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The Sichuan basin is an intracontinental basin in central China containing extensive Paleozoic, Mesozoic, and Cenozoic sedimentary sequences of varying thicknesses. We used seismic recordings from 189 regional earthquakes with magnitude Ms 4.0–7.0 occurring from 2010 to 2020 recorded by 22 stations from the China Digital Seismological Observation Network to estimate the kappa values (κ0) in the Sichuan basin using Lg waves and coda waves. The Lg and coda κ0 values agree well with each other and show positive correlation with the thickness of sediments in the basin. The average κ0 for the Sichuan basin is estimated as 0.0475 s, similar to results reported in previous studies. The average estimate of κ0 is 0.06 s for stations in the western part of the basin that are underlain by sediments approximately 8 km thick. The quality factor Q of Lg waves in the crustal waveguide is estimated as Q(f)=335f0.72. We estimated site response in the Sichuan basin from Lg spectral inversion, coda spectral ratios, and Lg horizontal to vertical spectral ratios, respectively, and investigated correlation between the site response values and sediment thickness. Consistent patterns are observed in the three sets of site response, which are clearly dependent on the thickness of sediments. Maximum averaged amplification factors of the sediments occur around 2–4 Hz reaching ∼4.5 for sites overlying 8 km sediments. Stronger attenuation effects are observed at stations lying on thicker sediment columns at frequencies higher than 9.66 Hz. This spatial dependence of low-frequency amplification and high-frequency attenuation should be incorporated in ground-motion prediction models for the Sichuan basin. The results of this study can be applied to sites in the Sichuan basin where the thickness of the sedimentary section exceeds 2 km.

Site response in the Changjiang Delta in eastern China was studied using Lg Fourier amplitude spectra. We used broadband seismograms recorded at 70 stations from 62 earthquakes with magnitude (Ms) varying from 3.5 to 5.0 during 2009–2021. The crustal quality factor Q and site response in the Changjiang Delta were obtained simultaneously from regression of Lg Fourier acceleration amplitude versus frequency. The κ0 of each individual station was subsequently calculated from a regression of the high-frequency site terms versus frequency. The site terms exhibit obvious dependence on sediment thickness in the Changjiang Delta. The site amplification factor reaches ∼7–10 for stations overlying sediments ∼8–9 km thick in the northern Jiangsu basin. The site terms were found to behave consistently as a function of sediment thickness over the frequencies of 0.56–24.86 Hz. Site amplification shows a positive correlation with sediment thickness at lower frequencies (

Three-dimensional P- and S-wave velocity (VP and VS) models are determined for the crust containing the main aftershock cluster of the 2011 Mineral, Virginia, earthquake using local earthquake tomography. The inversion uses a total of 5125 arrivals (2465 P- and 2660 S-wave arrivals) for 324 aftershocks recorded by 12 stations. The inversion volume (22 × 20 × 16 km) is completely contained within the Piedmont Chopawamsic metavolcanic terrane. The models are well resolved in the central portion of the inversion volume in the depth range 1–5 km; good resolution does not extend to the hypocenter depth of the mainshock. Most aftershocks are located within a northeast-trending, southeast-dipping region containing negative VP anomalies, positive VS anomalies, and VP/VS ratios as low as 1.53. These velocity results strongly argue for the presence of quartz-rich rocks, which we attribute to either the presence of a giant quartz vein system or metamorphosed orthoquarzite sandstones originally deposited on the Laurentian passive margin and subsequently incorporated into the Chopawamsic thrust sheets during island arc collision in the Taconic orogeny.

The moment magnitude (M-w) similar to 7 earthquake that struck Charleston, South Carolina, on 31 August 1886 is the largest historical earthquake in the United States east of the Appalachian Mountains. The fault(s) that ruptured during this earthquake has never been conclusively identified, and conflicting fault models have been proposed. Here we interpret reprocessed seismic reflection profiles, reprocessed legacy aeromagnetic data, and newly collected ground penetrating radar (GPR) profiles to delineate faults deforming the Cretaceous and younger Atlantic Coastal Plain (ACP) strata in the epicentral area of the 1886 earthquake. The data show evidence for faults folding or vertically displacing ACP strata, including apparent displacements of near-surface strata (upper similar to 20 m). Aeromagnetic data show several northeast (NE)-trending lineaments, two of which correlate with faults and folds with vertical displacements as great as 55 m on the seismic reflection and radar profiles. ACP strata show only minor thickness changes across these structures, indicating that much of the displacement postdates the shallowest well-imaged ACP strata of Eocene age. Faults imaged on the seismic reflection profiles appear on GPR profiles to displace the erosional surface at the top of the upper Eocene to Oligocene Cooper Group, including where railroad tracks were bent during the 1886 earthquake. Some faults coincide with changes in river trends, bifurcations of river channels, and unusual river meanders that could be related to recent fault motion. In contrast to our interpreted NE fault trends, earthquake locations and some focal mechanisms in the modern seismic zone have been interpreted as defining a nearly north-striking, west-dipping zone of aftershocks from the 1886 earthquake. The relationship between the modern seismicity and the faults we image is therefore enigmatic. However, multiple faults in the area clearly have been active since the Eocene and deform strata in the upper 20 m, providing potential targets for field-based geologic investigations. Published version Public domain – authored by a U.S. government employee

The central and eastern United States (CEUS) is an area of generally low-to-moderate seismic hazard with a number of large cities with high seismic risk, a history of occasional damaging earthquakes, and seismic activity induced by wastewater disposal. Seismic monitoring in the CEUS, which began at the beginning 1900s, has undergone many changes through time. Over the past two decades, broadband digital seismic stations connected by internet communications have become widespread. Modern data processing systems to automatically locate earthquakes and assign event magnitudes in near-real time have become the norm, and, since the inception of the Advanced National Seismic System in 2000, more than 10,000 earthquakes have been located and cataloged. Continuously recorded digital seismic data at 100 samples per second are allowing new avenues of research into earthquake source parameters, ground-motion excitation, and seismic wave propagation. Unfortunately, over the past two decades the number of regional seismic network (RSN) centers has diminished due to consolidations and terminations, as funding has tightened. Nevertheless, the public in different parts of the CEUS still looks to local experts for information when earthquakes take place or when they have questions about earthquakes and seismic hazard. The current RSNs must evolve to encompass the need for local seismic information centers and to serve the needs of present and future research into the causes and effects of CEUS earthquakes.

Oilfield wastewater disposal causes fluid pressure transients that induce earthquakes. Here we show that, in addition to pressure transients related to pumping, there are pressure transients caused by density differences between the wastewater and host rock fluids. In northern Oklahoma, this effect caused earthquakes to migrate downward at ~0.5 km per year during a period of high-rate injections. Following substantial injection rate reductions, the downward earthquake migration rate slowed to ~0.1 km per year. Our model of this scenario shows that the density-driven pressure front migrates downward at comparable rates. This effect may locally increase fluid pressure below injection wells for 10+ years after substantial injection rate reductions. We also show that in north-central Oklahoma the relative proportion of high-magnitude earthquakes increases at 8+ km depth. Thus, our study implies that, following injection rate reductions, the frequency of high-magnitude earthquakes may decay more slowly than the overall earthquake rate., Oilfield wastewater is commonly discarded by pumping it into deep geologic formations, but this process is now known to cause earthquakes. Here, he authors show that high-density oilfield wastewater may sink deeper in the Earth’s crust than previously considered possible, thus increasing fluid pressure and inducing earthquakes for years after injection rates decline.

A decade of study into the Virginia earthquake that damaged D.C. and reverberated up and down the Atlantic coast in 2011 has shed light on rare, but risk-laden, seismicity in eastern North America.

We used our previously published Lg-wave spectral ratio model to develop a model of pseudospectral acceleration (PSA) response ratios at sites in the Atlantic and Gulf Coastal Plain, relative to a reference site condition defined as the mean response for site locations outside the Coastal Plain. The model is strongly dependent on sediment thickness. The results of this study can be used to predict PSA response, for linear behavior, at sites in the Atlantic or Gulf Coastal Plain with a known thickness of Coastal Plain sediment, given a ground-motion model for reference site conditions outside the Coastal Plain region of the central and eastern United States.

Background The aim of the BSP090 project is the establishment of European Pharmacopoeia Chemical Reference Substances (CRSs) in combination with corresponding standard ELISA methods for quantification of major allergens in allergen products. Here, we present data of a Phl p 5-specific sandwich ELISA that proved suitable for the quantification of Phl p 5, one of the major Timothy grass (Phleum pratense) pollen allergens. Methods A Phl p 5-specific ELISA system was assessed with respect to accuracy, precision, inter-assay (within laboratory) and inter-laboratory variations, in a ring trial including 14 laboratories in Europe and the USA. Model samples containing recombinant Phl p 5a CRS as well as native grass pollen extracts were analysed. Each participant was instructed to perform at least one preliminary assay to familiarise with the protocol, followed by three independent assays. Results The candidate standard ELISA proved suitable to quantify recombinant and native Phl p 5 with satisfactory precision (93% of results within ±30% acceptance range). Inter-assay variation (max. GCV 24%) and especially inter-laboratory variation (max. GCV 13%) showed conclusive results. When assessing accuracy by means of recovery of recombinant spikes from a grass pollen extract matrix, similarly satisfactory spike recovery results were observed for the two spikes with higher concentrations (all within ±30% acceptance range), whereas recovery of the lowest concentration spike was slightly poorer with mean results of six laboratories exceeding acceptance range. Conclusions Based on the collaborative study results, the assessed Phl p 5-specific immunoassay is appropriate to be proposed as European Pharmacopoeia standard method.

The Mw 5.8 earthquake that occurred in Louisa County, Virginia, on 23 August 2011 provided an opportunity to record with several “high density” seismic arrays, in addition to traditional, sparse temporary seismic networks. Traditional aftershock networks consist of a few dozen stations spread over tens of kilometers. As a result, the recorded seismic waveforms suffer from spatial aliasing that is so severe that many types of waveform processing are not applicable. Here we report the results of recording with a large number of oil industry-type instruments deployed at a spacing that is an order of magnitude closer than in traditional deployments. The objective was to image subsurface structure with array methods, using the aftershocks as sources. The dense array recorded continuously for 12 days and consisted of 172 vertical component seismometers that were placed at 200–400 m and a 60 km long three-component regional profile with stations every 2 km. We demonstrate how processing techniques from Vertical Seismic Profiling can produce high-resolution 3-D reflection images of structure beneath the array. These images display reflectivity that correlates with that observed on a nearby deep reflection survey collected by the U.S. Geological Survey. Of particular interest is a strong reflector imaged across multiple profiles. Our analysis demonstrates how a surface array of seismometers can provide 3-D images of structure using microearthquake sources when wavefields are sampled sufficiently densely.

We used aftershocks of the 2011 Mineral, Virginia, earthquake to study geometrical spreading at hypocentral distances less than 60 km in the central Virginia seismic zone. Sixty‐nine aftershocks, occurring from 25 August 2011 through 24 December 2011, provided the data. We used the coda‐normalization method to estimate the attenuation coefficient associated with geometrical spreading. We filtered the time‐domain signals in several octave‐wide frequency bands and examined attenuation of peak S ‐wave amplitude in the 1.0–30.0 Hz frequency range. Amplitude was assumed to decrease as a function of hypocenter distance R according to R − γ . The coefficient of attenuation γ was examined for the three‐component S ‐wave amplitudes, with corrections for SH and SV radiation patterns. We observed no systematic frequency dependence of γ . The coefficient of attenuation for the radial and transverse components, assuming infinite quality factor Q , derived as a weighted mean over the entire range of frequencies (1–30 Hz), are both 1.51±0.05. The weighted mean value of the attenuation coefficient on the vertical component over the same range of frequencies is 1.45±0.05, slightly less than for the horizontal components. We corrected the data assuming three Q models. The estimated geometrical spreading coefficients are in the 1.30–1.46 range, depending on the assumed Q model and component, which is only slightly less than the estimates of γ determined assuming infinite Q . The estimated attenuation coefficients differ significantly from the value of 1.0 expected for a whole space. The results for the horizontal components are in agreement with previous full‐wavefield modeling. However, the observed vertical‐component attenuation is substantially less than that predicted by the synthetics. The depths of the earthquakes are less than 8 km, so these results may not be representative of geometrical spreading in parts of eastern North America where earthquakes occur at greater depths. Online Material: Table of earthquake hypocenters and focal mechanisms.

The southern United States experienced extensional tectonics during the early Mesozoic development of the Gulf of Mexico and subsequent accumulation of up to 12 km of marine sediment. Few seismic stations have operated in the Gulf Coastal Plain for extended periods of time, and data for constraining ground‐motion prediction models are sparse. Previous studies found that the region differs from other parts of eastern North America in terms of Lg attenuation. The Earthscope Transportable Array was in the south‐central United States in 2010–2012, during a time of increased seismicity. That circumstance provided data for investigating Lg propagation. Sixteen earthquakes with magnitudes in the 3.2–5.6 range occurred in Oklahoma, Arkansas, and Texas and were recorded to distances of 1000 km. Stations in the coastal plain of Texas, Arkansas, Louisiana, and Mississippi exhibit strong attenuation of the Lg phase, compared with stations located to the north in the Ouachita orogenic belt and cratonic platform. Q associated with the crustal waveguide underlying the Gulf Coastal Plain was estimated as Q =365 f 0.62. However, Lg blockage due to crustal thinning and anelastic attenuation due to the presence of several kilometers of sedimentary deposits occurs near the Gulf Coast. The average κ value south of latitude 33° N is 96±10 ms. A remarkable linear correlation exists between the attenuation parameter κ and the thickness of post‐Jurassic sediments in the study region, such that stations near the coast of Texas, Louisiana, and Mississippi, which overlie ∼12 km of sediments, exhibit values of κ ∼160 ms. This strong spatial dependence of attenuation has important implications and should be incorporated in the development of ground‐motion prediction models using the approach suggested here. Online Material: Figures showing maps of regression residuals and receiver terms for 12 frequency bands.

Rationale: Individuals with asthma may be at higher risk of becoming severely ill from COVID-19 which targets the respiratory tract and may cause asthma exacerbations. Serological testing can be useful to assess the true spread of COVID-19 and help protect vulnerable individuals. The SARS-CoV-2 spike and nucleocapsid proteins are the primary viral antigens against which antibodies are raised. We developed an efficient method for production of select SARS-CoV-2 proteins in E. coli to facilitate the development of diagnostics, research, and drug discovery. Methods: SARS-CoV-2 Spike-RBD, full-length Nucleocapsid, and Nucleocapsid RNA binding domain (BD), were expressed in E. coli under IPTG induction. The proteins were purified using multi-step chromatography techniques. The purity of the SARS-CoV-2 proteins was assessed by LC-MS/MS, and their IgG reactivity tested using COVID-19 positive patients’ sera by ELISA. Results: The Spike-RBD and Nucleocapsid proteins were expressed with high yields. The purified proteins had a relative abundance of >95% as assessed by LC-MS/MS with only trace contamination of host cell proteins. All three proteins showed high IgG reactivity (titers >1/10,000) against COVID-19 sera (n=50), with Spike-RBD and Nucleocapsid RNA-BD exhibiting the highest sensitivity. Conclusions: Production of high quality SARS-CoV-2 proteins is feasible in E.coli and the purified proteins will provide useful tools to study the immune responses involved in COVID-19 including antibody and T cell responses, epitope mapping, diagnostics and drug discovery.

An eight‐station seismic network was installed in August 2011 in the epicentral area of the 1886 Charleston, South Carolina, earthquake, within and near the town of Summerville. The network operated for one year and located 134 earthquakes with duration magnitudes ranging from −1.8 to 2.6. The earthquakes occurred in a tabular zone striking ∼N186°E, with dip of about 43° to the west. The focal depths range from 13 km to the top of the early Mesozoic section at a depth ∼1 km. The dimensions of the seismic zone are ∼23 km along strike and 15 km down‐dip. Many of the earthquakes are concentrated in the 2–6.5 km depth range, near shallow faults imaged on seismic‐reflection profiles adjacent to the Ashley River. Our hypocenter relocations of 228 earthquakes occurring in the period 1977–2005 are consistent with the results obtained from the recent one‐year station deployment. The 48 well‐constrained focal mechanisms derived from the one‐year deployment are predominantly reverse motion, and ∼30% exhibit north–south‐trending nodal planes consistent with the orientation of the seismic zone. The seismicity near Summerville has characteristics in common with the aftershock sequence of the 23 August 2011 Mineral, Virginia, earthquake. We interpret these results to indicate that the modern seismicity is the lingering aftershock sequence of the 1886 shock and that the mainshock occurred on a south‐striking, west‐dipping fault plane with predominantly reverse motion, possibly with a component of right‐lateral strike‐slip. Most moment release probably occurred at depths greater than 6 km. Online Material: Tables listing hypocenters and focal mechanisms, and an animation showing hypocenter profiles oriented along different azimuths.

The aftershocks of the 23 August 2011 M w 5.7 Mineral, Virginia, earthquake were recorded by 36 temporary stations installed by several institutions. We located 3960 aftershocks from 25 August 2011 through 31 December 2011. A subset of 1666 aftershocks resolves details of the hypocenter distribution. We determined 393 focal mechanism solutions. Aftershocks near the mainshock define a previously recognized tabular cluster with orientation similar to a mainshock nodal plane; other aftershocks occurred 10–20 km to the northeast. A large percentage of the aftershocks occurred in regions of positive Coulomb static stress change, and ∼80% of the focal mechanism nodal planes were brought closer to failure. However, the aftershock distribution near the mainshock appears to have been influenced strongly by rupture directivity. Aftershocks at depths less than 4 km exhibit reverse mechanisms with north‐northwest‐trending nodal planes. Most focal mechanisms at depths greater than 6 km are similar to the mainshock, with north‐northeast‐trending nodal planes. A concentration of aftershocks in the 4–6 km depth range near the mainshock are mostly of reverse type but display a 90° range of nodal‐plane trend. Those events appear to outline the periphery of mainshock rupture, where positive Coulomb stress transfer is largest. The focal mechanisms of aftershocks at depths less than 4 km and those greater than 6 km, along with the mainshock, point to the possibility of a depth‐dependent stress field prior to the occurrence of the mainshock. Analysis of earthquake occurrence using a new magnitude scale () indicates a Gutenberg–Richer law b ‐value of 0.864 and an Omori law p ‐value of 1.085, indicative of a typical aftershock sequence. Online Material: Catalogs of aftershock location, magnitude, and focal mechanisms.

The focus of this study is to determine the frequency-dependent quality factor function Qffor the Caribbean region. The analysis considers the Lg portion of 2685 three-component waveforms. Waveforms are selected from 116 earthquakes that occurred between 2006 and 2013 with moment magnitude Mw ranging from 4.6 to 7.0. Spectral amplitudes over 12 distinct passbands from 0.1 to 12.8 Hz are calcu- lated only for waveforms with a signal-to-noise ratio of 5 or better. In the regression model, the vertical component and the geometric mean of two horizontal components are used to estimate Qf � . A geometrical spreading function with spectral amplitude decay of R �0:5 is used for distances beyond 100 km. The following quality factor functions for the assumed geometrical spreading are obtained: Q H � 310f 0:54 for the horizontal components, and Q V � 235f 0:65 for the vertical components.

Ground shaking due to earthquakes in the eastern United States (EUS) is felt at significantly greater distances than in the western United States (WUS) and for some earthquakes it has been shown to display a strong preferential direction. Shaking intensity variation can be due to propagation path effects, source directivity, and/or site amplification. In this paper, we use S and Lg waves recorded from the 2011 central Virginia earthquake and aftershock sequence, in the Central Virginia Seismic Zone, to quantify attenuation as frequency‐dependent Q ( f ). In support of observations based on shaking intensity, we observe high Q values in the EUS relative to previous studies in the WUS with especially efficient propagation along the structural trend of the Appalachian mountains. Our analysis of Q ( f ) quantifies the path effects of the northeast‐trending felt distribution previously inferred from the U.S. Geological Survey (USGS) “Did You Feel It” data, historic intensity data, and the asymmetrical distribution of rockfalls and landslides.

The Mw 5.8 earthquake of 23 August 2011 (17:51:04 UTC) (moment, M0 5:7 × 10 17 N·m) occurred near Mineral, Virginia, within the central Virginia seis- mic zone and was felt by more people than any other earthquake in United States history. The U.S. Geological Survey (USGS) received 148,638 felt reports from 31 states and 4 Canadian provinces. The USGS PAGER system estimates as many as 120,000 people were exposed to shaking intensity levels of IV and greater, with approximately 10,000 exposed to shaking as high as intensity VIII. Both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast- striking reverse fault that nucleated at a depth of approximately 7 2 km. The distri- bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western United States (Horton and Williams, 2012). Near- source and far-field damage reports, which extend as far away as Washington, D.C., (135 km away) and Baltimore, Maryland, (200 km away) are consistent with an earthquake of this size and depth in the eastern United States (EUS). Within the first few days following the earthquake, several government and aca- demic institutions installed 36 portable seismograph stations in the epicentral region, making this among the best-recorded aftershock sequences in the EUS. Based on modeling of these data, we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry, area of rupture, and observations of the aftershock sequence mag- nitude-frequency and temporal distribution. The observed slope of the magnitude- frequency curve or b-value for the aftershock sequence is consistent with previous EUS studies (b 0:75), suggesting that most of the accumulated strain was released by the mainshock. The aftershocks define a rupture that extends between approxi- mately 2-8 km in depth and 8-10 km along the strike of the fault plane. Best-fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes N36°E and dips to the east-southeast at 49.5°. Moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations, both indicating reverse slip along a northeast-southwest striking southeast- dipping fault plane.

The 23 August 2011 M w 5.7 Virginia earthquake was studied using local and teleseismic recordings. The earthquake was a shallow reverse rupture in the central Virginia seismic zone. The epicenter was at 37.905° N, 77.975° W, with focal depth 8.0 km. A few local stations recorded both the mainshock and several of the larger aftershocks. This allowed location of the mainshock epicenter relative to the accurate locations of aftershocks recorded by a temporary local deployment of stations. The aftershocks define a planar zone oriented in agreement with the mainshock focal mechanism nodal plane. The mainshock focal depth was determined by comparing teleseismic waveforms with synthetics. Local and teleseismic recordings show evidence of a complex rupture, and were used to locate two large subevents relative to a small initial subevent. The initial slip episode had moment of roughly , and was followed 0.75 s later by a subevent with a moment of approximately that amounted to approximately 60% of the total moment release. A third subevent with moment approximately occurred 1.57 s after rupture initiation. The mainshock rupture occurred at the base of the early aftershock zone. Rupture initiated near the southwestern corner of the aftershock zone and proceeded to the northeast along strike and up‐dip. The three subevents may have involved a small fault area: the estimated distance between the initial and final subevent is only 2.0 km. However, the total rise time of the earthquake was comparatively large. The estimated distance between the subevents and the origin time difference between subevents suggests a slow rupture velocity of 1.3–1.7 km/s. This was a consequence of the rupture being comprised of two short‐duration energetic slip events that were well separated in time along with a small, possibly low stress‐drop, initiation event.

Horizontally layered velocity models were used with point‐source and finite‐fault sources to investigate geometrical spreading and the relative amplitudes of vertical and horizontal ground acceleration within 120 km of the source. Full‐wave‐field simulations were done for a range of focal depths and for strike‐slip and reverse focal mechanisms. The attenuation of the geometric mean of randomly oriented horizontal‐component maximum acceleration amplitudes, averaged over all azimuths, significantly exceeds the theoretical geometrical spreading for far‐field body waves in a homogeneous whole space for hypocentral distances less than approximately 60 km. The behavior of the vertical component is different from the horizontal: vertical attenuation near the epicenter is greater and is more dependent on source mechanism and depth. Because of the rapid near‐source decay of the direct S wave, reflections from the mid‐lower crust and Moho control the maximum amplitude of the vertical‐component acceleration in the 60–120‐km hypocenter distance range, resulting in a flattening of the vertical amplitude‐distance relation. Near‐source vertical maximum amplitudes averaged over all source–receiver azimuths tend to be less than the geometric mean horizontal amplitude for strike‐slip focal mechanisms, but, near the source for reverse faults, the azimuthally averaged vertical‐component amplitude exceeds that of the geometric mean horizontal. The modeling indicates that similar vertical‐ and horizontal‐component geometrical spreading and approximately constant horizontal/vertical amplitude ratios observed in connection with the Lg phase at distances greater than approximately 100 km in eastern North America may not hold at smaller distances. Ground‐motion prediction models for the vertical component near the source may need to incorporate strong geometrical spreading and dependence on radiation pattern.

The seismic design of structures sometimes necessitates the use of synthetic strong ground motion time histories (European Committee for Standardization 2003; International Code Council 2000). Toward this end, the stochastic method with a point-source representation of the seismic source is a fast and efficient way to generate synthetic time histories ( e.g. , Boore 2003). While other modeling procedures may be more refined and physically realistic ( e.g. , full finite-fault simulations), they generally require a larger number of input parameters for which calibration relations do not exist (see Douglas and Aochi 2008, and references therein). Even for well-recorded earthquakes, these parameters are difficult to develop calibration relations for because of (1) the observed variability in the results from earthquake source process inversion and its dependence on available data ( e.g. , Custodio et al. 2005) and (2) the overall lack of confidence in even the best estimates of the parameters controlling fault rupture (Monelli and Mai 2008; e.g. , Monelli et al. 2009). The simple seismological models also have advantages over empirical ground motion predictive equations (GMPE) (Abrahamson and Shedlock 1997; Power et al. 2008), although the forms of the source, path, and site functions in the simple seismological models may be somewhat less flexible than empirical GMPEs when trying to fit existing data. Seismological models can provide information on the physical nature of the parameters controlling the strong motion while the GMPEs cannot ( e.g. , Boore 2003; Olafsson et al. 2001; R. Sigbjornsson and Ambraseys 2003). Moreover, despite the increase in strong motion recordings over the last couple of decades, and presumably the corresponding increase in knowledge, there are still considerable differences among the median ground motions estimated using the various GMPEs. These differences are a measure of epistemic uncertainty and have not been …

The study focuses on evidence of Cenozoic faulting in the epicentral area of the 1886 Charleston, South Carolina, earthquake and its connection with Mesozoic structure. The seismic data consist of several reflection profiles collected near Summerville, South Carolina, in the period 1975–1983. Reprocessing of the data reveals an extensive early Mesozoic extensional basin, approximately 20 km in width, between Summerville and Charleston. The basin is delineated by the geometry of reflections that image early Mesozoic volcanic and sedimentary rocks and by positive magnetic and gravity anomalies. Cenozoic compressional reactivation of Mesozoic extensional faults is imaged in the interior of the basin. The northwestern boundary of the basin is marked by a sharp gradient in the magnetic field. Folded Cretaceous and Tertiary Atlantic Coastal Plain sediments in association with diffractions and truncated reflections from the early Mesozoic section at four locations along this magnetic gradient indicate that the northwestern basin boundary is faulted. Instrumentally located earthquakes are clustered at the location of the faults imaged in the interior of the basin and in proximity to the northwestern basin margin. Modeling of magnetic and gravity data indicates that the upper crust beneath the seismically imaged structural basin is composed largely of mafic rocks to a depth of at least 4 km. We propose that the Charleston earthquake occurred due to compressional reactivation of a Mesozoic fault in a localized zone of intense early Mesozoic continental rifting.

The study compares the capabilities of modern short-period seismograph systems with those using broadband sensors. The results indicate that dual-gain recording using 1-Hz seismometers will capture essentially all of the available information in the seismic wavefield generated by moderate magnitude shocks ( M 4.0–6.0) at regional distances, with dynamic range sufficient to record on-scale a magnitude 6.0 event at approximately 55 km. Short-period instrument operation in seismically active areas remains an effective means of collecting weak-motion data for basic seismological research relevant to public safety in the eastern United States.

A seismic reflection profile collected in 1981 southeast of Summerville, South Carolina, was reprocessed to investigate the recent observation of unusual features. The reprocessing included geometrical spreading and attenuation correction, minimum-phase filtering, and spiking deconvolution, which led to improved velocity analysis and residual static correction. The result gives an improved image of the shallow crust in the epicentral area of the 1886 Charleston earthquake. There is clear evidence of a down-to-the-east steeply dipping fault with approximately 200 m of vertical offset, displacing lower Mesozoic sedimentary and volcanic rocks. Diffraction from fault edges is responsible for the observation of unusual events with abnormal move-out, which led to the discovery of the faulting. The overlying Cretaceous and Tertiary sedimentary section shows approximately 10 m of reverse up-to-the-east displacement, resolved by the data to within 100 m of the ground surface. Two other near-vertical faults with down-to-the east offset of lower Mesozoic units are inferred from the data immediately to the northwest of the major fault. The locality is on the north side of the Ashley River, near the place known as Gregg’s Landing, and it coincides with the epicenters of modern seismic activity and maximum shaking effects documented in 1886. The Charleston earthquake was very likely associated with this faulting.

The seismic quality factor Q for P waves in Atlantic Coastal Plain sediments is estimated using data from the 2004 U.S. Geological Survey seismic survey in eastern Virginia. The estimates are based on spectral ratios derived from reflections and sediment-guided P waves in Late Cretaceous and Tertiary sediments within the annular trough of the Late Eocene Chesapeake Bay impact structure. The estimates of Q for the frequency range of 10–150 Hz are from 75 to 100, with the best estimate of 80 based on multichannel stacking of spectral ratios from receivers in the offset range of 200–2000 m. This result is approximately a factor of 2 larger than the results previously reported for the Charleston, South Carolina, area, and it is approximately one-half of that recently reported for the Mississippi Embayment.