bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated and frequency-band magnitude, two alternative measures of the size of an earthquake
Authors: Howell B. F. , Lundquist G. M. , Yiu S. K.
Published: September 2021

Integrated magnitude substitutes the r.m.s. average amplitude over a pre-selected interval for the peak amplitude in the conventional body-wave magnitude formula. Frequency-band magnitude uses an equivalent quantity in the frequency domain. Integrated magnitude exhibits less scatter than conventional body-wave magnitude for short-period seismograms. Frequency-band magnitude exhibits less scatter than body-wave magnitude or integrated magnitude for both long- and short-period seismograms. The scatter of frequency-band magnitude is probably due to real azimuthal effects, crustal-transfer-function variations, errors in compensation for seismograph response, microseismic moise and uncertainties in the compensation for attenuation with distance. To observe azimuthal variations clearly, the crustal-transfer functions and seismograph response need to be known more precisely than was the case in this experiment, because these two sources of scatter can be large enough to explain all of the observed variations.
Seismic studies: South central Illinois earthquake of November 9, 1968
Authors: Stauder William , Nuttli Otto W.
Published: September 2021

The largest earthquake to occur in the central Mississippi seismic region this century took place in south central Illinois on November 9, 1968. The hypocenter and origin time based on observations from twelve regional stations varying in epicentral distance from 171 to 549 km, are 37.95°N, 88.48°W, h = 25 km, 0 = 17h01m42.0s ± 0.2s.

Travel times of P at stations distant less than 2600 km indicate regional mantle variations, corresponding to rays bottoming at depths down to 650 km. Beyond this point travel times show a much smaller dependence, if any, on region. For stations in the central United States P times may be fitted by two straight line branches which intersect at about 600 km. The first branch corresponds to Pn, the second to rays refracted from a surface at depth 97 km with a velocity below it of 8.37 km/sec. At larger distances (48°-100°) there are non-azimuth dependent residuals with respect to the Herrin Tables averaging about −1.5 sec, indicating a source-region correction with respect to these tables.

Body wave magnitude was determined to be mb = 5.54 ± 0.44 for stations for which Δ > 25°, and mb = 5.44 ± 0.29, using Evernden's formula, for Pn in eastern North America. Surface waves give a value Ms = 5.2.

The fault plane solution determines two nodal planes each striking approximately north-south and dipping 45° to the east and to the west, respectively. This corresponds to dip slip, reverse motion, and to a horizontal east-west axis of compressional stress. While there are no mapped faults in the immediate epicentral region, the motion indicated is in conformity to that along the Wabash Valley Fault System 10 miles to the east.
Note on an aftershock study, south central Illinois earthquake of November 9, 1968
Authors: Stauder William , Pitt Andrew M.
Published: September 2021

In an effort to monitor aftershock activity following the southern Illinois earthquake of November 9, 1968, a network of ten high gain seismic stations was established in the vicinity of the epicenter of the earthquake. The network began recording on the fourth day after the earthquake and operated for a period of ten days. During this time only one very small aftershock was recorded. The hypocenter of this shock was about 10 km south and at the same depth as that of the main shock.

Permanent stations of the region recorded two other aftershocks within two days of the main shock, and one more three and a half months later. The exceptionally low level of aftershock activity is an anomalous feature of the Southern Illinois-Southeast Missouri seismic zone.
Strong earthquake motion and site conditions: Hollywood
Authors: Duke C. M. , Luco J. E. , Carriveau A. R. , Hradilek P. J. , Lastrico R. , Ostrom D.
Published: September 2021

abstract

An investigation was made to determine the feasibility of isolating the effects of site conditions on strong earthquake accelerograms. The set of accelerograms recorded simultaneously in 1952 at the roof, in the basement and on the ground outside the 14-story Hollywood Storage Building was chosen for analysis. Fourier spectra were computed for the two horizontal components at each of the three recording places and were used after smoothing to compute the ratios of spectra for adjacent points. Dynamic models of the subsurface conditions, the foundation and the building were established. Certain of the spectral ratios were also determined theoretically.

The primary result is the development of a method of isolating effects of site conditions in Fourier spectra of accelerograms. Good theoretical checks were obtained on soil-structure interaction and structural response in the east-west direction. The absence of bedrock accelerograms prevented the obtaining of a theoretical check on free-field amplification, although plausible bedrock Fourier spectra were obtained. The subsurface model should be useful for further analyses.
The earthquake volume
Authors: Duda Seweryn J.
Published: September 2021

A method is presented enabling one to estimate the volume of seismic events with all possible magnitudes and focal depths. The underlying observational data are either the travel times of body waves, or the equivalent magnitude calibration curves for body waves, if the absorption of body waves is neglected.

The method is applied to the newest P-wave travel times. The distance from the focus to a point at which a given critical strain existed during the event is computed. The volume within strains larger than the critical prevailed during the event is obtained as a function of magnitude and focal depth. The volume so found is in agreement with a previous determination of the earthquake volume as a function of magnitude.
Event identification for test ban control
Authors: Ericsson Ulf A.
Published: September 2021

This paper describes a method to determine the usefulness of seismological event identification criteria for underground test ban control with or without on-site inspection. The method rests upon the notion that such control should be deterrent, by confronting a prospective violator with a certain disclosure probability at a politically determined level. Simple decision theory is then applied to the statistical properties of identification measures, to find the required compromise between a sufficient probability to disclose explosions and a not too high incidence of false alarms about earthquakes. A clean separation between the political requirements and the seismological capabilities is obtained. The latter are expressed by identification curves similar to the receiver operating characteristics curves employed in telecommunications analysis. The political requirements appear as geometrical conditions on the identification curves, expressing the required deterrence, the number of yearly explosions and earthquakes to be considered and the permitted number and quality of inspections, in the case of control with inspection. In the case of control without inspection, the acceptable rate of false alarms is included. The method also shows how identification criteria are most efficiently exploited.

Application to some published observations shows identification by short-period body-wave magnitudes and long-period surface-wave magnitudes to be most efficient. It remains, however, to extend the analysis to weak events and low signal-to-noise ratios. For applications the acquisition of proper statistics is essential.
Spectral characteristics of central Nevada microearthquakes
Authors: Douglas Bruce M. , Ryall Alan , Williams Ray
Published: September 2021

Fourier amplitude spectra were computed for 40 central Nevada microearthquakes, selected to consider, independently, effects of azimuth and distance from known sources. Spectra were averaged for groups of events to eliminate peculiarities of individual records and emphasize group characteristics. Spectral characteristics did not behave systematically as a function of azimuth from the recording site to the source, but peak spectral frequency was found to correlate strongly with event magnitude and to some degree also with focal distance. These preliminary results suggest that recordings of small earthquakes and microearthquakes can be used to provide detailed information on the character of seismic signals related to properties of the source and propagation path.
The 1968 Inangahua earthquake: Report of the university of canterbury survey team
Authors: Shepherd R. , Dodd T. A. H. , Sutherland A. J. , Moss P. J. , Carr A. J. , Gordon D. R. , Bryant A. H.
Published: September 2021

Observations are reported on the Inangahua earthquake of May 24 1968. The earthquake (magnitude 7) was felt widely in the South Island of New Zealand. An accelograph recorded a maximum of 0.35 g, 18 miles from Inangahua. There were two fatalities and wide damage.
Synthesis of nonstationary seismic signals
Authors: Beaudet Paul R.
Published: September 2021

Synthetic seismograms are a powerful tool which can be used to approximate the complex signature which an inhomogeneous, anisotropic, and imperfectly elastic Earth imparts to seismic waves generated by underground nuclear detonations. The concept and design of a time-varying analog filter for generating synthetic seismograms which approximate real seismograms observed from underground nuclear explosions have been developed. The basic design of this filter exploits a non-stationary characteristic commonly observed on seismograms, the gradual increase of period with time.

The parameters of the time-varying analog filter were determined on the basis of the characteristics of the radial component of 50 seismograms recorded from underground nuclear detonations encompassing a wide range of yields (80 to 1000 kt) and distances (50 to 550 km) from the detonation. These parameters determine the time-varying response of the analog filter to a white noise input. The comparison of the spectra of synthetic and real seismograms indicates that the synthetic seismograms generated with the time-varying analog filter are close approximations to real seismograms having equivalent yield and range parameters.
Tectonic stresses in Southern Alaska in relationship to regional seismicity and the new global tectonics
Authors: Gedney Larry
Published: September 2021

Fault plane solutions and a strain release map imply that Southern Alaska performs in the role of a sink area unlike that of more classic trench-arc combinations. A broad, apparently interrelated zone of seismic activity extends from the Aleutian Trench to the base of the Alaska Range. While hypocentral distribution and relative seismicity imply that the entire area is performing as a sink for the North Pacific plate, fault plane solutions at the base of the Alaska Range are inconsistent with this premise. It is suggested that Cook Inlet and the lowlands north of Anchorage may represent an ancient trench.
Accumulation of tectonic strain in California
Authors: Savage J. C. , Burford R. O.
Published: September 2021

The shear-strain accumulation in five tectonically-active areas of California has been calculated from triangulation data supplied by the U. S. Coast and Geodetic Survey. Three of the areas lie along active sections of the San Andreas fault. Near Hollister, no appreciable strain accumulation was detected for the period 1930 to 1962. The movement of the fault blocks there appears to be accommodated by slip on the San Andreas and Calaveras faults. Near Cholame, the only appreciable accumulation of shear strain in the period 1932 to 1962 appears to be associated directly with slip on the San Andreas north of Cholame, slip which probably occurred during the 1934 Parkfield earthquake. Significant strain accumulation was confined to a zone centered on the San Andreas fault and extending 10 km on either side. Some of this strain was released in the 1966 Parkfield earthquake. In Imperial Valley, an average accumulation of γ = 0.4 μstrain per year right-lateral (referred to vertical planes parallel to the Imperial fault) shear strain extends over a zone perhaps 100 km wide centered on the Imperial fault. It appears that this shear pattern may be resolved into two zones of shear, one concentrated near the Imperial fault and the other near the San Andreas fault. No appreciable shear-strain accumulation was detected in the two areas that do not lie on the San Andreas fault—Santa Barbara channel for the period 1880 to 1923 and Owens Valley for the period 1934 to 1956.
Lateral variation of rayleigh-wave dispersion characteristics in Australia
Authors: Gupta Harsh K. , Negi Janardan G.
Published: September 2021

Rayleigh wave dispersion data on Australia by Bolt and Niazi (1964) and Thomas (1969) are examined in detail in the period range of 20 to 40 sec. The dispersion characteristics correspond well to region 7 in Santô's (1965) classification. A further and similar inspection of the African mass, Brazilian shield, Canadian shield etc. reveals that the entire family of shield areas systematically belongs to Santô's regions 6 and/or 7. They are uniformly characterized by the absence of appreciable lateral velocity gradients in clear contrast to corresponding extremely steep gradients for high seismicity areas.
Determining magnitude from Lg
Authors: Baker R. G.
Published: September 2021

In this paper, an empirical method is developed for determining magnitude of seismic events from the amplitude of Lg phases recorded at local to regional distances from the events. The data used were obtained from Long Range Seismic Measurements (LRSM) reports for 78 seismic events associated with explosions conducted the Atomic Energy Commission.

Preliminary investigation showed that magnitudes (M) calculated from Lg recordings had less scatter than body-wave magnitudes (m) reported for the same events and stations. A sixth-degree polynomial was found to give the best fit to log amplitude/period (A/T) values plotted as a function of epicentral distance. Amplitude-distance correction factors (Q) are presented in a chart.

Magnitudes from Lg were compared to the average unified magnitudes from LRSM shot reports. For 60 of 68 events, the standard deviation for M was less than that for m. The M values for all of the events were normalized to magnitude 5.0, and average residuals were found for 69 reporting stations. A plot of the residuals on a map indicates that they represent station corrections rather than azimuthal variations. Apparent station corrections (s) are presented for 23 LRSM stations.
A study of the Earth's crust and upper mantle using travel times and spectrum characteristics of body waves
Authors: Gurbuz B. M.
Published: September 2021

The aim of this paper is to investigate the velocity distribution and structure of the Earth's crust and upper mantle from the close collaboration of theory and experimental results of travel times and spectrum characteristics of body waves. The interpretation was based on 38 seismic records which were obtained from the “Project Early Rise” experiment during July 1966. The results refer to the area bounded by latitudes 49°W and 51°30′ and longitudes 93°W and 98°W. A least-squares analysis of the travel-time data was made and the uncertainties of the slopes, intercept times, and corresponding velocities were determined. The observed wide-angle reflections were used to calculate the root mean square velocities applying the T2 - X2 method. Depth calculations for the velocity discontinuities and seismic depth contour maps were made. A model was constructed, and the validity of the proposed new model was tested by comparing the observed travel times, spectrum-amplitude ratios, and relative phase shifts of body waves with theoretically expected values.

Evidence is given for three discontinuities in the Earth's crust with velocities of 6.11 ± 0.01 km/sec, 6.8 ± 0.08 km/sec, and 7.10 ± 0.04 km/sec at average depths 18 ± 2 km and 25.5 ± 0.9 km. Velocities in the uppermost part of the mantle were determined as 7.90 ± 0.05 km/sec and 8.48 ± 0.05 km/sec with interfaces at the average depths of 34 ± 1 km, and 47 ± 1 km, respectively.
Surface waves in multilayered elastic media. Part II. Higher mode spectra and spectral ratios from point sources in plane layered Earth models
Authors: Harkrider David G.
Published: September 2021

Phase and amplitude spectra of Rayleigh and Love waves are presented for two Earth models, one oceanic and one continental shield. The spectra of the first three Rayleigh modes and the first four Love modes are tabulated for point sources at selected depths. These tables along with computer algorithms described here allow one to estimate the amplitude spectra at nontabulated source depths.

The use of spectral ratios as a means of determining source depth is investigated. A source depth of 20 km is obtained for the Fallon earthquake of July 20 1962. This depth agrees with previous estimates but the technique requires a fault-plane orientation which differs from radiation pattern solutions.
Soil strain near a nuclear detonation
Authors: Olsen C. W.
Published: September 2021

Radial and transverse strain seismometers using 6.1-m Invar rods were installed 457, 914, and 1524 m from ground zero on a nuclear detonation at the Nevada Test Site. The detonation, Hutch, took place in alluvium at a depth of 548 m and gave a body-wave magnitude of 5.4 ± 0.2. Dynamic and quasi-static strain data were recorded along with triaxial accelerations at the 914-m location.

The dynamic data show large strains (2 × 10-3 and considerable shear-wave activity related to the subsurface structure. Decay with range, corrected for the inelastic region, shows dependence of peak amplitudes of about R-3, but influence of the alluvium is present. The quasi-static data show large strain steps (> 10-4) at the two nearer stations and considerable dependence on alluvium depth. The strain decay with time is not consistent with that observed on Benham, and, at 914 m, appears to be a permanent step, similar to that observed on the Jorum event.
The microearthquake activity of Mt. Rainier, Washington
Authors: Unger John D. , Decker Robert W.
Published: September 2021

A network of five high-gain portable seismographs was operated around Mt. Rainier, Washington, from July 13 to August 11 1968, to study microearthquakes associated with this volcano. Approximately 345 microearthquakes were detected during the 30-day recording interval. Of these, hypocenters and magnitudes were determined for 65 selected events. The microearthquakes were concentrated in two general regions: (1) about 80 per cent were in a roughly concentric pattern around the western side of the volcano at depths ranging from 0.5 to 15 km, and (2) about 8 per cent were beneath the summit crater at depths ranging from 0.2 to 20 km. About 75 per cent of the microearthquakes were at depths less than 5 km. These two groups of microearthquakes can be further defined genetically, as the first may be teatonic earthquakes not related directly to volcanic processes and the second appear to be earthquakes possibly of volcanic origin. The cumulative frequency versus magnitude relation for the tectionic microearthquakes is

log ⁡ N = 5.2 − 0.82 ( 8 − M ) .
Analyses of earthquake ground motions at Japanese sites
Authors: Kiefer F. W. , Seed H. Bolton , Idriss I. M.
Published: September 2021

Ground motions at several Japanese sites are evaluated using recently-developed techniques which involve assessing the base-rock motion at the site due to an earthquake, establishing the properties of the overlying soil layers, and computing the response at the ground surface using a lumped-mass-analysis procedure. The maximum acceleration and the form of the response spectra for ground motions recorded at the several sites agree reasonably well with the computed values. It is concluded that where the soil conditions can be reliably determined, the analytical procedures offer good promise as a means of considering the effects of local soil conditions in the prediction of ground response.
Oceanic mantle phases recorded on hydrophones in the Northwestern Pacific at distances between 9° and 40°
Authors: Walker Daniel A. , Sutton George H.
Published: September 2021

abstract

Compressional- and shear-wave arrivals recorded on hydrophones at Midway, Wake, and Eniwetok from 85 earthquakes occurring along the circum-Pacific arc extending from the Aleutian Islands through the Solomon Islands indicate significant differences in the velocity structure in the mantle beneath the deep Northwestern Pacific Basin and the shallower East Caroline Basin-Ontong Java Plateau-Nauru Sea area. For paths in the Northwestern Pacific mantle, travel times of apparent first arrivals are less than Jeffreys-Bullen (J-B) P and S times for distances out to 20° and are increasingly greater than J-B times for distances between 20° and 33°. At distances greater than 33°, P arrivals agree well with J-B times and S arrivals are absent. Out to 30°, compressional and shear travel times fit straight lines of 8.28 ± 0.03 and 4.79 ± 0.04 km/sec, respectively. For the shallower area to the south, compressional travel times are close to J-B times for P out to 18° and are greater than J-B times for distances between 18° and 22°. At distances greater than 22°, P arrivals agree well with J-B times. Out to 24°, the compressional travel times fit a straight line of 8.47 ± 0.48 km/sec. For this area S arrivals are unclear or not apparent.
A microearthquake survey in Kenya
Authors: Molnar Peter , Aggarwal Yash Pal
Published: September 2021

abstract

A microearthquake survey was conducted in Kenya from December 1969 to March 1970. The recorded activity was confined to the rift system, and, in the main eastern rift, the activity was greatest in the south and decreased northward. Approximate locations of earthquakes showed that activity was not restricted to a central zone in the rift but was scattered throughout it. Depths of focus were shallow—less than 15 km. The most active region was in the Kavirondo rift near the site of a series of earthquakes in March 1968; microearthquakes were concentrated in a very small region approximately 3 to 4 km deep and in a region with dimensions less than 2 km. The locations support the interpretation that these events reflect movement on the Lambwe fault.
Transformation of earthquake displacement field for spherical earth
Authors: Wason Hans R. , Singh Sarva Jit
Published: September 2021

abstract

An addition theorem for spherical waves is used to transform the displacement field due to an arbitrary shear dislocation in an unbounded homogeneous medium with origin at the focus to that in a coordinate system with origin at the center of the Earth. The final results are expressed in terms of the eigenvector solutions of the vector Naviér equation of dynamical elasticity. Some serious mistakes in recent papers on the subject have been pointed out.
Causes of regional variation of magnitudes
Authors: Ward Ronald W. , Toksöz M. Nafi
Published: September 2021

abstract

Data from the short and long-period seismographs at the NORSAR in Norway are used to investigate the discrimination of earthquakes and underground nuclear explosions using surface-wave versus body-wave magnitude (Ms versus mb). Earthquakes and explosions occurring within the western United States and recorded in Norway exhibit either anomalously large surface waves or anomalously low compressional body waves compared to events from central Asia. These data, as well as the results of other investigators, indicate an anomaly of 0.8 to 1.0 in Ms or 0.6 to 0.8 in mb or some linear combination of the two. The mechanism producing anomalously large Ms values from a region for explosions and the cause of lower mb values are investigated in terms of stress relaxation triggered by an explosion and regional variations in attenuation in the upper mantle beneath both the source region and the receiver region.

The method of short-period amplitude spectral ratio is applied to the records of the waves from five deep events to determine the difference in attenuation beneath different receivers. The relative Q model inferred from these data for the upper mantle from 50 to 750 km depth is QLASA = 75, QTFSO = 175, and QNORSAR = 390. The circum-Pacific island arc exhibits an apparent source attenuation asymmetry. The data from the mid-Atlantic ridge indicate that strong attenuation may be associated with parts of the ridge.

The relative difference of the Q model between LASA and NORSAR results in a difference in mb of 0.40 for distances of 60° to 80°, which agrees well with the observed differences in mb. We conclude that regional variations of attenuation in the upper mantle play an important role in regional differences in Ms versus mb relationship.
Elastic-wave propagation in two evenly-welded quarter-spaces
Authors: Ottaviani Mario
Published: September 2021

abstract

This paper deals with elastic-wave propagation in two evenly-welded quarter-spaces. A compressional line source can be located at any point within either medium. The numerical solutions to this problem have been obtained by using the finite difference method. A computer program has been written to obtain synthetic seismograms of the horizontal and vertical displacements at all nodes of the superimposed grid, for the following cases: (a) elastic-wave propagation in a quarter-space, and (b) elastic-wave propagation in two quarter-spaces.

Reflected, converted, transmitted, and diffracted phases are identified and interpreted. Surface and interface waves, originated at the corner by diffraction of the source pulse, are investigated as a function of the rigidity contrast and the velocity contrast between the two media and of the position of the source.

Two-dimensional seismic modeling techniques have been used to provide a qualitative experimental verification of the numerical results.
Experimental determination of the dynamic properties of a bridge substructure
Authors: Shepherd R. , Charleson A. W.
Published: September 2021

abstract

As part of an investigation of the dynamic properties of bridge substructures, a series of steady-state vibration tests were undertaken on a multispan continuous deck bridge at several stages during construction. In this paper the method of testing is outlined and the measured natural frequencies and derived values of equivalent viscous damping are presented. The results confirm that the bridge does behave in a manner reasonably consistent with the design assumptions. At the small values of vibration amplitude generated, an equivalent viscous damping of the order of 4 per cent of critical was determined for the completed bridge.
The relationship between two- and three-dimensional elastic-wave propagation
Authors: Dampney C. N. G.
Published: September 2021

abstract

A technique similar to inverting Abel's equation is used to invert the descent of dimensions method between three-dimensional, cylindrically-symmetric and two-dimensional wave propagation. The end result is a very simple relationship between the two types of wave propagation. Apart from its intrinsic interest, the large number of two-dimensional studies reported in the literature could now be related to their three-dimensional counterparts.
Travel-time errors in the laterally inhomogeneous earth
Authors: Lomnitz Cinna
Published: September 2021

abstract

Travel times from earthquakes or explosions contain both positive and negative systematic errors. Positive skews in travel-time residuals due to epicenter mislocation, and negative skews due to lateral inhomogeneity in the Earth, are analyzed. Methods for travel-time estimation are critically reviewed. Recent travel-time tables, including the J-B tables, are within the range of root-mean-square travel-time fluctuations; the J-B tables are systematically late but cannot be reliably improved by least-square methods. Effects of lateral inhomogeneity at teleseismic distances can be estimated by chronoidal methods independently of standard tables, but the available explosion data are insufficiently well-distributed in azimuth and distance for this purpose.
Seismic characteristics of underground nuclear detonations
Authors: Mueller Richard A. , Murphy John R.
Published: September 2021

abstract

A seismic-spectrum scaling model based on an analytic approximation to the nuclear seismic-source function is described and evaluated in terms of the behavior of a large body of measured spectral data. The results of the scaling analysis indicate that the yield, depth of burial and emplacement medium of the nuclear device play significant roles in defining the seismic-spectrum scaling of underground nuclear detonations. Results are presented which indicate that cube-root-yield scaling of the nuclear seismic-source function is not appropriate. For events buried sufficiently deep for containment, the scaling theory predicts frequency-dependent yield exponents ranging from 0.90 at low frequencies to 0.45 at high frequencies. These yield-scaling exponents are in good agreement with empirical relations statistically derived from measured data.
Seismic characteristics of underground nuclear detonations
Authors: Murphy John R. , Mueller Richard A.
Published: September 2021

abstract

An expression is derived for the elastic energy produced by a contained, underground nuclear detonation using an analytic approximation for the pressure profile acting at the elastic radius. The resulting static strain energy and radiated energy equations are evaluated as a function of yield and depth of burial for detonations in tuff and rhyolite. It is shown that, for a given medium, the elastic-energy efficiency depends only on the depth of burial (h) of the device and is proportional to h0.72. Moreover, for the particular scaling relations used, the strain energy shows the same depth dependence as the radiated energy. Seismic-spectrum scaling theory is applied to an analysis of nuclear seismic-source functions, giving results which are in good agreement with the observed differences in the teleseismic magnitude determinations. A magnitude-energy equation is derived for underground nuclear detonations and is noted to be in poor agreement with the Gutenberg-Richter equation. This discrepancy is interpreted to be an indication that the radiated energy from small earthquakes may typically have been underestimated.
A method for synthesizing realistic strong ground motion
Authors: Trifunac Mihailo D.
Published: September 2021

abstract

A new method of synthesizing artificial accelerograms, based on knowledge of the temporal and spatial properties of the energy-release mechanism, incorporates the effects of local geology through theoretical group-velocity dispersion data for a given site. It is assumed that most of the near-field strong ground motion caused by shallow or surface faulting or explosions is represented by energy propagating through the low-velocity surface-wave guide. The new method of generating artificial accelerograms realistically models strong ground motion for applied structural analysis and theoretical investigations of the response of hysteretic-type structures, soil-structure interaction, and statistics of failure.
A seismic discriminant based on focal mechanism
Authors: Syed Atiq A. , Kisslinger Carl , Nuttli Otto W.
Published: September 2021

abstract

Utilizing the observation that a predominant focal mechanism exists for a given hypocentral region, a seismic discriminant based on body-wave magnitude has been developed. This discriminant enables one to identify earthquakes that do not fit mechanisms expected from plate tectonics. It also sorts out explosions as anomalies, even for those regions in which the focal mechanism results in compressional first motions at most or all available seismograph stations.
The relationship between teleseismic body-wave magnitude m and local magnitude ML from New Zealand earthquakes
Authors: Gibowicz S. J.
Published: September 2021

Relationships between the magnitudes ML and m for 123 New Zealand earthquakes occurring between 1950 and 1967 and having 4.6 ≦ ML ≦ 7.3 have been found. Deep- and shallow-focus shocks were considered separately. There is a linear relationship between ML and m, the slope being the same for both deep and shallow events. Values of ML for deep events are consistently 0.5 magnitude larger than those for shallow events having the same value of m. The relationship between m and ML for New Zealand earthquakes differs significantly from that obtained by Gutenberg and Richter in California.
Evidence for the existence of locally-generated body waves in the short-period noise at the Large Aperture Seismic Array, Montana
Authors: Iyer H. M. , Healy John H.
Published: September 2021

The approximate hexagonal configuration of LASA subarrays enables their use as omnidirectional arrays. This property is used to study the phase velocity of short-period seismic noise at different frequencies. It is found that the noise in the low-frequency band consists mainly of surface waves traveling with average velocities in the range 3.0 to 3.5 km/sec. The high-frequency noise, in the band 0.45 to 1.0 Hz, has an average velocity of about 6.0 km/sec. It is quite likely that the high-frequency noise has the nature of locally-generated body waves. Statistical analysis of Pg velocities observed during a crustal refraction experiment at LASA lends support to this hypothesis.
Interaction of a shear wall with the soil for incident plane SH waves
Authors: Trifunac M. D.
Published: September 2021

The closed-form solution of the dynamic interaction of a shear wall and the isotropic homogeneous and elastic half-space, previously studied only for vertically-incident SH waves, is generalized to any angle of incidence. It is shown that the interaction equation is independent of the incidence angle, while the surface-ground displacements heavily depend on it. For the two-dimensional model studied, it is demonstrated that disturbances generated by waves scattering and diffracting around the rigid foundation mass are not a local phenomenon but extend to large distances relative to the characteristic foundation length.
Residuals and velocities of Pn waves recorded by the San Andreas seismograph network
Authors: Kind Rainer
Published: September 2021

Travel-time residuals were calculated for Pn arrivals from four nuclear explosions and 10 earthquakes recorded by the U.S. Geological Survey's San Andreas seismic telemetry network. Arrivals at stations west of the fault are earlier than at stations east of the fault. Stations on basement rocks indicate a variation in crustal thickness of about 5 to 9 km across the fault at the center of the network. The average mantle velocity after correcting for the residuals is 8.0 km/sec. The Pn waves traveling from the east, when corrected for crustal delay, have a velocity of 7.7 to 7.8 km/sec. Waves traveling from the north or south, after the same corrections, have a Pn velocity of 8.0 to 8.2 km/sec. This difference may be caused by an anisotropic upper mantle, but additional data from seismic sources in the Pacific will be required to confirm this result.
Residual dispersion measurement—a new method of surface-wave analysis
Authors: Dziewonski A. , Mills J. , Bloch S.
Published: September 2021

Measurements of group velocities by means of band-pass filtering lead to systematic errors when group in velocity changes rapidly with frequency. A new method hereafter referred to as “residual dispersion measurement” avoids this difficulty by transforming the signal prior to the filtering. An observed seismogram is cross-correlated with a theoretical seismogram in which the dispersion approximates the observed dispersion within a few per cent. Dispersion of the resulting pulse can be measured with a much higher precision, since du/dω has been reduced by at least an order of magnitude. In addition, the method can be employed iteratively to obtain a greater precision of measurement.

The dispersion of mantle Rayleigh waves is measured from a sum of 48 auto-correlograms of the recordings of the Alaskan earthquake of March 28, 1964. Group and phase velocities are obtained for order numbers between 0S9 and 0S47. It is estimated that the absolute error of the group-velocity measurement does not exceed 0.015 km/sec.

The analysis of a sum of 13 auto-correlograms of horizontal component seismograms with predominantly transverse motion reveals that the fundamental-mode Love-wave data may be contaminated by higher torsional modes. Comparison of several sets of average Love-wave phase velocities shows a discrepancy of the order of 0.4 per cent in the period range from 350 to 170 sec. The corresponding figure for Rayleigh waves is less by at least an order of magnitude.
Response spectrum solution for earthquake analysis of unsymmetrical multistoried buildings
Authors: Gibson R. E. , Moody M. L. , Ayre R. S.
Published: September 2021

Modal analysis and response spectra are use to develop an approximate method for earthquake analysis of unsymmetrical multistoried buildings modeled as shear-flexible cantilever beams. The beam has constant mass per unit length and a linear variation of elastic shearing resistance along its length. Existing modal solutions are used and response spectra for two horizontal earthquake components are included in the analysis. Solutions for a typical building are presented and compared with an exact form of solution.
Complex roots of the Stoneley-wave equation
Authors: Pilant Walter L.
Published: September 2021

The equation governing elastic waves propagating along a solid-solid interface is found to have sixteen (16) independent roots on its eight (8) associated Riemann sheets. The range of existence (in terms of material parameters) for the real root corresponding to the propagation of Stoneley waves has long been known. It is found that outside this range there are two types of behavior. If the material of greater density has a velocity slightly greater than that of the material of lesser density, the unattenuated Stoneley waves make a transition to attenuated Interface waves, i.e., they leak energy away from the interface as they propagate along it. If the more dense material has a velocity more than about three times that of the less dense, then the Interface-wave root disappears and energy is propagated along the interface as Rayleigh waves. This Rayleigh-wave propagation is associated with a different root of the fundamental equation. On the other hand, if the material of greater density has a velocity much lower than that of the material of lower density (a case that is difficult to find physically), then no energy will be propagated along the interface at all. This result was unexpected. Some rather interesting behavior of the 16 roots was noted as the physical parameters were varied over a wide range. In addition to the normal collisions between pairs of roots, and between individual roots and branch points (with attendant Riemann sheet jumping), it was found that some roots go through the point at infinity and return with a change in sign. At least one unexpected case of a multiple root was found. Another case was noted in which a pair of complex roots change quadrants in the complex phase-velocity plane, leading to a discontinuity in root type. Finally, it was noted that, in a cyclic variation of the material parameters, it is possible to choose a path such that the roots, when followed individually, will not return to their original values. In fact, as many as five cycles in parameter space can be accomplished before the roots return. All this strange mathematical behavior seems to have no physical significance, but has been presented to increase understanding of the general behavior of the dispersion relations associated with elastic-wave propagation.
Highrise building characteristics and responses determined from nuclear seismology
Authors: Blume John A.
Published: September 2021

abstract

Reliable measurements and detailed analyses of the responses of many buildings to ground motion resulting from underground nuclear explosions are providing new and valuable information on the structural-dynamic properties and behavior of real buildings. Much, if not all, of this knowledge is applicable to the problem of resisting natural earthquake ground motion, and it is being obtained as a byproduct of the AEC underground explosive nuclear safety program which is concerned with developing techniques for making reliable predictions of response and any damage.

Information is provided on oscillator spectral response values, building responses, modal contributions and combinations versus elapsed time and at times of maximum response, variations in natural periods, foundation material interaction, and biaxial motion in the horizontal plane. Data are shown for nuclear events JORUM and HANDLEY and then compared to those of prior major events. In addition, peak responses of certain Las Vegas buildings to the distant February 1971 San Fernando earthquake (U.S. Geological Survey, 1971) are provided and compared to responses to nuclear events.
Oceanic mantle phases recorded on seismographs in the Northwestern Pacific at distances between 7° and 40°
Authors: Sutton George H. , Walker Daniel A.
Published: September 2021

abstract

Body-wave data recorded on hydrophones at Midway, Wake, and Eniwetok and on seismographs at Midway, Wake, and Marcus indicate the following for the mantle under the Northwestern Pacific Basin: a zone of low P-wave velocity with a thickness of about 75 km beginning in the uppermost 100 km of the Earth, perhaps very close to the M discontinuity; a wave guide immediately below the M discontinuity which propagates 3 to 8 Hz energies of compressional and shear phases with velocities of 8.28 ± 0.03 and 4.79 ± 0.04 km/sec, respectively, to great distances (observed to 33°, with the wave guide for compressional phases being considerably more efficient than the wave guide for shear phases); and, an asthenosphere of low Q for frequencies of 3 to 8 Hz as compared to that for material above and below.

Similar data for the East Caroline Basin-Ontong Java Plateau-Nauru Sea area indicate the following: a wave guide immediately below the M discontinuity which propagates 3 to 8 Hz energies of compressional phases with a velocity of 8.47 ± 0.48 km/sec to at least 22°; a weaker wave guide for shear phases than observed for the area to the north; an asthenosphere of low Q for frequencies of 3 to 8 Hz as compared to that for material above and below; and a velocity distribution somewhat different from that for the area to the north since, for normal refracted-mantle P phases recorded in the distance range of 22° to 40°, travel-time residuals are generally slightly negative for the area to the north and slightly positive for the area to the south.
Effects of site and propagation path on recorded strong earthquake motions
Authors: Lastrico Roberto M. , Duke C. Martin , Ohta Yutaka
Published: September 2021

Accelerograms from the 1952 and 1954 Kern County and the October 1933 Signal Hill earthquakes were used with detailed site models in an attempt to isolate the principal site, path, and source contributions in the recorded motions. Site models 20,000 ft deep were developed from soil, water and oil borings, geological reports, and near-surface refraction surveys at four accelerograph sites in Los Angeles and one at Taft, California. Analysis was based on linear system theory, using Fourier spectra and hypothesizing vertically incident shear waves.

The four subsurface site models at Los Angeles were adjusted within the uncertainties of the model properties to minimize the standard deviation of computed 1952 bedrock motions. These stations were close together relative to the epicentral distance. Resulting subsurface transfer functions showed, generally, highest amplifications at the Hollywood station and lowest at UCLA, with a 100 per cent range based on the latter.

Attenuation in the crustal path was evaluated using computed bedrock motions and incorporating the data at Taft. The exponent of distance for geometrical spreading was close to minus one. The damping along the path, expressed as Q, was 550 for the 1952 case and 62 for the 1933 case. A spectrum was obtained for the ratio of the source functions for the 1952 and 1954 earthquakes.
The connection between elastodynamic representation theorems and propagator matrices
Authors: Kennett B. L. N.
Published: September 2021

Two independent powerful methods in elastodynamics have been developed over the last few years: these are the use of representation theorems and propagator matrix techniques. The connection between these two approaches is derived in this paper. This is then used to show the equivalence of approximate techniques in elastic wave scattering based on representation theorems and a recent method based on matrix theory.
Distribution, focal mechanisms, and frequency of earthquakes in the Fairview Peak area, Nevada, near the time of the BENHAM explosion
Authors: Smith B. E. , Coakley J. M. , Hamilton R. M.
Published: September 2021

Six portable seismographs were operated for 30 days in a network centered 25 km south of the epicenter of the 1954 Fairview Peak earthquake. The recording period lasted from 15 days before to 15 days after detonation of the one-megaton BENHAM underground nuclear explosion 250 km to the southeast of the Nevada Test Site on December 19, 1968. Approximately 950 earthquakes were detected within about 30 km of the network. No evidence was found that the explosion affected the rate of earthquake occurrence. Locations were computed for 152 earthquakes. The epicentral pattern shows north and northeast trends about 1 to 3 km wide. Focal depths range from 5 to 14 km. The main zones of activity seem to have a near-vertical orientation. Composite fault-plane solutions suggest that faulting within zones is not consistent with a single focal mechanism. Instead, a variety of mechanisms is indicated, consisting primarily of north-striking right-lateral oblique-slip, and northeast-striking dip-slip movements. In both cases, the pressure axis is near vertical and the tension axis is near horizontal, striking about S60°E.
Tectonic stress and the source mechanism of the Imperial Valley, California, earthquake of 1940
Authors: Trifunac M. D.
Published: September 2021

The Imperial Valley earthquake was a multiple sequence (Trifunac and Brune, 1970) with at least four events occurring during the main energy release. These four events, recorded on the strong-motion seismograph in El Centro, located about 10 km NW from the instrumentally determined epicenter, and nine aftershocks recorded in the next 5 min are re-examined in this paper to test an approximate source theory (Brune, 1970). This theory predicts the shape of the body-wave spectra in terms of the seismic moment and stress drop. By fitting theoretical spectra to the spectra calculated from the strong-motion accelerogram, moment and stress drop can be estimated for each of the multiple events. Inasmuch as the average displacements at the fault and the source dimensions can be derived from the known moment and stress drop, the pattern of average displacements along the fault was computed from the instrumental records. A test of the theory, then, consists of comparing the fault displacements derived from seismograms with the fault displacements observed at the surface (Buwalda, unpublished field notes). For the Imperial Valley earthquake, agreement between these two independent methods of measurement is good, suggesting that the above theory is an adequate first approximation for the spectra of body waves. The stress drop variations along the fault, inferred also from the above theory, indicate two areas of major stress concentration located near the northwestern and southeastern ends of the dislocation. The stress drops for various events varied from about ten to several hundred bars.