bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectral characteristics of the P codas of Eurasian earthquakes and explosions
Authors: Evernden J. F. 
Published: September 2021

Abstract
Spectral analysis of “infinite velocity sum” subarray beams at LASA for the P codas of 36 explosions and 23 earthquakes indicates the presence of 6 to 9 Hz energy well above noise level for large explosions and earthquakes. A discriminant (D), based on use of the full spectral bandwidth from 0.4 to 9 Hz, successfully discriminates all Eurasian explosions and shallow-focus earthquakes. The basic character and contrast in spectral composition of the source spectra of earthquakes and explosions is discussed. It is pointed out that the discriminant (D), when use is made of signals recorded in the range 60° to 90°, is as or more successful in discriminating events of near mb 4.0 as those at and above mb 6.0, and the basis for this success is clarified.
It is suggested that proper use of P coda spectral discriminants appears capable of achieving identification essentially at the detection threshold of a network, while circumventing such problems as refined depths of focus, mixed events, etc.
The relationship between group velocity and phase velocity for finite, discrete observations
Authors: Nyman Douglas C. , Gupta Harsh K. , Landisman Mark 
Published: September 2021

abstract
The well-known relationship between group velocity and phase velocity, 1/u = d/dω (ω/c), is adapted to the practical situation of discrete observations over a finite frequency range. The transformation of one quantity into the other is achieved in two steps: a low-order polynomial accounts for the dominant trends; the derivative/integral of the residual is evaluated by Fourier analysis. For observations of both group velocity and phase velocity, the requirement that they be mutually consistent can reduce observational errors. The method is also applicable to observations of eigenfrequency and group velocity as functions of normal-mode angular order.
Transmission and reflection of Rayleigh wave through a step
Authors: Martel L. , Munasinghe M. , Farnell G. W. 
Published: September 2021

abstract
The transmission and reflection of a Rayleigh wave through a step on a homogeneous half-space of Poisson's ratio σ = 0.253 have been investigated by a seismic models method. The experimental results show good agreement with numerical ones obtained by finite-difference calculations when the wave is incident onto a downward step. Phase shifts are given both for the upward and downward steps. The characteristics of the transmitted wave do not depend much on the direction of propagation but those of the reflected wave are clearly direction-dependent. In each case the transmission and reflection coefficients and phase shifts depend on the ratio of step height to wavelength.
The group delays are calculated and they are positive or negative depending on the period. About 80 per cent of the incident energy is converted into body waves when the step is higher than 0.3 times the wavelength of the Rayleigh wave.
Converted shear waves as seen by ocean bottom seismometers and surface buoys
Authors: Lewis Brian T. R. , McClain James 
Published: September 2021

abstract
It is found that ocean bottom seismometers (O.B.S.) deployed in sedimented areas produce markedly different seismograms from surface hydrophones. These differences are found to be due to ringing on the O.B.S. records produced by converted shear waves trapped in the sediment layer. These shear waves do not propagate into the water and hence the hydrophone record is much “cleaner” than the O.B.S. record. It is also shown that the presence of refracted shear waves like P-S-P and P-S-S may be related to the presence of a sedimentary layer in some areas. It is suggested that the disappearance of refracted S waves in some areas without sediment is related to high attenuation and/or very low shear velocities caused by cracks and inhomogeneities in the crust. Under sedimented areas the cracks may be sufficiently filled so as to substantially reduce the attenuation and/or increase the bulk shear velocity.
An optimal strategy for searching the best fault-plane solution using wave-amplitude data
Authors: Khattri Kailash 
Published: September 2021

abstractThis paper presents an optimum search procedure known as the Fibonacci Technique for abstracting the earthquake-source parameters from the amplitude data of seismic waves. The power of the method has been demonstrated by determining the fault-plane solution of a deep-focus earthquake using the P-wave spectral amplitude data.
Numerical simulation of earthquake sequences
Authors: Rundle John B. , Jackson David D. 
Published: September 2021

abstract
Numerical simulation of earthquake occurrence using a one-dimensional fault model demonstrates that (a) the linear behavior of the magnitude-frequency relation is not an immutable law but rather is dependent on the mechanical properties of the fault, (b) “randomness” as measured by adherence to Poissonian statistics does not preclude useful prediction by statistical means, (c) the rate of occurrence of simulated earthquakes is in good agreement with the Kolmogorov model in which seismicity is related primarily to the stored elastic energy in a fault system, and (d) the occurrence of foreshocks and aftershocks can be well explained by the occurrence of stress-induced crack nucleation.
The Lima earthquake of October 3, 1974: Intensity distribution
Authors: Espinosa A. F. , Husid R. , Algermissen S. T. , de las Casas J. 
Published: September 2021

abstractThe epicenter of the October 3, 1974, earthquake was 80 km west of Lima at 12.2°S and 77.67°W. This earthquake caused severe damage in Lima and vicinity, producing a maximum Modified Mercalli intensity of IX in a few small scattered areas in Lima. The Modified Mercalli intensity in Lima varied from V to IX; in towns south of Lima the intensity exceeded VIII. The areas of high intensity, both in Lima and along the coast, appear to be related to unfavorable soil conditions or to a high water table, as is evident in the areas where large damage and/or differential settlement took place. Slumping was also observed along the coastal road south of Lima. In Callao differential earth settlement was associated with liquefaction of the soil. Pockets of high intensities, such as in the districts of La Molina and Chorrillos, are correlated with possible local ground-amplification effects. Subsidence of up to 35 cm took place in some areas along the wave-cut terrace in Miraflores, and 15 cm of subsidence was observed in Chorrillos. The isoseismal map constructed for Lima can be used in a preliminary zonation of Lima for potential earthquake effects.
The Lima earthquake of October 3, 1974: Damage distribution
Authors: Husid R. , Espinosa A. F. , de las Casas J. 
Published: September 2021

abstract
The October 3, 1974, earthquake caused severe damage to buildings of adobe and quincha construction, and also to masonry, reinforced masonry, and reinforced-concrete structures in Lima and vicinity. Most of the damage to well-built structures was due, in part, to the lack of lateral resistance in the original design and to the fact that this earthquake had more energy around 0.4 seconds period than prior destructive earthquakes. Water tanks on the roofs of structures with four or five stories were damaged. Well-engineered single-story buildings were less affected than taller structures.
Considerable structural damage to reinforced-concrete structures occurred in the districts of Barranco, La Campiña Molina, and Callao. In La Campiña three-story building partly collapsed and other buildings sustained considerable damage. In La Molina, the buildings of the Agrarian University sustained severe damage, and some collapsed. In Surco, the district adjacent to La Molina, there was no appreciable damage. In Callao, a four-story building collapsed, and the upper half of a concrete silo collapsed. In reinforced-concrete structures, column ties were frequently small in diameter, widely spaced, and not well connected. Usually, the reinforcement of resisting elements had no relation to their stiffnesses. Front columns in school buildings were restrained by high brick walls and had rather short effective lengths to allow building displacement in that direction. The windows in the rear walls gave the rear columns a much greater effective length. Therefore, a longitudinal displacement induces large shear forces in the front columns where most of the severe damage occurred. This problem was not considered in the design of these structures.
The determination of source properties by the linear inversion of seismograms
Authors: Stump Brian W. , Johnson Lane R. 
Published: September 2021

abstract
A method has been developed allowing the direct inversion of seismograms to obtain an estimate of the seismic source, as characterized by its equivalent force moment tensor. With reasonable assumptions the problem can be shown to be linear in both the frequency and time domains and least-squares methods are used to estimate the source mechanism. In the synthetic tests that have been run, several possible uses of the method have been investigated. With a satisfactory station distribution the source mechanism can be recovered using complete seismograms from three component stations or several P arrivals on vertical components. The method is useful in distinguishing multiple events including explosions. The errors of the fits are determined in the procedure and yield information such as the bandwidth of useful data in the frequency domain and error estimates for fault-plane solutions in the time domain fits.
p-Δ curves for a point source lying on a boundary
Authors: McMechan George A. 
Published: September 2021

abstract
A point source located at a boundary is an approximation to the physical configuration of an earthquake or an explosion at the ocean bottom. The p-Δ curves that correspond to arrivals from such a source, as observed at the ocean surface and at the ocean bottom, can be constructed by geometrical manipulations of the surface source to surface receiver p-Δ curve. p-Δ curves for multiply reflected arrivals can also be similarly constructed.
A note on causality problems in the numerical solution of elastic wave propagation in cylindrical coordinate systems
Authors: Herrmann Robert B. 
Published: September 2021

abstract
Harkrider noted the presence of noncausal, nonpropagating near-field terms in the cylindrical shear wave potentials for dislocation sources. He stated that these noncausal terms drop out when the total displacement field is calculated using both SV and SH shear wave potentials. When calculating realistic far-field radial and tangential displacement time histories, one must be careful in how the higher order distance terms are truncated in order to avoid the presence of noncausal terms in the time histories. Examples of this effect for tangential displacements due to a 90° dip-slip dislocation source as well as a 90° vertical strike-slip source are given to demonstrate the numerical problem.
Geodolite measurements near the Briones Hills, California, earthquake swarm of January 8, 1977
Authors: Savage J. C. , Prescott W. H. 
Published: September 2021

abstract
Two geodetic stations, the positions of which are frequently monitored by geodetic distance-measuring techniques, were located 5 and 10 km from the epicentral area of the Briones Hills earthquake swarm (maximum magnitude ML = 4.3) of January 1977. Although a 10 μradian postearthquake tilt change was recorded at a nearby tiltmeter, no significant change in geodetic distances could be detected at a sensitivity of at least 0.5 ppm. A simple dislocation model of the main earthquake in the swarm would predict no observable change in either tilt or geodetic distance.
A study of the apparent change in the foundation response of a nine-story reinforced concrete building
Authors: Foutch Douglas A. , Jennings Paul C. 
Published: September 2021

abstract
Forced vibration tests of the Millikan Library building, a nine-story reinforced concrete shear-wall structure, were conducted in 1966 and 1967, before the San Fernando earthquake, and again in 1974. The measured foundation response of the structure reported for the two tests was significantly different: in the earlier tests, motion of the foundation in the N-S direction contributed only about 3 per cent to the total roof motion, whereas in the more recent tests almost 30 per cent of the roof motion was contributed by foundation compliance. A lengthening of the fundamental period of vibration of 11 per cent was also noted.
The purpose of this study is to examine the indication that the foundation response of the structure may have changed because of the earthquake. To determine whether the observed changes in foundation response are consistent with the change in natural period, two analytical models of the Millikan Library building were developed. Both of these models include the effects of foundation compliance and one includes the effects of shear deformations in the walls of the structure. The results of these simple analyses show the changes of mode shape and period observed between the two tests to be consistent.
From the analysis, and from an examination of what is thought to be minor earthquake damage at the ground floor level of the structure, the authors conclude that the most probable cause of the differences observed in the two tests is the loss of rotational and translational stiffness provided by retaining walls, concrete slabs and other stiff, but brittle elements.
A time-domain study of the attenuation of 10-Hz waves in the New Madrid seismic zone
Authors: Nuttli Otto W. 
Published: September 2021

AbstractFrom a time-domain study, the amplitude of 10-Hz P waves in the New Madrid seismic zone was found to fall off as the inverse 1.4 power of the epicentral distance. The amplitude of 10-Hz Lg waves was found to decay as for an Airy phase with a coefficient of anelastic attenuation of 0.006 km-1. In almost all cases the Lg motion was found to be larger than that of P, even at epicentral distances of 5 km and less. Thus design earthquake motions need to be concerned with Lg waves, whose coda also have a longer duration than those of the P waves.The apparent Q for the 10-Hz Lg waves is 1500, identical to that found previously by Nuttli (1973) for higher mode 1-Hz Lg waves. The attenuation of 10-Hz Lg waves is sufficiently small that one must pay attention to their damage potential at distances as large as a few hundred kilometers.
P-velocity models of the southern Diablo Range, California, from inversion of earthquake and explosion arrival times
Authors: Alan Steppe J. , Crosson Robert S. 
Published: September 2021

Abstract
Velocity models are developed for the region in and around the southern Diablo Range, lying just east of seismically active portions of the San Andreas and Calaveras faults in central California. An iterative damped least-squares inversion procedure is used to simultaneously estimate hypocentral parameters, station delays, and velocities in a horizontally layered crustal model. Arrival times from both earthquakes and explosions of known location and origin time are used as data. The procedure used has the potential to detect low-velocity layers if they exist. The models obtained show a rapid increase in velocity to about 5.5 km/sec at 3 km depth, another rapid increase to about 6.0 km/sec at 6 km depth, and a roughly linear increase below 6 km with the velocity reaching approximately 6.7 km/sec at a depth of 15 km.
Transfer functions for the seismic research observatory seismograph system
Authors: McCowan Douglas W. , Lacoss Richard T. 
Published: September 2021

Abstract
Transfer functions are given for all basic elements of the Seismic Research Observatory (SRO) seismograph system. These include the seismometer, response shaping filters, and anti-alias filters. With these transfer functions the amplitude and phase responses can be calculated at any frequency by the evaluation of a ratio of polynomials in s = iω. Amplitude and phase response plots and impulse responses are given for the most important overall transfer functions. In addition, long- and short-period group delays have been calculated by numerical differentation of phase responses. In the long-period case a simple polynomial approximation to the group delay is given as an aid in interpretation of data. The transfer functions are exact and follow from the integral design of the system.
Three-dimensional numerical simulations of dynamic faulting in a half-space
Authors: Archuleta Ralph J. , Frazier Gerald A. 
Published: September 2021

abstract
A method is presented for the computation of near-field particle displacements and particle velocities resulting from a dynamic propagating, stress relaxation occurring on a finite fault plane embedded within a three-dimensional semiinfinite medium. To check our numerical procedure we compare our results for a circular fault in a full space with Kostrov's (1964) analytic solution for a self-similar propagating stress relaxation.
We have simulated two bilateral strike-slip earthquakes differing only in hypocentral location and examined the particle motion on the traction-free surface and on the rupture surface. Focusing of energy is evident in both ruptures. The static displacement on the rupture surface overshoots the theoretical static value by approximately 25 per cent. For the rupture that nucleated at depth the free surface almost doubled the particle velocities along the fault trace as compared with the rupture that nucleated at the free surface.
Our numerical results indicate that for an earthquake occurring on a semi-circular fault with radius of 10 km, an effective stress of 100 bars and a rupture velocity of 0.9β in a medium characterized by β = 3 km/sec, α = α=3β and a density of 2.7 gm/cm3 particle velocities can reach 400 cm/sec and displacements 250 cm.
We also compare our numerical results with the observations made by Archuleta and Brune (1975) for a spontaneous stress relaxation on a semi-circular crack in a prestressed foam rubber block.
Numerical study of diffraction of plane elastic waves by a finite crack with application to location of a magma lens
Authors: Fehler Michael , Aki Keiiti 
Published: September 2021

abstractLocation, shape, and size of near-surface heterogeneities in the Earth may be determined by active or passive seismic diffraction experiments. An array of geophones would be set up to record near-field wave motion resulting from diffraction by the inhomogeneity. As an example of such inhomogeneities, we study the diffraction of plane P and S waves by a finite two-dimensional crack as a function of wavelength and direction of incident wave. We develop a method which can be used to solve for diffraction effects by empty and fluid-filled (zero viscosity) cracks. The magnitude of the effect of the fluid in the crack is governed by a parameter called the crack stiffness factor which is the ratio of bulk modulus of the fluid in the crack to the rigidity of the solid divided by the crack aspect ratio.The diffraction problem is solved using the finite difference scheme developed by Madariaga (1976) to study dynamic crack propagation problems. It is found that a crack has little effect on wave motion for incident wave with wavelengths greater than 10 times the crack length. For wavelengths less than 5 times the crack length there is a complicated diffraction pattern. The amplitude and phase of both components of motion are affected by the crack. We find that the diffraction effect decreases as the crack stiffness factor increases. For wavelengths less than 2 times the crack length there is a region of reduced amplitude (shadow zone) behind an empty crack. Relative phase of two components of particle motion varies rapidly with position inside the shadow zone.The results of the theoretical calculation are used to try to locate the edge of a magma lens in Kilauea Iki Crater, Hawaii. It is found that the ratio of vertical-to-horizontal displacement and the direction of rotation of initial particle motion measured by a seismic array located on the floor of the crater agree qualitatively with what the theory predicts. The edge of the magma found by this method shows excellent agreement with the one inferred from the distribution of seismic events originating in the crust of the lava lake (Aki et al., 1977).
Preliminary analysis of the spectral content of P and S waves from local earthquakes in the Garm, Tadjikistan region
Authors: Rautian T. G. , Khalturin V. I. , Martynov V. G. , Molnar P. 
Published: September 2021

abstract
This paper reports preliminary results of an analysis of the spectral content of seismic waves from over 1,000 local earthquakes in the Garm, Tadjikistan region. Very low values of Q (∼100) were obtained for the Mesozoic and Cenozoic sedimentary rocks of the Peter I Range compared with those in the crystalline rock of the South Tien Shan (Q ≳ 500). For events with the same low frequency spectra, earthquakes in the South Tien Shan are recorded with more energy at higher frequencies than earthquakes in the Peter I Range, at least in part, because of the greater attenuation of the sedimentary rock in the latter region. There is a wide variety of spectra radiated by earthquakes throughout the Garm region, but a marked difference between spectra radiated by earthquakes from these two regions is not apparent. Nevertheless although calculated stress drops of earthquakes appear to vary considerably throughout the region, there appears to be a dependence on the type of rock in which the earthquakes occurred. The variation in calculated stress drops, however, is greater within either region than between the two. For most regions and for most of the range of seismic moments studied the shape of the spectrum is relatively independent of seismic moment. Consequently, calculated stress drops increase with seismic moment, with the functional dependence varying from region to region. For the largest events, the spectrum shifts to lower frequencies with increasing moment and stress drops become essentially independent of moment. Preliminary results suggest that the stress drops are not detectably different for earthquakes with thrust or normal faulting fault-plane solutions. A limited amount of data are consistent with a change in spectral content and stress drop of earthquakes in the vicinity of and before stronger earthquakes but a clear, consistent pattern is not yet evident. Toward high frequencies, S-wave spectra both begin to decrease at lower frequencies and seem to decrease more rapidly than P-wave spectra, in contrast with predictions of published dislocation models of earthquakes.
t* for S waves with a continental ray path
Authors: Burdick L. J. 
Published: September 2021

abstract
The purpose of this study was to determine t* for S waves with ray paths under the continental United States. The data set consists of long- and short-period body waves from the Borrego Mountain earthquake as observed in the northeastern U.S. The P wave forms are dominated by the sP phase and the SH wave forms by the sS. It is assumed that there are no losses in pure compression so that the relative attenuation rate of P and S waves is known. The initial source radiation is determined from the sP phase and the value of tβ* from the spectral content of the S wave. The results indicate that tβ* is 5.2 ± 0.7 sec along this ray path. Long- and short-period body waves from some deep South American events are used to test for lateral asymmetry of the Q distribution under the U.S. No lateral amplitude variation exists in this data, but this result is difficult to correlate with many previous results. The t°* value for a 600-km deep earthquake appears to be about 3 sec. A comparison of these values with values computed from current models of the Earth's Q distribution indicates that the models are slightly too high in Q overall and that more of the total body-wave attenuation occurs above 600 km than is indicated by the models.