bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationship of mine tremors to induced stresses and to rock properties in the focal region
Authors: McGarr A. , Spottiswoode S. M. , Gay N. C. 
Published: September 2021

Abstract
Focal coordinates for a suite of tremors associated with deep-level tabular mining were determined with uncertainties of about 35 m and the tremor positions were analyzed in terms of the stress field induced by mining in the immediate vicinity. All tremors occurred in a region of 300 m in extent and at depths near 3.1 km; their magnitudes ranged from −1.5 to 2.5. The source rock in this region has no groundwater, whatsoever. The two major factors governing the occurrence of tremors appear to be the change in the stress field from its virgin state and the strength of the rock. The positions of tremor foci coincide closely with the region where changes in the stress field due to mining are maximal. Most of the tremors were located in regions where the maximum principal stress induced by mining exceeded 1 kb or where the minimum principal induced stress was less than −160 bars, compressive stresses taken as positive. Nearly all of the tremors were located above the gold-bearing reef. Strength tests in uniaxial compression indicated that the rock above the reef is about 1.4 kb stronger than that below; Young's modulus is also higher for rock above the reef. These results suggest that tremors tend to occur in regions where the rock is capable of storing the most elastic strain energy before failure. Underground observations of shear failure indicate that tremors are the result of the rupture of previously intact rock. The fact that the majority of seismic foci occurred in regions where the stress field is calculated to be well below that required for rock fracture argues for the existence of localized residual stresses of large magnitude.
Surface strong motion associated with a stick-slip event in a foam rubber model of earthquakes
Authors: Archuleta Ralph J. , Brune James N. 
Published: September 2021

Abstract
In this paper, we present and interpret dynamic displacement data for a stick-slip event in a foam rubber model of earthquake faulting. Static displacement data are used to infer the stress drop of about 0.016 μ, where μ is the shear modulus. The rupture velocity 0.7 β, where β is the shear-wave speed, is also inferred from the data. The observed particle displacement and particle velocity data are compared with analytical and numerical predictions. Doppler focusing of energy by rupture propagation is clearly observed. No large transverse displacement pulse such as that observed at Station 2 of the Parkfield earthquake is observed. In addition to its value for testing analytical and numerical predictions, the laboratory model provides much needed information on the distribution of strong ground motion in the neighborhood of a fault and thus helps in the problem of microzonation for earthquakes.
A magnitude scale for local earthquakes in South Australia
Authors: Stewart Ian C. F. 
Published: September 2021

Abstract
To minimize dispersion in local magnitude estimates due to different instrumental bandwidths, a scale has been established to allow for the average source spectrum, geometrical attenuation, and frequency-dependent absorption. The data used to derive the scale parameters were from S waves recorded in South Australia from 1967 through 1970, in the frequency range 1 to 10 Hz, and for epicentral distances up to 5°. The magnitudes were mainly in the range 1.5 to 3.5. The local scale MN is given by
M N = 4.85 + log A g + 0.84 log Δ + 0.0003 f Δ / 2.3 − 2.89 log f + 2.45 ( log f ) 2 + c
where Ag mm is the ground amplitude at f Hz at Δ km epicentral distance, and c is a station correction.
The dispersion in observations of magnitude has probably been reduced by use of the scale to near the theoretical limits, allowing for possible source radiation patterns. The relationship of the scale to other measures of magnitude is uncertain, but MN may be approximately equivalent to the local Richter magnitude ML for the magnitude range (1.5 &lt; ML &lt; 3.5) commonly observed in South Australia.
The scle is limited in use to data in the ranges given above, for local earthquakes in South Australia. Modification is necessary before such a magnitude scale can be applied elsewhere or to different data ranges.
A source theory for complex earthquakes
Authors: Blandford R. R. 
Published: September 2021

AbstractEarthquake source theories of Haskell, Brune, and Savage have been drawn upon to develop a description of an earthquake as a major slip accompanied by many smaller tensional and slip events. We find natural explanations of several previously unexplained observations, such as:Robustness of the MS: mb discriminant,P corner frequency higher than S corner frequency for shallow earthquakes,High-frequency P/S amplitude ratio higher for shallow earthquakes than previous theories predict,Increase of complexity as a function of third moment,Small mb relative to MS for transform faults.(This can also be explained by emergent short-period P wave forms or by a low-Q region underlying the source).The theory predicts that MS:mb populations of earthquakes and explosions will not converge at small magnitudes. The theory also suggests that the standard interpretations of corner-frequency measurements can provide only a lower limit to fault-plane dimensions and, in combination with the moment, only an upper limit on stress drop.
The effect of oceanic sediments on surface-wave propagation
Authors: Weidner Donald J. 
Published: September 2021

abstract
Several characteristics of oceanic surface waves can be altered by the presence of low rigidity sediments along the propagation path. Love and Rayleigh waves from mid-Atlantic ridge earthquakes bear many effects of oceanic sediments. The general absence of these surface waves for periods shorter than about 15 sec can be attributed to either attenuation or scattering in thin sediments. Thin sediments also disperse short-period Love waves. Sediments whose thickness exceeds about 2 km are responsible for removing surface-wave energy with periods up to 40 sec. These sediments also alter the particle motion of Rayleigh waves and are responsible for a complicated dispersion relation. These thick sediments substantially reduce the surface-wave phase velocity at periods in excess of 100 sec.
A technique for computing surface-wave properties
Authors: Massé Robert P. 
Published: September 2021

abstract
A technique is presented which makes possible the calculation of total-path properties of surface waves which traverse any number of geological regions. Rayleigh- and Love-wave parameters which may be computed with the technique include phase- and group-velocity dispersion, travel time, matched filters, attenuation, quality factors, lateral refraction, and multipathing. The technique has applications both in research of Earth structure and in automatic signal processing.
Microearthquakes at Flathead Lake, Montana: A study using automatic earthquake processing
Authors: Stevenson Peter R. 
Published: September 2021

abstract
A nine-station portable seismic net, 50 km in diameter, was operated for 50 days in late 1971 near Flathead Lake, Montana at the juncture of the southern extension of the Rocky Mountain trench and the northern section of the Intermountain Seismic Belt. During the time the net was in operation, 259 locatable earthquakes ranging in coda magnitude from 0.1 to 3.3 were recorded. The earthquakes fall in two source regions approximately 15 km apart. In the northern region, the focal depths average 5 km, while those in the southern region range from 5 to 12 km. During part of the recording period, the activity in the southern region defined a planar zone striking north-northwest with a dip of 70° to the east-northeast. The better-defined fault-plane solutions in the region suggest northsouth compression. A procedure for automatically picking the first arrivals with a computer was used in analyzing the data.
Spatial attenuation of intensities for central U.S. earthquakes
Authors: Gupta Indra N. , Nuttli Otto W. 
Published: September 2021

abstract
Attenuation of ground motion in the central United States has to be determined principally using the Modified Mercalli (MM) intensity observations because of the absence of instrumental strong ground-motion data. Nuttli's previous studies of Mississippi Valley earthquakes indicate that higher-mode surface waves produce the largest ground motion except possibly in the near-field region. Particle velocity rather than acceleration correlates directly with intensity and the coefficient of anelastic attenuation has an average value of 0.10 per degree. Using data from isoseismals of the November 9, 1968, southern Illinois and the December 16, 1811, New Madrid, Missouri earthquakes and assuming a linear relationship between log(A/T) and MM intensity, attenuation is expressed by the equation, valid for I(R) ≧IV (MM), I ( R ) = I 0 + 3.7 − 0.0011 R − 2.7 log ⁡ R ; for R ≧ 20 k m where R is the epicentral distance in kilometers.
This relationship shows fairly good agreement with isoseismals of many large earthquakes in the central United States and may therefore be useful in providing realistic estimates of spatial attenuation and hence of design earthquakes for a given site. It can also be sometimes useful in estimating the epicentral intensity of an earthquake whose maximum intensity is not reliably known.
Seismicity of Northern Anatolia
Authors: Dewey James W. 
Published: September 2021

abstract
Earthquakes of magnitude 5.0 and greater that occurred in 1930-1972 in northern Anatolia have been relocated in order to define more accurately the characteristics of recent seismicity. The revised epicenters were determined either by joint epicenter determination (JED) or singly, with travel-times modified by JED-calculated source-station adjustments. Calibration epicenters were assigned on the basis of published field studies of the earthquakes.
Many characteristics of the occurrence of magnitude 5.0 and greater earthquakes on the North Anatolian fault are similar to characteristics of small-earthquake seismicity on California's San Andreas fault. Earthquakes tend to be concentrated on or near particular sections of the North Anatolian fault, suggesting intrinsic differences in mechanical properties along the fault. The relocated epicenters support the hypothesis that fault rupture in large and great earthquakes will begin in regions of small and moderate earthquakes; the rupture of the large earthquake then propagates into sections of the fault that normally have a low level of activity.
From 1939 through 1967, seven earthquakes of magnitude 6.8 or greater ruptured the North Anatolian fault from east to west for a distance of 800 km. Several sections of the fault zone were active before the occurrence of the large earthquakes of 1939-1967. Foreshock activity also extended tens of kilometers away from the fault zone. The time intervals between successive magnitude 6.0 or greater earthquakes on the fault are not consistent with a constant velocity of source migration; a model is proposed here in which these time intervals are equal to the duration of nonelastic effects precursory to the earthquakes.
In western Turkey, the burst of normal-fault earthquakes in 1969-1970 was concentrated in distinctly separated source areas. The distribution of aftershocks to the earthquake of March 28, 1970 suggests that the surface fault scarps accompanying this earthquake are a distorted representation of the normal fault plane at depth.
The Kinnaur earthquake of January 19, 1975: A field report
Authors: Singh S. , Jain A. K. , Sinha P. , Singh V. N. , Srivastava L. S. 
Published: September 2021

abstract
On January 19, 1975 an earthquake of magnitude 6.8 occurred in the border districts of Himachal Pradesh, India. The earthquake caused considerable loss of life and varying degrees of damage to construction in the area. Traditional and recent buildings suffered extensive damage. Landslides, rock falls and avalanches caused considerable damage to the Hindustan-Tibet road. Extensive fissures in the ground developed at the epicenter. Greatest damage was noted along the N-S trending Kaurik-Chango fault following the Parachu and Spiti river valleys, suggesting its genetic interrelationship with the earthquake.
Local changes of sea level before large earthquakes in South America
Authors: Wyss M. 
Published: September 2021

abstract
Vertical movements of the crust along the South American west coast are estimated from mean annual sea level (MASL). At an average distance of 400 km, 13 stations recorded sea level more or less continuously since 1941. The standard deviation of MASL from 20-year means is typically about 3 cm. Using reference stations reduces the standard deviation to 0.5 to 1.5 cm and therefore elevation changes of 3 cm can be resolved with 99 per cent confidence, if they last for more than 5 years. At Chimbote (Peru) uplift of about 5 cm was recorded in 1961. Six and nine years later the 1966 and 1970 Peru earthquakes (M = 7.6 and 7.8) occurred at distances of 130 and 23 km, respectively. An uplift of about 3 cm appears to have preceded the Antofagasta earthquake (M = 6.8) by 6 years. At 100 km north of the 1960 Chile rupture (M = 8.6) sea level remained unchanged between 1955 and 1970. Because all tide gauge stations in South America are located in active tectonic areas it is difficult to identify small land elevation changes by comparison with reference stations.
Preliminary empirical model for scaling Fourier Amplitude Spectra of strong ground acceleration in terms of earthquake magnitude, source-to-station distance, and recording site conditions
Authors: Trifunac M. D. 
Published: September 2021

abstract
An empirical model for scaling Fourier Amplitude Spectra of strong earthquake ground acceleration in terms of magnitude, M, epicentral distance, R, and recording site conditions has been presented. The analysis based on this model implies that:
It has been shown that the uncertainties which are associated with the forecasting of Fourier amplitude spectra in terms of magnitude, epicentral distance, site conditions, and component direction are considerable and lead to the range of spectral amplitudes which for an 80 per cent confidence interval exceed one order of magnitude. A model has been presented which empirically approximates the distribution of Fourier spectrum amplitudes and enables one to estimate the spectral shapes which are not exceeded by the presently available data more than 100 (1 - p) per cent of time where p represents the desired confidence level (0 &lt; p &lt;1).
Seismic study of earthquakes in the Lake Mead, Nevada-Arizona region
Authors: Rogers A. M. , Lee W. H. K. 
Published: September 2021

abstract
A nine-station telemetered array was installed around the Boulder Basin portion of Lake Mead, Nevada-Arizona. During 112 years of monitoring, approximately 1,360 events were detected in the magnitude range −1.0 ≦ ML ≦ 2.9, and half this number were locatable. Many of the events, which ranged in depth from 0 to 13 km, can be associated with mapped faults. In particular, epicenter lineations clearly indicate activity on portions of steeply dipping faults on the east side of Boulder Basin, which generally confirms Carder's earlier work (Carder, 1945, 1948, 1970). The strike of these faults is approximately north. Focal mechanisms are in agreement with this strike and show right-lateral motion on near-vertical faults. The tension axis for this solution is oriented northwest-southeast in agreement with the stress pattern for other parts of the Basin and Range Province.
Although lake load increased 20 per cent during the monitoring period, neither number of events nor energy release shows a correlation with this change. Carder (1970) found similar results for periods after 1949. A higher b value (1.45) was obtained than in the past, and lower monthly energy release was observed than in the late 1930's and 1940's when seismic activity at Lake Mead was first recorded. A 2-yr seismicity map of southern Nevada, including the monitoring period, shows that Lake Mead activity is now no greater than that of the surrounding area.
The pre-Lake Mead seismic history is not well known because the founding of Boulder City occurred just a few years before Lake Mead was impounded. The existence of earthquakes in the region before the reservoir was filled has been questioned in the liteature. However, a search of the Las Vegas Review Journal for felt reports pre- and postimpoundment and compilation of a catalog of the largest events from the literature confirm that there was a significant increase in the number of felt events at Las Vegas after the reservoir was filled.
The results indicate that the filling of Lake Mead has triggered release of tectonic stresses having the same orientation as the regional stress field. These stresses are probably being released in a way that is more dependent on tectonic stress buildup than on small changes in pore pressure (∼ 1 bar) due to fluctuating lake level. Given that the shear strength of rock decreases with increasing pore pressure, one might explain the decreasing energy release since the 1940's and the high b value as due to a decrease in elastic-energy density of the rock. A test of this hypothesis based on the order of magnitude of energy released seems to support it.
Filling of Ramganga reservoir, Kalagarh, U.P., India and its possible influence on seismic activity
Authors: Singh S. , Agrawal P. N. , Arya A. S. 
Published: September 2021

abstract
The construction of a 125-m-high earth-and-rock-fill dam across the river Ramganga near Kalagarh was completed in early 1974. Its reservoir with a capacity of 2.49 ×109 m3 was partially filled during the 1974 summer monsoon. A detailed seismicity study has been made using the data from 2 month's microearthquake recording to determine the possible effect of reservoir filling. No interrelationship of seismic activity and reservoir filling has been found.
Seismic source functions and magnitude determinations for underground nuclear detonations
Authors: Murphy John R. 
Published: September 2021

abstractA variety of near-regional, regional, and teleseismic ground-motion data have been used to evaluate proposed models of the nuclear seismic source function for underground detonations in tuff/rhyolite emplacement media. It has been found that both the near-regional broad-band seismic data and the teleseismic body-wave magnitude data are consistent with the modified source model proposed by Mueller and Murphy (1971) but not with the simple cube-root of the yield-scaling source model. In particular, the observed linearity and slopes of the body-wave magnitude-yield curves as well as the observed variation of P-wave period with yield have been found to be fully compatible with the modified source model. On the other hand, it has been concluded that the observed long-period surface-wave data are inconsistent with a simple, spherically symmetric source model. The results of a preliminary analysis have suggested that this discrepancy may be related to the spall closure phenomenon.
Acoustic emission and creep in rock at high confining pressure and differential stress
Authors: Lockner D. , Byerlee J. 
Published: September 2021

Abstract
Two samples each of Weber Sandstone and Westerly Granite were tested under triaxial compression at 1 kb confining pressure. Axial load was increased in steps, and the acoustic emission generated in the samples during primary creep was monitored. The rate v of acoustic emission events was found to decrease exponentially at each stress level, obeying the law log v = β − αN, where N is the total number of microseismic events that have occurred and α and β are constants. By assuming that acoustic emission is proportional to inelastic deformation, this relation can be compared to empirical creep laws. It is similar to the relation given by Lomnitz and fits the data more closely than other creep laws that were functions of time rather than number of acoustic emission events. The value of α was found to decrease systematically with increasing differential stress, and in one experiment became negative before sample failure.
Source parameters of moderate size earthquakes and the importance of receiver crustal structure in interpreting observations of local earthquakes
Authors: Helmberger Donald V. , Johnson Lane R. 
Published: September 2021

Abstract
Broadband observations of three central California earthquakes as recorded on opposite sides of the San Andreas fault zone are studied. The earthquake mechanisms are of the strike-slip type occurring along the fault at epicentral distances between 15 and 30 km. The seismograms obtained at the two sites are distinctly dissimilar in both amplitude and wave shape even though they are at roughly the same azimuth. We suppose that the earthquake excitation is identical for the two sites and that the differences in seismograms are caused by the receiver structure. The problem is idealized by assuming that the first 10 sec of each record can be modeled synthetically with a point shear dislocation embedded in a half-space with a two-layer upper-crustal model appropriate for each site. The results determined by matching the observations indicate that the durations for these events with ML = 4 to 5 are about 0.3 to 0.6 sec. Furthermore, the results demonstrate that accurate estimate of source parameters can only be accomplished after a detailed appreciation of crustal structure.
A method for the separation of interfering surface waves and the computation of their dispersion
Authors: Michaels Paul 
Published: September 2021

Abstract
A practical technique for separating two surface waves that interfere, producing beats, is accomplished by a generalized least-squares inversion. A sinusoid consisting of a polynomial phase function is fit via least squares to both the envelope and the carrier wave forms of a digitized signal. The phase functions of the two interfering waves are then determined via a modulation equation. The derivative with respect to time of each phase function yields the frequency dispersion curves. Determinations of both group- and phase-velocity dispersion curves are discussed and a numerical example of the technique is given.
Seismic velocity determinations in the New Madrid seismic zone: A new method using local earthquakes
Authors: Mitchell Brian J. , Hashim Braik M. 
Published: September 2021

AbstractA new method is developed and used to determine compressional- and shear-wave models for the crust in the northernmost portion of the Mississippi embayment. A nonlinear least-squares process fits contiguous straight lines to data obtained using a seismic network, and yields apparent velocities and points of intersection of the lines.The compressional-wave model consists of a 5.6-km-thick layer with a velocity of 6.19 km/sec overlying an 18.1 -km-thick layer with a velocity of 6.38 km/sec. These are underlain by material having a velocity of 7.17 km/sec. Since the shear-wave data are characterized by a large amount of scatter, only a two-layer model was obtained. It consists of a 21.5-km-thick layer having a velocity of 3.62 km/sec above material with a velocity of 4.10 km/sec. These models are overlain by variable thicknesses of sediments of the Mississippi embayment.The travel times of compressional waves at short distances indicate that the great preponderance of earthquake foci lie at shallow depths. Although the travel times are relatively insensitive to small changes in depth for these shallow earthquakes, few data points imply depths greater than about 10 km, and most are compatible with shallower depths.