bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generation of SH-type motion by torsion-free sources
Authors: Singh Sarva Jit 
Published: September 2021

abstract
The problem of a spherical cavity in an infinite medium is re-examined. The spectral displacement and stress fields are derived when arbitrary tractions are prescribed over the surface of the cavity. This also yields the solution of the problem of the release of pre-existing stress within a spherical zone. The particular case when the radius of the cavity is small in comparison with the wavelength under consideration is discussed in detail. The nature of the tractions is obtained which, when applied at the surface of the cavity, yield the same displacement field as radiated by various point sources. Equivalent body forces are obtained for the release of pre-existing tensile and shear stresses within a spherical zone of small radius. In the course of the analysis, it is shown that an apparently torsion-free source is capable of generating SH-type motion.
The effect of simple topography on seismic waves: Implications for the accelerations recorded at Pacoima Dam, San Fernando Valley, California
Authors: Boore David M. 
Published: September 2021

abstract
A precise analysis of the influence of topographic and geological effects on the significant ground motions recorded near Pacoima Dam during the San Fernando, California, earthquake of February 9, 1971, is an immensely complicated task. Calculations for simple models give results that suggest the following general conclusions: (1) the topography should have influenced the recorded ground motion, and (2) this influence seems to be an amplification of the higher-frequency accelerations by as much as 50 per cent, but is relatively unimportant at the lower frequencies (which control the maximum particle velocities).
Earthquake magnitude probabilities and statistical independence for Mexico City earthquakes
Authors: Ferraes Sergio G. 
Published: September 2021

Abstract
The absolute and the conditional earthquake magnitude probabilities are defined by direct enumeration of the successive earthquake magnitude observations.
We make the assumption of independence of earthquake magnitude events in Mexico City earthquakes and then show by experimental data that the assumption of randomness, and consequently the model, is not a good one. Using the X2 statistic to check the statistical dependence, it is found that there is some statistical association between the magnitudes of 221 successive earthquakes felt in Mexico City with magnitude 4.5 or greater. In other words, the observed sequence of discrete earthquake magnitudes for the Mexico City area is nonrandom.
Finally, the concept of energy is used to give a physical interpretation of the significance of the nonrandomness.
Theoretical and observed noise in a high-sensitivity long-period seismograph
Authors: Fix James E. 
Published: September 2021

Abstract
Theoretical expressions for the spectra of the noise in a galvanometer, a seismometer, and a seismometer-galvanometer seismograph are derived from electrical analog circuits and from the Johnson noise of the resistive elements in these circuits. The contributions of the internal damping of the seismometer and of the galvanometer, and of the series resistor to the total potential energy of the thermal noise in a high-sensitivity long-period seismograph are explicit in the expressions. The theoretical thermal spectra agree with observations made at Las Cruces, New Mexico (LC-NM), and at Queen Creek, Arizona (QC-AZ). At LC-NM, the outputs from two matched vertical seismographs were subtracted to obtain estimates of the individual seismograph noise at periods from 4 to 800 sec. Additional experiments demonstrated that the seismograph noise between 10 and 1,000 sec could be estimated equally well by replacing the seismometer: (1) with a resistor, (2) with a coil and magnet oriented vertically or north-south, or by (3) rigidly blocking the seismometer mass. The observed spectra from LC-NM indicate an excess noise in the electronics of the galvanometer phototube amplifier (GPTA) having a one-over-f character at periods longer than 300 sec. At QC-AZ, seismograph noise was recorded with a resistor substituted for the seismometer. The observed noise spectra agree identically with the theoretical noise spectra at periods from 25 to 60 sec and with theoretical noise spectra plus a 1/f noise in the GPTA electronics at periods out to 2,560 sec. The QC-AZ observed and theoretical noise spectra are plotted from 3 to 2,560 sec as the mean-square voltage at the seismograph output and as the root-mean-square displacement of the ground that would produce the same signal as the noise. Typical minimum vertical amplitude spectra of the microseismic background are above the instrument noise spectra in the period range from 3 to 2,560 sec. The agreement between the theoretical thermal noise spectra and the two sets of observational spectra confirms the validity both of the theoretical expressions and of the experimental procedures.
Evidence for a high-velocity lithospheric plate under northern Nevada
Authors: Koizumi Carl J. , Ryall Alan , Priestley Keith F. 
Published: September 2021

Abstract
P-wave residuals at stations of the Nevada seismic network are analyzed for 80 teleseisms distributed over a range of azimuth and epicentral distance. For South American earthquakes (azimuth 120° to 140° from Nevada), teleseismic P arrivals at northern Nevada stations Lovelock, Battle Mountain, and Elko are early by as much as 1.4 sec relative to the Tonopah station to the south. The North Reno station has early arrivals, relative to Tonopah, for Leeward Islands earthquakes, at an azimuth of 100° from the station. Interpretation of these residuals indicates the presence of a high-velocity lithospheric plate, striking northeast and dipping southeast, under northern Nevada. The high-velocity plate is interpreted as a paleosubduction zone.
Magnitude-recurrence relation for central Mississippi Valley earthquakes
Authors: Nuttli Otto W. 
Published: September 2021

abstract
Earthquake magnitudes are estimated for all known felt earthquakes in the central Mississippi River valley seismic region for the interval 1833 through 1972. The resulting data-set is examined for completeness, and used to determine a magnitude-recurrence relation. The value of the slope b in the recurrence equation is found to be 0.87 ± 0.11 for 95 per cent confidence limits using the maximum likelihood method, and 0.92 ± 0.08 using weighted least squares.
An ocean-bottom seismometer capsule
Authors: Prothero William A. 
Published: September 2021

abstract
An ocean-bottom seismometer capsule containing a 1-Hz vertical seismometer and triggered digital recording system has been developed and tested off the coast of San Diego. The output of the seismometer is continuously digitized at 64, 128, or 256 samples per second. The digital data is mixed with a time code and passed through a 256 sample shift register which acts as a delay line. It is then mixed with synchronization characters, serialized, encoded, and recorded on a SONY TC800B tape recorder which is turned on when a seismic event occurs. The event trigger occurs when the seismic signal jumps to at least twice the time-averaged input signal. Data are recovered using the same recorder for playback and a decoder which provides an analog output for field data interpretation or a digital output for computer analysis. The capsule itself falls freely to the ocean bottom. After a predetermined time it is released from a 150-lb steel tripod and floats to the surface. A dual timer and explosive bolt system provides a high recovery reliability. A number of seismic events have been measured in field tests and the system has proven to be extremely simple to check out, diagnose, and deploy.
Weakly coupled potentials for high-frequency elastic waves in continuously stratified media
Authors: Richards Paul G. 
Published: September 2021

Abstract
A simple construction is given, in terms of potentials, for assigning P and S components of elastic-wave displacement in media with depth-dependent density and Lame parameters. Attention is focused on spherically symmetric media, with radial dependence of material properties, and the asymptotic methods used are expected to be accurate for seismic body waves and surface waves with period less than about 1 min. Novel features of the construction include: (a) its completeness (all possible displacements are represented by the potentials), (b) the development of second-order wave equations, for the P and S potentials, which explicitly display a coupling coefficient, and (c) demonstration of the way in which P and SV components of displacement decouple as frequency increases. Previous work has given constraints on the medium such that P and SV decouple completely: these constraints are here simplified and are seen to arise naturally in the context of the present potential representation. The coupling coefficient (between P and SV) is examined in a variety of earth models.
Source mechanisms for Wilmington Oil Field, California, subsidence earthquakes
Authors: Kovach Robert L. 
Published: September 2021

abstractAn unusual set of man-made “earthquakes” was generated in the Wilmington Oil Field, California, during the exploitation of this field. The Wilmington Oil Field was the classic example of an elliptically shaped subsidence bowl produced by the extensive withdrawal of the underlying oil. This surface subsidence produced horizontal shear stresses relieved several times by damaging sudden horizontal movements on very shallow slippage planes. Damaging shocks occurred in 1947, 1949, 1951, 1954, 1955, and 1961. These shocks produced seismograms, primarily composed of surface waves, which present an interesting opportunity to study seismic source mechanisms inasmuch as the focal depth, amount of slip, and source dimensions are known. Rayleigh-wave amplitude spectra for these events reveal seismic moments ranging from 5 × 1022 to 1.7 × 1023 dyne-cm, in good agreement with moments inferred from field observations. A key feature of the subsidence shocks is that very low rupture velocities (0.1 to 0.3 km/sec) were involved. The inferred stress drops indicate that the subsidence shocks must have involved a significant fraction of the available strain energy.
The solution of theoretical seismic problems by best rational function approximations for Laplace transform inversion
Authors: Longman I. M. , Beer T. 
Published: September 2021

Abstract
In a recent paper, the first author has developed a method of computation of “best” rational function approximations ḡn(p) to a given function f̄(p) of the Laplace transform operator p. These approximations are best in the sense that analytic inversion of ḡn(p) gives a function gn(t) of the time variable t, which approximates the (generally unknown) inverse f(t) of f̄(p in a minimum least-squares manner. Only f̄(p) but not f(t) is required to be known in order to carry out this process. n is the “order” of the approximation, and it can be shown that as n tends to infinity gn(t) tends to f(t) in the mean. Under suitable conditions on f(t) the convergence is extremely rapid, and quite low values of n (four or five, say) are sufficient to give high accuracy for all t ≧ 0.
For seismological applications, we use geometrical optics to subtract out of f(t) its discontinuities, and bring it to a form in which the above inversion method is very rapidly convergent. This modification is of course carried out (suitably transformed) on f̄(p), and the discontinuities are restored to f(t) after the inversion.
An application is given to an example previously treated by the first author by a different method, and it is a certain vindication of the present method that an error in the previously given solution is brought to light.
The paper also presents a new analytical method for handling the Bessel function integrals that occur in theoretical seismic problems related to layered media.
Deep structures of the southern Tyrrhenian basin and P-wave residuals at Messina
Authors: Bottari Antonio 
Published: September 2021

Abstract
In this article, P travel-time residuals for the Messina station are analyzed in order to investigate the Tyrrhenian upper mantle, which is considered to be crossed by a lithospheric slab.
A first set of 24 residuals derived from deep earthquakes of the southern Tyrrhenian Sea show early arrivals of, on the average, −1.3 sec at Messina. In addition, these negative residuals are associated with initial motion of the dilatation type. On the contrary, the few deep earthquakes which produce, as first motion, a compression at the Messina station, are associated with late arrivals of about 1 sec. These results are considered and discussed in order to analyze the hypocentral mechanism and P-wave transmission through the lithospheric slab.
A second and wider analysis is then extended to 206 earthquakes which have, with respect to Messina, an epicentral location in the distance range 16° to 103° and azimuthal orientation Z in the interval 180° to 380°. The first conclusion from this analysis is that the P travel times observed at Messina for epicentral distances in the range 20° to 103° and 245° ≦ Z ≦ 380° are generally 0.5 to 3 sec less than those given in the Jeffreys-Bullen tables.
Finally, a further improvement on the foregoing result has been obtained. This gives further confirmation of the consistency of regional variations of the P travel times with a slab model for the Tyrrhenian deep structures. As a matter of fact, the comparison between the travel times of Messina and a standard provided by observations in the stations of Rome and Trieste confirms early arrivals of about 1 sec on the seismic paths which cross the upper mantle in the southern Tyrrhenian region.
Statistical analysis and interpretation of surface-wave anelastic attenuation data for the stable interior of North America
Authors: Herrmann Robert B. , Mitchell Brian J. 
Published: September 2021

Abstract
As a byproduct of determining the source characteristics of some earthquakes and underground nuclear explosions, a body of fundamental-mode Rayleigh- and Love-wave anelastic attenuation values is available for propagation paths in the stable interior of North America in the 5- to 50-sec-period range. The anelastic attenuation values were obtained from four earthquakes occurring in the New Madrid seismic region, one earthquake in the northern Hudson Bay region, and three underground nuclear explosions in the western United States. In obtaining the anelastic attenuation data, a simple statistical test was applied to test the reliability of the observations. The anelastic attenuation coefficients are presented together with their 95 per cent confidence levels.
A stochastic form of the Backus-Gilbert inverse formalism was applied to a subset of these data to yield a Qβ model for the stable interior of North America. The model is characterized by relatively low Qβ values for the upper crust and a rapid transition to much higher values for the lower crust.
Crustal structure in central New Mexico interpreted from the gasbuggy explosion
Authors: Toppozada Tousson R. , Sanford Allan R. 
Published: September 2021

abstract
Interpretation of a seismic profile extending 548 km southward from the GASBUGGY nuclear test of December 10, 1967 resulted in a crustal model for central New Mexico. The crust is 39.9 km thick below the Paleozoic “basement”. It consists of an upper crust 18.6 km thick having P velocity 6.15 km/sec, and a lower crust 21.3 km thick having P velocity 6.5 km/sec. The apparent upper mantle velocity is 8.12 km/sec. This model applies near the crossover distance, 50 km west of Albuquerque. Additional information from earthquakes and explosions suggests that the upper crustal velocity drops to 5.8 km/sec in the Rio Grande rift, and that the true upper mantle velocity is 7.9 km/sec. The low upper crustal velocity in the Rio Grande rift can be detected on the record section of the GASBUGGY profile.
Crustal structure in Southern Central America
Authors: Matumoto Tosimatu , Ohtake Masakazu , Latham Gary , Umana Jorge 
Published: September 2021

abstract
Seismic data from explosions and local earthquakes are used to determine shallow crustal structure near Managua, Nicaragua, and to derive a complete crustal model for northern Costa Rica. A new method, referred to as the minimum apparent velocity (MAV) method, has been developed and applied in the analysis of local earthquake data. The results indicate that the MAV method of multilayer analysis, when combined with well-determined station corrections, can be quite useful in regions of high seismicity. Based upon the analysis presented here, the total thickness of the crust beneath the central volcanic province of northern Costa Rica is about 43 km. Four crustal layers are identified with compressional-wave velocities of 2.6, 5.1, 6.2, and 6.6 km/sec. The upper mantle velocity is 7.9 km/sec. The major features of this model closely resemble those of other seismically active, marginal zones of the Pacific.
Seismic risk in linear source regions, with application to the San Andreas fault
Authors: Douglas Bruce M. , Ryall Alan 
Published: September 2021

abstract
A method is described for determining recurrence times as a function of distance to the causative fault and magnitude, for earthquakes distributed along a linear source zone. The method takes into account rupture length, which is scaled to magnitude, and permits direct calculation of approximate return periods for peak ground-motion parameters for large earthquakes, when the appropriate attenuation functions are known. Several examples are presented using instrumentally determined seismicity along the San Andreas fault zone. Results illustrate the necessity of incorporating rupture length in calculations related to seismic risk; for large earthquakes, it is also necessary to use a source region large enough to contain the rupture zones of all such events. For a site in the San Andreas fault zone we find that the recurrence time to be within 10 km of the causative fault of an earthquake with M ≧ 8 is 200 to 300 years, depending on the choice of maximum magnitude (8.6 or 8.4). For a site on the fault in the Hollister region, we find that recurrence times to be within 10 km of the rupture due to events of M ≧ 5, 6 and 7 are, respectively, 12, 45 and 105 years.
The accuracy of soil response estimates using soil-to-rock spectral ratios
Authors: Beresnev Igor A. , Wen Kuo-Liang 
Published: September 2021

Abstract
Spectral ratios between soft soil and reference rock sites are often used to predict the sedimentary site response to earthquakes. However, their relationship with the genuine site-specific amplification function is often unclear. We compare the soil-to-rock spectral ratios between the stations that are 3.3 km apart with the “genuine” response given by the ratios between the surface and 17 and 47 m downhole. Data from the SMART1 array in Taiwan are used. The “weak” and “strong” motion records are addressed separately to allow for nonlinear soil response. The soil-to-rock spectral ratios are nearly identical to the “true” amplification at the frequencies from 1 to 10 Hz, if the finite depth of the borehole is taken into account. They correctly capture the strong-motion deamplification effect. However, the soil-to-rock spectral ratios are roughly 1.4 times more uncertain than surface-to-47-m ratios. In summary, the soil-to-rock spectral ratios can be considered as the reliable estimates of the real site response.
Earthquake slip rise time and rupture propagation: Numerical results of the quantum earthquake model
Authors: Rydelek Paul A. , Selwyn Sacks I. 
Published: September 2021

Abstract
We continue to investigate the properties of an earthquake model that is based on the physically reasonable assumption that some small section of the fault, referred to as a quantum, must have the same failure criteria (Sacks and Rydelek, 1995). In the simplest case studied to date, the failure criteria is controlled by the physics of Coulomb failure. When this section fails, there is a redistribution of the stress drop onto nearest neighbors. These neighboring quanta, if already near failure, may produce further rupture and so forth for neighbors of neighbors. For larger events comprised of many failed quanta, this cascade process produces a rupture front of limited width and with a variable rate of propagation. In the rupture front, there can be multiple reactivation (i.e., the cycle of fracturing and healing), which governs the duration of the rise time; this rise time is found to be of much shorter duration than the total rupture time of the event. In addition, even though the failure parameters of the quanta are somewhat similar (within 20%), the chaotic behavior of the faulting process and the stress redistribution from numerous smaller events leading up to a large event can give rise to apparent nonphysical asperities, i.e., subregions with larger than average slip. That such characteristics are observed in real earthquakes lends support to the underlying physics that governs our model.
Far-field aftershocks of the 1906 earthquake
Authors: Steeples Don W. , Steeples Dan D. 
Published: September 2021

Abstract
During the 24 hr following the great San Francisco, California, earthquake of 18 April 1906, separate seismic events were felt at Paisley, Oregon; Phoenix, Arizona; Los Angeles, California; and Brawley, California (MMIX). Using probability theory, we show that the occurrence of felt earthquakes in each of these widespread locations on the same day would constitute a rare event. Rates of felt-earthquake occurrences over a 9-yr period from 1897 to 1906 were determined for the four different regions that experienced earthquakes within 24 hr after the 1906 event. We modeled the likelihood of occurrence of these aftershocks in the spirit of the “ball-in-the-box” probability problem, and the results indicated a very high probability that the aftershock zone of the great earthquake extended at least 500 km beyond the extent of ground breakage, implying a disturbance of the stress field over an area at least two to three times longer than the fault break itself.
Reflected seismic waves and their effect on strong shaking during the 1989 Loma Prieta, California, earthquake
Authors: Catchings R. D. , Kohler W. M. 
Published: September 2021

Abstract
Our data indicate that critical and postcritical reflections from crustal layers and the Moho produced increased shaking at discrete distances along the San Francisco Peninsula during the 1989 Loma Prieta earthquake. These reflections may have produced an increase in amplitude that is as much as 10 times greater than that of the direct arrival. Peak amplitude-distance patterns measured from explosive sources, synthetic seismograms, aftershocks, and the mainshock of the 1989 Loma Prieta earthquake indicate that (1) point sources, such as explosions, produce similar peak amplitude-distance relations as distributed, double-couple sources when the crustal structure is approximately a Poisson solid; (2) peak amplitudes from smaller point sources (explosions) may be scaled to those of larger sources (earthquakes); and (3) reflections caused a pattern of high amplitudes at specific distances along the San Francisco Peninsula that geographically correlates with areas of reported damage following from the Loma Prieta mainshock. Our study indicates that critical and postcritical reflections were stronger influences on the locations of strong shaking than local geology because a number of sites around the San Francisco Bay that are underlain by unconsolidated sediments experienced much less shaking than sites that were underlain by hard rock. Furthermore, some severely shaken hard-rock sites were farther from the epicenter than many of the less severely shaken “soft-sediment” sites. Models of the regional crustal structure and seismic-wave propagation paths may be useful in identifying sites around the San Francisco Bay region that are at risk due to reflected seismic energy, and this type of analysis may be useful in other seismically active regions.