bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some autoregressive models for short-period seismic noise
Authors: Tjøstheim D. 
Published: September 2021

abstract
It is shown that short-period seismic noise at the NORSAR seismic array can be described by a parametric model having the form X ( t ) − a 1 ( t ) X ( t − 1 ) − … − a p ( t ) X ( t − p ) = Z ( t ) where X(t) is used to denote the noise process. This is a nonstationary generalization of the standard autoregressive models allowing time-varying autoregressive coefficients and a nonstationary white-noise residual process Z(t). The coefficients a1(t), a2(t), …ap(t) and the residual variance σ2z(t) are estimated using data from the NORSAR seismic array. It is found that the short-period noise at NORSAR is quite satisfactorily described by a third-order (p = 3) model. Also, it is found that the nonstationary character of the noise is due primarily to time variations of the residual variance and the lower order autoregressive coefficients.
The thin sedimentary layer of the Sonoran Embayment
Authors: Wilhelm R. , McIntyre R. G. , Slusher H. S. 
Published: September 2021

abstract
Five earthquakes from the Gulf of California, recorded at the John W. Kidd Memorial Seismological Observatory of The University of Texas at El Paso, are analyzed to estimate the thickness of the sedimentary layer of the Sonoran Embayment located southwest of El Paso, Texas and bounded on the western extremity by the Sierra Madre Occidental. The seismograms are digitized at 12-sec intervals and filtered in the time domain with a Parzen lag window to regenerate the fundamental-mode Rayleigh waves. Arrival times of these short-period surface waves are reduced to the time required to propagate through the Sonoran Embayment. The data are studied by Savarensky's method and by spectral analysis to yield group-velocity dispersion values. The results of the two distinct methods agree well. Theoretically obtained dispersion curves, in which the indexing parameter is layer thickness, are fitted to the velocity dispersion points. It is found that the sedimentary layer of the Sonoran Embayment is 2 to 3 km thick.
Statistical analysis of microearthquake activity near San Andreas geophysical observatory, Hollister, California
Authors: Udias Agustin , Rice John 
Published: September 2021

Abstract
Microearthquake activity during the 4-year interval 1968 to 1971 in a region of 25 km radius, centered on the San Andreas fault near Hollister, has been monitored by means of high-gain high-frequency seismographs which allow detection of events as small as magnitude zero within the region. The distribution of the 4764 microearthquakes shows a high degree of clustering. The series of time intervals between consecutive shocks can be described approximately by a gamma distribution whose shape parameters for different samples change from 0.3 to 0.8. The exponential probability plots of the {Δti} series for 265 larger regional earthquakes over 10 years result in a constant value of the hazard function except for small values of time where the hazard is higher. The variance-time and intensity functions show a varying degree of interdependence between events for each year and a long-term dependence up to 80 days for the period 1968-1971. The time scale of clustering has been estimated. Inferences based on short-term microearthquake studies may be grossly misleading.
Details of microearthquake swarms in the Columbia basin, Washington
Authors: Malone Stephen D. , Rothe George H. , Smith Stewart W. 
Published: September 2021

Abstract
Three microearthquake swarms in the Columbia River basin of eastern Washington have been studied by means of a small portable seismic network. Earthquakes in this area typically occur in swarms, concentrated both temporally and spatially. One unusual characteristic of the three swarms studied was the shallow focal depths of all events. Most events located had depths less than 1 km; none were deeper than 2 km. Composite focal mechanism solutions indicate that more than one fault surface is active in any one swarm. All events had some thrust component with the axis of maximum compression oriented roughly in a north-south direction.
P-wave amplitude variation with epicentral distance and the magnitude relations
Authors: Kaila K. L. , Sarkar Dipankar 
Published: September 2021

Abstract
Investigation of the variation of P-wave amplitudes and d2T/dΔ2 with epicentral distance reveals that the amplitudes in the distance range up to 100° can be represented by seven discontinuous curves. The discontinuous nature of the amplitude curves can be explained due to the possible existence of first- or second-order velocity discontinuities in the upper and lower mantle of the Earth. Seven magnitude relations corresponding to these amplitude curves are given, which yield consistent magnitudes for nuclear explosions as well as for shallow earthquakes.
Earthquake precursors
Authors: Rikitake Tsuneji 
Published: September 2021

Abstract
An analysis of existing earthquake precursor data leads to a conclusion that the precursors reported so far can be classified into three types, i.e., A1, A2 and B types. Most of type B precursors, observed in terms of anomalous tilts and strains or foreshocks, have no magnitude-dependent precursor time. Meanwhile the A2-type precursors observed by means of geodetic work, changes in seismic-wave velocities and the like seem to have a precursor time which is closely correlated to the magnitude of coming earthquakes. A precursor of this type may possibly be interpreted by the current theory of dilatancy. The A1-type precursors, observed mostly several hours prior to the main shock, may be caused by a creep-like failure before the main rupture of the Earth's crust.
Probabilities for an anomalous signal of various geophysical elements to be related to a forthcoming earthquake are estimated on the basis of the existing data of precursors.
A feasible strategy for predicting a large earthquake as suggested by the present study will be as follows: First of all, we monitor accumulation of crustal strain by means of geodetic work. The next task is to detect an A2 signal which would arise from a highly strained crust sooner or later. If the spatial extent of the A2-type precursor is known, it is possible to estimate roughly the magnitude as well as the occurrence time of the coming earthquake. Finally, detection of an A1-type precursor, if it should occur, would provide a short-range forecast having a time span of hours.
Diffraction of Love waves by perfectly rigid and perfectly weak half-planes
Authors: Kazi M. H. 
Published: September 2021

Abstract
In this paper we investigate the transmission and reflection of Love waves, normally incident on a perfectly rigid half-plane or a perfectly weak half-plane, which lies in a layer of uniform thickness, overlying a semi-infinite solid. The half-plane is parallel to the interface of the two materials and lies in the upper layer. The perfectly rigid half-plane is a domain of vanishing displacement, whereas the perfectly weak half-plane is a domain of vanishing traction. We use the Wiener-Hopf technique based on an approach due to D. S. Jones (1952). Such a method has previously been employed by R. Sato (1961) in his paper on Love waves incident on a change of thickness in the surface layer.
We set up the two boundary value problems, and obtain analytical solutions for transmitted and reflected Love and channel waves in the case of the rigid as well as the weak screen. We draw the following conclusions:
Finally, we show the connection between the problem of Love waves past a weak screen and Sato's problem of Love waves incident on a vertical step discontinuity in the surface layer, from the thicker to the thinner side.
Seismic waves in a wedge
Authors: Alterman Z. , Nathaniel R. 
Published: September 2021

abstract
The equations for elastic-wave propagation caused by an explosive point source are solved, by a finite difference scheme, for the case of an elastic wedge, with free boundary.
Varying the wedge angle shows that the amplitude of the motion, at the corner, increases as the wedge angle is decreased. The results indicate that for wedges with angles varying from 0° to 180°, the amplitude decreases with decreasing β/α (shear- to compressional-wave velocity). The corner of the wedge generates surface waves and the elliptical particle motion in the waves is analyzed. The particle motion is elliptic and the major axes of the ellipses are inclined at half the wedge angle to the free surface.
The surface wave travels to the corner from where it is “transmitted” and reflected.
Surface waves are shifted by 180° - θ after transmission.
For the case of a quarter plane, we get the same result as Alterman and Loewenthal (1970).
Rayleigh waves from high-gain long-period stations: Signal extraction, amplitude determination, and separation of overlapping wave trains
Authors: Berg Eduard 
Published: September 2021

abstract
For a signal-to-noise ratio between 0.2 and 0.1 on the original single-component records, amplitudes for Rayleigh waves over oceanic paths of 155° at station MAT and 98° at station KIP have been determined as 12 mμ and 24 mμ peak-to-peak, respectively, with a standard error of less than 11 per cent. In each case the processed correlation signal is the highest in a half-hour record. The method makes use of preliminary high-pass filtering and normalized reference earthquake-matched filtering, and takes full advantage of the well-dispersed oceanic surface wave.
The method also provides high resolution of co-located events with short time separation, or of widely spaced events with Rayleigh waves arriving nearly simultaneously at a single station, when the summed vertical and radial matched filtered components are used. Examples include: (1) clear separation and amplitude determination at stations KIP and MAT of two MS = 6.5 earthquakes located 0.7° and 145 sec apart off the coast of central Chile; (2) clear separation at station KIP of a Novaya Zemlya mb = 4.8 event from interfering Rayleigh waves of an mb = 5.0 Kermadec Island earthquake arriving 120 to 140 sec prior to the searched event, with almost complete elimination of interference on the summed vertical and radial processed components; and (3) clear separation at station KIP of two co-located mb = 4.4 and 4.5 earthquakes 6 min apart off the coast of Chile, with determination of their amplitudes in the presence of interfering Rayleigh waves from two central Alaska earthquakes, the first (mb = 4.1) arriving 15 min prior to the first Chile Rayleigh wave and the second between the two Chile arrivals.
The single-station threshold reached (10 and 25 digital units, p-p) for stations MAT and KIP at 155° and 98°, respectively, corresponds to an MS = 3.3 and probably can be improved further.
Dependence of magnitude statistics on strain rate
Authors: McGarr A. 
Published: September 2021

Abstract
Magnitude statistics (log N = a − bM) were measured for mine tremors and for the Parkfield earthquakes, listed by McEvilly, Bakun and Casaday (1967), in conditions of varying rates of aseismic ground deformation. Aseismic deformation rates were estimated using a tiltmeter in the ERPM gold mine and using results from small geodetic networks, reported by Smith and Wyss, for the region near Parkfield, California. In the magnitude-frequency relationship, b is independent of the rate of aseismic deformation, ε˙,anda=logε˙+Κ, where K is a constant. Thus, the level of seismicity appears to be determined by the rate of aseismic ground deformation. Changes in shear stress of the order of 100 bars do not have any measurable effect on the magnitude statistics.
Microtremor analysis of local geological conditions
Authors: Katz Lewis J. 
Published: September 2021

abstractThe application of microtremor spectra in predicting frequency-dependent amplification effects of local site geology was investigated. Long time-interval (&gt; 45 min) microtremor data were used to estimate Power Spectral Density (PSD) plots. Peaks occurring in these PSD plots were correlated with peaks of transfer functions (Haskell, 1960 and 1962) calculated from known geological models. The resulting apparent positive correlations indicate that a procedure of estimating PSD plots from long time intervals of microtremor data would be useful in predicting response spectra for earthquake risk evaluation.
Effects of local geological conditions in the San Francisco Bay region on ground motions and the intensities of the 1906 earthquake
Authors: Borcherdt Roger D. , Gibbs James F. 
Published: September 2021

abstract
Measurements of ground motion generated by nuclear explosions in Nevada have been completed for 99 locations in the San Francisco Bay region, California. The recordings show marked amplitude variations in the frequency band 0.25 to 3.0 Hz that are consistently related to the local geological conditions of the recording site. The average spectral amplifications observed for vertical and horizontal ground motions are, respectively: (1, 1) for granite, (1.5, 1.6) for the Franciscan Formation, (3.0, 2.7) for the Santa Clara Formation, (3.3, 4.4) for alluvium, and (3.7, 11.3) for bay mud. Spectral amplification curves define predominant ground frequencies in the band 0.25 to 3.0 E for bay mud sites and for some alluvial sites. Amplitude spectra computed from recordings of seismic background noise at 50 sites do not generally define predominant ground frequencies.
The intensities ascribed to various sites in the San Francisco Bay region for the California earthquake of April 18, 1906, are strongly dependent on distance from the zone of surface faulting and the geological character of the ground. Considering only those sites (approximately one square city block in size) for which there is good evidence for the degree of ascribed intensity, the intensities for 917 sites on Franciscan rocks generally decrease with the logarithm of distance as
Intensity = 2 . 6 9 - 1 . 9 0 log ( Distance in kilometers ) . ( 1 )
For sites on other geological units, intensity increments, derived from this empirical relation, correlate strongly with the Average Horizontal Spectral Amplifications (AHSA) according to the empirical relation
Intensity Increment = 0 . 2 7 + 2 . 7 0 log ( AHSA ) . ( 2 )
Average intensity increments predicted for the various geological units are −0.3 for granite, 0.2 for the Franciscan Formation, 0.6 for the Great Valley sequence, 0.8 for the Santa Clara Formation, 1.3 for alluvium, and 2.4 for bay mud. The maximum intensity map predicted on the basis of these data delineates areas in the San Francisco Bay region of potentially high intensity for large earthquakes on either the San Andreas fault or the Hayward fault. The map provides a crude form of seismic zonation for the region and may be useful for certain general types of land-use zonation.
Study of seismological evasion
Authors: Evernden Jack F. 
Published: September 2021

abstract
This paper discusses seismological aspects of various proposed means of obscuring or hiding the seismic signatures of explosions from a surveillance network. These so-called evasion schemes are discussed from the points of view of both the evader and the monitor. The analysis will be conducted in terms of the USSR solely because that country is so vast and the geological/geophysical complexities of the country are so great that the complete spectrum of hypothesized evasion schemes requires discussion.
Part I of this paper was a general discussion of evasion schemes, placing the concepts within the reality of general factors influencing effective use of the techniques. Part II described techniques for quantitative investigation of evasion schemes when the only noise problem is normal microseismic noise, and gave analyses of several seismological networks as regards their capabilities to restrain imagined clandestine testing by the USSR under such noise conditions. This part of the paper (part III) describes techniques appropriate for use when the noise problem is interference due to codas of P and surface waves from earthquakes, and it will give analyses of capabilities of several seismological networks to restrain use of such codas for effective evasion.
An electronic long-period seismograph for surface-wave dispersion studies
Authors: Wielandt E. , Mitronovas W. 
Published: September 2021

abstract
A long-period seismograph has been developed where the galvanometer photographic recording has been replaced by an electronic amplifier-filter circuit and ink recording, at comparable cost. The system has been tested carefully and found to be superior to conventional systems in some respects, especially in the stability of the transfer function and in the ease of installation and calibration. Critical but still satisfactory features are the dynamic range of the amplifier and the accuracy of the ink pen recorder. Both items are discussed in some detail.
Focal mechanism of the August 1, 1975 Oroville earthquake
Authors: Langston Charles A. , Butler Rhett 
Published: September 2021

abstract
Long-period teleseismic P and S waves from the WWSS and Canadian networks are modeled to determine the focal parameters for the main shock in the Oroville earthquake series. Using the techniques of P first motions, wave-form synthesis, and phase identification, the focal parameters are determined as follows: dip 65°; rake −70°; strike 180°; depth 5.5 ± 1.5km; moment 5.7 ± 2.0 × 1024 dyne-cm; and a symmetric triangular time function 3 sec in duration. This is a north-south striking, westward dipping, normal fault with a small component of left-lateral motion. The time separation between the small foreshock and mainshock appears to be 6.5 sec at teleseismic distances, rather than 8.1 sec as observed at short distances.
Attenuation of Love and Rayleigh waves across the Pacific at periods between 15 and 110 seconds
Authors: Mitchell B. J. , Leite L. W. B. , Yu Y. K. , Herrmann R. B. 
Published: September 2021

abstract
Average surface-wave attenuation coefficient values along with their 95 per cent confidence limits are determined at periods between 15 and 110 sec for paths across the Pacific Ocean. Values for the fundamental Rayleigh-mode decrease from 3.2 × 10−4km−1 at a period of 15 sec to about 0.95 × 10−4km−1 at the longest periods. Love-wave attenuation coefficient values decrease from 3.8 × 10−4km−1 to about 0.95 × 10−4km−1 over the same period range. Although these values are tentatively taken to correspond to the fundamental Love-mode, higher-mode contamination may bias the observed attenuation coefficient values over the short-period portion of the period range. Attenuation coefficient values for both Rayleigh and Love waves are higher than values previously determined for the stable interior of North America over much of the period range between 15 and 40 sec.
Theoretical seismograms were computed and used as an aid in evaluating the effects of continental margin complexities and higher-mode interference on the attenuation coefficient determinations. Results indicate that the relatively large confidence limits for Rayleigh waves, especially at shorter periods, may reflect continental margin complexities. Higher-mode interference in combination with continental margin complexities produce even greater uncertainty in the determination of the attenuation coefficients for Love waves.
Teleseismic residuals prior to the November 28, 1974, Thanksgiving Day earthquake near Hollister, California
Authors: Cramer Chris H. 
Published: September 2021

abstract
Teleseismic arrivals at 30 stations in the vicinity of Hollister, California, have been analyzed for P-velocity variations prior to the magnitude 5.1 November 28, 1974, Thanksgiving Day earthquake. The teleseismic arrivals for large circum-Pacific source events during the period of May through December, 1974, have been analyzed using the method of two-station relative residuals with a correction for observed azimuthal variations. The data contain no significant travel-time delays associated with this event to within 0.1 sec and all 30 stations analyzed exhibited stable travel-time residuals during the study period. In particular, residuals at station OCR for South and Central American sources whose ray paths pass within 2.5 km of the hypocenter exhibit no time changes. Assuming at least a 10 per cent P-velocity charge for anomalous zones, these observations restrict the maximum possible P-velocity anomaly zone that might have been associated with this particular event to within 3 to 4 km of the hypocenter.
Automated high-precision amplitude and phase calibration of seismic systems
Authors: Berg Eduard , Chesley Duncan M. 
Published: September 2021

abstract
Automated amplitude and phase response of the complete seismometer-recording system is obtained from step inputs to the calibration coil. High accuracy is achieved by summing as many pulses as desired (to eliminate background noise) by a correlation technique and subsequent Fourier analysis. The only parameters required are the seismometer mass, the Cal-coil constant (referred to the center of mass if appropriate) and current, and the precise onset time of one reference calibration current, which are all very stable over long time periods. Application to the High-Gain Long-Period system at KIP yields the magnification curve from only six pulses with less scatter (&lt; ± 5 per cent for periods larger than 20 sec) than routine steady-state calibrations.
Time-domain determination of earthquake fault parameters from short-periodP-waves
Authors: Somerville Paul G. , Wiggins Ralph A. , Ellis Robert M. 
Published: September 2021

abstractSource parameters of two shallow earthquakes have been determined by the time-domain analysis of short-period teleseismic recordings. For each event, the effect of the receiver crust was deconvolved from a set of globally distributed recordings using the homomorphic method. The resulting seismograms were compared with the form of the elastic-wave radiation computed from Savage's model of radially spreading rupture on a plane elliptical fault surface. This time-domain approach has permitted the determination of several kinematic parameters pertaining to the dynamics of rupture that are not ordinarily evaluated from spectral analysis. These parameters are rupture velocity, the direction of farthest rupture propagation, and the duration of a ramp dislocation time function which was prescribed to be the same everywhere on the fault surface. The application of a general linear inverse scheme has shown that the model parameters (notably rupture velocity and dimension) are only weakly coupled. Inversion is also used to determine the range of acceptable parameter values and indicates the importance of array recordings in constraining the models. A consistent discrepancy between the observed and model seismograms during the first half-cycle of motion is attributed to the incorrect prescription of the dislocation time function. It is suggested that a space-dependent function determined theoretically by Kostrov in 1964 would tend to remove this discrepancy.