bluuebunny/crossref_metadata_2025_split huggingface dataset:
The San Fernando earthquake and public school safety
Authors: Hudson D. E. , Jephcott D. K. 
Published: September 2021

abstract
The San Fernando earthquake was an unusually valuable test of school safety because: (1) there were several hundred schools having structures of all types in the heavily shaken area, including 10 schools within 5 miles of the epicenter; (2) the severity of ground motion is believed to have been near the maximum to be expected for an earthquake of any size—a number of campuses were subjected to major ground cracking and deformation; (3) since there were many instruments in the area, the details of the earthquake ground motion are better known than for any other earthquake. On some campuses, pre-Field Act buildings, renovated pre-Field Act buildings, and new buildings existed side by side, and direct comparisons show the efficacy of the Field Act and the associated plan check and field inspection procedures in reducing the earthquake hazard to an acceptably low level. No structural failures, that would have been likely to cause serious injury or death if the buildings had been normally occupied at the time of the earthquake, occurred in any buildings built to current standards. There were, however, some failures of nonstructural elements that could have resulted in a hazardous situation and demonstrate the need for upgrading requirements in this area of building construction.
The response of a linear viscoelastic solid to a weak spherical explosion
Authors: Blake Thomas R. 
Published: September 2021

abstract
We study spherical waves which are produced by a weak spherical explosion in a linear viscoelastic solid. The wave front, final displacement, and stress fields, and the large time velocity and stress signals are examined. It is shown that the large time velocity and stress signals are dominated by a wave which has the character of a diffuse N wave propagating with the equilibrium speed of sound and decaying inversely as the square of the radial distance.
Interaction of a shear wall with the soil for incident plane SH waves: Elliptical rigid foundation
Authors: Wong H. L. , Trifunac M. D. 
Published: September 2021

abstract
The closed-form solution of the dynamic interaction of an elastic shear wall and the elastic homogeneous half-space, previously known only for the rigid foundation with circular cross section, has been generalized to apply for the foundation with elliptical cross section. It is shown that the interaction equation depends on the incidence angle of plane SH waves and that this dependence gradually disappears as the elliptical cross section approaches the circular one. The effectiveness with which the rigid foundation can scatter the incident energy has been found to increase with the depth of the foundation.
Reflection of SH waves from anisotropic transition layer
Authors: Thapliyal V. 
Published: September 2021

abstract
The effects of anisotropy on the reflection of SH-waves (horizontally polarized shear waves) from a transition layer are studied. The transition layer is sand-wiched between two isotropic homogeneous half-spaces and is constituted by a medium which is both anisotropic and inhomogeneous. The SH-wave potentials are obtained for an anisotropic inhomogeneous medium in which both the anisotropy factor (ratio of the horizontal rigidity to the vertical rigidity) and vertical velocity vary with depth. An expression for the reflection coefficient of SH waves is obtained when the material mentioned above forms a finite transition zone between two isotropic homogeneous half-spaces. For further generalization, a second-order discontinuity along with the first-order on eis being assumed in the material properties, at the boundaries of the transition layer. The mathematical and numerical analyses show that the anisotropy factor, found at the top of the transition layer (N0/M0) produces considerable effect on the reflection coefficient for an obliquely incident SH wave. It has been noted that the greater the thickness of the transition layer, the greater is the dependence of the reflection coefficient upon the value of the anisotropy (N0/M0). The minima and maxima of the reflection of seismic energy are found dependent on the value of anisotropy. For greater values of the anisotropy, these maxima and minima shift toward the lower values of the wavelength of the propagating wave (or toward the higher values of the thickness of the transition layer). In fact, the values of the reflection coefficient at which these maxima and minima of seismic energy occur are found greater for the higher values of anisotropy. The effects of anisotropy are found more pronounced for the larger angles of incidence. This remains so until the angle of refraction becomes imaginary. However, no effects of the anistropy factor are found on the reflection coefficients for a normally incident wave. The results, mentioned above, are therefore discussed only for the obliquely incident wave. A geophysically interesting situation has been chosen for studying, quantitatively, the effects of the anisotropy factor on the reflection of SH waves.
Parkfield, California, earthquake of June 27, 1966: A three-dimensional moving dislocation
Authors: Trifunac M. D. , Udwadia F. E. 
Published: September 2021

abstract
Recordings from five strong-motion accelerograph stations have been used to derive a three-dimensional dislocation model for the Parkfield Earthquake. The model consists of a buried fault which extends from a depth of 3 km to a depth of 9 km below the ground surface. It appears from the analysis, which considers various fault lengths, that the zone of significant faulting was the 20-km-long northwestern section of the fault. The rupture velocity has been found to be between 2.4 and 2.5 km/sec and the dislocation amplitudes have been found to be about 120 cm. There have been comparisons made of the model results with geodetic data on static deformations and creep measurements following the event. In contrast with several other source mechanism studies of the Parkfield event, this model yields a picture which appears to be very consistent with both the dynamic strong-motion measurements as well as the available geodetic and creep data.
Amplitudes of horizontally refracted Love waves
Authors: Gregersen S. , Alsop L. E. 
Published: September 2021

abstractLove-wave transmission and reflection are studied numerically for a vertical interface between two layered models. By a new method of approximation, the transmission and reflection coefficients can be computed for propagation directions differing from normal incidence. We consider the Love mode as a superposition of propagating plane SH waves in a surface layer and an inhomogeneous plane SH wave falling off with depth in the half-space below. The method is based on satisfying all boundary conditions on the vertical interface and computing the coupling between the interface stress displacement pattern and the transmitted/reflected Love modes. The computations are done rapidly on a small computer.The transmission coefficients change rapidly with period. For propagation from ocean to continent, they increase with decreasing periods in the interval 60 to 20 sec. The opposite trend is found for propagation from continent to ocean. The amplitude transmission coefficient curves show almost no dependence on the angle of incidence except for large angles. The fine structure of the curves is similar to that for plane SV waves incident on an interface between two homogeneous elastic media. Love-wave amplitude observations at OBS on the ocean bottom northwest of San Francisco and at BKS in Berkeley also show these trends as a function of period and of angle of incidence.
A dislocation model for the Parkfield earthquake
Authors: Anderson John 
Published: September 2021

abstract
Using the Haskell formulation relating the displacement time history on a fault surface to the displacement time history at a point in an infinite space, a propagating dislocation has been used to model the Parkfield, California, earthquake of June 27, 1966. Reasonable agreement is obtained with displacement from doubly integrated accelerograms using a model with a propagation velocity of 2.8 to 3.0 km/sec, displacement of 25 cm, and particle velocity at the fault of greater than 10 cm/sec. From the model, trigger times of the accelerometers can be estimated and are up to 4 sec after the first P arrivals. A high-frequency phase on the vertical accelerogram can be related to P waves originating from irregularities of the rupture process. Calculation of surface-wave arrival times shows that (1) surface waves may be important on the displacement records before body-wave arrivals ended and (2) when the observations diverge from the model, it could be due to surface waves.
Evidence for postearthquake slip in the Fairview Peak, Dixie Valley, and Rainbow Mountain fault areas of Nevada
Authors: Savage J. C. , Church J. P. 
Published: September 2021

abstract
The U.S. Coast and Geodetic Survey ran first-order level surveys in 1934, 1955, and 1967 across the fault zone associated with the 1954 sequence of earthquakes at Rainbow Mountain (M = 6.6 and 6.8), Dixie Valley (M = 6.8), and Fairview Peak (M = 7.1) in Nevada. The difference between the 1955 and 1967 surveys clearly shows distinct anomalies over distances of several kilometers at all but one of the fault scarps mapped after the 1954 earthquakes. The anomalies resemble deformation produced by normal faulting extending to a depth of at least several kilometers and, consequently, are interpreted as implying continued slip on the earthquake faults in a period beginning at least 6 months after the earthquake. At the Fairview Peak Fault, the inferred postearthquake slip is about 5 per cent of the displacement observed at the time of the earthquake. The difference between the 1955 and 1967 surveys suggests an overall tilt of 2 mm/km down to the west extending over a 90-km distance crossing the fault zone. The difference between the 1934 and 1955 surveys suggests an overall tilt of 0.8 mm/km down to the east extending over a 200-km section. However, these regional tilts might be due to unusually large systematic errors in the level surveys. Gravity and seismic-refraction surveys indicate that the region as a whole is isostatically compensated, although the mountain ranges and intervening basins are not individually compensated. Thus, the regional elevation changes, if they exist, cannot be accounted for by isostasy.
A seismic refraction survey along the southern Rocky Mountain Trench, Canada
Authors: Bennett G. T. , Clowes R. M. , Ellis R. M. 
Published: September 2021

abstract
An unreversed seismic refraction profile has been recorded in the southern Rocky Mountain Trench from 50°N to 53°N. Using blasts from two open-pit coal mines, 44 recordings were obtained over a distance of 540 km. These were combined into a record section in which instrument and shot variations were included to show amplitude variations along the profile. Interpretation involved Weichert-Herglotz integration of p-delta curves to obtain a velocity-depth structure and the calculation of synthetic seismograms for comparison with the record section.
Refractors with apparent P-wave velocities of 6.5 to 6.6 km/sec and 8.22±0.04 km/sec are interpreted as the surface of the Precambrian basement and the Mohorovičić discontinuity, respectively. A prominent travel-time delay associated with the 6.5 km/sec branch is interpreted in two possible ways. One explanation is the existence of a crustal low-velocity zone beginning 3 km beneath the basement, depth of 6.5 km, and having a depth extent of 9 to 15 km with associated velocities of 5.5 to 6.1 km/sec, respectively. The second interpretation proposes a high-angle crustal fault near Radium. The resultant model has an up-fault structure with depth to basement of 6.5 km and depth to the M-discontinuity of 51 km and a down-fault structure with corresponding values of 12.1 and 58 km. On the basis of gravity and magnetic trends, the fault strikes northeasterly. In either interpretation, a velocity gradient is present in the lower crustal section and the thickness of the crust is in excess of 50 km. Analysis of larger amplitude arrivals shortly after the Pn phase is consistent with the interpretation of a low-velocity zone, 8 km beneath the M-discontinuity and approximately 7 km thick.
Pulse distortion and Hilbert transformation in multiply reflected and refracted body waves
Authors: Choy George L. , Richards Paul G. 
Published: September 2021

abstract
Many seismic body waves are associated with rays which are not minimum travel-time paths. Such arrivals contain pulse deformation due to a phase shift in each frequency component. For sufficiently high frequencies, the phase shift each time a ray touches an internal caustic is π/2 and frequency-independent. The distorting effect of a frequency-independent phase shift is successfully observed in seismograms from events in several regions. The data examined are long-period (T &gt; 9 sec). They include deep earthquakes (depth &gt; 500 km), in which a series of well-separated S phases (S, sS, SS and sSS) are available. These show that the wave form of SS, which has been distorted in propagation through the Earth, can be derived from the wave form of sS, which is not distorted. Shallow events, in which multiple S phases overlap, also exhibit behavior predicted by phase distortion. Rays supercritically reflected or refracted at a discontinuity in the Earth also suffer a constant phase shift, which in general can have any value. An important case is SKKS: its undistorted wave form resembles that of SKS, which has a minimum travel-time path.
Without exception, all the distorted wave forms bear little or no resemblance to the original wave form. That is, neither the first arrival of energy nor the subsequent relative position of peaks and troughs on a distorted wave form appear at the ray theoretical times. Thus, T-Δ curves constructed by choosing arrival times to correspond to the first arrival of energy may be biased. Similarly, doubt is cast on differential travel times chosen from first motions, or from averaging several points on what appear to be corresponding peaks and troughs of two wave forms. Some of the rays most important to seismology, in which the distortion phenomenon occurs, include P and S (where d2T/dΔ2 &gt; 0), PKPAB, PP, SS, and SKKS. Removal of phase distortion in the data is computationally straightforward. By exploiting the resulting wave forms to full advantage in correctly picking arrival times, we may hope to improve velocity models of the Earth. It is shown that matched filtering to obtain differential travel times is appropriate for certain pairs of body waves if they are phase-corrected.
Crustal structure of the Baltic Shield beneath Umeå, Sweden, from the spectral behavior of long-period P waves
Authors: Leong Lap Sau 
Published: September 2021

abstract
The method of spectral ratio response for crustal thickness determination beneath a receiving station, using long-period P waves of teleseismic events, has been applied. The purpose of this study is to investigate further the already well-depicted shield structure in Sweden beneath the WWSSN station at Umeå, the methodical procedure involved in this inversion problem, and possible sensitivity of the method to lateral variations of the shield area beneath the recording station. Teleseismic events from the Okhotsk Sea, Mongolia, and Hindu Kush regions are considered. Results suggest a value of 42 km for the two-layer crustal model beneath Umeå with possible lateral variations in velocity and/or dipping M-discontinuity surface to the east. It is proposed that a quantitative measure of the reliability of amplitudes and periodicity of peaks of the response ratios and indications of possible lateral anisotropy are obtained by treating the horizontal P-wave component both as a radial component of a three-component vector field and as being along the great circle through the epicenter and the receiving station.
From antimoment to moment: Plane-strain models of earthquakes that stop
Authors: Andrews D. J. 
Published: September 2021

abstract
Some simple cases of the seismic gap model are examined in plane strain. Numerical solutions are found for near-field elastodynamic motion coupled to frictional sliding on a fault. Rupture velocity is specified, but the dynamic solution is otherwise dependent only on the initial state. The initial seismic gap is a non-uniformity of past slip on the fault plane. It is termed an antidislocation and is characterized by its antimoment and its energy. Sliding stops naturally in this model, even with uniform material properties. The moment of the calculated earthquake is dependent on the difference between the kinetic friction level and the background shear-stress level and is independent of rupture velocity. If initial states are scaled to have equal antimoments, and if the stress scale is normalized according to the initial energy, then the earthquake moment is nearly independent of the shape of the initial antidislocation. The ratio of radiation reaction stress (apparent stress) to weighted mean stress drop is 0.36±0.04 for all cases calculated. Non-dependence of earthquake moment on rupture velocity and the shape of the initial antidislocation is expected to carry over to three-dimensional cases. The final fault dislocation is smoother than the initial dislocation in every case calculated. Nonuniform friction or a nonplanar fault is required to get a dislocation rough enough to produce succeeding earthquakes.
Strong ground motion of the San Fernando, California, earthquake: Ground displacements
Authors: Hanks Thomas C. 
Published: September 2021

abstract
Two hundred and thirty-four components of ground displacement are the basis of an investigation of long-period strong ground motion in southern California arising from the San Fernando, California, earthquake. The displacement data are obtained from the double integration of strong-motion accelerograms via the base-line adjustment and filtering operations routinely performed in the series “Strong Motion Earthquake Accelerograms”. These procedures can recover long-period data from strong-motion accelerograms with considerable accuracy. Many-station comparisons of displacement data for which the station spacing is small compared to the wavelengths of interest reveal that uncertainties in displacement are less than 1 cm in the period range 5 to 8 sec, 1 to 2 cm at periods near 10 sec, and 2 to 4 cm in the period range 10 to 15 sec, for a data sensitivity of approximately 7.6 cm/g. For limited variations in epicentral distance (R) and source-station azimuth (ϕ), ground displacements show a strong coherence; for wider variations in R and ϕ, many of the observed variations in the displacement wave forms are easily attributable to well-understood seismological phenomena. Seismic moment, source dimension, radiation pattern, rupture propagation, the development of surface waves and their subsequent dispersion, and azimuthal variations in the gross geological structure all appear to have first-order significance in fashioning the gross amplitude and frequency content of the displacement wave forms and in explaining observed variations with R and ϕ. The essential simplicity of these displacement wave forms offers considerable optimism that long-period strong ground motion can be realistically synthesized with advance knowledge of the earthquake source parameters and gross geological structure.
On correlation of seismoscope response with earthquake magnitude and Modified Mercalli Intensity
Authors: Trifunac M. D. , Brady A. G. 
Published: September 2021

abstract
A quantitative measure of the Modified Mercalli Intensity Scale for earthquakes in the western United States has been developed by correlating the peak seismoscope relative displacement response, Sd, with the reported site intensity, IMM. This correlation can be approximated by
S ̄ d ( cm ) ≈ 1 49.2 10 0.288 I MM
for IMM ≦ VIII and is characterized by one standard deviation of about 0.7 S̄d. The data used in this study do not indicate an obvious type of dependence of Sd on local site conditions.
A method for computing the analog of the local earthquake magnitude, Mseismoscope, has been presented for possible use in strong-motion seismology and for scaling earthquakes by close-in measuremients, when other seismological instruments may go off scale.
Bear Valley, California, earthquake sequence of February-March 1972
Authors: Ellsworth William L. 
Published: September 2021

abstract
The earthquake sequence of late February and March 1972 involved movement along the San Andreas fault and within the crustal wedge enclosed by the branching San Andreas and San Benito faults near Bear Valley, San Benito County, California. Activity was mainly confined to three distinct zones of strike-slip faulting: the short north-trending aftershock zone of the M 3.5 earthquake of February 22, 1972, the aftershock zone of the M 5.0 Bear Valley earthquake of February 24, 1972 located along the San Andreas fault, and the west-trending aftershock zone of the M 4.6 earthquake of February 27, 1972. The north-trending and west-trending zones lie between the two major splays of the branching fault system. Focal mechanism solutions from events in these zones are consistent with the transfer of horizontal, dextral displacement from the San Andreas fault to the San Benito, Paicines and Calaveras faults within the Bear Valley region. During the 18 months preceding the February 1972 sequence, the hypocentral regions of both the M 5.0 and M 4.6 shocks were characterized by concentrations of small earthquakes. Aftershock source areas of these two events progressively expanded during the course of the aftershock sequence. Estimates of the mainshock rupture surface for these events based on the distribution of aftershocks range over a factor of 4 owing to the irregular distribution of aftershocks and the rapid growth of the aftershock zone.
The origin of short-period precursors to PKP
Authors: Wright C. 
Published: September 2021

abstract
An investigation of the origin of precursors to short-period PKP phases has been undertaken using 23 earthquakes recorded at the Yellowknife Array at distances between 123° and 143°. In particular, the pattern of slowness and azimuth changes with time has been examined for coherent bursts of energy occurring throughout the precursor wave train. These temporal changes demonstrate that the precursor energy is most satisfactorily explained by scattering from small inhomogeneities at the core-mantle boundary or in the lowermost mantle, both before P-wave energy enters the core and when it re-emerges into the mantle. Moreover, scattering before entry into the core seems to generate the larger amplitudes. The bulk of the data cannot be attributed to reflection or sharp upward refraction from velocity discontinuities within the lower part of the outer core, although there is some ambiguous evidence for a reflecting interface at a depth of about 4850 km.
Epicentral deformation based on the dilatancy-fluid diffusion model
Authors: Singh Shri Krishna , Sabina Federico J. 
Published: September 2021

AbstractThe dilatancy-fluid diffusion model of the earthquake mechanism implies deformation of the epicentral area. Based on a result in the theory of thermoelasticity, we present a method for computing such deformation. Details are given for a dilating sphere and a dilating infinite cylinder buried in an elastic half-space. Given the volumetric strain of the dilatant region, the deformation measurements could be used to estimate the magnitude of the impending earthquake. Alternatively, a constraint on the volumetric strain can be obtained from deformation measurements before earthquakes that are preceded by dilatancy.