bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectra of S-waves radiated from bilateral fracture
Authors: Savage J. C. 
Published: July 2021

abstract
The phase and amplitude spectra of the S waves radiated from five different bilateral, tensile fractures in two-dimensional models are discussed. Two S waves, radiated in approximately opposite directions, were recorded for each fracture. The amplitude spectra display the regular sequence of holes first explained by Ben-Menahem. The phase spectra display a phase jump of π radians associated with each hole in the corresponding amplitude spectrum. The phase of the source-time function was extracted from the phase spectra; it is consistent with a representation of the source-time function by a ramp function of 14 μsec duration. An explanation of the observed spectra is given in terms of interference between the initial and stopping phases of the radiated signal. From this viewpoint Ben-Menahem's directivity method is seen as a procedure for detecting the stopping phase in dispersed wave trains. Finally, it is suggested that the analyses by Ben-Menahem and Toksöz of the phase spectra of the Kamchatka 1952 and Alaska 1958 earthquakes have not properly taken account of the phase jumps in the spectra.
Crustal structure in the Himalayan and Tibet Plateau region from surface wave dispersion
Authors: Gupta Harsh K. , Narain Hari 
Published: July 2021

abstract
Dispersion of Rayleigh and Love waves recorded at Seoul, Hong Kong, Shillong, New Delhi and Quetta by similar long-period seismographs has been studied for the Arctic region earthquake of 25th August 1964. The entire paths from the epicenter to the recording stations are continental. Waves recorded at Shillong, New Delhi, and Quetta pass through the high mountain regions of the Himalayas and Tibet Plateau while those recorded at Seoul and Hong Kong do not pass through these high mountain regions. Observed dispersion has been compared with theoretical dispersion curves computed for a three-layer earth model. This gives an average crustal thickness of about 45 km between the epicenter and Shillong, New Delhi and Quetta, 35-37 km between the epicenter and Seoul and Hong Kong and 65-70 km in the Himalayan and Tibet Plateau regions.
Short-period seismic energy radiation patterns from underground nuclear explosions and small-magnitude earthquakes
Authors: Sutton George H. , Mitronovas Walter , Pomeroy Paul W. 
Published: July 2021

abstract
Azimuthal radiation patterns of short-period (0.5-2.0 cps) seismic energy obtained from integrals of the seismograms from two underground nuclear explosions and two earthquakes are used to study the propagation and source characteristics of the Pg and Lg phases in the United States. In addition, the energy spectrum is divided into two bands, greater than and less than 1.4 cps, and the ratio of higher-to-lower-frequency energy is mapped to study the nature of propagation as a function of frequency. Both the total energy and the ratio show large fluctuations with azimuth and distance. However, a general correlation is found between the energy and ratio contours and the major tectonic provinces of the United States. This correlation is attributed to focusing, resulting from lateral variations in velocity and to regional differences in attenuation of the seismic energy. The range in the Q values across the United States, based on the assumption of symmetrical surface wave propagation, is from 200 to 1000, about a factor of 5. The transverse (T) component shows about the same total energy and ratio contour patterns as the vertical (Z) and longitudinal (L) components. Also, energy contour maps are similar to maps obtained using the maximum amplitudes of the Pg and Lg phases. For the events examined, it seems that the nature and distribution of tectonic features along the propagation path are more important in detemining the resultant radiation patterns than the initial conditions at the source. The particle motion at most stations does not give direct proof for the surface wave nature of the Pg and Lg phases, except that Pg tends to be longitudinal or mixed and Lg transverse or mixed.
Automated epicenter locations from a quadripartite array
Authors: Sokolowski T. J. , Miller G. R. 
Published: July 2021

abstract
A quadripartite seismic array has been installed on the island of Oahu, Hawaii, to supply additional data for the Tsunami Warning System of the USCGS. The nuclear explosion LONGSHOT on October 29, 1965, on Amchitka Island served in calibrating the epicenter location system. A moving cross-correlation determined the P wave time delays between the various station pairs. Time delays were then used in a least-squares method to obtain azimuth and emergence angles. The emergence angle is used with the Jeffreys-Bullen travel-time curve to obtain the distance to the source. The emergence angles obtained by using the observed station-pair time delays should be corrected to the emergence angles obtained by using the station-pair time delays as computed from the Jeffreys-Bullen travel-time curve. This comparison will then compensate for the anomalies of the Pacific area. With the values for azimuth and distance, one can then arrive at an approximate epicenter location for earthquakes of normal depth. This method can be used for those situations which require an epicenter location within minutes after the earthquake has been recorded. Methods developed here are designed for an on-line computer.
A micro-earthquake survey of the San Andreas fault system in southern California
Authors: Brune James N. , Allen Clarence R. 
Published: July 2021

abstract
Micro-earthquakes have been systematically recorded with magnitudes down to -1.3 at more than 60 sites along the San Andreas fault system in southern California during intervals of 2 days to 1 year, representing more than 35,000 hours of usable records. Eight trailer-mounted instruments were operated with peak gains of 4-8 million at 20 cps with noise levels averaging about 0.1 mu amplitude of ground motion.
Observed micro-earthquake activity varies from virtually nil along the central section of the San Andreas fault to more than 75 shocks daily in the Imperial Valley. Quietest is the 300-km segment between Cholame and Valyermo; more than one year of recording at Lake Hughes indicates an average of only one micro-earthquake within 24 km every nine days. Activity increases northward from Cholame toward Hollister, and southward it increases abruptly near Valyermo and continues high along major branches of the fault southeast into Mexico, with the exception of the Banning-Mission Creek fault southeast of Desert Hot Springs. Most areas where regional strain or fault creep have been demonstrated by geodetic measurements are also areas of high micro-earthquake activity. Existence of an area of minimal micro-earthquake activity within a broad region of active tectonism, and indeed along the very segment of the fault that broke in the great 1857 earthquake, suggests that short-term micro-earthquake activity is not necessarily positively correlated with long-term activity and with earthquake hazard, and in some areas the relationship may be inverse. However, areal distribution of micro-earthquake activity is grossly similar to that of larger earthquakes (M ≧ 3) during the past 29 years, and in many areas micro-earthquake activity can be approximately predicted by extrapolation of 29-year recurrence curves based solely on larger earthquakes.
Reflection and transmission of elastic waves in a system of corrugated layers
Authors: Levy A. , Deresiewicz H. 
Published: July 2021

abstract
The scattered field generated by normally incident body waves in a system of layers having small, but otherwise arbitrary, periodic deviations from plane parallel boundaries is shown to consist of superposed plane body and surfacetype waves. Results of numerical computations for two like half-spaces separated by a sinusoidally corrugated single layer, and by two layers, reveal the variation of the amplitude of the field with ratios of velocities, densities, impedances, and with those of depth of layers and wavelength of the boundary corrugations to the wavelength of the incident wave.
A search for small, deep earthquakes using quadripartite stations in the Andes
Authors: Suyehiro Shigeji 
Published: July 2021

abstract
To identify small, deep earthquakes in South America quadripartite nets of about one km in size were set up in Toconce, Chile and Cuzco, Peru. During the period of observation the U. S. Coast and Geodetic Survey identified two fairly large, deep earthquakes in northern Argentina within about a month by teleseismic observations, but neither foreshocks nor aftershocks associated with these earthquakes during the period of observation may indicate that there are comparatively few small, deep earthquakes as compared with shallow earthquakes.
In Toconce, at the foot of the Andes, there was a systematic azimuthal distortion in apparent velocity and in direction of propagation, whereas in Cuzco, on the Altiplano, such a distortion was not found.
Washington State earthquakes 1840 through 1965
Authors: Rasmussen Norman 
Published: July 2021

abstract
A tabulation has been made of approximately 850 earthquakes, in Washington State and near its borders, between 1841 through 1965. This list was compiled from previously published scientific reports, newspaper accounts, and unpublished epicenter computations from the University of Washington Seismograph Station. Shocks of intensity V or less are not complete prior to about 1900 because of sparse population making reporting incomplete. There appears to be an increase of larger intensity and magnitude earthquakes since 1936 in Washington State, and especially in the Puget Sound area since 1949.
Magnitude determination at regional and near-regional distances in the United States
Authors: Evernden J. F. 
Published: July 2021

abstract
This report deals with the problems of variation of Pn amplitudes in the regional and near-regional distance ranges (200-2100 kilometers). The data used were recorded by Long Range Seismic Measurement vans of the VELA Seismological Center as a result of earthquakes throughout the United States and numberous nuclear and chemical explosions in the same region.
It is shown that the patterns of Pn amplitudes versus Δ in Western United States and Eastern United States are markedly different and that these differences are related to different velocity structures in the two regions. These differences extend to at least 150 kilometers depth.
Neither the Western United States nor Eastern United States amplitude patterns conform even approximately to that predicted or suggested by Gutenberg and Richter in the 1000-2000 kilometer range. The predicted zone of low-amplitude signals in that distance range does not exist and overestimation of magnitude by as much as 1.5 magnitude units is frequently done because of failure to properly understand the patterns of radiation.
By proper calibration of the Western United States by use of numerous events, it is now possible to make consistent estimates of magnitude at all distance ranges for most explosions and earthquakes. Obtaining consistent estimates of amplitude as a function of distance for a particular event requires a knowledge of the energy distribution between the several refracted phases used between 200 and 2500 kilometers distance. Data on hand show that the energy partition function is reasonably uniform throughout the regions investigated but that locally it may vary radically, resulting in a ten-fold change in relative excitation of two refracted phases.
Patterns of energy radiation and decay are probably approximately determinable from knowledge of velocity structure and vice versa. Both are best determinable from explosion data where origin time and focus are accurately known.
Truncated crustal transfer functions and fine crustal structure determination
Authors: Leblanc Gabriel 
Published: July 2021

abstract
A seismic pulse is influenced by the various media through which it has travelled. The crust is known to have a considerable influence. With the use of the Thomson-Haskell matrix formulation, the crustal effect can be easily calculated. Because a time window is imposed on the signal, it is necessary to take into account this truncation in calculating the theoretical crustal effects. A method to obtain truncated crustal transfer functions is presented.
It is suggested that the frequency analysis of short-period P waves can yield detailed information on the crustal structure at a given station when selected truncated transfer functions are used as crustal inverse filters. The basis for deciding upon a particular model is the optimum match between one of a series of spectra corrected for a series of crustal models and the approximated spectrum of the incident pulse obtained through the averaging of many well grouped spectra.
The earthquake P phases which penetrate the earth's core
Authors: Shurbet D. H. 
Published: July 2021

abstract
Travel times of all earthquake phases which enter the core as P and emerge as P are explained in terms of a core model containing two velocity discontinuities. Amplitudes of PKIKP and PKP change little with changes in distance from the source except in the rangeΔ = 142° to Δ = 152°. In this range large amplitubes are observed which result from the simultaneous arrival of two phases as well as large amplitudes which represent the PKP1 - PKP2 caustic.
Amplitudes in the caustic allow detection of events perhaps smaller than magnitude 4. In all distance ranges PKIKP and PKP are useful in magnitude determination, but added care must be taken if they are used in the distance range where amplitudes are large. Magnitudes determined from PKIKP and PKP are very consistent as are focal depths. The PKJKP phase is small if present at all.
Spatial and temporal clustering of deep and shallow earthquakes in the Fiji-Tonga-Kermadec region
Authors: Isacks Bryan L. , Sykes Lynn R. , Oliver Jack 
Published: July 2021

abstractA study of the tendency of deep and shallow earthquakes in the Fiji-Tonga-Kermadec region to cluster in space and time revealed that (a) in general, deep earthquakes do not form either aftershock sequences of swarms of the types commonly observed in series of shallow shocks throughout the world; (b) a small percentage of the deep earthquakes cluster in the form of multiplets, i.e., small numbers of events closely grouped in space and time; and (c) during the 7-year interval studied, clustering of the shallow events in the Kermadec region was markedly greater than that of shallow events in the Tongan region; clustering of shallow events in the Tongan area was, in turn, greater than that of the deep shocks in the Fijian region. The data provide new constraints for hypotheses of focal mechanisms.Most deep multiplets were doublets, and in no case were more than 12 events observed per multiplet. Resolution of the analysis was sufficient to show that, in the case of at least one multiplet, separation between events was smaller than 2 km, but that in other cases it was larger than 5 km. Separations between events in time were sometimes smaller than 2 seconds, but in no case was the relation in time and space such that a later event of a multiplet could not have been dependent upon an earlier event, i.e., the time between events was greater than that required for seismic wave propagation between the two foci.A narrow linear feature about 60 km long is defined by a spatially progressive sequence of deep multiplets that were observed during 1965. These deep multiplets are also confined to a narrow range of depths between about 625 and 660 km. This feature seems to form a portion of the lower edge of the narrow inclined zone of deep earthquakes. Patterns of first motions radiated from earthquakes in the linear feature are generally similar to one another and are in agreement with a model of the source corresponding to a double-couple or shear dislocation. Variations among the radiation patterns, although minor, are distinct and indicate some heterogeneity in the detailed distribution of stress. The data of this study do not support the hypothesis of a volumetric phase change as the mechanism of the deep-focus earthquakes. Although there is no existing hypothesis that does predict completely the results determined here, the data appear to agree best with the mechanism proposed by Orowan.A significant source of data for this work is a new network of five seismograph stations now operating in Fiji and Tonga. This study, under the U.S. Upper Mantle Program, is part of a more comprehensive investigation of deep earthquakes in the region.
Analysis of accelerograms—Parkfield earthquake
Authors: Housner G. W. , Trifunac M. D. 
Published: July 2021

Abstract
Integrated velocities and displacements show that near the fault at Cholame the surface motion exhibited a transient horizontal displacement pulse of approximately ten inches amplitude and one and one-half seconds duration, normal to the fault. Although 50 per cent of g ground acceleration was recorded at the fault, the ground motion attenuated rapidly with distance and at ten miles from the fault the maximum acceleration was reduced to one-tenth of its near-fault value. The ground motion also changed its character with distance, losing its pulse-like directional characteristic and becoming isotropic. Computed response spectra are presented and the large spectrum ordinates for this shock of relatively small magnitude and moderate destructiveness indicate that in an engineering sense the Parkfield ground motion is in a different class from such large destructive ground motions as El Centro 1940, Tehachapi 1952, and Olympia 1949.
Wave propagation in inhomogeneous elastic media
Authors: Eason G. 
Published: July 2021

Abstract
The propagation of waves in an inhomogeneous elastic solid whose elastic parameters depend on one space coordinate only is considered. The stress and displacement components are assumed to depend on this same space coordinate and time alone. It is shown that the wave equation, with variable wave speed, is the basic equation governing the propagation of shear waves in spherical or cylindrical coordinates as well as the propagation of longitudinal waves in a rod. The values of the elastic parameters which permit a particular simple solution are determined and some problems are then discussed for these solids.
Strain steps associated with earthquakes
Authors: Wideman C. J. , Major M. W. 
Published: July 2021

Abstract
Strain steps have been observed following earthquakes ranging in magnitude from 3.0 to 8.5. An empirical relationship is derived which indicates that the magnitude, M, of the smallest earthquake from which a strain step of the order of 10−9 may be expected at a distance of Δkm is:
M = 1.1 + 1.7 log ⁡ Δ 10 .
Fault length is related empirically to earthquake magnitude by the equation
M = 3.3 + 1.7 log ⁡ L 10
Where L is fault length in km. Comparison of these two equations shows that strains of the order of 10−9 may be expected at distances of approximately 20 fault lengths.
The fault length versus magnitude equation presented is shown to be compatible with a previously published energy-magnitude relationship
log ⁡ 10 E = A + 1.8 M .
Strain steps are shown to have two characteristics which are similar to those of surface waves. The speed of propagation is nearly constant over a wide range of epicentral distances. Depending upon whether the travel paths are continental or oceanic, the speeds are, respectively, 3.0 ± 0.3 km/sec or near 3.6 km/sec. The strain step amplitude dependence upon distance is like R -3/2.
Stress drop in earthquakes
Authors: King Chi-Yu , Knopoff Leon 
Published: July 2021

abstract
A correlation is made between earthquake magnitude and parameters of fault trace on the basis of dislocation theory. For earthquakes with magnitudes M between 5.5 and 8.5, the correlation with fault length L and the maximum horizontal or vertical offset D (both in cm) is approximately
log L D 2 = 2.24 M − 4.99.
Combining this result with a magnitude-energy formula, it is found that the stress drop is dependent upon magnitude, with the fractional stress drop increasing with magnitude.
High frequency microseisms from a known source
Authors: Sanford Allan R. , Carapetian Ara G. , Long Leland T. 
Published: July 2021

abstract
Trains moving through the Rio Grande Valley at Socorro are a known isolated source of short-period microseisms. Power spectra at five different locations indicate that the train noise is confined to a narrow band (&lt; 3 cps) of frequencies. In general, the frequency limits and peaks of the power spectra shift to lower values with an increase in distance from the source. Peaks in the power spectra, which range from 1.80 to 4.75 cps, do not correlate with mechanical interactions of the train with the track.
Particle motions for randomly selected samples of train noise are extremely complex and no dominant component of motion—Rayleigh or Love—can be identified. However, for samples of noise showing the same regular frequency on all components of ground motion, a strong fundamental mode Rayleigh wave can generally be found.
Phase-velocity measurements at a distance of about 17000 feet from the train indicate that a major amount of the train noise at Socorro is being propagated as a fundamental mode Rayleigh wave. The average of over two hundred phase velocity determinations was 1400 ft/sec, a value that corresponds closely to 0.92 of the shear velocity of the surface layer at the recording location. Other observations at the same location indicate normal dispersion of fundamental mode Rayleigh waves, but the change in phase velocity with frequency (in the range of 2 to 5 cps) appears to be quite small.
Seismicity of Iranian Plateau and Hindu Kush region
Authors: Niazi Mansour , Basford Jeffrey R. 
Published: July 2021

abstract
Over 1400 earthquakes of magnitude 4 and above which occurred between 20° and 40° North Latitudes and between 40° and 75° East Longitudes during the decade ending on June 30, 1967 are analysed. On the basis of the computed strain release, seismicity maps are constructed for the first and second halves of the period. Three or possibly four seismic zones in the eastern Turkey-Caucasus region, along the marginal heights of the Iranian Plateau, in the Hindu Kush region, and West Pakistan are delineated. The magnitude-frequency relationship of the earthquakes which occurred in Iran during this period is discussed.
A surface wave particle motion discrimination process
Authors: Simons R. S. 
Published: July 2021

Abstract
A digital computer process is described which examines the three-componen particle-motion pattern of seismic data as a function of frequency and uses this information to discriminate against all motion except surface waves arriving from some pre-assigned direction. Application of the process to long-period data has shown that it can substantially improve the signal-to-noise ratios of Love and Rayleigh waves from earthquakes and underground detonations.
A synthesis of short-period P-wave records from distant explosion sources
Authors: Kogeus (Korkman) Kaj 
Published: July 2021

Abstract
A computer program is developed for computation of theoretical seismograms. The program treats explosive sources in layered crustal structures and computes frequency-domain functions for the crust, mantle and instrument transfers. The product of these is Fourier-inverted to give the seismograph trace. A brief study of parameter variation is presented.