Comment on “The 1886 Charleston, South Carolina, earthquake: Relic railroad offset reveals rupture” by Roger Bilham and Susan E Hough
No abstract available.
South Carolina↗
Geology topics
Martin C. Chapman
Publications and source records attributed to Martin C. Chapman.
Preliminary observations of the April 5th, 2024, Mw4.8 New Jersey earthquake
On 5 April 2024, 10:23 a.m. local time, a moment magnitude 4.8 earthquake struck Tewksbury Township, New Jersey, about 65 km west of New York City. Millions of people from Virginia to Maine and beyond felt the ground shaking, resulting in the largest number (>180,000) of U.S. Geological Survey (USGS) “Did You Feel It?” reports of any earthquake. A team deployed by the Geotechnical Extreme Events Reconnaissance Association and the National Institute of Standards and Technology documented structural and nonstructural damage, including substantial damage to a historic masonry building in Lebanon, New Jersey. The USGS National Earthquake Information Center reported a focal depth of about 5 km, consistent with a lack of signal in Interferometric Synthetic Aperture Radar data. The focal mechanism solution is strike slip with a substantial thrust component. Neither mechanism’s nodal plane is parallel to the primary northeast trend of geologic discontinuities and mapped faults in the region, including the Ramapo fault. However, many of the relocated aftershocks, for which locations were augmented by temporary seismic deployments, form a cluster that parallels the general northeast trend of the faults. The aftershocks lie near the Tewksbury fault, north of the Ramapo fault.
New Jersey↗
Sediment thickness map of United States Atlantic and Gulf Coastal Plain Strata, and their influence on earthquake ground motions
With the recent successful accounting of basin depth ground-motion adjustments in seismic hazard analyses for select areas of the western United States, we move toward implementing similar adjustments in the Atlantic and Gulf Coastal Plains by constructing a sediment thickness model and evaluating multiple relevant site amplification models for central and eastern United States seismic hazard analyses. We digitize and combine existing sediment thickness data sets into a composite surface that delineates the base of Cretaceous sediments under the Atlantic Coastal Plain and the base of Mesozoic sediments under the Gulf Coastal Plain. Amplification models dependent on sediment thickness, site natural period, and source-to-site path length are compared with data sets of observed ground motions to evaluate the ability of the new models to improve ground motion estimates. We find that the amplification models can account for observed trends in sediment-thickness and period-dependent residuals, but some tuning is required. For example, the model of Chapman and Guo requires a reference V S 30 , the time-averaged shear-wave velocity within 30 m of the Earth’s surface, for non-Coastal Plain sites, which we estimate to be between about 1 and 2 km/s. Along with our sediment thickness model, we estimate a velocity profile for application to the Harmon et al. site-natural-period-based model in order to best match the Chapman and Guo period dependence for a broad range of sediment thicknesses. The Next Generation of Attenuation models for the eastern United States Gulf Coast path-based adjustment models can also account for seismic attenuation in the Coastal Plain sediments and reduce the standard deviation of total residuals. If enacted in the U.S. Geological Survey National Seismic Hazard Model, these amplification models will reduce predicted short-period (<1 s) and increase predicted long-period (>1 s) ground motions in the Coastal Plains appreciably.
Earthquake Spectra↗
U.S. Geological Survey coastal plain amplification virtual workshop
In early October of 2020, the U.S. Geological Survey (USGS) held a virtual workshop to discuss Gulf and Atlantic Coastal Plains site-response models. Earthquake researchers came together to assess (1) research related to proposed Coastal Plains amplification models and (2) USGS plans for implementing these models. Presentations spanned a broad range of topics from Atlantic and Gulf Coastal Plains geophysical properties including seismic velocity and attenuation, to ground motion amplification models and their impacts on seismic hazard. Interspersed with these presentations were discussions regarding the definition and extent of the Atlantic and Gulf Coastal Plains, potential complexities of wave propagation in the Atlantic and Gulf Coastal Plains, and problems that need to be overcome to implement various proposed site-response models. Based on feedback from this workshop, the USGS working group on Coastal Plain Amplification is considering applying published models that depend on sediment thickness. The working group is also exploring potential application of models that depend on the length of path traversed across the Coastal Plain, including the Gulf Coastal Plain ground-motion model adjustments from the Next Generation Attenuation Relationships for the Eastern United States.
Gulf and Atlantic Coast Plains↗
Sediment thickness and ground motion site amplification along the United States Atlantic and Gulf Coastal Plains
Past and present research on earthquake ground motions along the Atlantic and Gulf Coastal Plains and Mississippi Embayment show significant period-dependent site response that is not presently accounted for in ground motion models. These deviations are strongly correlated with the thickness of Mesozoic and younger syn- and post-rift sediments. With the recent incorporation of deep basin depth measurements in the U.S. Geological Survey National Seismic Hazard Model for select regions in the western United States, we move toward a similar analysis in the greater Coastal Plains region by constructing a sediment thickness model and considering three new site response models conditioned on sediment thickness. As of the preparation of this conference paper, we have performed a preliminary evaluation of the Chapman and Guo model and find that the predicted ratio between pseudo-spectral accelerations for the Coastal Plains relative to the continental interior are broadly consistent with our independent dataset.
Atlantic and Gulf Coastal Plains↗
Amplification of earthquake ground motions in Washington, DC, and implications for hazard assessments in central and eastern North America
The extent of damage in Washington, DC, from the 2011 M w 5.8 Mineral, VA, earthquake was surprising for an epicenter 130 km away; U.S. Geological Survey “Did-You-Feel-It” reports suggest that Atlantic Coastal Plain and other unconsolidated sediments amplified ground motions in the city. We measure this amplification relative to bedrock sites using earthquake signals recorded on a temporary seismometer array. The spectral ratios show strong amplification in the 0.7 to 4 Hz frequency range for sites on sediments. This range overlaps with resonant frequencies of buildings in the city as inferred from their heights, suggesting amplification at frequencies to which many buildings are vulnerable to damage. Our results emphasize that local amplification can raise moderate ground motions to damaging levels in stable continental regions, where low attenuation extends shaking levels over wide areas and unconsolidated deposits on crystalline metamorphic or igneous bedrock can result in strong contrasts in near-surface material properties.
Washington, DC↗
Preface
This book grew out of a topical session on “Central Virginia Earthquakes of 2011: Geology, Geophysics, and Significance for Seismic Hazards in Eastern North America” at the 2012 The Geological Society of America (GSA) Annual Meeting in Charlotte, North Carolina (USA). It also benefitted from related sessions at other meetings. The goal of this volume, The 2011 Mineral, Virginia, Earthquake, and Its Significance for Seismic Hazards in Eastern North America , is to bring together as much information as possible on lessons learned from this rare event. Chapters encompass a wide range of geoscience, engineering, and related studies of this earthquake and its effects from the epicentral area in central Virginia to Washington, D.C., and beyond. The intended audience is a broad spectrum of geoscientists, engineers, and decision makers interested in understanding earthquakes and seismic hazards in eastern North America and other intraplate settings. Chapters by Berti et al. (21), Chapman (2), Costain (8), Davenport et al. (15), Green et al. (9), Heller and Carter (10), Horton et al. (14), Hughes et al. (19), Powars et al. (23), Pratt et al. (16), Roeloffs et al. (7), Shah et al. (17), Stephenson et al. (3), Walsh et al. (18), and Wells et al. (12) are expansions of presentations at the 2012 GSA meeting. The volume also contains chapters from recent studies that were not presented at the GSA meeting, including those by Bobyarchick (22), Burton et al. (20), Dreiling and Mooney (5), Li et al. (11), McNamara et al. (4), Pollitz and Mooney (6), and Shahidi et al. (13). Following an overview and synthesis by the volume editors (1), chapters are arranged under the topical headings “Seismology and Regional Effects,” “Earthquake Damage, Geotechnical, and Engineering Investigations,” “Aftershocks, Geophysical Imaging, and Modeling,” “Geologic Investigations—Epicentral Area,” and “Geologic Investigations— Central Virginia Seismic Zone and Nearby Faults.” We thank the authors for their contributions and the many scientists and engineers who contributed time and expertise in reviewing manuscripts to substantially improve the quality of the volume. These reviewers include Gail Atkinson, Christopher Bailey, Richard Berquist, Kimberly Blisniuk, Paul Bodin, Aaron Bradshaw, Clive Collins, Ariel Conn, Randy Cox, Haitham Dawood, James Dewey, John Ebel, David Fenster, Alexander Gates, Kathleen Haller, Gregory Hancock, Robert Hatcher, William Henika, Paul Hsieh, Steven Jaumé, Jeffrey Kimball, Charles Langston, Jongwon Lee, Andrea Llenos, John McBride, Scott Olson, Michael Oskin, Brent Owens, Gilles Peltzer, Mark Quigley, Dhananjay Ravat, David Saftner, Arthur Snoke, Jamison Steidl, Kevin Stewart, Alice Stieve, Danielle Sumy, Ertugrul Taciroglu, Roy Van Arsdale, Mason Walters, Chiyuen Wang, Yang Wang, Richard Whittecar, Lorraine Wolf, Clint Wood, Liam Wotherspoon, and some anonymous reviewers.
Virginia↗
The 2011 Mineral, Virginia, earthquake and its significance for seismic hazards in eastern North America: overview and synthesis
The 23 August 2011 M w (moment magnitude) 5.7 ± 0.1, Mineral, Virginia, earthquake was the largest and most damaging in the central and eastern United States since the 1886 M w 6.8–7.0, Charleston, South Carolina, earthquake. Seismic data indicate that the earthquake rupture occurred on a southeast-dipping reverse fault and consisted of three subevents that progressed northeastward and updip. U.S. Geological Survey (USGS) "Did You Feel It?" intensity reports from across the eastern United States and southeastern Canada, rockfalls triggered at distances to 245 km, and regional groundwater-level changes are all consistent with efficient propagation of high-frequency seismic waves (∼1 Hz and higher) in eastern North America due to low attenuation. Reported damage included cracked or shifted foundations and broken walls or chimneys, notably in unreinforced masonry, and indicated intensities up to VIII in the epicentral area based on USGS "Did You Feel It?" reports. The earthquake triggered the first automatic shutdown of a U.S. nuclear power plant, located ∼23 km northeast of the main shock epicenter. Although shaking exceeded the plant's design basis earthquake, the actual damage to safety-related structures, systems, and components was superficial. Damage to relatively tall masonry structures 130 km to the northeast in Washington, D.C., was consistent with source directivity, soft-soil ground-motion amplification, and anisotropic wave propagation with lower attenuation parallel to the northeast-trending Appalachian tectonic fabric. The earthquake and aftershocks occurred in crystalline rocks within Paleozoic thrust sheets of the Chopawamsic terrane. The main shock and majority of aftershocks delineated the newly named Quail fault zone in the subsurface, and shallow aftershocks defined outlying faults. The earthquake induced minor liquefaction sand boils, but notably there was no evidence of a surface fault rupture. Recurrence intervals, and evidence for larger earthquakes in the Quaternary in this area, remain important unknowns. This event, along with similar events during historical time, is a reminder that earthquakes of similar or larger magnitude pose a real hazard in eastern North America.
Virginia↗