bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variability in explosion body-wave magnitudes: An analysis of the RULISON/GASBUGGY anomaly
Authors: Murphy J. R. , Archambeau C. B. 
Published: July 2021

AbstractAn analysis of the RULISON/GASBUGGY mb anomaly is presented which encompasses comparative studies of near-regional, regional, and teleseismic data recorded from these two explosions, as well as theoretical simulation analyses of selected near-regional and teleseismic data sets. Previously proposed explanations for this mb anomaly, such as differences in explosive source coupling and variations in upper mantle attenuation beneath the two test sites, are critically examined and shown to be inconsistent with various aspects of the observed data. However, both long-period and short-period evidence is presented, which indicates that significant tectonic release accompanied the RULISON explosion. It is demonstrated that the short-period, near-regional SH observations from RULISON can be theoretically explained by an explosion-induced tectonic release equivalent to a 250 to 300 bar stress drop at the elastic radius of the explosion. The inferred prestress field is homogeneous to first order and oriented as a pure shear on planes dipping at about 45°, with normal, or dip-slip displacements occurring as a consequence of stress relaxation. Such a tectonic release mechanism would be expected to decrease the associated explosion mb value by more than 0.3 units and, therefore, can provide a quantitative explanation of the observed RULISON/GASBUGGY mb anomaly. We conclude that tectonic release can significantly affect the short-period teleseismic P waves from explosions, at least in cases where the tectonic stress is large and favorably oriented.
Estimation of slowness-dependent source and receiver corrections forP-wave travel times
Authors: Tralli David M. , Johnson Lane R. 
Published: July 2021

AbstractTectonically regionalized tau estimates are used to obtain seismic P-wave travel-time corrections for lateral variations in the Earth's crust and shallow-mantle velocity structure. The corrections, in the form of estimates of tau perturbations, are functions of slowness and are assessed for both the source and receiver regions. The functional form is derived analytically and allows interpretations of causative velocity anomalies. Corrections for both ray path endpoints constrain effects typically assigned solely to the receiver, thereby helping assess systematic errors in hypocentral parameters. Over 1.25 million ISC Bulletin P-wave ray paths are used to estimate tau perturbation functions for seven types of tectonic regions. Particular attention is given to the problem of uniformly sampling all tectonic regions at all propagation depths in the mantle.Estimates of source and receiver tau perturbations are consistently less than 1 sec and show a definite and systematic difference between the travel-time correction functions for oceans and continents. Source tau perturbations are indicative of negative velocity anomalies in the shallow mantle beneath oceanic regions and positive anomalies beneath continental regions and oceanic trenches. Heterogeneity confined to the upper 250 km of the mantle suggests velocity variations within ±5 per cent of the lateral mean over a depth interval of approximately 100 km. Differences between the receiver and source perturbations for a common tectonic region are attributed to variations in the characteristic crustal structure of the region, constrained by the receiver perturbation, and errors in origin time and/or focal depth, determined from the source perturbation. The estimates of perturbation functions therefore suggest systematic regional biases in crustal structure and hypocentral parameters. A less than average crustal thickness in oceanic regions and greater thickness in stable continental regions is indicated. Furthermore, it appears that the origin times of sources in oceanic regions are systematically determined too late and/or focal depths located too shallow, whereas origin times of sources in continental regions are systematically determined too early and/or focal depths located too deep.
Comparison of source scaling relations of eastern and western North American earthquakes
Authors: Somerville P. G. , McLaren J. P. , LeFevre L. V. , Burger R. W. , Helmberger D. V. 
Published: July 2021

AbstractSource scaling relations have been obtained for earthquakes in eastern North America and other continental interiors, and compared with a relation obtained for earthquakes in western North America. The scaling relation for eastern North American earthquakes was constructed from measurements of seismic moment and source duration obtained by the waveform modeling of seismic body waves. The events used include nine events of mbLg magnitude 4.7 to 5.8 that occurred after 1960, and four earlier events with magnitudes between 5.5 and 6.6. The scaling relation for events in other continental interiors was used for comparative purposes and to provide constraints for large magnitudes. Detailed analysis of the uncertainties in the scaling relations has allowed the resolution of two important issues concerning the source scaling of earthquakes in eastern North America. First, the source characteristics of earthquakes in eastern North America and other continental interiors are consistent with constant stress drop scaling, and are inconsistent with nonconstant scaling models such as that of Nuttli (1983). Second, the stress drops of earthquakes in eastern North America and other continental interiors are not significantly different from those of earthquakes in western North America, and have median values of approximately 100 bars. The source parameters of earthquakes in eastern North America are consistent with a single constant stress drop scaling relation, whereas the source parameters of earthquakes in western North America are much more variable and show significant departures from an average scaling relation in which stress drop decreases slightly with seismic moment.
Seismotectonics of the Newport-Inglewood fault zone in the Los Angeles basin, southern California
Authors: Hauksson Egill 
Published: July 2021

AbstractThe Newport-Inglewood fault zone (NIF) strikes northwest along the western margin of the Los Angeles basin in southern California. The seismicity (1973 to 1985) of ML ≧ 2.5 that occurred within a 20-km-wide rectangle centered on the NIF extending from the Santa Monica fault in the north to Newport Beach in the south is analyzed. A simultaneous full inversion scheme (VELEST) is used to invert for hypocentral parameters, two velocity models, and a set of station delays. Arrival time data from three quarry blasts are included to stabilize the inversion. The first velocity model applies to stations located along the rim and outside the Los Angeles basin and is well resolved. It is almost identical to the starting model, which is the model routinely used by the CIT/USGS southern California seismic network for locating local earthquakes. The second velocity model applies to stations located within the Los Angeles basin. It shows significantly lower velocities down to depths of 12 to 16 km, which is consistent with basement of Catalina Schist below the sediments in the western Los Angeles basin. The distribution of relocated hypocenters shows an improved correspondence to mapped surface traces of late Quaternary fault segments of the NIF. A diffuse trend of seismicity is observed along the Inglewood fault from the Dominguez Hills, across the Baldwin Hills to the Santa Monica fault in the north. The seismicity adjacent to Long Beach, however, is offset 4 to 5 km to the east, near the trace of the subsurface Los Alamitos fault. The depth distribution of earthquakes along the NIF shows clustering from 6 to 11 km depth, which is similar to average seismogenic depths in southern California. Thirty-nine single-event focal mechanisms of small earthquakes (1977 to 1985) show mostly strike-slip faulting with some reverse faulting along the north segment (north of Dominguez Hills) and some normal faulting along the south segment (south of Dominguez Hills to Newport Beach). The results of an inversion of the focal mechanism data for orientations of the principal stress axes and their relative magnitudes indicate that the minimum principal stress is vertical along the north segment while the intermediate stress is vertical along the south segment. The maximum principal stress axis is oriented 10° to 25° east of north. Reverse faulting along the north segment indicates that a transition zone of mostly compressive deformation exists between the Los Angeles block and the Central Transverse Ranges.
Velocity structure of Silent Canyon Caldera, Nevada Test Site
Authors: Leonard Michael A. , Johnson Lane R. 
Published: July 2021

Abstract
A laterally averaged, one-dimensional P- and S-wave velocity structure is obtained for Silent Canyon Caldera, located beneath Pahute Mesa at the Nevada Test Site. The velocity models are derived from a linearized damped least-squares travel-time inversion for slowness gradient perturbations. A total of 72 P- and 20 S-wave travel times generated from 13 different explosions, obtained at locations above the caldera, are used in the inversion. The structure is modeled using linear velocity gradients in a series of horizontal layers. The inversion produces a model in which velocity for P waves increases from 1.5 km/sec at the surface to 4.5 km/sec at 2.3 km depth and from 1.0 km/sec at the surface to 2.3 km/sec at 2.0 km depth for S waves. The P- and S-wave models produce travel-time residuals which are typically less than 0.1 and 0.2 sec, respectively, which is within observational error. In an attempt to estimate the degree of lateral velocity variations over which the one-dimensional model averages, waveform data collected above the caldera are examined for indications of a laterally heterogeneous structure.
Strong ground motion in the 1983 Borah Peak, Idaho, earthquake and its aftershocks
Authors: Jackson Suzette M. , Boatwright John 
Published: July 2021

Abstract
Thirteen strong-motion accelerographs sited in a permanent array at the Idaho National Engineering Laboratory (INEL) were the closest instruments to the MS = 7.3 1983 Borah Peak, Idaho, earthquake. They recorded the event at epicentral distances of 90 to 110 km. The peak horizontal accelerations or peak ground accelerations (PGAs) at the basement and free-field sites of the array ranged from 0.022 to 0.078 g. For 2 weeks after the main shock, the U.S. Geological Survey maintained an array of digital seismographs in the epicentral area; these instruments recorded six large aftershocks at epicentral distances of 4 to 45 km. The largest of these aftershocks also triggered four accelerographs in the INEL array. PGAs for the main shock are estimated by two separate analyses. First, the attenuation of the PGAs from the largest aftershock is used to extrapolate the far-field PGA into the near-field, obtaining estimates of 0.54, 0.58, 0.21, and 0.24 g at epicentral distances of 11, 12, 16, and 18 km, respectively. Second, paired recordings for a set of small aftershocks, obtained from a near-field station (U.S. Geological Survey portable instrument) and a far-field station (INEL telemetered station), were used together with an INEL main shock acceleration time history to generate four synthetic accelerograms for a hypothetical recording site 18 km southeast of the main shock. The PGAs measured from these synthetic accelerograms are 0.08, 0.14, 0.15, and 0.23 g.
Investigation ofmbandMSformulas for the Western United States and their impact on theMS/mbdiscriminant
Authors: Denny Marvin D. , Taylor Steven R. , Vergino Eileen S. 
Published: July 2021

AbstractThe impact of regional mb and MS formulas on regional MS/mb discrimination is investigated using a large number of Western United States earthquakes and explosions. Comparison of NEIS mb values with regional mb values shows a systematic error of 1.2. Additionally, a simple analysis of variance shows that the variance of the magnitude estimate is reduced when log(A) replaces log(A/T). These changes, along with a refinement of the distance correction, yield a new regional mb for the Western United States given by mb = log(A) + 2.4 log(Δ) − 3.95 + cj, where A = 0 to peak amplitude in nanometers, Δ is the distance in kilometers, and ci is a station correction. Usage of this formula improves the performance of regional MS/mb discrimination by a factor of 2 to 6.
Effect of lowQsediments and crustalQonLgattenuation in the United States
Authors: Mitchell Brian J. , Hwang H. J. 
Published: July 2021

AbstractQ values for Lg and its coda exhibit significant lateral variations across the United States, some of which correlate with known variations in the thickness of shallow sedimentary layers. The possibility that all variations in Lg attenuation are caused by changes in the thickness of shallow sediments is investigated by computing multi-mode synthetic seismograms for crustal models with various thicknesses of low-Q sediments. Using crustal velocity and Q models obtained in previous studies, and reasonable values for the thicknesses and intrinsic Q values of sediments in several regions, we find that the variation of Lg Q values between the Appalachian and Rocky Mountains can easily be produced by varying accumulations of sandstone and shale of Mesozoic age and younger. By contrast, throughout most of the Western United States, neither the low Lg Q values which have been observed nor the regional variation of those values can be explained by accumulations of low-Q sediments. Instead, their explanation appears to require low and laterally varying values of Q in the crystalline crust.
Effects of observational errors in relating magnitude scales and fitting the gutenberg-richter parameter β
Authors: Bender Bernice 
Published: July 2021

AbstractIn order to use historic earthquakes to estimate future seismicity of a region, the analyst usually first converts earthquake sizes that have been recorded in various ways (e.g., mb, MS, ML, and I0) to a common scale (e.g., mb), by fitting the coefficients ai and bi in an assumed linear relationship mb = ai + bimi between mb and each of the other size measures mi. He then combines mb values (either recorded mb or fitted m^b) for all earthquakes to estimate a Gutenberg-Richter rate parameter, αmb, and distribution parameter, βmb. However, even if magnitude scales are linearly related over some range, when observational errors are present and earthquakes have been incompletely recorded at lower magnitudes or terminate abruptly at some finite mmax, estimates âi, b^i may be highly biased and uncertain. Less biased estimates of b^i can be obtained if only magnitude values in the interior of the range are used in the fitting. Errors in b^i carry over into estimates βmb(i) obtained using magnitudes converted to m^b from mi. This means that even if a large number, N, of mi values are converted to mb values, the variance of β^mb(i) using these magnitudes may depend primarily on the sizes of the observational errors and on n the number, of pairs (mb and mi) used to fit b^i, rather than on N. An estimate βmb(i) may be obtained without converting magnitudes mi to mb by estimating β^i (the distribution parameter for mi) using the N mi values and then setting β^mb(i)=β^i/b^i. Individual estimates 1/βmb(i) for various scales, mi, may be weighted and combined, and then inverted to obtain an estimate of βmb that has a lower variance than does the estimate obtained using all the earthquakes simultaneously. This study particularly considers estimates involving I0, epicentral intensity, because often I0 is the only size recorded for an earthquake. A relatively large range of magnitudes corresponds to a single intensity, making the analysis more complicated for this case.
Attenuation and backscattering from local coda
Authors: Dainty Anton M. , Duckworth Robert M. , Tie An 
Published: July 2021

AbstractCoda decay and excitation for local events were examined at Mammoth Lakes and Morgan Hill, California, Monticello, South Carolina, and New Brunswick, Canada, in the frequency range of 3 to 50 Hz. The single-scattering theory of attenuation and coda generation was used to interpret the data. Coda decay was parameterized by the total apparent turbidity, which is inversely proportional to the conventional coda Q, and the backscattering turbidity, which is proportional to the ratio of the coda power at the time of the direct S and the energy of the direct S pulse. This is a scattering parameterization, since turbidities are cross-sections per unit volume; the term “apparent” is used for the total apparent turbidity because in actuality this parameter contains the effect of anelastic attenuation as well as scattering. For short times (less than 10 sec), the total (apparent) turbidity determined from coda decay was about 0.1 km−1 for all regions, or a Q of about 60 (3 Hz) to 1000 (50 Hz). The backscattering turbidity determined from coda excitation at short times is often larger than the total apparent turbidity and thus indicates strong, multiple scattering in the upper crust, especially for frequencies in the 3- to 10-Hz range. This means that coda Q is not equivalent to direct S Q in this frequency range, since it does not include the full effect of scattering. At times longer than 10 to 15 sec for the codas from Monticello and New Brunswick, the coda energy appeared to be channeled into a horizontally propagating mode such as Lg. This change was seen as a change in decay rate and excitation; the total turbidity for this portion of the coda was lower than for short codas, about 0.01 km−1, indicating less scattering. At Monticello, the conditions for the validity of the single-scattering theory appeared to be satisfied, meaning that coda Q includes the effect of scattering and is a proper measure of the Q of the wave type that makes up the coda—most likely Lg. The backscattering turbidity, which is controlled solely by scattering, and the total apparent turbidity at Monticello both show a minimum around 10 Hz. This correlation between coda excitation and decay indicates that a substantial portion (at least 50 per cent) of coda Q in this case is due to scattering. The evidence for strong scattering observed in other codas indicates that scattering will play an important role in attenuation at those sites also. Codas from California, however, did not show the phenomenon of a change at 10 to 15 sec, indicating either that this mode is not present or that it is more strongly scattered. All of the scattering observed in this study probably occurs in the crust. Reverberation under the station cannot be excluded for most codas, but the existence of two types of coda at Monticello and New Brunswick demonstrates that this cannot be the dominant mechanism at these sites.
Calculation of the inplane Green's functions for a layered viscoelastic solid
Authors: Xu P.-C. , Mal A. K. 
Published: July 2021

Abstract
A method is presented for the accurate and efficient calculation of the dynamic Green's functions for a layered viscoelastic solid under plane strain conditions. The method is based on the classical wavenumber integral representation and a delta matrix formulation of the elastodynamic field. The high efficiency is achieved through the introduction of a new quadrature scheme in which the kernels of the wavenumber integrals are represented by means of polynomials in finite and semi-infinite panels, and the resulting oscillatory integrals are evaluated analytically. The accuracy of the results are controlled through the use of an adaptive procedure whereby the number of panels are increased successively until the desired accuracy is reached, with no previous function evaluations wasted. The computer program currently runs on IBM PCs for all multi-layered structures at all finite frequencies.
On the apparent change in dynamic behavior of a nine-story reinforced concrete building
Authors: Luco J. E. , Trifunac M. D. , Wong H. L. 
Published: July 2021

AbstractApparent changes, over time, of the dynamic behavior of a nine-story reinforced concrete building are examined to determine their plausibility and possible sources. The apparent variations include changes of the resonant frequencies and of the relative contribution of the soil-structure interaction effects during forced vibration tests. Experiments by different researchers on the importance of the soil-structure interaction effects lead to conflicting interpretations of the contribution from the rocking response which differ by factors of 24 and 14 in the transverse and longitudinal directions. These differences are not realistic and may have resulted from errors in the data reduction for the initial experiments. The variations in resonant frequencies are considered to be mainly a result of stiffness degradation of the superstructure as a consequence of the San Fernando earthquake of 1971.
Aftershocks of the 13 December 1982 North Yemen earthquake: Conjugate normal faulting in an extensional setting
Authors: Langer C. J. , Bollinger G. A. , Merghelani H. M. 
Published: July 2021

AbstractThe North Yemen epicentral locale in the southwestern part of the Arabian Peninsula is 200 to 300 km landward from the active rifting of the Red Sea and Sea of Aden. The magnitude 6.0 (MS and mb) main shock of 13 December 1982 locally caused considerable death, injury, and damage and was followed by an extensive aftershock sequence. A 12-day study employing a 10-station portable seismograph network was conducted between 29 December 1982 and 9 January 1983.Hypocentral locations were determined for 230 shocks selected from the thousands of recorded events (duration magnitudes between 1.8 and 4.6). These aftershocks define a source volume that is roughly 20 × 20 × 10 km. From that volume, about half (∼110) of only the best-constrained hypocenters with depths greater than 3 km were selected for detailed analysis. The 110 aftershock data set was divided into subsets according to geographic position (northern and southern) and temporal sequencing (a distinct aftershock sequence late in the monitoring period). A series of composite focal mechanisms show the aftershocks are dip-slip faulting (normal) on planes with north-northwest to northwest strikes and with dips that are variable in amount (∼30° to ∼80°) and direction (southwest and northeast).The strike and extensional nature of these composite focal mechanism solutions are in good agreement with the main shock focal mechanisms, the surficial and bedrock geology of the epicentral area, and the linear surface cracks observed in the field there following the December main shock. We interpret the spatial distribution of our results to describe conjugate faulting episodes associated with north-northwest striking faults.