bluuebunny/crossref_metadata_2025_split huggingface dataset:
Travel-time curves for a low-velocity channel in the upper mantle
Authors: Dowling John , Nuttli Otto 
Published: July 2021

abstract
Velocities within the earth can be determined from body wave time-distance (T-D) data by the Herglotz-Wiechert method provided the velocity does not decrease too rapidly with depth. Until the present time, the properties of T-D curves for rapid decreases of velocity with depth have been considered only qualitatively.
This paper presents a technique for calculating a T-D curve for any velocity distribution, including continuous and discontinuous increases and decreases of velocity with depth. Some properties of T-D curves are quantitatively studied by systematically varying the characteristics of a single model and noting the corresponding variations in the calculated T-D curves. From this it is concluded that a significant low-velocity channel may not be evidenced by a shadow zone but rather by an overlapping of two distinct branches of the T-D curve. It is further concluded that the presence of a shadow zone implies a very gentle velocity gradient below the low-velocity channel.
By fitting a calculated T-D curve to observed data one can determine velocity as a function of depth even when the velocity decreases rapidly with depth, when a low-velocity channel exists. Observed T-D data for two underground nuclear explosions (gnome and bilby) measured in four different azimuths were fitted with T-D curves calculated for assumed velocity distributions. It is concluded that these data can be satisfied by a low-velocity channel for P waves in the upper mantle. The character of this channel (depth, thickness and velocity) was determined in each azimuth. The depth to its top was shallow (70 ± km) in the western U.S. and deep (125 ± km) in the eastern U.S. The velocity gradient below the channel is sharp enough to produce no prominent shadow zones. There are significant lateral changes in upper mantle velocities in the western U. S.
Ground motion accelerogram analysis including dynamical instrumental correction
Authors: Jenschke V. A. , Penzien J. 
Published: July 2021

abstract
Due to inertial and damping characteristics of strong motion seismographs, recorded ground motion accelerograms may in some cases be sufficiently in error to significantly affect the results obtained when generating standard response or Fourier spectra. Therefore, the objectives of this paper are to present an analytical method of generating standard spectra which will eliminate the above instrumental error and to show the significance of this error by presenting some sample results obtained from accelerograms representing both earthquakes and underground nuclear explosions.
High frequency microearthquakes recorded at Quetta, Pakistan
Authors: DeNoyer John 
Published: July 2021

Abstract
Numerous high frequency microearthquakes were recorded on a special portable magnetic tape recorder at Quetta, Pakistan, during the summer of 1962. These microearthquakes have maximum particle velocities between 30 and 50 cps. Many of the foci appear to be almost directly under the recording station. The focal distance for the nearest of these earthquakes appears to be less than one km. The source for these earthquakes may result from “bedding plane slippage” as strain accumulates in sediments adjacent to a high angle fault.
The S wave project for focal mechanism studies earthquakes of 1962
Authors: Stauder William , Bollinger G. A. 
Published: July 2021

Abstract
The Department of Geophysics of Saint Louis University has instituted a routine program for the determination of the focal mechanism of the larger earthquakes of each year using methods developed for the use of S waves in focal mechanism studies. Suites of records from selected stations are assembled from the WWSS microfilm file for each earthquake of interest. A combination of P-wave first motion and S-wave polarization data is then used to determine graphically the mechanism of the earthquakes.
Thirty-six earthquakes of 1962 were selected for study. The focal mechanism solutions are presented for twenty-three of these shocks. There is evidence of patterns characteristic of the focal mechanism of earthquakes occurring in Kamchatka, the Aleutian Islands and South America.
A complete presentation of all the data and of all the solutions is available in a more lengthy report.
Wave propagation phenomena at an irregular infinite interface: Part I: Theory
Authors: Adams W. M. , Chang Chung-Po 
Published: July 2021

Abstract
Much wave propagation theory is not generally useful because plane parallel boundaries are assumed. In the present paper, the theory for wave phenomena at an irregular infinite interface is developed. As most interfaces in the earth are irregular, such a theory should prove valuable. The Weber integral solution to the wave equation is interpreted using a dual limiting procedure to define a principal value. Numerical formulation and applications are given in following articles.
Computer program for automatic processing of Basin and Range seismic data
Authors: Ryall Alan , Jones Austin E. 
Published: July 2021

Abstract
A program has been written for the University of Nevada's IBM 1620 computer which locates epicenters of seismic events that occur within the Nevada region. The program utilizes readings of P and S waves at up to eight stations in the Basin and Range province, rejects readings for events which are outside the region of interest or events recorded at less than three Nevada stations, establishes trial epicenters for locatable events by means of a table-lookup routine which utilized P-time differences between pairs of stations, and adjusts the trial epicenter by a least-squares procedure based on a sloping-layer crustal model derived from recent U. S. Geological Survey seismic refraction profiles. Epicenters calculated by the program are found to be affected by near-surface structural irregularities in the vicinity of receiving stations, but are not affected either by near-surface features in the source region or direction of the propagation paths with respect to regional structural trends. Traveltime delays calculated for Nevada seismographic stations appear to correlate with Bouguer gravity anomalies at the station sites.
The stopping phase on seismograms
Authors: Savage J. C. 
Published: July 2021

Abstract
Model studies have demonstrated that the stopping phase, an event which originates at the termination of rupture, may be identified on long-period strain recordings. A tentative identification of the stopping phase has been made on ultra-long-period seismograms of three major earthquakes (Montana, 1959; Chile, 1960; and Alaska, 1964). The events chosen lead to reasonable estimates of the length of rupture associated with the earthquake. A second type of stopping event, the breakout phase, must occur when a rupture intersects a free surface. A two-dimensional model study indicates that the breakout phase should be a prominent seismic event, particularly if the first motion is emergent. A review of studies of seismograms of earthquakes which produced surface faulting indicates that a prominent second event is often observed. However, there does not appear to be an adequate criterion to distinguish the breakout phase from the pP phase. Thus no certain identification can be made.
Surface wave dispersion in the Tonga-Fiji region
Authors: Hunkins Kenneth , Kuo John T. 
Published: July 2021

Abstract
Rayleigh, Love, and PL wave dispersion was investigated for 33 shocks in the Tonga-Kermadec arc and for one shock in the New Hebrides arc. The records were taken at Suva, Fiji with Lamont-I.G.Y. long-period seismographs. All epicenters were relocated using a least squares method programmed for a high-speed digital computer. The shocks were classified into five groups according to region. Each group has similar dispersion characteristics. Lower velocities were found beneath the Lau and South Fiji basins than beneath the Tonga and Fiji ridges. PL waves reflect the same velocity changes found for Rayleigh and Love waves. All the dispersion data are intermediate between typical continental and typical oceanic values. A theoretical calculation for a 21.5 km thick crust with a 7.0 km/sec lower layer was found to fit a path which includes the Lau basin, Fiji ridge, and Fiji basin.
Note on the use of reciprocity theorem for obtaining radiation patterns
Authors: Gupta Indra N. 
Published: July 2021

Abstract
Expressions for the horizontal and vertical displacements at the surface of an elastic half space when plane harmonic P or SV waves are incident at any given angle are already known. On the basis of the reciprocity theorem, these expressions are used to obtain “far-field” radiation patterns of P and SV waves due to horizontal and vertical forces applied at the free surface.
Radiation pattern of mantle Rayleigh waves and the source mechanism of the Hindu Kush earthquake of July 6, 1962
Authors: Chander Ramesh , Brune James N. 
Published: July 2021

abstract
The source mechanism of the Hindu Kush earthquake of July 6, 1962 (magnitude 634-7, focal depth 218 km) was studied by comparing the observed amplitude and phase radiation patterns of mantle Rayleigh waves of 150 sec and 200 sec period with theoretical radiation patterns of Rayleigh waves from single- and double-couple point sources, and by considering evidence from Love waves and the shape of P and S pulses. The solution for the source mechanism, which is consistent with all the body wave and surface wave data available for this earthquake, is a double couple acting as a step function in time, with nodal planes oriented as determined from P wave data. Since for waves with periods greater than about 5 sec, the source appears to be an ideal point source, the radius of the equivalent source volume is estimated to be less than 10 km. For Rayleigh waves of 150 sec period, the agreement between observed and theoretical phases (for the above source model) is greatly improved by assuming regional phase velocities instead of a uniform phase velocity for all areas. It is concluded that with the accuracy currently attainable, a study of Rayleigh waves alone cannot determine the source mechanism of an earthquake uniquely.
Propagation of a P-pulse in a solid sphere
Authors: Alterman Z. , Abramovici F. 
Published: July 2021

abstract
An exact solution is obtained for the displacement of the surface of a uniform elastic solid sphere of radius a due to an impulsive compressional pulse from a point-source situated at a distance b from the center. The duration of the source is δa/c where c denotes the shear-wave velocity, and its time-variation is such that the surface-displacement stays finite when the time tends to infinity.
The solution is applied to a source at a distance of one-eighth of the radius below the surface, approximating a deep-focus earthquake. Theoretical seismograms, radial and angular component, are given at distances 0 &lt; ϑ &lt; π for a source of duration 0.03a/c. Rayleigh waves are clearly seen at ϑ ≧ 45 °. Groups of reflected waves, especially predominant in the angular component, have the velocity of the lowest Airy phase in the group-velocity dispersion-curves. Diffracted waves, discussed in a previous paper, are found here again and in certain cases have an amplitude seven times larger than the amplitude of the direct pulse and also larger than any of the reflected pulses at the same distance. The transformed phases PSn, P2Sn have in general larger amplitude than the reflected Pn. Arrival times, initial amplitudes, reflection and convergence coefficients of pulses are obtained by steepest descents analysis and compared with the complete results.
Physical and topographic factors as related to short-period wind noise
Authors: Robertson Herbert 
Published: July 2021

abstract
Median values of seismic noise in the period range of 0.3 to 1.3 sec were obtained from recordings at vaults of the Pole Mountain and WMSO arrays. Interquartile ranges were used to measure dispersions about the medians. Medians of the noise at Pole Mountain ranged from 0.91 mµ to 2.20 mµ in November 1962. The former value was obtained for a vault that was located in dense granite at the base of a massive granite outcrop; the latter value was obtained for a vault in a slab of dense granite located on a grassy plain. This indicated that topographic shielding from wind rather than density of bedrock affected noise. As a test of this idea, wind protection numbers were assigned to vaults Z1 through Z9 of the WMSO array based on comparative topographic shielding with respect to a known wind direction. Noise values increased as wind numbers decreased. Topographic protection and vault construction limited wind noise at WMSO.
A study of the Northwestern Pacific upper mantle
Authors: Walker Daniel A. 
Published: July 2021

abstract
A fundamental problem of earthquake seismology is the occurrence of the upper mantle low-velocity channel. This study is intended to examine its existence in the upper mantle below the Northwestern Pacific on the basis of body-wave arrivals at a bottom-mounted hydrophone near Wake Island. A comparison of the observed travel times and the Jeffreys-Bullen travel times shows an extreme anomaly in the 21- to 33-degree range for both P and S waves. Assumed linear paths suggest a P-wave-channel upper boundary between 165 km and 185 km, and a lower boundary between 290 km and 542 km. Travel times for P and S waves indicate that the velocities in the channel remain constant at 8.1 km/sec and 4.65 km/sec respectively.
Determination of inhomogeneous media for which the vector wave equation of elasticity is separable
Authors: Hook Joseph F. 
Published: July 2021

Abstract
A generalization of the Helmholtz potential representation has recently been employed to effect separation of the vector wave equation of elasticity for certain types of inhomogeneous media whose properties vary with a single cartesian coordinate, z. For separability, the three constitutive parameters of the medium must satisfy a pair of simultaneous nonlinear differential equations. In this paper, integrals of these equations are derived which are explicit expressions for two of the parameters in terms of the third, whose functional form may be chosen arbitrarily. In the most general case, the arbitrary parameter must be the rigidity, μ For a special subcase, any one of the three parameters may take this role.
Deduction of earth strains from survey data
Authors: Frank F. C. 
Published: July 2021

abstract
In deducing earth strains from repeated triangulation surveys, it is advantageous to extract the shear components of strain γ1=(∈11−∈22)andγ2=(∈12+∈21) separately. Unlike the dilation and rotation components of strain, 12(∈11+∈22)and12(∈12-∈21), these shear components can be determined locally, each triangle giving one measurement for γ1 and γ2, without requiring knowledge from adjoining areas. It follows that it should be possible to extract much more and better information about the shear strains from existing survey data than has been extracted hitherto.
A comparison of earthquake magnitude with T-phase strength
Authors: Johnson R. H. , Northrop J. 
Published: July 2021

abstract
Records from SOFAR-depth hydrophones at widely spaced locations in the North Pacific were scanned for earthquake T phases. A source solution was obtained by computer for T-phase arrivals correlated at four or more hydrophones. Using this method, the number of events located on the North Pacific rim is about ten times greater than the number located by conventional body-wave determinations. It is concluded that the capability for location of earthquakes by T-phase arrivals extends down to about magnitude 3.6 for the North Pacific rim.
An interpretation of the first-arrival data of the Lake Superior Experiment by the time-term method
Authors: Berry M. J. , West G. F. 
Published: July 2021

abstract
The first-arrival data of the Lake Superior Experiment of 1963 have been interpreted by the time-term method. The analysis has shown the method to be well suited to this type of survey, and the results appear to be consistent and meaningful.
Approximately 500 first-arrivals from head waves generated at the Mohorovičić discontinuity, have been reduced to estimates of crustal time-terms at over 100 locations. A much shallower refracting surface (here called the Upper Refractor) furnished nearly 1,000 observations to yield upper crustal time-terms at the same locations. The analysis reveals the material beneath the UR and beneath the M to have velocities of 6.63 and 8.10 km/sec respectively. The surface of the Upper Refractor, on the basis of a simple interpretation of the time-terms, is revealed as undulating, coming close to the surface at the edges of the lake and reaching maximum depths of approxmately 15 km to the east and west of the Keweenaw Peninsula. On a similar basis the Mohorovičić discontinuity is revealed as an easterly dipping surface, having a depth of approximately 35 km at the west end of the lake and reaching a maximum depth of about 60 km in the region just west of the Keweenaw Peninsula. Eastwards, the time-term values fluctuate but do not increase or decrease systematically.
The velocity of the material lying above the Upper Refractor is not well determined, but appears to be roughly 5.5 km/sec. A perusal of geological literature suggests that this low velocity material is mostly sedimentary, filling a well-known synclincal basin whose axis bends around the Keweenaw Peninsula. This mainly sedimentary section is known to be underlain by a great thickness of igneous rocks, which in all probability corresponds to the Upper Refractor mapped by the seismic studies.
Hayward fault slippage in the Irvington-Niles districts of Fremont, California
Authors: Cluff Lloyd S. , Steinbrugge Karl V. 
Published: July 2021

abstract
Right lateral slippage on the Hayward fault has faken place in the Irvington and Niles districts of Fremont since the well known 1868 Hayward earthquake which produced surface ruptures from San Leandro to Warm Springs. This post-1868 movement has been occurring without being identified with strong earthquakes. Structures and railroads crossing the Hayward fault in the area under study date back to 1866. Fault slippage can be observed at ten separate locations along the strike of the Hayward fault in the Irvington-Niles districts of Fremont, California. One location predates the 1868 earthquake. There is no evidence for parallel lines of fault slippage within the approximately 200-foot wide fault zone. The slippage appears to have occurred within a 10-foot wide band parallel to the strike of the fault.
Structures and railroads built at different times during the past 100 years give a time-history of the slippage. The slippage, if any, between 1868 and 1909 is unknown. From 1909 until as late as 1949 or early 1950, there was no observed fault slippage. Approximately one-half foot of slippage occurred between about 1949 or early 1950 and about 1957, and no measurable slippage since 1957.
Displacements in the Claremont Water Tunnel at the intersection with the Hayward fault
Authors: Blanchard F. B. , Laverty G. L. 
Published: July 2021

abstract
Three cracks have been observed in the concrete lining of the Claremont Water Tunnel at its point of intersection with the Hayward fault zone. The cracks, which show a right-lateral sense of displacement, were not present fourteen years ago in 1950.
Damage to culvert under memorial stadium, University of California, Berkeley, caused by slippage in the Hayward fault zone
Authors: Radbruch Dorothy H. , Lennert Ben J. 
Published: July 2021

abstract
Slippage on a fault plane or sheared band in the Hayward fault zone has seriously damaged a cast-in-place concrete box culvert which carries the waters of Strawberry Creek under the University of California Memorial Stadium at Berkeley, California. Right-lateral movement of the fault or sheared band has offset the southwest-flowing creek so that the southwest portion has moved northwest with respect to the northeast portion. The two parts are connected by a northwest-trending section about 1,200 feet long, which flows in the culvert under the stadium. The fault crosses the culvert at a low angle, trending about 20° more to the north than the culvert, so that both tension and shear have been exerted on the culvert by right-lateral movement of the fault since the culvert was built in 1923. Two transverse cracks 1 inch wide and about 5 feet apart were noted when the culvert was inspected in 1948. In 1965 the maximum width of the cracks was 312 inches and the section of the culvert between the cracks appeared to have rotated clockwise. Total average separation of the cracks due to tension is about 4.1 inches; lateral offset of the culvert is 1.25 inches. Movement along the fault is estimated at 0.1 inch per year over the 42 years since the culvert was built.
Corrections to apparent azimuths and travel-time gradients for a dipping Mohorovičić discontinuity
Authors: Niazi Mansour 
Published: July 2021

abstractWhen a layer is overlying a half-space with a tilted interface, the refraction of seismic waves emerging from the half-space generally results in their reorientation away from the vertical plane of incidence, with the following consequences:A general formulation for the computation of the apparent azimuth and the angle of incidence at the free surface is obtained. The numerical corrections to the observed dT/dΔ and apparent azimuth, for a number of combinations of various dip angles and velocity contrasts, are tabulated.The tables may be helpful when the first and second derivatives of the travel time data are to be analyzed. Their comparison with observation can also be useful for making inferences about the underlying crustal structure. The latter approach has been applied to the P arrivals across the Tonto Forest Seismological Observatory (TFSO) array, Arizona. On the basis of these observations, the Mohorovičić discontinuity under the observatory appears to be dipping locally as much as eight degrees in the N70° ± 5°E direction.
Radiation from a realistic model of faulting
Authors: Savage J. C. 
Published: July 2021

abstract
The Knopoff-deHoop representation theorem has been used to calculate the form of the body waves radiated from an elliptical fault. Rupture is assumed to initiate at one focus of the ellipse and then spread out radially on the fault plane. Two cases are considered: 1) constant slip everywhere on the fault surface and 2) a variable slip which approaches zero at the fault edge. The radiation is calculated for distances from the fault which are large compared to the fault dimensions. The body waves are described by the product of two factors, one of which is the familiar equivalent-force system radiation pattern. The other factor includes the time dependence of the signal; it does not depend upon the direction of slip. The body waves exhibit two stopping phases. The theory is used to estimate the fault dimensions associated with six deep-focus earthquakes studied by Kasahara. The estimated fault dimensions are about twice the dimensions of the focal sphere as found by Kasahara. Finally, the difference between the phase spectrums of shallow and deep-focus earthquake radiation observed by Kishimoto is shown to be related to a difference in shape of the two fault surfaces; shallow-focus earthquakes appear to be associated with elongated fault surfaces, whereas deep-focus earthquakes are associated with more circular fault surfaces.