bluuebunny/crossref_metadata_2025 huggingface dataset:
Una sugerencia para las iniciales del anónimo traductor de «El contrato social» de Rousseau en 1812
Authors: Rodríguez Morín Felipe
Published: July 2021

Con el comienzo de la primavera de 1813, el sector más rancio del pueblo mallorquín —y el que no lo era tanto también— se vio convulsionado por la aparición de una traducción de El pacto social de Rousseau. En una remesa de 500 volúmenes, el envío remitido a Mallorca resultó poseer características particulares respecto de la edición matriz de 1500 ejemplares que había alumbrado las prensas valencianas de José Ferrer de Orga en 1812; entra ellas la de haber permutado el título por el subtítulo de la versión original: Principios del derecho político, y la de figurar estampadas en su portada las letras «A. G-M. y S.» como indicación del traductor, sobre las cuales se han venido barajando a lo largo del tiempo distintas teorías, y para las que ahora sugerimos nosotros un candidato.PALABRAS CLAVEPrincipios del derecho político, El contrato social, Antonio García Malo y Sánchez, Pedro Estala, Ignacio García Malo, Rousseau.  With the beginning of the spring of 1813, the most reactionayr sector of Majorcan people –and that wich wasn’t so much too- was thrown into upheaval by the publication of  translation of El pacto social by Rousseau. In an edition of 500 books the consignment which was delivered to Majorca turned out to have special characteristics with respect to the former edition of 1500 copies which José Ferrer de Orga’s Valencian presses had published in 1812. One of these features was that the title had been exchanged with the subtitle of the original edition: Principios del derecho politico, and that letters «A. G-M. y S.» were printed on its cover as a signal of the translator. These are initials about which several theories have been considered over time and, and for which we now suggest a candidate.KEY WORDSPrincipios del derecho político, El contrato social, Antonio García Malo y Sánchez, Pedro Estala, Ignacio García Malo, Rousseau.
José de CADALSO, «Ocios de mi juventud», edición de Miguel Ángel Lama,Madrid, Cátedra, colección «Letras Hispánicas», 2013, 421 págs.
Authors: Olay Valdés Rodrigo
Published: July 2021

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La historia de las ideas en el siglo XVIII: concepciones antiguas y revisiones necesarias
Authors: López François
Published: July 2021

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Relatos de viajes de extranjeros por la España del siglo XVIII. Estudios realizados hasta el presente
Authors: Aguilar Piñal Francisco
Published: July 2021

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Catorce cartas de Feijoo al P. Sarmiento
Authors: Arias Maximino
Published: July 2021

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Don Lope de Sierra Cienfuegos, Fiscal del Consejo de Castilla en el reinado de Carlos III
Authors: Anes Lidia
Published: July 2021

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El último discurso de Jovellanos en el Real Instituto Asturiano de Gijón
Authors: Caso Machicado María Teresa
Published: July 2021

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El concepto de Academia de Ciencias en el siglo XVIII español
Authors: Gil Novales Alberto
Published: July 2021

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La medicina en el «Diario de los Literatos» (1737-1742)
Authors: Tomsich Maria Giovanna
Published: July 2021

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La abuela autómata. Mecánica y androides en el siglo de las luces
Authors: Herrero Sánchez Jaime
Published: July 2021

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Ernest Lluch, un singular hombre de las luces
Authors: Llombart Vicent
Published: July 2021

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Tres manuscritos del padre Isla
Authors: Rodríguez Álvarez Ramón
Published: July 2021

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Jovellanos y Goya
Authors: Castañón Luciano
Published: July 2021

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Seismic energy generated by a sudden volume change
Authors: Randall M. J.
Published: July 2021

The recent suggestion that sudden phase transitions may provide a mechanism for earthquakes is examined mathematically for the simple case of sudden change of volume. Such a transition, even for a small density change, offers a much more concentrated source of seismic energy than does sudden faulting.
A rapid method for calibrating Willmore seismographs
Authors: Barr K. G.
Published: July 2021

A method is described for calibrating Willmore seismographs. It could be applied to any other electromagnetic seismograph having a galvanometer period substantially shorter than the seismometer period. The method is rapid and involves very little equipment. An overall accuracy of 20% in the velocity sensitivity is easily attainable.
A note on disturbances in a layered medium containing a magnetic field
Authors: Sinha D. K.
Published: July 2021

abstract

In recent years, Kaliski has contributed a series of papers on the interaction of elastic and magnetic fields and some of them, [1], [2], [3] are concerned with the propagation of waves in a semi-infinite medium either loaded or conditioned otherwise, at its free surface. Such problems, as Kaliski [1] has remarked, may have relevance in the practical seismic problem of detecting the mechanical explosions inside the earth. Moreover, their geophysical implications have also been examined by Knopoff [4[, Cagniard [5], Banos [6], and Rikitake [7]. The present note seeks to investigate disturbances in a medium consisting of two layers (one finite and the other infinite) of elastic medium intervened by a thin layer of vacuum. The vacuum is traversed by an initial magnetic field. The disturbances in the medium are assumed to have been produced by a time-dependent load on the free surface of the medium. The method of Laplace transform has been used to facilitate the solution of the problem.
Wave propagation phenomena at an irregular infinite interface: Part III: Rigid boundary
Authors: Adams W. M. , Schlesinger E. , Schubel E. K.
Published: July 2021

The problem is the scattering of a plane, simple harmonic acoustic wave from a rigid surface. The boundary is taken to be infinite and irregular, as defined in Part I. Numerical results obtained with an IBM 7094 computer are given. Suggestions for further research are presented also.
T phases from 80 Alaskan earthquakes, March 28-31, 1964
Authors: Northrop John
Published: July 2021

A large T-phase signal was received at Pt. Sur, California, from the Alaskan earthquake of March 28, 1964. Additional T phases were received from 90 per cent of the 80 aftershocks studied in the Kodiak Island area. The largest T phases were received from hypocenters beneath the upper portion of the continental shelf.
On the general solution of elastic wave equations in a homogeneous medium with applications to the study of earthquake source mechanisms
Authors: Roy Arabinda
Published: July 2021

The elastic wave equation in an isotropic homogeneous semi-infinite elastic medium has been transformed by a combination of Fourier and Laplace-transforms and the surface displacements due to general force-system in three mutually perpendicular directions have been directly obtained. By suitably specifying the force-system, the surface displacements for all possible types of point sources so far used, have been calculated, obtaining in particular, the results previously derived by Haskell for a dipolar point source of arbitrary direction. It has been shown that now the surface displacement for finite size of the source can be calculated for both body and surface waves. Expressions for the displacements at any point of the medium have been derived, giving in particular the displacements associated with incident wave in the medium, separately.
Origin and properties of microseisms from the standpoint of oscillator theory
Authors: Strobach Klaus
Published: July 2021

The generally large source area for seawave generated microseisms does not readily allow consideration of these events as unidirectional. Rather, these wave patterns must be due to a complicated interference system, whose properties can be described only by statistics. In this study it is postulated that the generation of microseisms results as the superpositon of the outputs of a large number N of seismic oscillators. These oscillators are randomly distributed both in space and time. This random distribution necessarily implies that the phase angles of incoming waves are randomly distributed too. The statistical properties of the resultant ground motion, outside of the generation area, is investigated theoretically. Special attention is given to the probability distributions of the vertical amplitudes and the horizontal vector amplitudes. Good agreement is found between these theoretical results and the measurements obtained from particle motion diagrams.

Additionally, the theoretical results lead to two methods for determination of the microseismic directions of approach. Both of these techniques were applied to the microseismic storm of January 28, 1963. This storm was generated by a well-developed cyclonic system off the east coast of the United States and Canada. Basic data for the study were obtained from the long-period seismograms of 5 stations (Rolla and Florissant, Mo., Bloomington, Ind., Dubuque, Iowa, and Ann Arbor, Mich.). The resulting analysis gave generation areas off the southern coast of Newfoundland and eastern coast of the United States.

Further use was made of the theory developed to investigate the character of the microseismic waves. This application showed the microseisms to be composed not only of clear, fundamental mode Rayleigh waves, but that Love wave motion was also present. Surprisingly the proportion of Love wave motion was found to be different at different stations. At Rolla, Florissant and Bloomington, it was predominant, while at Dubuque and Ann Arbor the Rayleigh wave motion was dominant.
PcP from the nuclear explosion BILBY September 13, 1963
Authors: Buchbinder Goetz G. R.
Published: July 2021

The core-reflected phase, PcP, from the BILBY event, received at stations between 19° and 88°, arrived early by an average of 1.80 seconds with respect to the Jeffries-Bullen tables. The standard deviation of these data was 0.77 seconds. The corresponding P phases were early by 1.34 seconds. The tables therefore need adjustments. If the core boundary is to be moved by more than 10 km from the value of 2898 km then the mantle seismic velocity immediately above the core must be changed also. The PcP/P amplitude ratios are nearly always much larger than those predicted theoretically.
Catalog of Nevada earthquakes, 1852-1960
Authors: Slemmons David B. , Jones Austin E. , Gimlett James I.
Published: July 2021

Nevada earthquakes for the period from about 1852 to 1961 are tabulated on I.B.M. punch cards. During this period 1,173 events with Nevada epicenters were felt, 586 others with Richter magnitudes above 4.0 were recorded and were probably felt by some residents, and approximately 220 were reported in nonspecific terms (e.g. “several aftershocks were felt”). High seismicity of this region is indicated by the fact that on an equal-area basis, during the period 1934-1960, Nevada has had the highest incidence of earthquakes per unit area of any of the conterminous Western States. The seismic activity shows a distinct tendency, statistically inadequate, for a 20-year cycle of activity, with peaks at about 1852(?), 1872, 1894, 1916, 1932-1933, and 1954. The general increase in number of events reported each year correlates well with the increase in Nevada population, but is probably modified by the development of: increasingly sophisticated methods of recording, spacing of seismographic stations, more intensive earthquake investigations of the United States Coast and Geodetic Survey, and changing population density and distritution.

A method is developed for correlating between Richter magnitude, earthquake intensity, and size of felt area. This permits estimation of earthquake magnitude for shocks that pre-date instrumental methods of recording.

The areal distribution of the earthquake epicenters does not indicate a noticeable change in pattern during this brief historic period, except possible recent intensification of activity near Lake Mead. Seismic activity is concentrated in three zones: a Western Nevada-Eastern California Zone which includes the northern Sierra Nevada frontal faults, Fish Lake Valley-Furnace Creek-Death Valley fault systems and Walker Lane; a 118° Meridian Seismic Zone which contains most of the historic surface faults; and a weak Southern Nevada Transverse Zone that includes the Lake Mead activity.
The earth's mantle
Authors: Leet L. Don , Leet Florence J.
Published: July 2021

It has been generally accepted for some time that the earth's mantle is “solid” (crystalline). But increasing complications arise as attempts are made to rationalize that state of matter with the growing list of properties of the mantle.

We suggest that materials of the earth's mantle are in a fourth state of matter, which we propose calling soliqueous—a combination of solid, liquid, and gaseous. It includes elements for forming water molecules and allows expanding superheated steam to supply the principal force for elevating and distorting land masses.

Bridgman's experiments on plastic deformation of materials at very high pressures revealed that spasmodic jerky yielding is characteristic. We propose plastic rupture in shear as the primary mechanism by which energy in the earth is converted to the vibrations of earthquakes.
Dispersive characteristics of the first three Rayleigh modes for a single surface layer
Authors: Mooney Harold M. , Bolt Bruce A.
Published: July 2021

abstract

The dispersive characteristics of a single elastic layer overlying an elastic half-space are examined in detail for the fundamental and the first and second higher modes of Rayleigh waves. Phase velocity, group velocity, and the ratio of horizontal to vertical surface displacement are computed as functions of dimensionless quantities proportional to period and wave number.

The significant range for the independent variable, B1T/H, proves to be largely independent of the parameters of the structure. The range is 1 to 20 for the fundamental, 0.3 to cutoff for the first higher mode, and 0.2 to cutoff for the second higher mode.

The most important parameter of the structure for Rayleigh wave dispersion is the shear velocity ratio. Variations in the Poisson's ratio in the surface layer and the density contrast may produce substantial effects. Poisson's ratio in the half-space is of least significance.

The dependence on model parameters of the long-period cutoff for the higher modes is determined.

Specific results are given for the following geophysical examples: continental crust, continental ice cap, sedimentary basin, alluvial overburden, and laboratory seismic models.
Earthquake response of inelastic shear buildings
Authors: Lee S. L. , Perelman D. S. , Fleming J. F.
Published: July 2021

abstract

A typical multi-story bilinear inelastic shear building is subjected to idealized earthquake motions. The dependence of the deflection of the structure, the maximum shear in each story, and the extent of the plastic deformation upon the period and amplitude of the earthquake, and the strain hardening coefficient of the structural material is shown. It is noted that, at least within the scope of this study, the maximum shears in the stories of the building are larger than the minimum seismic shear requirements of most of the building codes.
Amplitudes and energies of primary seismic waves near the hardhat, haymaker, and shoal nuclear explosions
Authors: Trembly Lynn D. , Berg Joseph W.
Published: July 2021

abstract

Records of near-source (0.3 to 20 km) primary seismic waves generated by the Hardhat, Haymaker, and Shoal underground nuclear explosions were analyzed in terms of displacement amplitude and energy variations with distance. The observed data were compared to similar data from a theoretical source model to determine the adequacy of the theoretical model.

There was evidence that a long-period displacement field existed near the explosions as predicted by the theoretical source. Scatter in the observed amplitude data made it difficult to distinguish between the long-period and the radiation fields. However, the variation of total energy of the observed primary seismic waves with distance showed the presence of the long-period field.

The comparison of observed and theoretical data indicates that a theoretical elastic source model approximated the observed sources.
A statistical discussion of Pn residuals from explosions
Authors: Freedman Helen W.
Published: July 2021

abstract

The problem of the statistical treatment of large numbers of Pn residuals is considered, using travel times to stations in California and Nevada from 43 explosions in Nevada. Techniques of data selection and weighting of observations are developed in order to estimate the distribution of residuals and to estimate station adjustments to Jeffreys-Bullen travel times. A new simple method of estimating the mean of a normal population from a truncated sample is given. An approximate analysis of variance showed a significant variation from one explosion to another in the mean Pn travel time. On the average, large magnitude explosions, detonated in metamorphic rock produced shortest, and most reliable, travel times. The station adjustments also differed significantly, ranging from −0.0 seconds at Fresno to −1.3 seconds at Calistoga; confidence intervals about the station adjustments had half lengths of the order of half a second. The results have implications for seismic studies which depend upon estimates of such station adjustments.
P-wave coupling of underground nuclear explosions
Authors: Springer Donald L.
Published: July 2021

abstract

P-wave amplitude data for underground nuclear explosions are correlated with detonation energy. Amplitudes are reproducible to 25 per cent when source media and propagation path differences are minimized. These data verify theoretical scaling relationships and establish relative coupling for various shot media. An empirical correlation of these amplitude data with dry porosity of the detonation medium indicates that a medium with 60 per cent dry porosity may couple explosive energy one-fourth or one-fifth as efficiently as does alluvium. The relationship of teleseismic magnitude to explosive yield for various types of low coupling shows that dry porous media give a significant reduction of seismic signals generated by underground nuclear explosions.
Use of reciprocity theorem for obtaining Rayleigh wave radiation patterns
Authors: Gupta I. N.
Published: July 2021

abstract

The reciprocity theorem is used to obtain Rayleigh wave radiation patterns from sources on the surface of or within an elastic semi-infinite medium. Nine elementary line sources first considered are: horizontal and vertical forces, horizontal and vertical double forces without moment, horizontal and vertical single couples, center of dilatation (two dimensional case), center of rotation, and double couple without moment.

The results are extended to the three dimensional case of similar point sources in a homogeneous half space. Haskell's results for the radiation patterns of Rayleigh waves from a fault of arbitrary dip and direction of motion are reproduced in a much simpler manner. Numerical results on the effect of the depth of these sources on the Rayleigh wave amplitudes are shown for a solid having Poisson's ratio of 0.25.
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

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

Maps 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

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

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

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

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

An 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

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

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

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.
Non-linearity test of an accelerometer system designed for the seismic near-field measurement
Authors: Reasenberg Paul
Published: July 2021

abstract

An accelerometer system designed for the seismic near-field measurement is described. The wide dynamic range of the system, and the anticipated acceleration spectral density require that the accelerometers be highly linear. A method for determining the linearity is described.
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.
Use of source arrays in studies of regional structure
Authors: Niazi Mansour
Published: July 2021

Seismograms of 26 underground explosions and two cavity collapses at the Nevada Test Site (NTS) and 26 well-recorded earthquakes in central California recorded by a vertical instrument at Berkeley have been studied. It is demonstrated that the use of source arrays instead of instrument arrays may provide information of general nature about the crust-upper mantle structure. The method can particularly be useful in regional reconnaissance of seismic areas with as few as a single recording instrument.

Times of four consistent arrivals on the NTS seismograms are analyzed. The first two arrivals with observed apparent velocities of 8.51 ± 0.47 and 6.41 ± 0.23 km/sec are interpreted as Pn and Pg phases, respectively. A later arrival, named PLP, with an observed slope corresponding to a velocity of 9.80 ± 0.86 km/sec is consistent with P-wave reflections from a depth of 227 ± 22 km.

The observed phases on the seismograms of central California earthquakes suggest a single-layer crust with an average thickness of 20.5 km to the south of Berkeley. The crustal longitudinal and shear velocities are 5.87 ± 0.05 and 3.46 ± 0.05 km/sec, respectively. The observed Pn and Sn velocities are 7.91 ± 0.12 and 4.40 ± 0.10 km/sec, respectively.
Leaking and normal modes as a means to determine crust-upper mantle structure for different paths to Sweden
Authors: Ibrahim Abou-Bakr K.
Published: July 2021

By using the leaking and normal mode dispersion curves, the average crustal and upper mantle structure is determined for seven different paths. The paths originate from earthquakes in Greece, Turkey, West Pakistan, Tibet, Kamchatka, Kurile Islands and Mexico. Records from Uppsala and Umeå, Sweden, are used. The characteristics of the leaking modes at different distances are examined. Surface waves are used to put more constraint on the models chosen using only the leaking wave data and to verify their mode of propagation.

A good fit for observational data of both the leaking mode (PL or PLH2) and the normal mode (Rayleigh) is found to one model for each path. The average crustal structures from Greece and Turkey to Uppsala are identical. The crustal and upper mantle models for paths from Tibet, West Pakistan, Kamchatka and Kurile Islands have approximately the same velocities but different crustal thicknesses. The dispersion characters of Mexican and North American paths are similar, while the average crustal thickness for the Asiatic paths is 5-15 km greater than for the Mexican path.

Since the dispersions of the leaking and normal modes are explained by one and the same structural model, it indicates that our hypothesis about the propagation of the leaking waves is true, and that a substantial portion of the long-period wave trains between the P and S waves can be explained in terms of these leaking modes.
Source dynamics of the Dasht-e Bayāz earthquake of August 31, 1968
Authors: Niazi Mansour
Published: July 2021

abstract

Radiation patterns of the P-wave first motion and S-wave polarization angle of the Dasht-e Bayāz earthquake of August 31, 1968, as well as its principal aftershock which occurred about 20 hours after the main shock are studied. The main shock data are consistent with the observed left-lateral strike-slip fault which accompanied it. The radiation pattern of the aftershock differs somewhat from that of the main shock and agrees with the directions of the secondary faulting in the area.

Several lines of evidence pointing to a multiple source for the main shock are presented. They include complexity of the body phases, low value of the rupture speed as studied from the analysis of the surface wave spectra, reported long duration of shaking and complicated pattern of striations produced by faulting. Energy, moment and stress drop associated with the main shock are estimated. The resulting mean value of stress drop over the faulted surface has a range of 40-100 bars. Based on the age of some well-built structures in the area, it is proposed that no earthquake as severe as the recent one has occurred near the location of the August 31, 1968 earthquake during the last 800 years.
The fairweather fault ten years after the southeast Alaska earthquake of 1958
Authors: Page Robert
Published: July 2021

abstract

Field observations made ten years after the southeast Alaska earthquake (M = 7.9) of 10 July 1958 reveal environmental and geomorphic changes in the Fairweather fault zone. Faulting associated with the earthquake killed many trees in the Crillon Lake region. Trees were tilted and later fell, and possibly were drowned because of changes in drainage conditions. A nearly vertical, 2-meter scarp in soil has been eroded to a slope of 35° to 40° in the decade since 1958.

Microearthquake activity sampled at a single site on the fault is at least equal to or possibly greater than that reported from active sites on the San Andreas and Denali faults. The distribution of S-P times is consistent with a uniform planar distribution of shocks on a segment of the fault that slipped in 1958. The expected seismicity from aftershocks of the 1958 earthquake is less, but not significantly less, than the observed seismicity.