bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure of the crust and upper mantle in the ALPS from the phase velocity of Rayleigh waves
Authors: Knopoff L. , Mueller S. , Pilant W. L. 
Published: July 2021

Abstract
The phase velocity method has been applied to the problem of the determination of the crust and upper mantle under the western Alpine crest and in the Alpine foreland to the north. An extensive data processing package has been designed so that Fourier analysis is applied to the determination of phase velocities, rather than the more usual peak-and-trough method. Effects of contamination by multipath interference, manifested in beats, can be minimized. Advantage is made of apparent azimuthal variations in phase velocity to yield a further refinement in the method whereby the tripartite results are assigned to discrete lines in the network rather than to the area swept out by the wave front.
The results show that a well-developed low-velocity channel for S is found throughout the region with a velocity of S in the channel of 4.2 km/sec. The top of the channel is at about 80 km depth. A new analysis of P-wave data shows a likely horizon for reflections at 220 km; this is taken to be the depth of the lower boundary to the channel.
The mean P-wave velocity in the lower crust is at least as high as 6.7 km/sec. The crustal and upper mantle structure vary significantly over relatively short distances. The Mohorovičić discontinuity is deepest under the crest of the Alps and shoals to the north and west; a well developed root has been found.
Seismicity, tectonism, and surface faulting in the western United States during historic time
Authors: Ryall Alan , Slemmons David B. , Gedney Larry D. 
Published: July 2021

AbstractMaps of tectonic flux are presented for the conterminous United States west of longitude 109°W, for periods of time before and after 1932, and for the entire historic period through 1961. The most active continuous seismic zone in this region during historic time extended over 750 km, from a point off the California coast near Ventura to Winnemucca in north-central Nevada. Although this zone is characterized by a discontinuous line of historic surface faulting, it is neither sharply defined by, nor closely related to structures along its path that are generally considered to be the major tectonic elements of the region.The broad areal extent of this, and five other active zones, suggests that the tectonic processes causing earthquakes and surface faulting in the western United States are distributed over broad regions, and are not confined to geologic or physiographic provinces.Seismicity maps for different periods indicate that seismic activity in some areas has shifted with time. Within major seismic zones, gaps in the seismicity pattern are filled in by successive large earthquakes.Recurrence curves support a high level of activity for the Ventura-Winnemucca zone, and they indicate a lower rate of activity for the San Andreas fault zone than for other areas in the region studied. Recurrence curves for the central California area indicate that the rate of activity in a given region may remain practically constant over periods at least as long as a century, whether or not large earthquakes occur in the region during those periods.There appears to be a general correlation between observed shear or slippage, and the seismicity of any given region.Based on these results, it is proposed that, where historic faulting has occurred in areas with little or no historic seismic activity, such faulting is due to the propagation of fractures into the inactive areas from adjoining seismic zones.
The effect of boundaries on wave propagation in a liquid-filled porous solid: X. Transmission through a stratified medium
Authors: Deresiewicz H. , Levy A. 
Published: July 2021

abstract
Reflection and transmission coefficients are calculated for the propagation of stress-waves through a system of porous layers separating two porous half-spaces. In order to facilitate computations attention is confined to normally incident disturbances. For the technically important case of materials having small pore size compact recursion formulas are deduced and from these several interesting phenomena can be predicted.
Static and dynamic characteristics of composite structures
Authors: Medearis Kenneth 
Published: July 2021

abstract
The results of a theoretical and experimental investigation regarding the static and dynamic characteristics of shear walls are described. Solutions were obtained for the natural frequencies, mode shapes, and response quantities for an appropriate mathematical model, consisting of a distributed mass shear panel having a concentrated roof load mass at its top. Damping for such a structure may be represented in terms of an experimentally determined equivalent viscous damping ratio, veq. Using numerical analysis techniques, appropriate equations were derived and programmed, and a digital computer used to obtain the desired response quantitites resulting from either harmonic or arbitrary forcing functions. The 1940 El Centro earthquake, N-S component ground accelerations were utilized for most of the latter calculations. Using experimentally obtained static-cyclic load-deflection curves, values of veq were found to average 0.08-0.10 for low design-type loads, a range which was further verified by vibration generator and “snap” test dynamic testing. It was thus deemed satisfactory to recommend constant damping ratios of 0.07-0.08 for response calculations. Numerical accuracy of the computer solutions was investigated, with it being noted the acceleration values provided a good criterion for stability of solutions. Being least accurate because of the numerical procedure used, the accelerations always became unstable at a time prior to that of the displacements, thus giving a simple check as to the time span of correct solutions. Another effective procedure simply involved making two computer runs with the same input data, but different time increments, and then comparing results. If results were basically the same, the larger time increment was adequate; otherwise, another run was made with an even smaller time increment, answers compared, etc., until results essentially agreed.
The Alaska earthquake of 28 March 1964: A complex multiple rupture
Authors: Wyss Max , Brune James N. 
Published: July 2021

abstract
The seismograms of the Alaskan earthquake of 28 March 1964 are characterized by multiple P-phases not predicted by the travel-time curves.
Seismograms with low magnifications from 80 stations covering distances from 40° to 90° and a wide range of azimuths were analyzed. The character of the P-wave portion of the seismograms is interpreted in terms of an approximate multiple-event source mechanism where the propagating rupture triggers larger distinct events. Six events were located using the Gutenberg sine-curve method. The times after the initial origin time were 9, 19, 28, 29, 44 and 72 sec respectively, and the events were located 35, 66, 89, 93, 165 and 250 km away from the initial epicenter. Dividing the distance by the delay-time gives an average rupture velocity of 3.5 km/sec.
Excitation of mantle Rayleigh waves of period 100 seconds as a function of magnitude
Authors: Brune James N. , King Chi-Yu 
Published: July 2021

Abstract
The excitation of mantle Rayleigh waves of 100 seconds period as a function of magnitude is studied using data from 91 earthquakes in the magnitude range 5.0 to 8.9. The data were recorded on a wide variety of instruments including Milne-Shaw horizontal pendulums and modern long-period high-gain inertial seismographs. The larger earthquakes studied range in time from 1923 to 1964. Mantle Rayleigh wave amplitudes are corrected to a distance of 90° and plotted as a function of surface wave magnitude. The data are compared with theoretical curves based on a moving source model and two statistical models discussed by Aki. It is concluded that for large earthquakes the source may be approximated by a point couple which propagates a distance given approximately by the length of the aftershock zone.
An investigation and application of the crustal transfer ratio as a diagnostic for explosion seismology
Authors: McCamy Keith 
Published: July 2021

Abstract
Because the spectral behavior of seismic first arrivals contains much information about the nature of the transmission path, the Thomson-Haskell matrix formulation for the response of layered systems has received much attention. In particular, the transfer ratio, i.e., the ratio between the vertical and horizontal transfer functions, invites study because it can be compared with the ratio spectrum, an observable quantity, independent of the source function and characterizing the model alone. An investigation of this quantity as a function of the parameters in the layered model shows that it is insensitive to densities in the model, that the shear velocities in the model are less critical than the layer thicknesses and compressional velocities, and that it is probably impossible to numerically invert the problem uniquely, that is, to find a unique model whose calculated transfer ratio matches the observed ratio spectrum of a seismogram. The transfer ratio can provide a useful and sensitive constraint on models derived from other methods, however. By searching the parameter space around several different types of models, models which satisfy observed ratio spectrums in the least square sense can be found. Inspection of these models' transfer ratios and response functions discriminates between model types which are acceptable and those which are not.
Triggering of microearthquakes by earth tides, and other features of the Truckee, California, earthquake sequence of September, 1966
Authors: Ryall Alan , VanWormer J. D. , Jones Austin E. 
Published: July 2021

abstract
During an earthquake sequence near Truckee, California, in September 1966, several thousand aftershocks were tape-recorded on a small, tripartite seismic array. Using playbacks of these recordings, together with seismograms from three nearby stations, focal coordinates were calculated for 79 of the larger aftershocks, and epicenters were determined for an additional 29 shocks. The focal region in which these earthquakes were located had approximate dimensions 3 × 6 × 10 km, with its long axis trending N22°E and plunging about 45°NE. Focal depths ranged from 0.8 to 10.3 km, and there was a gradual migration of aftershocks from the vicinity of the main shock at the deeper, northeast end of the zone, to the shallower, southwest end.
Variations in the hourly rate of occurrence of aftershocks for the period September 13-29 were cross-correlated with an earth-tide record for the same period, and a statistically significant positive correlation was found between these two sets of data. The earthquake frequency trace was also subjected to a power-spectrum calculation, and was found to contain periodic components identical to those of the principal components of the solid-earth tides.
A P-wave fault-plane solution for the main shock agreed both with the line of surface breakage and with a plane fitted to the zone of aftershock foci. Of 245 observations of first-motion for well-located aftershocks, all but 11 were explained by a single type of mechanism, with slight variations in orientation. The determination of 494 magnitudes for earthquakes of this sequence provided the basis for a discussion of problems connected with the interpretation of frequency-magnitude curves. The velocities of waves Pg and Sg were determined for a line extending southeast of Truckee, along the axis of the Sierra Nevada.
Diagnostic diagrams and transfer functions for oceanic wave-guides
Authors: Abramovici Flavian 
Published: July 2021

abstract
The variation of frequency F as a function of wave number K and the associated spectral transfer function are computed for different modes in a complex oceanic wave-guide. The model consists of a fluid layer resting upon a three-layer elastic half-space. The layers and the half-space are homogeneous.
The comparison of theoretical results with measured power spectra for two records taken in the Pacific Ocean shows qualitative agreement stressing strongly the role of the leaking compressional organ-pipe modes which are not continuations of normal modes beyond cutoff frequency.
The mathematical procedure consists in the integration of the second-minor propagator equation of Gilbert and Backus (1966). The determinant representing the secular function is computed directly rather than by summing the products of its elements. This improves both accuracy and computing time. The integration can be reduced to that of a third-order nonlinear differential system which, for K = 0, splits into two Riccati equations.
The (F, K)-diagram corresponding to every mode is obtained by a technique based on properties of similar diagrams for simple oceanic and continental structures.
Effect of an elastically restrained boundary on SV-wave radiation patterns
Authors: Huang Y. T. 
Published: July 2021

Abstract
In the solution of elastic wave propagation equations applied to solid earth, it is customarily assumed that free boundary conditions are satisfied at a surface which is in contact with the atmosphere. Situations which depart from this boundary condition have now been studied for arbitrary combinations of the Lamé elastic constants. The solutions are given for a homogeneous, isotropic half space.
The thickness of the crust in central United States and La Paz, Bolivia, from the spectrum of longitudinal seismic waves
Authors: Fernandez Luis M. , Careaga Jose 
Published: July 2021

Abstract
The ratio of the vertical and horizontal components of the P phase provides a crustal transfer function which is independent of the frequency content of the source and is a function only of the angle of incidence of the rays and the crustal parameters of the site where the observation is taken.
This ratio of the vertical and horizontal spectra corresponds to the tangent of the apparent angle of emergence and as such this apparent angle is a function of the frequency. Spectra of this type have been obtained in the central United States and in La Paz, Bolivia, for large magnitude teleseisms. The observed curves have been compared with theoretical universal curves corresponding to one- and two-layer models.
Average results for several observations give a crustal thickness in the central United States of 42 kilometers and a mean P velocity of 6.6 kms/sec. For the Bolivian Andes at La Paz, the crustal thickness obtained is 64 kms and the mean P velocity 6.7 kms/sec. These results are in good agreement with similar determinations obtained by independent methods.
Amplitude curves of seismic body waves between 5° and 25°
Authors: Vane˘k Jiří 
Published: July 2021

abstract
Amplitude-distance curves of seismic body waves in the distance range between 5° and 25° derived for the region of Southeastern Europe and the northern part of Asia Minor are presented. The shape of the amplitude curves indicates the complex character of wave groups denoted as P and S. It appears that these wave groups are composed of many wave types which arrive in comparable travel times and produce a complicated interference pattern of the P- and S-wave groups. At different epicentral distances different wave types predominate, thus forming the maximum of the wave group in question.
Estimation of surface focusPtravel times
Authors: Herrin Eugene , Tucker William , Taggart James , Gordon David W. , Lobdell John L. 
Published: July 2021

AbstractAn iterative technique was used to locate some 400 earthquakes, estimate corrections to the Jeffreys-Bullen P travel times and estimate azimuthally dependent station adjustments (station corrections). An oversimplified model for the upper 700 km of the mantle was adopted in order to provide a standard for the investigation of regional variations in travel times. In the estimation procedure only data for epicentral distances in the range 20° to 105° were used, and the data were truncated to remove gross errors. The new P travel times are generally 2 to 3 sec less than those given in the Jeffreys-Bullen Tables.
A seismic event counter for active volcanoes
Authors: Decker R. W. 
Published: July 2021

Abstract
Changes in the numerical frequency of microearthquakes have been observed at various active volcanoes. Identification of these periods of change can be made with a short-period, vertical seismometer driving a simple tally register counting circuit. A fully portable prototype model tested at various active volcanoes provided rapid estimations of the occurrence of microearthquakes. On Kilauea Volcano, Hawaii, the numerical results correlate very well with counts made from conventional seismograms. The device is no substitute for continuous seismic records, but provides a very simple method of monitoring changes in local seismicity which can then be evaluated by more sophisticated equipment.
A method for estimating the uncertainty of seismic velocities measured by refraction techniques
Authors: Borcherdt R. D. , Healy J. H. 
Published: July 2021

ABSTRACT
Time residuals from 75-km segments of 18 crustal seismic-refraction profiles in the Basin and Range province are used to investigate the validity of the linear-regression model and to make large sample estimates of the variance in the travel time distributions.
A formula for unbiased estimates of velocity uncertainty is derived, assuming a linear trend with distance for the variances of the travel-time distributions. If the recording units are symmetric about the center of the recording interval, this formula is equivalent to the one derived assuming the variances are equal.
At the 95-per cent confidence level the chi-squared test implied 84 per cent of the time-residual samples were inconsistent with the hypothesis that their parent populations had Gaussian distributions. If the number of recording locations expceeds 8, confidence limits computed without the Gaussian assumption suggest the departures from normality are not significant for velocity uncertainty estimates.
The large sample estimates of the time-residual populations may be applicable to other areas. This evidence motivated the development of a method, requiring very little numerical calculation, for estimating uncertainties in velocities. The method requires, in addition to the large sample estimates of the travel time variances, information on the quality of the data, the location of the recording interval, and the number of recording units. The method is useful for the design of new experiments and independent estimates of uncertainty reported in the literature.
Rayleigh wave particle motion and crustal structure
Authors: Boore David M. , Nafi Toksöz M. 
Published: July 2021

Abstract
A feasibility study was made concerning the use of the ellipticity of the Rayleigh wave particle motion for determining earth structures. Variational parameters were computed empirically for both the ellipticity and phase velocity of Rayleigh waves in the period range T = 10-50 seconds. It was found that, in general, the ellipticity and phase velocity are about equally sensitive to structural perturbations, but that near-surface low-velocity sedimentary layers influence the ellipticity much more strongly than they do the phase velocity. Anelasticity has a minor effect on the ellipticity, whereas the presence of interfering waves can have a significant influence.
A test of the independence between ellipticity and phase velocity indicated that in our period range ellipticity does contribute independent information, and thus provides an additional constraint toward uniqueness.
Using data from LASA, both ellipticity and Rayleigh- and Love-wave phase velocities were measured and the results interpreted in terms of a crustal structure. The ellipticity data proved useful when combined with the phase velocity and some structures that fit the phase velocity data could be rejected on the basis of ellipticity.
The relation between fault plane solutions for earthquakes and the directions of the principal stresses
Authors: McKenzie Dan P. 
Published: July 2021

abstract
The stresses involved in shallow earthquakes and their occurrence along fault planes suggest that they occur by failure on weak planes, rather than by brittle fracture of a homogeneous material. Possible orientations of the stress tensor are examined to determine what limits fault plane solutions can place on the orientation of the greatest principal stress. For the general case of a triaxial stress, the only restriction is that this stress direction must lie in the quadrant containing P, but may be at right angles to the P direction. Thus shallow earthquakes impose a few limitations on the orientation of the stress tensor. In contrast the fault plane solutions from deep earthquakes are best explained by fracture of a homogeneous material, with the greatest principal stress directed down the dip of the earthquake zone.
Rayleigh waves in southern New Guinea
Authors: Brooks J. A. 
Published: July 2021

abstract
A shear velocity structure having features similar to the Gutenberg model for the upper 200 km of the mantle is consistent with features of higher mode Rayleighwave group-velocity dispersion curves in the period range 4 to 30 seconds, for paths across southern New Guinea. Pronounced discontinuities appear to be absent within the crust where shear velocities are expected to gradually increase with depth. Clearly dispersive second mode (M21) Rayleigh waves, well separated in time from the fundamental mode, are shown for path lengths less than 2000 km. Frequencies excited show some dependence on focal depth. Stationary wave groups of period 10-20 seconds, very like the Sa phase, and generated by earthquakes of focal depth between 100 and 160 km coincide with expected normal mode group arrivals.
Modeling of seismic signals from large underwater explosions to predict the spectra and covariance functions
Authors: Plutchok R. , Broome P. 
Published: July 2021

abstract
A model is presented which makes it possible to accurately predict the power spectrum and the covariance function of seismic signals generated by large under-water shots. It is shown by comparison of predicted and measured data for several large underwater explosions that the spectrum and covariance depend almost entirely on parameters such as source depth, water depth and first bubble pulse period. It is further demonstrated that averaging of the spectra from widely dispersed seismic stations for a given signal is a useful method for reducing non-source-related effects.
Precision of epicenters obtained by small numbers of world-wide stations
Authors: Evernden Jack F. 
Published: July 2021

abstract
A fundamental error in the application of the confidence ellipse concept to the estimation of location error is demonstrated. The change in procedure required to be statistically sound and to achieve agreement with observations is explained and illustrated. The resultant procedure is then applied to the estimation of the network detection capability on a world-wide basis of the WWSSN.