bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crustal deformation by earthquakes and explosions
Authors: Ben-Menahem Ari , Gillon Allon 
Published: September 2021

abstract
Static displacements were calculated for an earth model which consists of a single layer of thickness H overlying a homogeneous half space. Localized sources simulating earthquake and explosion foci are placed at depths h=H2andh=32H. The ensuing surface deformation is evaluated as a function of the epicentral distance for a typical continental crust model.
A new technique is used for the quadrature of the displacement integrals. By this method one is able to calculate 1000 layer-integrals of the type
F m n ( x , t ) = ∫ 0 ∞ y n e − x y J m ( t y ) d y 1 + ( A + B y 2 ) e − 2 y + D e − 4 y ,
with an accuracy of 0.1 per cent, in less than 2 minutes.
It is found that for epicentral distances r &gt; 20H the displacements decay like (r/H)−α where 2 &lt; α &lt; 5. For compressional and strike-slip displacements at all depths and for dip-slip source above the layer, 2 &lt; α &lt; 3. For a dip-slip source located below the layer, 3 &lt; α &lt; 5. Maximal displacements for wr, ur, ux, uy and uz occur at approximately r ≃ 0.8h and decay with source's-depth like h−3/2.
Decay rate of P-wave amplitudes from nuclear explosions and the magnitude relations in the epicentral distance range 1° to 98°
Authors: Kaila K. L. 
Published: September 2021

abstract
Study of the decay rate with epicentral distance of P-wave amplitudes from nuclear explosions in the distance range 1° to 98° has revealed that instead of the continuous amplitude curve of Gutenberg, the amplitudes are most appropriately represented by six discontinuous curves. Corresponding to these six amplitude decay curves, magnitude relations were worked out. The new magnitude relations yield consistent magnitudes for nuclear explosions as well as earthquakes independent of epicentral distance over the entire distance range of 1° to 98°. The magnitude values are however slightly shifted towards the higher side by 0.22 magnitude unit (at M = 4.5) as compared to those predicted by the Gutenberg-Richter method. Magnitudes are evaluated for Logan, Blanca and Salmon explosions using the new magnitude relations and they agree fairly well with the published magnitudes for these events determined by other workers using the Gutenberg-Richter method.
These amplitude decay curves when compared with the travel-time curves of Carder (1964) do show a reasonable correspondence between the starting points of amplitude curves and the distances where the deeply refracted phases from plausible velocity discontinuities in the mantle start appearing as first arrivals on the surface of the Earth.
The effects of radiation patterns on magnitude estimates
Authors: von Seggern David 
Published: September 2021

abstract
With a double-couple force system as a model of an earthquake source mechanism, the radiation pattern theory of Ben-Menahem is employed to show that the far-field measurement of its strength can theoretically vary by more than a magnitude unit using either surface waves or body waves depending upon the angles of slip motion and fault dip for a source at a constant depth. The magnitude values determined by surface and body waves do not change linearly in relation to slip and dip angles nor do they change linearly in relation to one another. Random selection of locations within the radiation pattern is used to determine the extent of scatter in magnitude determinations which could be attributed to station distribution relative to the source. The scatter in surface-wave versus body-wave magnitude plots for earthquakes could be severe if only a few stations are used to obtain average magnitude values. A method of obtaining consistent estimates of surface-wave magnitude in practice is discussed.
The Peru-Bolivia border earthquake of August 15, 1963
Authors: Chandra Umesh 
Published: September 2021

abstract
The seismograms of the deep focus Peru-Bolivia border earthquake of August 15, 1963 reveal the presence of a number of conspicuous phases occurring within 15 seconds of the first P onset. These phases cannot be explained on the basis of known travel-time curves. Accordingly, the earthquake is interpreted to have occurred in a series of jerks during the course of fault propagation, or in other words it is composed of multiple events. Only one of these events, following the first event, at which the amplitude of the recorded motion becomes suddenly very large, has been located in this study. The focal mechanism solution of this earthquake has been determined from the P wave first motion and amplitude data. Consideration of the direction of rupture propagation determined from the multiple event analysis makes it possible to identify the fault plane in the mechanism solution. The parameters of the fault plane, length and speed of rupture between the two events have been determined.
Evolutionary power spectral density of strong-motion earthquakes
Authors: Liu S. C. 
Published: September 2021

AbstractThis paper presents the evolutionary (time-dependent) power spectral density curves of six strong-motion earthquakes. The earthquake accelerograms are treated as piecewise-separable and the frequency-independent modulating function is estimated by applying the mean square minimization criterion. The results show that, as the time increases, the power spectral densities of earthquakes can vary both in magnitude and in peak location over the frequency axis. The analysis demonstrates that the nonstationary characteristics of earthquakes can be reasonably assessed by a simple computation procedure and the information thus obtained can be helpful in developing improved stochastic models for earthquake simulation.
Statistical analysis of seismic data on earthquakes in the area of the Vrancea focus
Authors: Săcuiu Ion , Zorilescu Dan 
Published: September 2021

abstract
The present contribution deals with distribution laws of the earthquake's magnitude, the number of earthquakes (by modelling the generation process as a Poisson process) and the time interval between two successive earthquakes.
The most important conclusion arrived at is that in the area of the Vrancea focus the distribution of the magnitudes is lognormal and brings forth a frequency-magnitude relation of the form
log λ ( Μ ) = a + b log M + c ( log M ) 2 ,
not a linear one.
A correlation between the magnitude and the time interval of two successive earthquakes is considered and a series of seismic indices are introduced.
Reflection from the free surface of an inhomogeneous media
Authors: Acharya H. K. 
Published: September 2021

abstract
A study of the reflection of compressional waves for an elastic, isotropic, inhomogeneous medium in which compressional and shear-wave equations are separable, reveals that, if the properties of the medium are varying slowly, then for real incidence the reflection coefficient for the free surface is complex and the phase change upon vertical reflection is not 180° as is the case for a homogeneous media.
Long period SHn
Authors: Filson John 
Published: September 2021

abstract
The theory of Cagniard applied to the model of a point source of torque in a layer overlying and welded to a half-space of higher velocity has been used to approximate satisfactorily observed long-period SHn wave forms recorded from regional shallow earthquakes in California. The model assumed is consistent with a crustal thickness of about 20 km in extreme western central California. An effective source time duration of about 10 secs appears reasonable for the earthquakes considered in the magnitude range of 5 to 5.5
Fast evaluation of source parameters from isolated surface-wave signals
Authors: Ben-Menahem Ari , Rosenman Martin , Harkrider David G. 
Published: September 2021

abstract
Tables for spectral displacements of seismic surface waves from shear dislocations in flat multilayered earth models were prepared. Earth response functions for seven modes (R11, R21, R12, L0, L1, L2, L3) at six periods (300 sec, 250 sec, 200 sec, 150 sec, 100 sec, 50 sec) and three paths (continental, oceanic, shield) were calculated for the source-depth range of 10 to 600 km at intervals of 5 km until 200 km, and thereafter at intervals of 10 km. Ground motion is given in micron-seconds for the three fundamental shear dislocations, each of strength U0dS = 103 (m × km2) and a delta-function time-dependence.
The tables provide the means for rapid evaluation of source parameters from spectral radiation patterns of amplitudes and initial phases.
Methods for computing ray paths in complex geological structures
Authors: Sorrells G. G. , Crowley J. B. , Veith K. F. 
Published: September 2021

abstractThe mathematics for computing three-dimensional ray paths are developed for the case where medium consists of a series of constant-velocity layers separated by planes or spherical interfaces. These relations are used to investigate the cause of the LONGSHOT travel-time anomaly. The results of the investigation suggest that the anomaly could be caused by the presence of a thick slab of high-velocity material which dips steeply beneath the Aleutian arc and terminates at a depth of 300 km.
The elastic residual field of a very long strike-slip fault in the presence of a discontinuity
Authors: Rybicki Kacper 
Published: September 2021

abstract
On the basis of dislocation theory, formulas for the elastic residual field of a long strike-slip fault in a half-space with a vertical and horizontal discontinuity are given. The obtained results are applied to the 1966 Parkfield-Cholame earthquake. There is good agreement between the calculated residual stress field and the distribution of aftershocks.
The influence of an underlying layer on the residual-surface displacements and strains of a long, vertical strike-slip fault located in the surface layer was found. Both displacements and strains diminish faster as a function of distance from a fault in the presence of a more rigid underlying layer. The computed results show that the dislocation model of a fault in a homogeneous half-space can be inadequate in many cases.
Location capability of various seismic networks
Authors: Evernden J. F. 
Published: September 2021

abstract
Capabilities of various continental-wide and worldwide short-period seismic networks are described. It is stressed that the proper approach to design of a worldwide network is the use of a limited number of high-quality stations rather than the use of many inferior stations. Such a result is expected because of the variation of P amplitude with epicentral distance.
Comparison of some widely-used strong-motion earthquake accelerometers
Authors: Eisenberg A. , McEvilly T. V. 
Published: September 2021

abstract
A series of shaking table and tilt tests were conducted with several commonly used strong-motion earthquake accelerographs. Table accelerations up to 0.5 g, both sine waves and recorded earthquake accelerograms, were used to evaluate response characteristics in the 1- to 50-Hz band under strong-motion conditions. All instruments performed within 10 per cent of manufacturers' specifications. No serious parasitic resonances were observed. Timing systems accuracies should be improved for intra-instrument detailed spectral comparisons. The general intuitive feel that mechanical, electronic and recording simplicity are a measure of expected performance for unattended instruments was reinforced by the tests.
The Peru earthquake of May 31, 1970: Some preliminary seismological results
Authors: Lomnitz C. 
Published: September 2021

abstractThe 1970 Peru earthquake was a multiple shock. The first widely-recorded shock had a magnitude of about 5; within 20 sec there were at least four larger earthquakes, at least two of which exceeded magnitude 7. Focal mechanisms appear to be complicated, with at least one major shock yielding compressions at distances of 25° to 30° to the northeast. Most aftershocks occur at depths of 40 to 70 km; their first motions are sometimes reversed with respect to the main shocks. The seismic history of the region includes one comparable earthquake in 1725 but no events of similar magnitude thereafter. The town of Ranrahirca was not destroyed by the 1970 mud flow but by an earlier event in 1962.
Geological aspects of the May 31, 1970, Perú earthquake
Authors: Plafker George , Ericksen George E. , Fernández Concha Jaime 
Published: September 2021

abstract
Geological effects of the destructive May 31, 1970, Perú earthquake (Ms = 7.7) extended over roughly 65,000 km2 of west-central Perú. Earthquake-triggered slope failures of all types that occurred throughout the mountainous parts of the region extensively damaged transportation routes and irrigation canals and temporarily dammed some rivers and lakes. The geologically most important and spectacular of these, a cataclysmic debris avalanche from between 5,500 and 6,400 m altitude on the north peak of Huascarán Mountain, buried the city of Yungay and part of Ranrahirca (elevation about 2,500 m) with a loss of more than about 18,000 lives. The debris avalanche involved 50-100 million m3 of rock, ice, snow, and soil that traveled 14.5 km from the source to Yungay at an average velocity of between 280 and 335 km/hr. Exceptionally rapid movement of the avalanche is indicated by eyewitness accounts, by topographic irregularities as high as 140 m that were overridden, and locally by boulders weighing several tons that were hurled as much as 1,000 m beyond its margins. A pulse of muddy water from the debris avalanche that swept down the Río Santa 160 km to the sea inundated farms and small settlements, buried highway and railroad routes, and destroyed the diversion dam and access bridge to a major hydroelectric plant.
The extensive destruction to communities and an additional estimated 20,000 casualties resulted primarily from failure of adobe and masonry structures which had little shear resistance to lateral forces imposed by seismic shaking. The degree of damage to buildings and to transportation routes was aggravated in some areas of saturated unconsolidated deposits by differential compaction, downslope slumping or sliding, lateral spreading of liquefied sediments toward free faces, and possibly amplification of seismic vibrations.
The absence of surface tectonic displacements or of a significant tsunami and the spatial distribution of the main shock and aftershocks suggest that the earthquake originated by movement on a fault, or faults, beneath the continental shelf at depths between 45 and 65 km.
A study of the Earth's crust near Gauribidanur in Southern India
Authors: Arora S. K. 
Published: September 2021

abstract
A hypothetical two-layered model has been evolved for the Earth's crust near Gauribidanur. The model is found to be consistent with the local earthquake and rockburst data obtained at Gauribidanur seismographic array. Sixty-seven well-recorded seismic events have been studied for this purpose. First arrival conditions for some of the phases in a “near-source” (epicentral distance Δ ≦ 10°) seismogram have been derived and subsequently made use of in establishing the nature of the first arriving phases pertaining to the available data. Thickness of the top granitic layer and the depth of Moho below this layer are found to be about 16 km and 19 km, respectively. Observed velocities are 5.67, 6.51 and 7.98 km/sec for P phases, and 3.46, 3.96 and 4.61 km/sec for the corresponding S phases. Values of the crustal parameters given by this study have been used in estimating the relative differences in travel times corresponding to various observed phases. These travel times may improve the precision with which earthquakes in this region could be located. Typical geographical and geological features of the region are also briefly described.
The Ceres, South Africa, earthquake of September 29, 1969
Authors: Green R. W. E. , Bloch S. 
Published: September 2021

abstract
Aftershocks following the Ceres earthquake of September 29, 1969, (Magnitude 6.3) were monitored using a number of portable seismic recording stations. Earthquakes of this magnitude are rare in South Africa. The event occurred in a relatively densely-populated part of the Republic, and resulted in nine deaths and considerable damage. Accurate locations of some 125 aftershocks delineate a linear, almost vertical fault plane. The volume of the aftershock region is 3 × 9 × 20 km3 with the depth of the aftershocks varying from surface to 9 km. Aftershocks following the September event had almost ceased when another large earthquake (Magnitude 5.7) occurred on April 14, 1970. Following this event, the frequency and magnitude of aftershocks increased, and they were located on a limited portion of the same fault system delineated by the September 29th aftershocks. Previously-mapped faults do not correlate simply with the fault zone indicated by the aftershock sequence.
The transition between 2- and 3-dimensional waves in seismic models
Authors: Parham R. T. , Sutton D. J. 
Published: September 2021

abstract
Experimental determinations of the velocity of compressional waves in plates of varying thickness are presented. Measurements indicate that if the thickness of the plate is less than about 0.2 of the wavelength, the concept of propagation in a “thin” 2-dimensional plate is valid. For thicknesses greater than this and up to about 0.75 of the wavelength, the velocity steadily increases until the “3-dimensional” propagation velocity is reached.
Radiation from supersonic faulting
Authors: Savage J. C. 
Published: September 2021

abstract
The far-field radiation from a simple fault model is given by the radiation pattern associated with the appropriate strain nucleus (e.g., double couple) multiplied by a fault propagation factor. For a unilateral fault model the propagation factor is F ( c ; t ) = ζ bd [ H ( τ ) − H ( τ − ( L / ζ ) ( 1 − ( ζ / c ) cos ψ )) ] / ( 1 − ( ζ / c ) cos ψ ) where ξ is the velocity of fault propagation, b is the fault slip, d is the fault width, τ = t − r0/c, r0 is the distance of the observer from the initial point of faulting, c is the velocity of the seismic wave, H(τ) is the unit-step function, L is the length of the fault, and ψ the angle between r0 and the direction of fault propagation. This representation is valid for both subsonic and supersonic fault propagation. The latter case is important because Weertman (1969) has recently shown that spontaneous faulting may propagate at supersonic velocities. Because the propagation factor is always positive, the nodal planes for the radiation are the same as for the appropriate strain nucleus. Finally, it is shown by the application of this equation that the radiation from a screw dislocation segment is represented by the double-couple nucleus, not the compensated linear-vector dipole nucleus as recently suggested by Knopoff and Randall (1970).
The velocities in the outer core
Authors: Hales A. L. , Roberts J. L. 
Published: September 2021

abstract
Earlier studies of the velocity distribution in the outer core have been based on the travel times of SKS.SKS arrivals can only be observed satisfactorily for arc distances at the surface greater than 85°. This lower limit of observation of SKS corresponds to an arc distance of 40.2° within the core. Thus the velocities in the outermost 250 km of the core are based upon an extrapolation. We have used observations of the difference in time of arrival of SKKS and SKS to obtain core travel times extending the range of observation down to a Δ within the core of about 14°. The velocity distribution thus found is significantly lower than those of Jeffreys (Bullen, 1963) and Randall (in press) near the core mantle boundary.
An analysis of some local earthquake phases originating near the afar triple junction
Authors: Searle R. C. , Gouin P. 
Published: September 2021

abstract
A study of Pn, Sn and Lg phases from 86 earthquakes which have occurred within 12.4° of WWSS station AAE is presented. Travel-time curves for each phase have been determined, and the corresponding seismic velocities have been deduced from them. Velocities of 7.95 km/sec and 4.29 km/sec were found for Pn and Sn respectively. Two different Lg velocities were found: 3.50 km/sec for ray paths between Uganda and Addis Ababa, and 3.73 km/sec for ray paths in the Red Sea and northern Ethiopia. The travel-time curves also allow an upper limit of 48 km to be placed on the crustal thickness under AAE.
Regional variations in the efficiency of propagation of Sn and Lg are discussed. Efficient propagation of Lg from epicenters near the center of the Red Sea suggests that not all of the Red Sea floor is pure oceanic crust. Sn is not propagated across northern Afar, suggesting that a gap occurs in the lithosphere there, but it is propagated efficiently across much of southern Afar. Finally, the seismic parameters deduced here indicate the existence of a widespread region of high temperature, low velocity, low density upper-mantle material underlying the Afar triple junction and the surrounding regions.
Seismic source summary for U. S. underground nuclear explosions, 1961-1970
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 1961-1970 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 intended to furnish all available source data for studies of seismic sources, as well as studies of seismic transmission characteristics of the Earth.
Regional variations of source properties in southern California estimated from the ratio of short- to long-period amplitudes
Authors: Wyss Max , Brune James N. 
Published: September 2021

abstract
The ratio of short- to long-period amplitude is expressed in terms of apparent stress, rigidity times energy over moment (μEG/M0), for 277 earthquakes in California. A map showing the apparent stresses is compiled. In general, the Mendocino and San Andreas faults as well as the Gulf of California area are regions of large surface-wave excitation and little short-period radiation (low apparent stress). Away from the main fault zones, the apparent stresses tend to be higher. Regions of conspicuously low surface-wave excitation (high apparent stress) are the Laguna Salada-Sierra Juarez region in northern Baja California, the California-Nevada border region north of Bishop, and the region associated with the bend of the San Andreas between San Bernardino and San Gorgonio Mountain. A detailed comparison of earthquakes with accurately-known depths at Parkfield and Borrego Mountain indicates two important differences in apparent stresses between these two source regions. The apparent stress at all depths is larger at Borrego Mountain than at Parkfield, and it increases with depth at Borrego Mountain, whereas it remains constant at all depths at Parkfield. The explanation for the variation of surface-wave excitation (apparent stress) is not known for certain, but it could be related to variations in true stress.