current design ground motion for the Xianshuihe Fault area is not adequate.
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