bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation of a layered, elastic, half-space by uniformly moving line loads
Authors: Dunkin J. W. , Corbin D. G.
Published: September 2021

abstract

When a layered half-space is subjected to loads which move uniformly along its surface, the deformation of the half-space depends on the manner in which the load couples into the surface-wave modes. The uniform speed of the load selects those parts of the modal spectra that have phase velocities equal to the load speed. The restriction that the phase velocity be real leads to novel dispersion relations for the leaky modes, but the trapped mode dispersion relations are the usual ones. In this paper general expressions are derived for the solution for uniformly moving line loads on an elastic half-space containing an arbitrary number of layers. In addition to the modal contributions, the solution contains contributions from source singularities and a line integral that reduce to the static solution as the load speed tends to zero. The details are worked out for the special case of a single low-speed layer lying on a high-speed half-space. For the modes, real and imaginary parts of frequency and velocity amplitudes at various depths are presented as functions of frequency. Total velocity waveforms are shown for selected load speeds and depths.
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 > 20H the displacements decay like (r/H)−α where 2 < α < 5. For compressional and strike-slip displacements at all depths and for dip-slip source above the layer, 2 < α < 3. For a dip-slip source located below the layer, 3 < α < 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

This 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

abstract

The 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

abstract

The 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.
Zero baseline correction of strong-motion accelerograms
Authors: Trifunac Mihailo D.
Published: September 2021

abstract

A new method is proposed for standard baseline correction of strong-motion accelerograms. It is based on high-pass filtering of the uncorrected digitized accelerogram data. Unlike the parabolic baseline correction, the new method has well-defined frequency transfer function properties which are largely independent of the record length.
The propagation of Love waves across nonhorizontally layered structures
Authors: Lysmer John , Drake Lawrence A.
Published: September 2021

abstract

A finite element technique is developed to study the propagation of Love waves across nonhorizontally-layered structures. A half-space is approximated by a rigid base at great depth. Previous results of other authors are confirmed. Detailed models of a continental boundary and of a structure including a slab of lithosphere dipping downard at an angle of 45° are analyzed. For incident fundamental Love-mode motion, at a period of 25 sec, on either side of the model of a continental boundary, the total energy in all of the reflected modes is found to be less than 0.1 percent of the incident energy, while the energy in the transmitted higher modes is 48 percent of the incident energy. These results are strikingly different from the results for previous models of a continental boundary. For incident fundamental Love-mode motion, at a period of 25 sec, on the “oceanic” side of the model including the dipping slab, the total energy in the reflected modes is found to be approximately 1 percent of the incident energy, and that in the transmitted higher modes, 36 per cent of the incident energy. For incident fundamental Love-mode motion, at a period of 25 sec, on the “shallow sea” side of the model including the dipping slab, the total energy in the reflected modes is found to be approximately 3 percent of the incident energy, and that in the transmitted higher modes, 34 percent of the incident energy.
On the computation of seismic ray travel times and amplitudes
Authors: Chapman C. H.
Published: September 2021

abstract

The usual methods of interpolating velocity-depth profiles cause discontinuities in the velocity gradient and anomalous geometrical ray amplitudes. Numerical methods are presented for interpolating a velocity profile and evaluating the ray integrals which avoid these difficulties. They allow smooth amplitude curves to be calculated directly. An example is given for the Herrin P velocity profile.
Reflections from discontinuities beneath antarctica
Authors: Adams R. D.
Published: September 2021

abstract

Early reflections of the phase P′P′ recorded at North American seismograph stations from nuclear explosions in Novaya Zemlya are used to examine the crust and upper mantle beneath a region of eastern Antarctica. Many reflections are observed from depths less than 120 km, indicating considerable inhomogeneity at these depths in the Earth. No regular horizons were found throughout the area, but some correlation was observed among reflections at closely-spaced stations, and, at many stations, reflections were observed from depths of between 60 and 80 km, corresponding to a likely upper boundary of the low-velocity channel. Deeper reflections were found at depths of near 420 and 650 km. The latter boundary was particularly well-observed and appears to be sharply defined at a depth that is constant to within a few kilometers. The boundary at 420 km is not so well defined by reflections of P′P′, but reflects well longer-period PP waves, arriving at wider angles of incidence. This boundary appears to be at least as pronounced, but not so sharp as that near 650 km. The deep structure beneath Antarctica presents no obvious difference from that beneath other continental areas.
Deformation of a multilayered half-space by stress dislocations and concentrated forces
Authors: Singh Sarva Jit
Published: September 2021

abstract

The problem of the static and dynamic response of a nonhomogeneous, isotropic, elastic half-space to stress dislocations and concentrated forces is discussed. Integral expressions for the displacements are obtained in the case of a two-layered half-space. Results of Singh (1970) are used to study the static deformation of a multilayered half-space caused by a point source placed at an arbitrary depth below the free surface. The source is represented as a discontinuity in the z-dependent coefficients of the displacement and stress integrands at the source level.
A note on the effect of simple topography on seismicSHwaves
Authors: Boore David M.
Published: September 2021

Finite difference calculations for SH-motion, as well as field observations, show that topography can have significant effects on seismic waves when the incident wavelengths are comparable to the size of the topographic features and the topographic slopes are relatively steep. These effects are frequency-dependent and can range from amplification to deamplification at a given site. For the models considered in this paper, amplifications of 75 per cent as compared to motions produced in regions of no topography were found. A qualitative discussion of the strong-motion accelerogram recorded at Pacoima Dam from the San Fernando earthquake of February 9, 1971, suggests that the recorded accelerations could, at any period, be expected to differ by 25 to 50 per cent from those that would have been recorded if no topographic features were present. The complex terrain precludes a prediction of the actual magnitude or sign of the difference. The present results are probably most significant from the viewpoint of engineering seismology, for the conditions required for a significant topographic effect are most likely to occur in the period range of engineering interest.
Disturbances in semi-infinite heterogeneous media generated by torsional sources. I
Authors: Sidhu R. S.
Published: September 2021

abstract

This paper studies the generation of axially symmetric transient SH waves in semi-infinite heterogeneous media in which μ and ρ vary with depth. The sources generating these waves are taken in the form of time-dependent torsional-body forces of finite dimensions. The solution is obtained using Hankel and Laplace transforms and Green's function. The disturbance from a buried point source of impulsive type is discussed in two cases, (a) μ = μo(1 + ɛz)2, ρ = ρo (1 + ɛz)2, (b) μ = μoe2az, ρ = ρoe2az. It is shown that, in contrast to the results for a homogeneous medium, in case (i), the wave reflected by the free surface generates secondary disturbances which trail behind the wave front and die out as t increases; the incident wave in this medium generates no such disturbance. In case (ii), however, both the incident as well as the reflected waves generate secondary disturbances.

Formal solution for the disturbance in a heterogeneous layer of finite depth with stress-free boundaries is discussed in Appendix II.
The use of body-wave spectra in the determination of seismic-source parameters
Authors: Hanks Thomas C. , Wyss Max
Published: September 2021

abstract

Teleseismic determinations of body-wave (P, S) spectra, interpreted in terms of the Brune (1970) seismic-source model, are used to estimate the parameters seismic moment (Mto) and source dimension (r) for three large, shallow, strike-slip earthquakes occurring on nearly vertical fault planes and for which the same parameters can be determined from field (F) data. These earthquakes are (1) the Borrego Mountain, California, earthquake (April 9, 1968) for which [Mo(P) = 10, Mo(S) = 6.6, and Mo(F) = 3.6] × 1025 dyne-cm and [r(p) = 14, r(S) = 23, and L/2(F) = 17] km; (2) the Mudurnu Valley, Turkey, earthquake (July 22, 1967) for which [-Mo(P) = 9.1, Mo(S) = 8.5, and Mo(F) = 7.4] × 1026 dyne-cm, and [r(P) = 39, r(S) = 48, and L/2(F) = 40] km; and (3) the Dasht-e-Bayāz, Iran, earthquake (August 31, 1968) for which [Mo(P) = 4.8, Mo(S) = 8.6, and Mo(F) = 18] × 1026 dyne-cm, and [r(P) = S1, r(S) = 48, and L/2(F) = 40] km. The Brune (1970) model is well-calibrated with respect to the determination of these parameters for the earthquakes considered. A minimum estimate for the radiated energy can be expressed in terms of Mo and r; this estimate is low by a factor of 10 with respect to the estimate obtained from energy-magnitude relations for these three earthquakes. The stress drops of these events are of the order of 10 bars.
Focal mechanisms of Indian earthquakes
Authors: Banghar A. R.
Published: September 2021

abstract

Focal mechanism solutions are presented for two earthquakes that occurred in peninsular India. The first motions of P, PKP and the polarization (or first motions) of S waves were used for this investigation. Both of these mechanisms are found to be associated with strike-slip faulting.
Aftershock sequence and focal parameters of the February 28, 1969 earthquake of the Azores-Gibraltar fracture zone
Authors: López Arroyo A. , Udías A.
Published: September 2021

The earthquake of February 28, 1969, which occurred about 500 km west of the Strait of Gibraltar, was felt over the entire Iberian Peninsula, in a wide region of Morocco, and south to the Canary Islands. It had a long sequence of aftershocks continuing for at least 10 months, but, nevertheless, most of the energy seems to have been liberated in the main shock of which the mb was 7.4.

The source mechanism solution indicates a fault plane striking N 67°W and dipping 68°SW, with motion principally of the strike-slip type. There also is some overthrusting. The horizontal extent of faulting is of the order of 90 km.
Application of prediction analysis to hypocenter determination using a local array
Authors: Peters David C. , Crosson Robert S.
Published: September 2021

Prediction analysis provides an efficient means of estimating errors in local earthquake hypocenter determinations using a dense array of seismometers. The standard errors of the hypocentral coordinates and the origin time due to random errors in the data and model parameters may be calculated rigorously for a least-squares hypocenter inversion procedure using arbitrary earth models. Contour maps of the estimated standard errors in the hypocenter parameters are plotted for two array configurations and for several earth models and event depths. These maps are useful in predicting the relative accuracy and difficulty of hypocenter location as a function of position in the array, and in selecting events with small relative error to be used in velocity-structure refinement in the vicinity of the array. In particular, the method may be used to provide a means of optimizing array geometry to provide maximum hypocenter control in specific target regions. Tests were made using hypothetical data with prescribed error distributions showing good agreement with the error analysis.
Quantitative seismicity maps of India
Authors: Kaila K. L. , Gaur V. K. , Narain Hari
Published: September 2021

Using the Kaila and Narain (1971) method, three quantitative seismicity maps have been prepared for the Indian subcontinent which are compared with regional tectonics. These are the A-value map, the b-value map and the return-period map for earthquakes with magnitude 6 and above where A and b are the constants in the cumulative regression curve represented by log N = A - bM. The A-value seismicity map shows that India can be divided into two broad seismic zones, the northern seismically highly active zone and the southern moderately active zone. In the northern active zone, a number of seismic highs have been delineated such as the Pamir high, the northwest-southeast trending Srinagar-Almora high, the Shillong massif high, the Arakan Yoma high and the West Pakistan highs. These seismic highs are consistent with the Himalayan tectonic trends. Contrary to this, two seismic highs fall in the Tibet plateau region which align transversely to the main Himalayan trend. In the southern moderately active zone, two seismic highs are clearly discernible, the east and the west coast high, the latter being seismically more active than the former. The least active zone encompasses the Vindhyan syncline and the areas of Delhi and Aravalli folding. Between this zone and the east coast high lies another moderately active zone which encloses the Godavari graben, western part of the Mahanadi graben and the Chattisgarh depression. The b-value seismicity map also demarcates the same active zones as are brought out on the A-value map. The return-period map of India for earthquakes with magnitude 6 and above shows a minimum return period of 100 years in the Pamirs, about 130 years in the various seismic highs in the northern active zone, 180 years on the west coast high, 200 years on the east coast high and about 230 years in the least active Vindhyan-Aravalli zone and the Hyderabad-Kurnool area. These quantitative seismicity maps are also compared with the seismic zoning map of Indian Standards Institution and seismicity maps of India prepared by other workers.
Elastic velocity anisotropy in the presence of an anisotropic initial stress
Authors: Dahlen F. A.
Published: September 2021

The effect of a homogeneous anisotropic initial stress on the propagation of infinitesimal amplitude elastic body waves in a perfectly elastic, homogeneous medium is investigated. If the medium is inherently isotropic in the reference configuration and if the magnitude τ0 of the deviatoric part of the initial static stress is small compared to the rigidity μ of the medium, then the apparent body-wave velocities of P waves are unaffected by the initial stress to first order in τ0/μ. The apparent body-wave velocities of S waves are rendered anisotropic to first order, and this effect is described explicitly. It is concluded that the direct effect of an anisotropic initial stress cannot contribute appreciably to the observed velocity anisotropy of horizontally propagating P waves in the oceanic upper mantle. Those observations require an inherent elastic anisotropy of the oceanic uppermantle material.
An earth-flattening transformation for waves from a point source
Authors: Hill David P.
Published: September 2021

An earth-flattening transformation is developed for wave-propagation problems that can be formulated in terms of uncoupled scalar Helmholtz equations. Through the transformation, wave problems in isotropic, spherically symmetric media with a specified radial heterogeneity can be expressed in terms of a flat geometry with a suitably vertical heterogeneity. The transformation is exact for homogeneous (no source) problems and is useful for normal mode studies. When a point source of waves is present, the earth-flattening transformation together with the Watson transform converts the reflected wave field from a sum over discrete, spherical eigenfunctions to an integral over continuous wave numbers in a flat geometry. The far-field form of this integral shares many properties with the Weyl integral and is useful for body-wave studies in a spherical earth.
Dilatancy, pore fluids, and premonitory variations of ts/tp travel times
Authors: Nur Amos
Published: September 2021

Nerseov et al. (1969) found that the travel-time ratio of shear and compressional waves, ξ = ts/tp varies prior to the occurrence of earthquakes in the Garm region, USSR. Laboratory results indicate that the decrease of ξ can result from dilatancy of rocks around the focal zone. The subsequent increase of ξ, which terminates with an earthquake, can be caused by the flow of ground water into the dilated zone. The increasing pore pressure weakens the rock and leads to the observed failure.
Estimated earthquake probabilities in the north circum-Pacific area
Authors: Shakal A. F. , Willis D. E.
Published: September 2021

abstract

Gumbel's extreme value theory is applied to the estimation of probabilities of occurrence and return periods for large earthquakes in the north circum-Pacific area, using earthquake data from 1930 through 1971. The probability model of Epstein and Lomnitz is discussed with reference to Gumbel's extreme value theory. Estimated probabilities and expected extremes within individual tectonic blocks are calculated and compared. The area of the Aleutian Arc between 155°W and 167°W is found to have about an 80 per cent probability of an Ms ≧ 8 earthquake by 1980.
Stick-slip propagation velocity and seismic source mechanism
Authors: Wu Francis T. , Thomson K. C. , Kuenzler H.
Published: September 2021

abstract

Earthquakes, at least the shallow ones, take place along pre-existing fault planes. The controlling factor is, therefore, friction, and the fault growth process resembles that of stick-slip propagation. We have simulated this process in a two-dimensional model. It is found that propagation velocity can range from sub-shear to 1.1 Vs (the latter is not a limiting value).
Determination of the seismograph phase response from the amplitude response
Authors: Bolduc P. M. , Ellis R. M. , Russell R. D.
Published: September 2021

abstract

Determination of the phase response of a minimum-phase seismic system directly from the amplitude response by the Hilbert transform is investigated. The error by this technique is found to be less than 2° with the major source of inaccuracy being the uncertainties in the amplitude data. This technique is useful for rapid determination of the phase response if the amplitude response is known.
Seismicity and tectonics of western Venezuela
Authors: Dewey James W.
Published: September 2021

abstract

New seismicity data on western Venezuela and northeastern Colombia are presented. Teleseismically recorded earthquakes from 1930 through 1970 have been relocated by Joint Hypocenter Determination (JHD) or with source-station adjustments calculated by JHD. Additionally, 540 days of recording have been obtained with local seismographs installed near the Boconó Fault.

The most intense shallow activity occurred north and south of the Tachira Depression along the eastern flank of the Cordillera Oriental of Colombia. The Boconó Fault Zone is seismically active; small shallow shocks were recorded in it by the local stations. Shallow earthquakes also occur in the Cordillera de Mérida away from the Boconó Fault.

The new hypocenters for the intermediate-depth Bucaramanga earthquakes define a smaller source volume than defined by previously computed hypocenters. A previously inferred southward-dipping seismic zone near Bucaramanga is probably spurious, a consequence of correlation between errors in latitude and errors in depth. If one assumes that these intermediate-depth earthquakes lie on a single lithospheric slab, that slab strikes approximately north and dips to the east.

The distribution of hypocenters and focal mechanisms support the platetectonic hypothesis that the present tectonics of northwestern Venezuela are a result of eastward motion of the Caribbean plate with respect to the South American plate. The principal interface between these two plates may have changed within the last 5 m.y. from a zone of underthrusting west of the Sierra de Perija to the predominantly right-lateral Boconó Fault Zone.
Ambient earth motion in the period range from 0.1 to 2560 sec
Authors: Fix James E.
Published: September 2021

abstract

Amplitude spectral density of the ambient earth motion in the vertical and horizontal directions at a quiet site are given in graphical and tabular form over the five decades of period from 0.1 to 2560 sec. Comparison of these spectra in the period range between 0.1 and 3 sec with the Brune and Oliver (1959) minimum curve and in the period range between 10 and 100 sec with spectra from the mines at Las Cruces, New Mexico, and Ogdensburg, New Jersey, indicate that in these period ranges the spectra are representative of the quietest seismograph stations presently known. These spectra can serve as a guide for seismologists and other scientists interested in the quiescent vibrations of the ground.
ZİHİNSEL YETERSİZLİĞİ BULUNAN BİREYLERİN MATEMATİK EĞİTİMİNDE ÖĞRETİM TEKNOLOJİLERİNİN KULLANIMI: BİR LİTERATÜR TARAMASI
Authors: Türel Yalın Kılıç , Akgün Kübranur
Published: September 2021

Özel eğitimde önemli yeri olan matematik eğitimi teknoloji kullanımına ihtiyaç duyulan başlıca alanlardan biridir. Bu noktada eğitimcilerin materyal alternatiflerini artırma konusunda ise teknolojik araçların önemli avantajlar sunduğu düşünülmektedir. Ancak alanyazın incelendiğinde konu ile alakalı yeterli sayıda çalışma ile karşılaşılamamaktır. Bu araştırmada ise özel eğitim hizmetlerinden yararlanan zihinsel yetersizliğe (ZY) sahip öğrencilerin matematik eğitiminde teknolojinin kullanımına ilişkin çalışmaların incelenmesi amaçlanmıştır. Betimsel tarama yöntemi kullanılarak gerçekleştirilen bu araştırma kapsamında Google Akademik, Web of Science, Science Direct, OpenThesis, Stanford Libraries ve YÖKTez veritabanları üzerinden anahtar kelimeler ile 2010-2021 yıl aralığında Türkçe ve İngilizce yayın dillerinde 22 çalışma incelemeye alınmıştır. İnceleme sonucunda farklı formatlarda öğrenme sürecine dâhil edilen teknoloji ürünlerinin genel olarak akademik başarıyı arttırma, davranışı sürdürme ve bilgiyi genelleyebilme açısından yardımcı rol üstlendiği belirlenmiştir. Kullanılan teknolojilerin ise sanal teknolojiler ve video destekli materyaller çevresinde yoğunlaştığı görülmüştür. Ayrıca çalışmalarda teknolojiden bilginin çoklu formda sunularak kalıcı hale getirilmesi ve öğrenci hatalarının anında geri bildirimler ile düzeltilmesi odağında faydalanılmıştır.
MİHAİL ŞOLOHOV’UN DURGUN DON ROMANI ÜZERİNE TEMATİK BİR İNCELEME
Authors: Tekeli Selin
Published: September 2021

Bir toplumun kültürel değerlerini ortaya çıkarmada temel kaynak söz varlığının incelenmesinden geçer. Özellikle yazılı kaynakların, edebi eserlerin söz varlığı açısından incelenmesi ve edebi metinlerde kullanılan sözcüklerin tespit edilmesi, ait olduğu toplumun kültürel unsurlarını ve tarihsel gelişim sürecini yansıttığı için dilin önemli bir kaynağı niteliğindedir. Çalışmanın konusunu 20. Yüzyıl Sovyet Rus yazarı Mihail Aleksandroviç Şolohov’un Durgun Don adlı romanında geçen sözcüklerin tematik incelemesi oluşturmaktadır. Ancak araştırmanın hacmini ve amacını aşmaması için çalışmamızda tematik sınıflandırma başlığı altında sadece ad soylu sözcükler incelenmiş diğer sözcük türlerine yer verilmemiştir. Eser boyunca kullanılan ve tekrar edilen bu sözcükler birçok madde başı altında toplanarak sözlüksel alan çalışması yapılmıştır. Don Kazak yaşamının açıkça gözler önüne serildiği bu eserde tespit edilen temalardan da anlaşılacağı üzere Don Kazaklarının gelenek, görenekleri, bakış açıları, kültürleri, sosyal hayatları, toplumsal ilişkileri, maddi ve manevi değerleri gibi birçok konuda önemli bilgiler edinmek mümkündür. Eserdeki temaların çeşitliliği ve zenginliği Şolohov’un üslubu ve dili ile ilgili de önemli tespitlerde bulunulmasını sağlamıştır. Araştırma sonucunda yazarın bu eserinden hareketle aynı kavram grubu içinde tespit edilen sözcükleri tematik olarak sınıflandırarak eserin tematik sözlüğünü oluşturmak ve Rusçanın sözcük hazinesine katkıda bulunmak amaçlarımız arasındadır.