bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crustal structure in the Himalayan foothills area of north India, from ‘P’ wave data of shallow earthquakes
Authors: Kaila K. L. , Reddy P. R. , Narain Hari 
Published: July 2021

Abstract
Travel times of Pg, P* and Pn waves of twenty shallow earthquakes with epicenters in the Himalayas and recorded at New Delhi, Chatra, Dehradun, Bokaro and Shillong Observatories of India were analyzed statistically to determine the crustal structure. A short seismic refraction profile about 15 kms long shot by the ONGC in the Punjab foothills enabled us for the first time to take into account, in the evaluation of crustal structure, the effect of the sedimentary layers which had been invariably neglected by the earlier workers. From the present study, the most probable crustal structure in the Himalayan foothills area of northern India, appears to consist of sedimentary layer 6 ± 1 kms (velocity 2.7 km/sec average), granitic layer 8 ± 5 kms (velocity 6.2 ± 0.1 km/sec) and basaltic layer 14 ± 7 kms (velocity 6.9 ± 0.1 km/sec), giving a total crustal thickness of 28 ± 8 kms. The upper mantle velocity in this area was found to be 8.2 ± 0.1 km/sec.
Geologic structure of the Taltal Area, Northern Chile, in relation to the earthquake of December 28, 1966
Authors: Arabasz Walter J. 
Published: July 2021

abstractThe Taltal area, which lies within the coastal cordillera of northern Chile, is dominated by a group of major active faults that cut a eugeosynclinal section of predominantly Jurassic andesites overlying Paleozoic metamorphic and plutonic rocks and intruded by Late Mesozoic plutons. The Atacama fault, a suggested regional strike-slip fracture parallel to the coastline, has been obliquely cut and left-laterally offset 10 km by the Taltal fault, which passes through the town of Taltal. Three distinctive features were found to be consistently offset 10 km by the Taltal fault: the easternmost strand of the Atacama fault, an intrusive contact, and a unique volcanic unit. Former continuity of the Atacama fault through the Taltal region is proposed, and subsequent disruption by the Taltal fault appears to have caused major structural readjustments in the still-active Atacama fault zone.The tentative offshore epicenter and aftershock distribution of the December 28 earthquake are not directly correlative with faults that have been mapped in the nearby on-shore areas; this lack of correlation is not surprising in view of the suggested depths of hypocenters in the lower crust or upper mantle.
The perturbation of Love wave spectra
Authors: Harkrider David G. 
Published: July 2021

abstractThe equations governing the variational principles for Love wave spectra are investigated. It is shown that assumptions used by earlier authors are not necessary to the validity of the variational techniques.Moreover it is demonstrated that except for a homogeneous plate, these assumptions are false for plane multilayered media and lead to incorrect expressions for group-velocity perturbations. The correct expressions are determined and examples of their use are given.
Rayleigh wave group velocities in central California
Authors: Sutton D. J. 
Published: July 2021

abstract
Experimentally determined Rayleigh-wave dispersion curves of group velocity are given for five paths from NTS to stations in the network operated by the Seismographic Station at U.C. Berkeley. Periods observed range from 4 to 14 seconds. Although, as expected, two different paths from NTS to the western edge of the Sierra Nevada resulted in similar curves, efforts to find empirical curves appropriate to the Great Valley and the Coast Ranges on the assumption of provinces with parallel boundaries were not successful. Estimates of group velocity across the Great Valley along the path NTS to BRK indicate velocities, in the period range 5–9 seconds, considerably lower than would be expected from crustal models so far suggested.
A study of P nodal solutions (1922-1962) in the Wickens-Hodgson Catalogue
Authors: Stevens Anne E. , Hodgson John H. 
Published: July 2021

abstract
Computer-determined P nodal solutions in the Wickens-Hodgson Catalogue were compared with earlier visually-determined solutions for the same earthquakes. Good agreement was found in about 40 per cent of the solutions. Lack of agreement was due chiefly to poor distribution of data in azimuth about the epicenter. Necessary, but not sufficient, conditions for well-defined nodal plane solutions were determined: there must be a minimum of 100 observations with at least two in each 90° segment of azimuth; data must be at least 80 per cent consistent with the selected nodal planes. Fourteen of the 618 earthquakes in the Catalogue met these requirements.
Diffraction of elastic waves by a rigid 90° wedge Part II
Authors: Kraut Edgar A. 
Published: July 2021

abstract
Integrals representing the reflected and diffracted elastic waves generated by the incidence of a plane compressional wave on a rigid quarter-plane are evaluated by an application of the Cagniard-De Hoop technique. It is shown that diffracted spherical waves radiate away from the tip of the quarter-plane at the shear and compressional wave speeds. The spherically spreading compressional wave excites secondary shear waves on the surfaces and edges of the quarter-plane. These secondary spherical wavelets envelope a ruled surface which is conical in shape at the edges of the scatterer. The envelope propagates away from the quarter-plane at the critical angle and forms a Mach wave or bow wave. The usual reflected shear and compressional plane waves are also present and combine with the diffracted waves to form the geometric shadow of the quarter-plane.
Estimation ofPcPtravel times and the depth to the core
Authors: Taggart James , Engdahl E. R. 
Published: July 2021

AbstractBased on a new P velocity distribution and observed PcP travel times from nuclear explosions, the core is estimated to have a mean radius = 3477 ± 2.0 km (depth = 2894 ± 2.0 km). Five velocity models were tested for the lower-most 90 km of the mantle. The PcP data suggest that the P velocity increases slightly with depth in this region. Tables of PcP travel times have been computed for the preferred model and a core radius of 3477 km.
Regional variations inPtravel times
Authors: Herrin Eugene , Taggart James 
Published: July 2021

AbstractAzimuthally dependent station corrections for 321 seismological stations were estimated using data from 400 large earthquakes (1961-1964) and 30 large explosions. 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. In addition, estimates of variance of station error distributions were computed.
Laser interferometer calibration system for extensometers
Authors: Hade G. , Conner M. , Kuo J. T. 
Published: July 2021

Abstract
A laser interferometer technique has been developed for calibrating extensometers at the Ogdensberg Station of Lamont Geological Observatory. It provides remotecontrolled calibration of both horizontal and vertical extensometers within the linear range of the transducer output.
The present calibration system consists of an electromagnetic driving unit and a Michelson interferometer. The transducer end of the extensometer is displaced longitudinally with an electromagnetic driving unit, which is excited by a variable low-frequency oscillator with a bandwidth of 0.0005 to 60 kHz. The resultant displacement is detected by counting fringe displacements of the interferometer with an Ne-He laser source. With this calibration system, motion as small as 0.03 micron can be determined with excellent repeatability and with errors of less than 5 per cent, in comparison with errors of more than 40 per cent for the optical calibration method previously used.
Universal dispersion tables
Authors: Anderson Don L. , Harkrider David G. 
Published: July 2021

AbstractThe universal dispersion theory, presented in Part I, is extended to allow computation of group velocity and amplitude partial derivatives. Tables giving the effect of a change in any parameter on phase velocity, group velocity and amplitude are given for two earth models, one oceanic and one continental shield. Tables are given for the fundamental and first three higher Love modes.These tables make it possible to compute dispersion parameters for the first four Love modes for any realistic earth model or to invert observations to an earth model. Attenuation of Love waves for an arbitrary distribution of Q versus depth can also be computed by using techniques previously described.
Aftershocks of the Truckee, California, earthquake of September 12, 1966
Authors: Greensfelder Roger 
Published: July 2021

Abstract
On September 12, 1966, at 16h 41m, an earthquake of magnitude 6.0 to 6.5 occurred about 10 km northeast of Truckee, California. Hypocenters of 158 after-shocks that occurred between September 14 and 25 were found to be within a volume 3 km wide by 10 km long by 12 km deep. The magnitude-frequency curve appears anomalous, as there seem to be too many shocks greater than magnitude 2 compared to the number of small ones under magnitude 0.5.
Nodal-plane determinations indicate two modes of faulting for the aftershocks. Strike-slip faulting with nodal planes striking N. 40°W. and N. 50°E. is dominant; secondary normal faulting occurs on nodal planes striking nearly north. An attempt is made to relate the strain release pattern of these aftershocks to major regional right-lateral shear and extension.
Measurement of static and dynamic response of the Green Building at the MIT campus to insolation and wind
Authors: Simon I. , Strong P. F. 
Published: July 2021

Abstract
Static and dynamic response of a 20-story concrete building (the Green Building at MIT, Cambridge, Mass.) to solar heating and wind was measured by means of a diamagnetic tiltmeter. Insolation of the front of the building causes a temporary tilt northwards of approximately 30 arc sec (measured on the 19th floor). Wind causes both tilting leewards and vibration of the building. The natural frequency of the cantilever mode of vibration of the building is 0.77 c/s. The bending stiffness of the building was determined both from the vibrations and from the steady tilt due to the average wind loading.
The ground effects of the Skopje July 26, 1963 earthquake
Authors: Poceski Apostol 
Published: July 2021

Abstract
Damage distribution in Skopje can be explained in terms of the seismic response of surficial soils. There exists a generally good correlation between the distribution of damage, the thickness of the surficial soil layer, and the predominant periods of microtremors. The most heavily damaged region is covered with about 20 to 30 meters of alluvium, and the predominant period of this alluvium is about 0.36 seconds. The alluvium in this heavily damaged region probably was shaken near its resonant frequency, and soil amplification may have reached three.
The greatest destruction was recorded along a belt which is defined by an abrupt change of the thickness of the alluvium. However, heavy destruction was also recorded on the shallow alluvium side, and no clear explanation exists for this.
Rayleigh wave dispersion in Australia
Authors: Thomas L. 
Published: July 2021

Abstract
The “two-station approximation” method of Brune, Nafe and Oliver (1960) has been used to find Rayleigh-wave phase velocities over nine paths between Australian WWSSN stations. Some simple shear-velocity distributions for each path have also been found, by inversion of the phase-velocity data. The lack of uniqueness of solutions to this inversion problem is illustrated by the presence of several distinct but numerically equally-good solutions for each set of phase-velocity data. Solutions (i.e., shear-velocity distributions) expected to represent the crust-mantle system more faithfully have been selected from these. The values, obtained in this way for shear-velocity distributions in the Australian paths studied, have been compared, and show that there is little variation between different parts of the continent.
The influence of geologic environment on seismic response
Authors: Alcock E. D. 
Published: July 2021

AbstractA brief review is given of the state-of-the-art and the theory involved in the influence of geology on seismic response. Several field experiments are described which were performed to determine the dynamic amplification of seismic response by alluvium. In the Dry Lake area (saturated alluvium) resonant depths of alluvium were observed at 500 feet and 1400 feet. This is in approximately the harmonic ratio as predicted by theory. In the Hidden Valley area (dry alluvium) the resonant depth of alluvium was observed at 300 feet. The ratio of 500 feet to 300 feet for the two areas is in fair agreement with the ratio of 7000 feet to 5300 feet for the velocities of the alluvium in the two areas as determined by the refraction surveys.
A technique for the analysis of transient seismic signals
Authors: Dziewonski A. , Bloch S. , Landisman M. 
Published: July 2021

Abstract
An analytical method, called the “multiple filter technique,” is shown to be a fast and efficient means of studying multi-mode dispersed signals. Amplitudes and phases, as functions of period and velocity, are determined from the output of a set of narrow-band digital filters. The group velocities and other dispersion parameters determined by this technique are concordant with theoretical values when the method is tested with synthetic seismograms. It can recover broader portions of the dispersion present in ordinary seismic recordings compared to the classical peak and trough method. A simple diagnostic diagram is introduced in order to study the time and frequency resolution permitted by this analytic technique.
Application of strain seismographs to the discrimination of seismic waves
Authors: Shopland Robert C. , Kirklin Richard H. 
Published: July 2021

abstract
Examination of microseisms recorded by strain and inertial seismographs at Wichita Mountains Observatory (WMO) has shown that the outputs of vertical strain and vertical inertial seismographs when combined through a linear filter do not provide a significant improvement of the signal-to-noise ratio in the frequency range 0.2 to 10 Hz. However, the ability of a combination of horizontal strain and inertial seismograph outputs to azimuthally discriminate between long-period surface waves arriving simultaneously from different epicenters is successfully demonstrated. The predicted response of strain seismometers to earth motion is verified by the existence of the proper phase and amplitude relationship, and high coherence among selected seismographs for single-source signals.
Precise determination of epicenters and origin times of surface focus seismic events
Authors: Arora S. K. , Manekar A. M. 
Published: July 2021

abstract
Epicenters and origin times pertaining to surface focus events, mainly underground nuclear explosions, have been determined using the method described in this paper with estimates comparable to those of United States Coast and Geodetic Survey (USCGS) determinations. Data used are crude estimates of apparent phase velocity and backbearing, supplied by a medium aperture seismic-array station (at Gauribidanur in South India) using time lags across the array arms, and the preliminary seismogram readings available from just four Indian World-Wide Network of Standard Seismographs (WWNSS) stations and less than five foreign stations. The method essentially solves a system of time-term equations until an ideal “minimum variance” is achieved to best fit the observed onset times. Provision has also been made in the method to give an allowance for onset-reading errors, if any to the extent of ±0.53 second for epicentral distances up to 10,000 km. Twenty-five Russian tests, LONGSHOT in the Rat Islands and five Nevada tests were tried with the present technique and results compared with corresponding USCGS and United Kingdom Atomic Energy Authority (UKAEA) determinations. For the epicentral regions under study, station time-residuals have also been obtained.
Static deformation of a spherical earth model by internal dislocations
Authors: Ben-Menahem Ari , Singh Sarva Jit , Solomon Faïza 
Published: July 2021

abstract
A localized displacement dislocation is placed inside a homogeneous non-gravitating elastic sphere. The ensuing deformation is obtained in the form of rapidly converging series for arbitrary values of the Poisson ratio and the source parameters. Surface displacements and strains are computed for various sources for an average earth model. The numerical results are mapped on tangential planes and displayed in several forms.
It is found that in the range 30° &lt; θ &lt; 120° the elongation strains fall off with the epicentral distance like Δ−α where 114 &lt; α &lt; 6, provided one proceeds along an arc which does not intersect a nodal line. In the lower hemisphere (90° &lt; θ &lt; 180°) relative to the source, seismic events such as the Chilean earthquake of May, 1960, should produce strains of the order of 10−9, which are on the threshold of detectability of modern extensometers, tiltmeters and rotationmeters.
The range in which the half-space approximation is valid is determined. It is demonstrated that global deformation patterns of major earthquakes can serve as a useful diagnostic tool for recovering the source's spatial characteristics.
Amplitude variations of Rayleigh waves—propagation across a continental margin
Authors: McGarr Arthur 
Published: July 2021

abstract
Seismograms from Berkeley and from a site on the deep ocean bottom off California were compared to ascertain the effect on Rayleigh waves of propagation across the continental margin. Amplitude ratios as a function of period were formed by dividing the spectral component at one recording site by that at the other recording site. In the period range from 14 to 25 sec and for near-normal incidence, the amplitudes of vertical displacement on the ocean bottom were two-thirds to one-third as large as those at Berkeley. Amplitude ratios for waves propagating in either direction across the margin are consistent within experimental error.
Comparison of the experimental amplitude ratios with ratios that were calculated by using a variational technique recently advanced by McGarr and Alsop suggests that there is a striking contrast in structure between Berkeley and the ocean-bottom site, which is about 235 km WNW of Berkeley. The velocities and densities of the lower crust and upper mantle beneath the oceanic site are much higher than those beneath Berkeley; this result is in qualitative agreement with the results of geophysical studies in this region using other techniques.
Electromagnetic seismograph constants by least-squares inversion
Authors: Mitchell B. J. , Landisman M. 
Published: July 2021

abstract
A least-squares method has been developed to determine the free periods and damping constants of an electromagnetic seismograph from its calibration pulse. The resulting values are correct to within a few tenths of one per cent for synthetic calibration pulses, even when moderate levels of microseismic noise are present.
The seismograph constants of the long-period vertical component at Dallas, Texas were determined from in situ measurements and compared with those calculated from the calibration pulse. The results agreed to within four per cent or better for the free periods and damping constants, after correcting for the linear trend and the base coordinate system of the observed pulse. The values differed by as much as 30 per cent when the linear trend and base coordinate corrections were ignored.
Two sets of instrumental constants from an unmatched pair of horizontal seismographs were determined from their calibration pulses. Directions of particle motion for a Love wave train recorded on the same instruments were computed before and after instrumental corrections; the results differed by as much as 8 degrees.
Spectral and correlation analysis of ground-motion accelerograms
Authors: Liu S. C. , Jhaveri D. P. 
Published: July 2021

AbstractThe autocorrelation function and the power-spectral density function of twelve strong-motion earthquake and three underground nuclear explosion accelerograms are obtained using a digital computer. The physical implications of the results and their application in modeling ground accelerations are studied. Simulations by the spectral approach, using filtered stationary processes, and simulations by the correlation approach, using linear, particularly autoregressive processes, are discussed in some detail.
Crust-mantle system in the central Aleutian region—A hypothesis
Authors: Murdock James N. 
Published: July 2021

Abstract
Seismic data acquired during the 1964 VELA UNIFORM Aleutian experiment have been used to construct a model of the local crust-mantle system. The M discontinuity of the model has a synclinal structure whose axis coincides with the islands of the arc. Just south of the islands, the shoaling M is terminated by a northward dipping thrust fault, resulting in a wedge-shaped crustal block sandwiched between mantle components.
An investigation of the Dasht-e Bayāz, Iran earthquake of August 31, 1968
Authors: Bayer Kenneth C. , Heuckroth Lorne E. , Karim Rajab A. 
Published: July 2021

abstract
On Augus&gt;t 31, 1968 at 10:47:37.4 G.M.T., the Khorassan Province of northeastern Iran was shaken by one of the most destructive earthquakes in Iranian history. The epicenter of the earthquake was about 250 kilometers south-southwest of Mashad, approximately 10 kilometers east of the measured surface fault. Its magnitude (Ms) was 7.3. A field investigation revealed that a number of villages were extensively damaged or destroyed, resulting in about 10,000 fatalities&gt; and 60,000 homeless residents.
Surface fractures were noted in several areas. Maximum horizontal displacement was a left-lateral movement of 4.1 meters east of Dasht-e Bayāz. The measured fault length was 25 kilometers. Inaccessibility to part of the area and a time limitation factor curtailed a more complete analysis of the possible fault extensions both to the west and east.
The extensive property damage is attributed principally to poor construction in the region. However, the location of some of the villages on alluvium with a shallow water table was a contributing factor in some instances.
In particular this paper analyzes the regional intensities, the effects on local structures, and the fresh surface faulting phenomenon resulting from the earthquake. Also presented are the results of the investigations on the temporal, spatial, and magnitude characteristics of all recorded seismic activity, before, after, and including the major event.
On the propagation of SH waves in a heterogeneous sphere
Authors: Roy Arabinda 
Published: July 2021

abstract
A complete solution for the wave propagation of an SH torque pulse in a heterogeneous sphere in which density and shear modulus vary as the power of the distance from the center of the sphere is worked out. The solution which is obtained in the form of an infinite series of Legendre polynomial, is transformed into an integral and the integral is evaluated at a saddle point. It is found that times of arrival of different reflected phases agree with those predicted by geometrical ray theory. Further, the expectations in case of a homogeneous earth are also valid in the heterogeneous case.