bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self-similar circular shear cracks lacking cohesion
Authors: Burridge Robert , Levy Cesar 
Published: September 2021

abstract
It has recently been shown (Burridge, 1973) that in two dimensions plane-strain shear cracks lacking cohesion may run at speeds ranging from the Rayleigh-wave to the S-wave speed or possibly at the P-wave speed. On the other hand, it has long been known that in antiplane strain, cracks lacking cohesion must run at least at the S-wave speed. Since locally at the edge of a three-dimensional crack there is a combination of plane and antiplane strain, we have sought and found solutions for circular shear cracks expanding at the S-wave speed and at the P-wave speed. These have finite shear tractions ahead of the crack and so may correspond to frictional sliding in the absence of cohesion.
The analysis combines the method of Kostrov (1964b) with the results of Burridge (1973).
We carry out a complete evaluation for the displacements and tractions on the fault plane, and far-field radiation for the S-wave-speed crack. The corresponding evaluations for the P-wave speed are not elementary and are not attempted here.
As far as the authors are aware, these are the first analytic solutions of three-dimensional crack problems which satisfy a physically plausible fracture criterion for failure under shear.
S-wave splitting: Key to earthquake prediction?
Authors: Ryall Alan , Savage William U. 
Published: September 2021

abstract
This paper presents a detailed analysis of S-wave data for two areas in western Nevada. Some of these data were used by Gupta (1973b, c) as the basis for his claim that large premonitory changes in the extent of stress-induced S-wave splitting are observed for moderate-sized earthquakes in Nevada. Analysis of particle motion for an earthquake sequence near Slate Mountain indicates that changes in S-wave splitting did not occur during that sequence. For the Mina area, comparison of S-wave signatures for 158 events occurring over a 3-year period resulted in the identification of numerous events that would be considered anomalous by Gupta's criteria, but these were not followed by larger earthquakes. The present state of knowledge on crustal structure and seismic source parameters in the western Basin and Range province is not sufficient to discriminate between stress-induced velocity anisotropy and the many other factors that contribute to the complexity of S-wave signatures.
A new method for the analysis of multi-mode surface-wave dispersion: Application to Love-wave propagation in the east Pacific
Authors: Forsyth Donald W. 
Published: September 2021

abstract
A new technique is presented for simultaneously measuring the average, regional phase velocity of two or more surface-wave modes, even if they travel with the same group velocity. Many observations are required over paths of varying length with earthquake sources of known focal mechanism. The phase of the signal observed at each station can be predicted if the initial phase of the source and the phase velocity and relative amplitude of each mode is known. The square of the difference between the observed phase and the predicted phase is summed over all paths for a set of trial phase velocities. The trial velocities which give the minimum sum correspond to the average phase velocity of each mode.
By applying this technique to Love-wave data from the east Pacific, the dispersion of the first higher Love mode was measured for the first time in an oceanic area. The phase velocity of the fundamental mode was found to increase with increasing age of the sea floor, probably as a result of the cooling of the oceanic lithosphere. The region was found to be anisotropic for Love-wave propagation, with the fastest velocities roughly perpendicular to the ridge. The degree of anisotropy appears to increase with increasing period.
Further studies on seismic discrimination
Authors: Evernden Jack F. 
Published: September 2021

abstract
Further data on the shape of the Ms: mb(6.5 ≧ mb ≧ 4.0) curve for shallow-focus (D &lt; 50 km) earthquakes are given along with theoretical explanations of the observed relationships. The frequency and probable cause of “anomalous” earthquakes is discussed. Capability of simple identification criteria (depth ≧ 50 km, detected Rayleigh waves of adequate amplitude, and/or location more then 25 km at sea), based on use of only a fraction of presently available data, is demonstrated. The magnitude of the mixed event (mixed surface waves of earthquakes) problem as it effects identification as well as procedures for circumventing the problem are demonstrated. Finally, recommendations are made for solving some other residual discrimination problems.
Premonitory seismic-wave phenomena before earthquakes near Fairview Peak, Nevada
Authors: Gupta Indra N. 
Published: September 2021

abstract
Anomalous variations in three different seismic processes have been observed before an earthquake of magnitude 4 on May 14, 1971 in the Fairview Peak region of central Nevada. The data used are the three-component seismograms from Tonopah (TNP) and Battle Mountain (BMN) as well as the vertical-component seismograms from several other seismographic stations. The observed precursory phenomena are (1) reorientation of the compressive stress axis: evidence for this is based on clear reversals of first motion of Pg at certain stations together with reversal of wave form of the SV component of Sg at BMN; (2) vertical migration of hypocenters: the PmP phase is often distinctly observed in central Nevada and the observed temporal variations in t(PmP)−t(Pg) at TNP indicate generally upward migration of foci before the main event; (3) changes in the extent of S-wave splitting: a large precursory increase is observed along the tensile stress direction and a small premonitory decrease along the compression direction. Similar but unidentical results have been obtained before another earthquake of magnitude 4 whereas all events of magnitude 3.5 or larger have been preceded by anomalous S-wave splitting along the tension direction. The various observed pre-earthquake processes appear to be interrelated and may be explained in terms of recent laboratory and theoretical results when applied to the tectonics of central Nevada. It seems highly desirable to attempt simultaneous observations of anomalous changes in more than one seismic process.
Shear-wave attenuation along the San Andreas fault zone in central California
Authors: Bakun William H. , Bufe Charles G. 
Published: September 2021

abstract
SH ground-displacement spectra (1 to 12 Hz) for 16 local earthquakes (Δ ≦ 18 km, 1.1 ≦ M ≦ 4.6) recorded at a common site situated atop the active trace of the San Andreas fault are used to estimate attenuation characteristics for propagation paths along the fault trace. t* = 0.10−0.13 (corresponding to an equivalent total path Qβ = 75−100) is appropriate for events with focal depths of ∼ 10 km.
Propagation-path effects, and not processes at the earthquake source, control corner frequencies for small (M ≲ 3) earthquakes for these highly attenuating paths. The results obtained here suggest that as a rule of thumb, if the true equivalent total path Q is as low as 4·ƒc·t, where ƒc is the estimated corner frequency and t the travel time, the corner frequency estimate is determined by propagation-path effects, not by processes at the earthquake source. In these cases, reliable estimates of source parameters can only be obtained if the appropriate propagation-path corrections are known.
Using Brune's model of shear-wave spectra, source dimensions L = 2r of less than 250 meters and stress drops greater than about 110 bar are estimated for the smaller events (1.1 ≦ M ≦ 2.2), using the equivalent total path Qβ obtained here. The seismic moments obtained in this study, together with data for larger central California events (2.4 ≦ ML ≦ 5.1) obtained by Johnson and McEvilly (1974), imply a linear log seismic moment-magnitude relation for 1 &lt; ML &lt; 5
log ⁡ 10 ( M 0 ) = ( 16.2 ± 0.1 ) + ( 1.52 ± 0.05 ) M L .
A note on the nonlinear response of the pendulous accelerometer
Authors: Rodgers P. W. 
Published: September 2021

abstract
When the pendulous accelerometer experiences large off-axis acceleration in a direction which produces significant along-the-boom acceleration, the dynamics of the instrument are altered and it becomes nonlinear in its response. The response to an off-axis horizontal acceleration step is derived and found to exhibit small changes in damping, overshoot, damped resonant frequency, and final value of boom position. The size of these effects is negligible for all but the largest accelerations and even then acceptable. The change in overshoot is the largest, about 5 per cent, for an AR-240 strong-motion accelerograph subjected to a 1-g horizontal acceleration step at 45° to the sensitive axis.
An expression is developed for the steady-state response to off-axis sinusoidal acceleration. In addition to the proper response, it contains both a double frequency term and a constant offset. The size of these terms is discussed and an example is given.
Prediction of pressure-generated earth motion using optimum filters
Authors: Douze E. J. , Sorrells G. G. 
Published: September 2021

abstract
The performance of long-period seismographs is often seriously degraded by atmospheric pressure variation; the problem is particularly severe at periods greater than 20 sec. The pressure variations associated with wind-generated turbulence and acoustic waves are sufficient to deform the surface of the Earth, thus adding to the background noise level recorded by the seismometer. If microbarographs are operated together with the seismograph system, a large percentage of the atmospherically generated noise can be eliminated by the use of optimum filters. The filters are designed based on the least-mean-squares criterion, with the seismograph time trace as the desired output and the microbarographs as the inputs. Single-channel filters, using only one microbarograph, located at the seismometer vault are used to attenuate wind-generated noise. In order to attenuate the noise on windless days from other pressure sources, multichannel filtering is usually necessary and therefore an array of microbarographs is required. The filters used to predict the wind-generated noise are shown to be stable despite the complicated source. The performance of the multichannel varies widely depending on the structure of pressure variations predominating in the atmosphere.
Attenuation of Modified Mercalli intensity with distance from the epicenter
Authors: Howell B. F. , Schultz T. R. 
Published: September 2021

abstract
Thirteen simple formulas describing the attenuation of Modified Mercalli (MM) intensity are compared to determine which best predicts observed values in North America. The equation (19) ln I = ln I o + a 2 − b 2 ln Δ − c 2 Δ based on the assumption that intensity is related to energy by the equation (12) I = k E P appears to be the most useful, although it is not the most precise. P was found to be approximately 1/6, indicating that MM intensity is proportional to the sixth root of energy or the cube root of amplitude.
The United States and southern Canada are divided into three attenuation provinces: a San Andreas province with an energy absorption coefficient of 0.015/km, an Eastern province with an absorption coefficient of 0.0031/km and a Cordilleran province with an absorption coefficient of 0.0063/km.
The different rates of absorption can be explained as the result of slightly greater average focal depths in the East than in the West, although the data are too scattered to prove that this is the cause. Greater depth of focus, especially if low-angle faulting is involved, would explain the lack of surface displacement with eastern earthquakes.
The effect of sonic rupture velocity on the ratio of S to P corner frequencies
Authors: Burridge R. 
Published: September 2021

abstract
In a recent paper Dahlen (1974) has used a simple model of shallow-focus earthquake faulting to study the ratio of S to P corner frequencies. The model predicts higher S than P corner frequencies, but, as he points out, observational studies have indicated the reverse.
It has been shown by Burridge (1973) and Burridge and Levy (1974) that rupture speeds up to the P-wave speed are to be expected on a purely frictional fault lacking cohesion but in Dahlen's calculations the rupture speed never exceeds the speed of S.
In this paper, we consider far-field radiation when the initial phase of rupture is a self-similar circular rupture zone spreading at the speed of P. For this model, we find that on 70 per cent of the focal sphere the P corner frequency is higher than that of S in accordance with the observations.
Microearthquakes in the Mono Lake-Northern Owens Valley, California, region from September 28 to October 18, 1970
Authors: Pitt A. M. , Steeples Don W. 
Published: September 2021

Abstract
A portable seismograph network was operated by the U.S. Geological Survey in the Mono Lake-northern Owens Valley, California, region in the autumn of 1970. From 20 days of recording, 74 microearthquakes were located. The geographic extent of the microearthquakes is similar to the historic seismicity from 1934 to 1970. Focal mechanisms are mostly right-lateral strike slip; one very good dip-slip solution was obtained. The relative tension axis was found to be very nearly east-west.
The use of duration as a measure of seismic moment and magnitude
Authors: Herrmann Robert B. 
Published: September 2021

Abstract
The observed relationship between magnitude and duration is shown to be a result of the particular shape of the signal coda as a function of time. If the envelope of the coda follows a t−q relationship with increasing time, then the magnitude, mτ, based on a duration τ is consequently of the form
m τ = q log ⁡ 10 τ + r .
A study of the duration-magnitude and duration-moment relationships for a set of central United States earthquakes indicates that the linear relationship between mτ and log10τ is valid only over a limited range. The departure from the simple linear dependence is explained in terms of instrumental response and the shift of the source-spectrum corner frequency with increasing event size.
The complex envelope in seismic signal analysis
Authors: Farnbach John S. 
Published: September 2021

Abstract
Some practical implications of the complex envelope representation of seismic signals are presented. Beginning with a look at an artificially constructed signal and proceeding to seismic records, it is seen that the complex envelope is more amenable to visual interpretation than the real signal itself. This is attributed to the natural separation of amplitude information from angle information afforded by the complex representation, and examples of arrival time measurement and P-coda correlation suggest that this leads to concrete seismological benefits. On this basis, it is suggested that the complex envelope may be a useful tool in seismic signal analysis.
Short-period Rayleigh-wave dispersion across the Tibetan Plateau
Authors: Chen W. P. , Molnar P. 
Published: September 2021

Abstract
Well-dispersed Rayleigh waves within the period range of 4 to 11 sec are observed at New Delhi (NDI) and Shillong (SHL), India, for seven earthquakes near and in the Tibetan Plateau from 1963 to 1971. The dispersion curves and the simply dispersed wave forms suggest a prominent overlying wave guide, probably sediments, in the Tibetan area. The thickness of such sediments is most likely between 2.5 and 7.0 km. The simple wave trains, without much distortion due to multipathing, are consistent with a relatively inert, recent tectonism in Tibet.
A fast, accurate method for computing group-velocity partial derivatives for Rayleigh and Love modes
Authors: Rodi W. L. , Glover P. , Li T. M. C. , Alexander S. S. 
Published: September 2021

Abstract
A method for quickly and accurately calculating Rayleigh- and Love-mode group-velocity partial derivatives with respect to model parameters (m) is developed. The method requires computer codes that calculate C, U, and ∂C∂m|ω and employs numerical differentiation of ∂C∂m|ω to yield ∂U∂m|ω. The method is fast because ∂C∂m|ω and ∂U∂m|ω for all the model parameters can be obtained at a given frequency from only two solutions of the period equation. The accuracy of the method is established with two examples. For Love waves, the group-velocity partials computed by this method agree exactly with those obtained analytically by Novotny (1970). For Rayleigh waves, comparison with a “brute force” calculation of group-velocity partials showed agreement to the order of 0.00002. Systematic inversion of group-velocity data separately or in combination with phase-velocity data is computationally feasible using this method.
Refined hypocenters and accurate reliability estimates
Authors: Veith Karl F. 
Published: September 2021

Abstract
A new method of correcting station arrival times for systematic source and station effects has been developed. The method yields source-region/station time (SRST) corrections which have a simple spatial variation and which are valid, in terms of yielding accurate focal depths and relative epicenters, over large areas. The method has been applied to over 200 earthquakes ranging in depth from about 10 to 650 km in the Kurile-Kamchatka-Okhotsk region. Resulting corrections are uniformly valid throughout an area of approximately one million square kilometers. Full utilization of the SRST corrections for the 25 close-in and 149 teleseismic stations was achieved by weighting each station's contribution to the computed hypocenters. The 95 per cent limits on the depth uncertainty cover the pP depth the appropriate percentage of the time regardless of the number or geometry of the stations in the observing network. The SRTS's for the close-in stations describe their arrival-time variations over the entire are structure and thus may be used in model studies to determine the structure and the epicenter bias.
Seismic intensities, “size” of earthquakes and related parameters
Authors: Evernden Jack F. 
Published: September 2021

Abstract
The simple model of an earthquake used in Evernden, et al. (1973) was extended to the conterminous United States and observed patterns of isoseismals for major earthquakes studied in relation to the model. Regional attenuation, a known major factor controlling isoseismal patterns, was quantitatively evaluated. Incorporating this regional variation into the model results in the prediction that in terms of energy released, the San Francisco earthquake of 1906 was 50 times as large as Owens Valley 1872 and more than 100 times larger than the Charleston 1886 and New Madrid 1811 earthquakes. All of these were probably of comparable “magnitude”. Other relevant parameters are investigated. Analysis of probability of occurrence of major earthquakes in the Eastern United States suggests average annual return times of intensity X and IX of thousands of years at least. Presently unknown local conditions may lead to much greater probabilities at some localities, and the importance of developing procedures for determining regions of abnormally high risk is stressed.
On crustal plates
Authors: Tocher Don 
Published: September 2021

Abstract
During the decade just past, developments in Seismology have played an active and central role in the development of the concept of Plate Tectonics. Observational Seismology has provided support for and verification of a number of the dynamic aspects of the hypotheses of continental drift, sea-floor spreading, transform faults and the underthrusting of the lithosphere at island arcs and some continental margins.
Those types of seismological evidence which bear on the question of the thickness of the lithosphere are either indirect or circumstantial, or both. As early as 1926, Gutenberg postulated the existence of a layer at a depth of 80 to 150 or 200 km, probably worldwide in extent, in which the velocities of seismic waves are slightly lower than in the immediately overlying layers. Some plate tectonics workers equate this low-velocity layer to the relatively-weak asthenosphere required by Plate Tectonics to underlie the stronger, more brittle lithosphere.
In this review, several lines of evidence are marshalled in support of a plate model of the continental crust in seismically active regions in which a layer of decoupling of an upper, lithospheric layer from the weaker substrate may lie in the crust itself at a depth of perhaps 10 to 15 km.
An analysis of tidal strain observations from the United States of America: I. The laterally homogeneous tide
Authors: Beaumont Christopher , Berger Jon 
Published: September 2021

abstract
Tidal strain observations from seven observatories in the continental United States have been analyzed and the results compared with the tide predicted for a radially stratified earth model. Included in the predicted tide are the effects of ocean-tide loading for all of the major oceans. We find that on average the load strains contribute 44 per cent of the total M2 tidal strain and 13 per cent of the total O1 tidal strain. The differences between the predictions of the radially stratified earth model and the observations are significant. We conclude that: (1) Love numbers deduced from most strain observations are not representative of average earth properties. (2) The phase of the areal strain is neither independent of the tidal loading nor of the local geological structure. Hence, to use such phase observations as a measure of the anelastic properties of the Earth is incorrect.
Synthesis of teleseismic P waves from sources near sinking lithospheric slabs
Authors: Ward Ronald W. , Aki Keiiti 
Published: September 2021

abstract
A wave theory method is used to determine the effect of a sinking lithospheric slab on short-period and long-period waves. We consider a simplified model of the lithospheric slab with a 10 per cent velocity contrast and compute both short-period and long-period theoretical seismograms from a P-wave source located in or near the slab. For this model, the ray-theoretical amplitude agrees quite well with the short-period amplitude. In the ray-theoretical shadow zone the long-period seismograms (15- to 25-sec dominant period) typically have amplitudes 50 per cent (or greater) of the direct P-wave amplitude and exhibit wave-form broadening. Similar wave-form broadening has been attributed to the dynamics of earthquake faulting. The effect of the lithosphere on long-period waves from nearby sources must be taken into account in studies which utilize the observed variation in wave-form broadening to infer earthquake source dynamics.
Seismotectonic maps of the European area
Authors: Kaila K. L. , Madhava Rao N. 
Published: September 2021

abstract
Seismicity maps based on A value, b value, and return period for earthquakes with magnitude 6 and above have been prepared for the European area using the Kaila and Narain (1971) method. For the preparation of these maps, a modified relation A = 6.36b − 1.00 has been used instead of the earlier relation where A and b are constants in the cumulative regression curve represented by log N = A − bM. The A-value seismicity map also shows regional tectonics superimposed on it, thus yielding the seismotectonic map of Europe. These seismicity maps reveal that the European area consists of seven main high seismic activity zones named as the Balkan high, the Aegean high, the Apennine-sicilian high, the Alps high, the Carpathian high, the Saharan-Pyrenees high and the Iceland-Arctic high which are described in detail with their relationship to regional tectonics. The b values determined by the new method and shown on the b-value seismicity map are compared with those determined by other workers using earthquake regression curves for various regions of Europe and they show a very good agreement with each other.