bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-frequency attenuation by a thin high-velocity layer
Authors: Mellman George R. , Helmberger Donald V. 
Published: September 2021

Abstract
The Cagniard-de Hoop method is used to investigate elastic-wave tunneling through a thin high-velocity layer. The results indicate high-frequency attenuation in the geometric shadow zone. Attenuation is roughly proportional to layer thickness. Comparison of results obtained by omitting the high-velocity layer but using an average Q operator shows that effects of the high-velocity layer are similar to Q effects, with the equivalent Q for a given layer thickness varying as a function of source-receiver distance. These attenuation effects are explained in terms of deformation of the de Hoop contour.
Variations of strong earthquake ground shaking in the Los Angeles area
Authors: Trifunac M. D. , Udwadia F. E. 
Published: September 2021

Abstract
Accelerograms recorded at six stations in the metropolitan Los Angeles area during the Borrego Mountain, 1968, the Lytle Creek, 1970, and the San Fernando, 1971, earthquakes in southern California have been studied. In comparing the ground motions recorded during different earthquakes at each of the six stations and in correlations of these motions recorded at different stations during the same earthquake, those aspects of the analysis which emerge from this study and are relevant for seismic zoning have been emphasized.
It has been found that the patterns of strong ground shaking in this area depend predominantly on the mechanism and the distance of an earthquake source from a recording station and that the local soil conditions played only a minor role in modifying the ground motion at this particular area. It has been shown that gross spectral characteristics of ground motion recorded at various stations can be approximately related by the seismic moment at the low-frequency end and by the stress drop at the high-frequency end.
Near-field observations and source parameters of central California earthquakes
Authors: Johnson Lane R. , McEvilly Thomas V. 
Published: September 2021

abstract
This is a study of source characteristics of 13 earthquakes with magnitudes between 2.4 and 5.1 located near the San Andreas fault in central California. On the basis of hypocentral locations and fault-plane solutions the earthquakes separate into two source groups, one group clearly related to the throughgoing northwest-trending San Andreas fault zone and the other apparently associated with generally north-trending bifurcations such as the Calaveras fault. The basic data consist of broad-band recordings (0.03 to 10 Hz) of these earthquakes at two sites of the San Andreas Geophysical Observatory (SAGO). Epicentral distances range between 2 and 40 km, and maximum ground displacements from 4 to 4000 microns were recorded. The whole-record spectra computed from the seismograms lend themselves to source parameter studies in that they can be interpreted in terms of low-frequency level, corner frequency, and high-frequency slope. Synthetic seismograms have also been used to estimate source parameters in both the time domain and frequency domain, and the results compare favorably with those estimated directly from the spectra. The influences of tilts and nonlinear response of the seismometer were considered in the interpretation of the low frequencies. Seismic source moments estimated from the low-frequency levels of the spectra show a linear dependence on magnitude with a slope slightly greater than 1. The geology at the recording site can contribute an uncertainty factor of at least 3 to the estimated moments. Observed corner frequencies are only weakly dependent on magnitude. Interpreted in terms of source dimension, these corner frequencies imply values of 1 to 2 km for the earthquakes of this study. The corner frequencies may also be interpreted in terms of the rise time source function, yielding values in the range 0.5 to 1.0 sec. The data indicate that the earthquakes of this study are all surprisingly similar in their fundamental source parameters, with only the seismic moment showing a strong dependence on magnitude.
P-wave amplitudes and magnitudes between 10° and 35°
Authors: McMechan George A. , Workman Warren G. 
Published: September 2021

abstract
The observed behavior of P-wave relative amplitudes, as a function of epicentral distance, between 10° and 35°, is controlled primarily by the velocity-depth structure of the upper mantle. P-wave synthetic seismograms calculated by the new quantized ray theory technique are used to determine theoretical log (A/T) versus log Δ curves from a number of upper mantle models. Maximum amplitude arrivals show less model dependence than the first arrivals in the same wave trains, and hence are more consistent magnitude indicators for regions where the upper mantle structure is poorly known. Log (A/T) versus log Δ curves vary considerably, but predictably, from model to model. This model-dependent variation can account for a major part of the large standard deviations usually associated with the calculation of magnitudes from body waves.
Seismotectonic maps of southwest Asia region comprising Eastern Turkey, Caucasus, Persian Plateau, Afghanistan and Hindukush
Authors: Kaila K. L. , Madhava Rao N. , Narain Hari 
Published: September 2021

abstractThree seismic activity maps, the A-value map, the b-value map and the returnperiod map for earthquakes with magnitude 6 and above, have been prepared for the southwest Asia region using the Kaila and Narain (1971) method, and the same are compared with regional tectonics. For the preparation of these maps, a modified relation A = 6.36b - 1.00 has been used instead of the earlier relation where A and b are constants in the cumulative regression curve represented by log N = A − bM. The A-value seismicity map reveals that the Southwest Asia region consists of a number of seismic high zones such as the Caucasus-Abul Samsar high, the Zagros high, the Shahrud-Doruneh high and the Hindukush-West Pakistan high. The Caucasus-Abul Samsar seismic high shows two superimposed trends, one NW-SE which is consistent with the Caucasus tectonic trend and the other NE-SW which is parallel to the Abul Samsar fracture zone. The Zagros seismic high runs in the NW-SE direction almost parallel to the Zagros thrust zone with diversions to the northeast at the two ends. High seismic activity is revealed in the Zagros foothills area rather than the thrust-zone. The Shahrud-Doruneh high shows a NW-SE trend parallel to Kopet Dagh, and, toward the west, it bends down aligning itself almost parallel to the Elburz mountains, thus indicating the possibility of a connection between this high and the Zagros high. The Hindukush-West Pakistan high runs in the NNE-SSW direction consistent with the tectonic trends in this area, indicating the highest seismic activity near the Yasman fracture zone. The b-value seismicity map also reveals the same seismic features as brought out by the A-value map. The b-values obtained by this new method over various regions of southwest Asia agree fairly well with those reported by other workers obtained from earthquake regression curves. The return-period map further brings out the zones of high and low seismic activity which are quite consistent with the A-and the b-value maps, and the regional tectonics.
A simplification in the calculation of motions near a propagating dislocation
Authors: Boatwright John , Boore David M. 
Published: September 2021

abstract
From Haskell's (1969) integral representations for the near-field displacements due to a propagating strike-slip and dip-slip dislocation, a solution is obtained for a dislocation “line source” by an analytic integration in the direction of the fault propagation. This reduces the numerical integration from a surface integral required for the usual evaluation of the near-field motion, to a one-dimensional integration over the fault width. Since the dislocation function modeled here is a Heaviside step function, these results may be extended to any arbitrary source time-function by convolving these displacements with the time derivative of the desired source function.
Seismic source summary for U.S. underground nuclear explosions, 1971-1973
Authors: Springer Donald L. , Kinnaman Ross L. 
Published: September 2021

abstract
A summary of information is presented for all announced U.S. underground nuclear explosions detonated during the 1971-1973 time period. The data include detonation times, locations, and depths of burial, as well as information about shot media and surface collapse (subsidence) phenomena. This summary is an addendum to a previous publication which covered the period 1961-1970, and includes some additions and corrections to that work.
Source dimensions of two deep earthquakes estimated from aftershocks and spectra
Authors: Wyss M. , Shamey L. J. 
Published: September 2021

abstractThe relation the spectral corner frequency and the source dimensions, r(P, S) = c(P, S)β/ƒ0 is tested for two deep earthquakes under the assumption that aftershocks approximately outline the rupture area. It was found that c = 0.37 as proposed by Brune (1970) leads to radii estimates within ±20 per cent of the radii outlined by the aftershocks.
Surface-wave magnitudes of Eurasian earthquakes and explosions
Authors: Nuttli Otto W. , Kim So Gu 
Published: September 2021

abstract
Body-wave magnitudes, mb, and surface-wave magnitudes, MS, were determined for approximately 100 Eurasian events which occurred during the interval August through December 1971. Body-wave magnitudes were determined from 1-sec P waves recorded by WWSSN short-period, vertical-component seismographs at epicentral distances greater than 25°. Surface-wave magnitudes were determined from 20-sec Rayleigh waves recorded by long-period, vertical-component WWSSN and VLPE seismographs. The earthquakes had mb values ranging from 3.6 to 5.7.
Of 96 presumed earthquakes studied, 6 lie in or near the explosion portion of an mb:MS plot. The explosion mb:MS curve was obtained from seven Eurasian events which had mb values ranging from 5.0 to 6.2 and MS values from 3.2 to 5.1. All six anomalous earthquakes were located in the interior of Asia, in Tibet, and in Szechwan and Sinkiang provinces of China. In general, oceanmargin earthquakes were found to have more earthquake-like mb:MS values than those occurring in the continental interior. Neither focal depth nor focal mechanism can explain the anomalous events.
Dependence on the elastic constants of surface deformation due to faulting
Authors: Converse Glenn , Comninou Maria 
Published: September 2021

Abstract
In general, the explicit expressions for surface displacements calculated from dislocation models of faulting in a half-space are restricted to the case λ = μ, where λ and μ are the Lamé elastic constants (e.g., Maruyama, 1964; Press, 1965; Mansinha and Smylie, 1971). It is obviously of some interest to know how the surface fields might be modified by other choices of the elastic constants. In this paper it is shown that the surface displacements depend upon the elastic constants only as linear functions of the Poisson ratio v. The intercepts and slopes of the linear functions, of course, vary with position on the free surface. The surface tilts and strains are also simple functions of the Poisson ratio.
Analysis of seismic response in the city of Las Vegas, Nevada: A preliminary microzonation
Authors: Murphy J. R. , Hewlett R. A. 
Published: September 2021

abstract
Ground motion data recorded at 26 different locations in Las Vegas from six underground nuclear tests have been used to perform a preliminary microzonation of the city. The microzonation results are presented in the form of contour maps of the average observed seismic response throughout the city in 12 different frequency bands covering the period range from 0.16 to 6.0 sec. These data indicate that variations in long-period seismic response of as much as an order of magnitude can be expected at sites only a few kilometers apart in the city. Simple models of surface-wave propagation in the surface layer of alluvium of variable thickness can account for much of the observed variability. However, it appears that surface waves reflected back from the valley boundaries at the base of the surrounding mountain ranges also have a significant effect on the measured response.
On the estimation of seismic detection thresholds
Authors: Ringdal F. 
Published: September 2021

abstract
The incremental detection capability of a seismic station, i.e., the probability of detection as a function of event magnitude, is usually estimated either by using the exponential magnitude-frequency relationship of earthquakes (the recurrence method) or by comparing the station detections to an independent reference system (the direct method). The recurrence method usually yields significantly lower 90 per cent thresholds than the direct method, while a hypothetical “true” threshold would lie between these values. This is explained theoretically as resulting from the global variance of observed signal amplitudes for a given seismic event. A maximum likelihood estimation procedure is developed for the direct method, and approximate confidence limits on the estimated detection thresholds are derived. The two estimation techniques are applied to determine the event detection capability of the NORSAR array for the Japan-Kuriles-Kamchatka region, and the results are related to previously published estimates.
Surface motions due to fault slip in the vertical mode with friction
Authors: Brock L. M. 
Published: September 2021

abstract
Approximations to the wave motions generated on the surface of an elastic half-space by slip in the vertical mode with friction on a fault plane of arbitrary dip are analyzed. The half-space is initially motionless under uniformly distributed tectonic stresses and hydrostatic stresses due to the weight of the material. The resistance to slip obeys the Coulomb model for static and kinetic friction. Slip is triggered along a line parallel to the fault surface trace. The moving edge of the slip zone extends toward the surface with a constant velocity. Homogeneous function techniques are used to derive the stresses and displacements for a general class of related problems as single integrals of analytic functions. The results are easily specialized to obtain approximate expressions for the wave-induced surface displacement and particle velocity components. For various values of the time, dip angle, coefficient of kinetic friction and rate of extension of the slip-zone edge, curves for the surface particle-velocity components are given. This paper will serve as a basis for future work.
A comprehensive study of long-period (20 to 200 seconds) earth noise at the high-gain worldwide seismograph stations
Authors: Murphy Andrew J. , Savino John M. 
Published: September 2021

abstract
The characteristics of long-period (20 to 200 sec) earth noise have been investigated at the 11 high-gain, long-period (HGLP) seismograph stations using as many as 3 years of analog seismograms and digital data from these stations. A major contribution of this study is the significant increase in the number of long-period earth-noise spectra that are available from areas of vastly differing geological and tectonic settings outside the contiguous United States. This information is important to the study of the long-period portion of the spectra of earthquakes and to the discrimination of earthquakes and underground explosions.
A significant feature of earth-noise spectra based on data from all the HGLP stations is a minimum between about 25 and 45 sec. This minimum spectra level is most pronounced at sites with more than 200 m of overburden. The level of earth noise generally recorded by vertical-component seismographs at both the shallow and deep stations is independent of local meteorological conditions if the seismographs are located on competent bedrock and are subject to rigid environmental controls.
The level of earth noise recorded by horizontal component seismographs at HGLP stations, however, is dependent on local meteorological conditions. This dependency decreases with increasing depth of overburden. The decay rate with depth of this horizontal earth noise is such that approximately 150 m of competent overbuiden is usually sufficient to attenuate about 90 per cent of the earth noise caused by local atmospheric conditions.
On viscosity and the inelastic nature of waves in geological media
Authors: Blake Thomas R. , Dienes John K. 
Published: September 2021

abstract
An asymptotic solution for spherical wave propagation in linear viscoelastic solids is compared with particle velocity measurements from underground explosive tests in tuff; the magnitudes of these experimental data are of the order of 5 ×102 cm/sec. The qualitative nature of the theoretical solution is similar to that of the measured velocity time histories. When material and kinematic parameters in the model are specified, good quantitative agreement is obtained with respect to radial attenuation of the magnitudes and radial growth of the wavelengths. Both the phenomenological character of the viscoelastic model and limitations on its applicability are discussed.
Source properties of a Blue MT. Lake earthquake
Authors: Anderson John G. , Fletcher Jon B. 
Published: September 2021

abstract
An accelerogram obtained at Blue Mt. Lake, New York is remarkable for the simplicity of its S-wave pulse. This results from (1) a nearly complete absence of scattering and reflections as second arrivals on the accelerogram, and (2) a very elementary earthquake source. The earthquake identified with this accelerogram had a magnitude mb = 2.2 and a hypocentral distance of about 1 km from the accelerometer. Spectral analysis of the S wave indicates the earthquake had a moment of 8 × 1018 dyne-cm, and a source radius of 20 to 40 m. When the accelerogram is integrated to obtain displacement, there is a step offset of about 5μ associated with a near-field component of the S-wave pulse. The S-wave, including the step offset, can be matched in remarkable detail by a dislocation model with a moment of 8.4 × 1018 dyne-cm.
P-wave spectra of nevada test site events at near and very near distances: Implications for a near-regional body wave-surface wave discriminant
Authors: Peppin William A. 
Published: September 2021

abstractSome 140 P-wave spectra of explosions, earthquakes, and explosion-induced aftershocks, all within the Nevada Test Site, have been computed from wide-band seismic data at close-in (&lt; 30 km) and near-regional (200 to 300 km) distances. Observed near-regional corner frequencies indicate that source corner frequencies of explosions differ little from those of earthquakes of similar magnitude for 3 &lt; ML &lt; 5. Plots of 0.8 to 1.0 Hz Pg spectral amplitude versus 12-sec Rayleigh-wave amplitude show a linear trend with unit slope over three orders of magnitude for explosions; earthquakes fail to be distinguished from explosions on such a plot. These spectra also indicate similar source spectra for explosions in different media (tuff, alluvium, rhyolite) which corroborates Cherry et al. (1973). Close-in spectra of three large explosions indicate that: (1) source corner frequencies of explosions scale with yield in a way significantly different from previously published scaling laws; (2) explosion source spectra in tuff are flat from 0.2 to 1.0 Hz (no overshoot); (3) the far-field source spectrum decays at least as fast as frequency cubed. Taken together, these data indicate that the following factors are not responsible for Peppin and McEvilly's (1974) near-regional discriminant: (a) source dimension, (b) source rise time, or (c) shape of the source spectrum.
Automatic seismic array and network detection
Authors: Wirth M. H. , Blandford R. R. , Shumway R. H. 
Published: September 2021

abstract
The theory of automatic detection at a seismic array by means of an F-statistic is extended to a network of such arrays. The results are generally valid for detection using other statistics. The arrays may have equal or different expected signal-to-noise ratios. Two techniques are discussed: (1) the voting detector in which K out of M arrays must detect; K is determined to be optimum; (2) an incoherent detector which detects on the sum of the subarray detection outputs. For small variation of signal and noise amplitudes between arrays, the detectors are found to be nearly equal in detection capability.
If the standard deviation of log10 (signal/noise) is 0.3, the incoherent detector becomes substantially superior to the voting detector and approaches the capability of a perfect beam of well-correlated signals. This result is in agreement with the few available empirical data.
The Canadian seismic array monitor processing system (cansam)
Authors: Weichert D. H. , Henger M. 
Published: September 2021

abstractAn on-line digital beamforming and detection system has been operating at the Canadian short-period array near Yellowknife since early 1974. The installation followed the renewed recognition of the important contribution this array can make to worldwide detection and location of small seismic events. System design is based on earlier Canadian experience. Daily event detection logs are available in Ottawa via dialed telephone line. Nonlinear beamforming is used to lower the false alarm rate at given detection level, and it is shown to perform as predicted. During the 6 winter and spring months, the detection threshold is mb 4.0 to 4.1 at 50 per cent false alarm rate. During summer and fall, organized surface-wave noise originating on Great Slave Lake raises this level to mb 4.6 to 4.7.
A microearthquake survey in northwest British Columbia and southeast Alaska
Authors: Rogers Garry C. 
Published: September 2021

abstract
In an 81-day period during the summer of 1969 four portable seismographs were operated in northwest British Columbia and southeast Alaska. One hundred and forty microearthquakes were detected. Epicenters were located near the Queen Charlotte-Fairweather fault and the Denali fault. The Chatham Strait fault showed no activity and only a few events were located in the Quaternary volcanic zone of British Columbia. A scattering of microearthquakes through the archipelago and the Coast Range and a concentration in the Glacier Bay region suggest that the seismicity may be more complex than the pattern indicated by the distribution of larger earthquakes. The most numerous seismic events recorded, numbering in the thousands, were low-frequency events emanating from a number of specific areas where large glaciers are located.