bluuebunny/crossref_metadata_2025_split huggingface dataset:
The south-central Illinois earthquake of November 9, 1968: Macroseismic studies
Authors: Gordon David W. , Bennett Theron J. , Herrmann Robert B. , Rogers Albert M. 
Published: September 2021

Abstract
The November 9, 1968 earthquake in south-central Illinois occurred in the New Madrid zone, a seismic zone associated with northeast-trending geological structure. Landforms in the epicentral area consist of nearly flat, glacial lake plains surrounding low, loess-covered hills. An extensive post office canvass and a field inspection of the epicentral area indicate that the strongest shaking (MM VII) took place in the Wabash and Ohio Valleys and adjacent lowlands of south-central Illinois. Characteristic damage included broken chimneys, fallen plaster, and occasional instances of collapsed parapets and overthrown tombstones. Observed rotations of tombstones and other objects in the epicentral area suggest a quadrant distribution of clockwise and counter-clockwise rotations.
Ocean microseism measurements with a neutral bouyancy free-floating midwater seismometer
Authors: Bradner H. , de Jerphanion Louis G. , Langlois Richard 
Published: September 2021

abstract
Seismometers in spherical aluminum pressure housings have been weighted to float stably at midwater depths in the ocean, and thus record water motions in a frequency band of 0.02 to 5 cps. Simultaneous records made with a midwater instrument at 1.2-km depth and a bottom instrument at 4.6-km depth showed coherence at spectral power peaks of leaky organ-pipe frequencies and additional coherence peaks at frequencies down to 0.025 cps. Twenty organ-pipe modes can be tentatively identified. The spectral power can be attributed almost entirely to microseismic motions in wave-guide modes. We conclude that the forcing functions for microseisms are broad enough so that deep ocean-bottom and midwater microseism spectral peak frequencies are characteristic of local bathymmetry.
Stationary phase approximation in focal mechanism determination
Authors: Chandra Umesh 
Published: September 2021

abstractTests of the stationary phase approximation method applied to P waves for the determination of focal mechanisms have been carried through for eight earthquakes selected from different geographic locations and depth ranges. The results are found to be in close agreement with the solutions obtained from S-wave polarization data for four earthquakes and in reasonable agreement for three earthquakes. In general, however, the P polarities are more consistent with S-wave polarization solutions than with the solutions obtained by the present method. The stationary phase solutions agree with the P-wave spectrum solutions determined in a previous study. The method is applicable to shallow-focus earthquakes, and to earthquakes of large magnitude in which methods using S-wave polarization data and P-wave spectra are difficult to apply.
Discrimination of earthquakes and explosions by the rayleigh-wave spectral ratio
Authors: Derr John S. 
Published: September 2021

Abstract
Limited data from a long-period vertical seismometer and the prototype of a new mercury tiltmeter at the station, Harvard, Massachusetts, tend to confirm that the Rayleigh-wave spectral ratio of short- to long-period energy provides a useful discriminant for underground explosions in the Western United States at distances of from 28° to 38° in the magnitude range of 3.5 &lt; Ms &lt; 5.6. This corresponds to discrimination in the range of 5.0 &lt; mb &lt; 6.3. The same spectral ratio, however, does not discriminate the large Milrow event in the Aleutians from earthquakes in the same region, possibly because of differences in earthquake source mechanisms in different regions and because this explosion released significant tectonic strain. The Rayleigh spectral ratio complements the Mg — mb discriminant by providing a clear separation of earthquakes and explosions in some geographical regions where earthquakes are of low stress drop and generally strike-slip in mechanism.
Microearthquake seismicity and tectonics of Coastal Northern California
Authors: Seeber Leonardo , Barazangi Muawia , Nowroozi Ali 
Published: September 2021

Abstract
This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes.
Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening.
The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino.
The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.
Analysis of Rayleigh-wave multipath propagation at LASA
Authors: Capon Jack 
Published: September 2021

Abstract
An investigation has been made of the multipath propagation of Rayleigh waves by using data obtained from the large aperture seismic array (LASA). The use of the LASA in conjunction with a high-resolution analysis technique provides a greater angular resolution and accuracy than was previously possible for the analysis of the multipath propagation. Measurements have been made of this phenomenon for the Rayleigh waves of 26 events distributed at various azimuths and distances from LASA. On the bas of these measurements reasonably good conjectures are made concerning the actual propagation paths for groups in the 20- to 40-sec period range. It is shown that in almost all cases these propagation paths can be associated with refractions and reflections at the continental margins.
Strain effects of nuclear explosions in Nevada
Authors: Boucher Gary , Malone Stephen D. , Homuth E. Fred 
Published: September 2021

abstract
The University of Nevada's three-component quartz-rod strain meter installation at Round Mountain, Nevada (38°42.1′N, 117°04.6′W) has recorded a number of underground nuclear explosions at the Nevada Test Site, beginning with the megaton-sized JORUM event September 16 1969. Both that explosion and the larger HANDLEY event on March 26 1970 produced static strain offsets of a few parts in 109 at Round Mountain. These offsets did not decay within the first few hours after the explosions. In both cases, the strain offsets were in the sense of ground extension radial to the shot point, which is inconsistent with the assumption of a pure compressive source of strain. The strain-change ellipse for the HANDLEY event was found to have a major strain axis of 11 × 10−9 extensional, oriented N 34°W, and a minor axis of 7.4 × 10−9 compressional. A single-component strain meter at Mina, Nevada, (38°26.3′N, 118°9.3′W) was operated for the HANDLEY event, and recorded a strain offset of 2.6 × 10−9 in the direction N 74°E. Strain offsets at the time of the largest collapse events following HANDLEY were observed at Round Mountain. These offsets had the same sense on each component as those following the explosion itself. This is interpreted as support for the hypothesis that the strain changes are tectonic in origin, and the explosion initiates the strain release. Small offsets were observed for three smaller explosions out of a total of 13 studied. The relationship between body-wave magnitude mb and maximum dynamic strains at Round Mountain may be described empirically by the equation Log S = − 13.4 + 1.10 mb. Because of its high sensitivity and stability, the Round Mountain strain meter is capable of obtaining useful measurements of dynamic and static strain effects of intermediate- to large-sized explosions, at distances ranging from 160 to 200 km.
Leaking modes in a crust with a surface layer
Authors: Dainty Anton M. 
Published: September 2021

abstract
Dispersion curves, attenuation functions and excitation functions for an explosive source at depth for four different models of the crust are presented for the leaking modes P(+, −), P(−, +) and π1(−, +). One of the objectives of the calculations was to determine the effect of a surface, low-velocity layer on the dispersion curves and attenuation functions. For the mode P(+, −) (the fundamental leaking mode), the differences are slight, while more pronounced differences are found for the other modes.
The variation of the excitation function with depth of the source has been studied. For the modes P(+, −), P(−, +) low frequencies are enhanced and high frequencies suppressed for one of the models as the source depth increases. According to this study, a source deep in the crust should be a more efficient exciter of the mode P(+, −) (the most commonly seen mode) than a near-surface source.
The Koyna earthquake of December 10 1967: A multiple seismic event
Authors: Gupta Harsh K. , Rastogi B. K. , Narain Hari 
Published: September 2021

abstract
The analysis of P waves recorded at seismological observatories and seismic arrays at teleseismic distances and strong motion seismographs located at Koyna Dam suggest the Koyna earthquake of December 10 1967 to be a complex multiple event. Six of the events could be identified, and the second and third events are located with respect to the initiation using the Gutenberg sine-curve method at distances of 6 and 17 km due south, the average rupture velocity being 3.4 km/sec. The findings are consistent with the field observations and the different origin times, epicenters and magnitudes reported for the earthquake. Seismic array records are found to be very useful in examining the multiplicity of seismic events.
Evaluation of computational algorithms for the Associated Legendre Polynomials by interval analysis
Authors: Wiggins Ralph A. , Saito Masanori 
Published: September 2021

abstract
An interval arithmetic that consists of tracing the number of significant figures during each calculation is applied to computational algorithms for the Associated Legendre Polynomial, Pnm(cos ϑ). The results indicate that the interval arithmetic scheme is a good estimator for the propagation of round-off errors and that one particular algorithm [a recurrence relation that relates Pnm (cos ϑ) to Pnn(cos ϑ)] is by far the superior computational scheme.
Comparison of three methods for calibrating a Willmore geophone
Authors: Donato R. J. 
Published: September 2021

abstract
This paper describes a simple method for calibrating a Willmore geophone without using a shake table. It is assumed that one of the mechanical parameters of the system is known—in this case, the mass. The results from this simplified method are compared with an a.c. bridge method in which the equivalent electrical impedance is measured and with another bridge method described by Willmore where the sensitivity is measured by a substitution method. The three methods give substantially the same sensitivity of 6.1 volts/cm/sec for the particular geophone, with an estimated accuracy of 2 per cent, and all agree to the manufacturer's approximate specification to within 7 per cent.
A source of major error in the digital analysis of World Wide Standard station seismograms
Authors: James David E. , Linde Alan T. 
Published: September 2021

abstract
A critical requirement in the digitization of analogue seismograms is that the y axis of the digitizing device be parallel to the recorded direction of swing of the galvanometer. Small misalignment of the seismogram on the digitizing table can produce major errors in the results of Fourier analysis and other digital techniques. In the examples discussed, the direction of the galvanometer swing was not parallel to the recording drum axis (the nominal direction of swing). Fourier spectra and group velocities are presented for cases in which the seismogram is aligned with the x axis of the digitizer: (1) parallel to the trace; (2) normal to the drum axis; (3) correctly aligned, normal to the direction of galvanometer swing. If the alignment is incorrect, the errors in the results are significant at both short and long periods and lead to erroneous geophysical conclusions. The magnitude of the errors increases with both the degree of misalignment and the amplitude of the recorded signal.
The motion excited by an impulsive source in an elastic half-space with a surface obstacle
Authors: Aboudi Jacob 
Published: September 2021

abstract
An elastic half-space having a surface obstacle of slightly different elastic constants whose deviation and shape of boundaries are small is considered. By combining a perturbation method and a finite difference solution, the motion of the half-space due to an impulsive source is given. Results show that Rayleigh and reflected waves are highly influenced by the existence of the obstacle and could give some indications for screening purposes of elastic waves.
Transformation of the earthquake displacement field for spherical earth—Static case
Authors: Wason Hans R. , Singh Sarva Jit 
Published: September 2021

abstract
Explicit expressions for the static displacement field for a Volterra dislocation and a center of compression in an infinite homogeneous medium are obtained. Using an addition theorem, the field is transformed to a polar coordinate system with origin at the center of the Earth. Expressions for the discontinuity in the motion stress vector across the concentric spherical surface through the source are then obtained. These results can be used in studying the deformation of a multilayered spherical earth model induced by internal sources by the Thomson-Haskell matrix method which has so far been mostly applied to dynamic problems.
Virginia's two largest earthquakes—December 22, 1875 and May 31, 1897
Authors: Bollinger G. A. , Hopper Margaret G. 
Published: September 2021

abstract
A study of the macroseismic effects associated with the two largest of Virginia's historic earthquakes, based primarily on journals and archival newspaper accounts, reveals that exceptionally large felt areas can be associated with moderate earthquakes in the middle Atlantic region. Occurring at opposite ends of the state, the two shocks exhibit similar effects to the north, which appear related to the surficial geology, but differing intensity distributions to the southwest, which may reflect the differences between the two areas that exist in the geological structure. Differences in focal depth and focal mechanism may also be contributing factors. The Giles County earthquake of May 31, 1897, in the folded Appalachian Province of western Virginia, is assigned a maximum intensity (MM) of VIII and a felt area of at least 280,000 square miles. The Chesterfield County earthquake of December 22, 1875, in the crystalline Piedmont Province near Richmond, had a maximum intensity (MM) of VII and a 50,000-square-mile felt region. In both cases the previously reported intensities and felt areas were found adequate. For the moderate seismicity of the Appalachians, an extremely long period, May 3 to June 6, of seismic and acoustic phenomena occurred in conjunction with the May 31, 1897 shock.
A new approach for preparation of quantitative seismicity maps as applied to Alpide Belt-Sunda Arc and adjoining areas
Authors: Kaila K. L. , Narain Hari 
Published: September 2021

abstractA new method is developed for preparation of quantitative seismicity maps of an area. In this method, the slope b of the cumlative regression curve log N = A − bM, is supposed to be variable from one region to another and not constant as assumed by Riznichenko (1958) in his seismostatistical method. Under such a premise of variable b, the seismicity at any place is defined as log of the area under the curve representing incremental number of earthquakes versus magnitude on linear graph paper, within the magnitude range M = M to M = Mmax. The log of the total area under such a curve from magnitude M = 0 to M = Mmax will represent A value on the cumulative regression curve, and the same can also be used as a measure of seismicity level in any region. Worldwide relations are established between N(occ) the cumulative number of earthquakes occurring in an area with magnitude 4 and above and those actually detected N(det). This enables one to define the ratio between log N(det) and log N(occ) as the detectability level D of an area. The constants A and b of the cumulative regression curves for various regions of the Earth (normalized to 2° × 2° grid area and 14-year period of earthquake observation) are found to be related to each other by the equation A = 6.35b − 1.41. Making use of this relation and the detectability level D, b and the normalized A values for every 2° × 2° grid area as at the equator can be calculated. These A or b values are then used to draw the seismicity maps for any region of the Earth.Using this new approach, a quantitative seismicity map based on A values has been prepared for the entire Alpide Belt-Sunda Arc and adjoining areas. This seismicity map has not only brought out the regions of high and low seismicity in great detail, but, at the same time, it also shows the trends of these highs and lows very clearly. This map is then compared with regional seismic zoning maps prepared by other workers covering small portions of this seismic belt and the two pictures are seen to show very good agreement both qualitatively as well as quantitatively.
Elastic multipole theory and seismic moment
Authors: Randall M. J. 
Published: September 2021

abstract
Relationships between dynamic and static elastic multipoles derived from a general solution of the elastic-wave equation allow the direct application of results from elastostatic theory to problems in earthquake mechanism. For any theoretical model, the impulse of wave displacement (with can easily be found from long-period seismograms) can be simply derived from the far-field static dilation.
Application to a generalized dislocation model shows that seismic moment is properly a tensor.
Upper mantle P-wave velocity structure in the Japan region from travel-time studies of deep earthquakes using a new analytical method
Authors: Kaila K. L. , Krishna V. G. , Narain Hari 
Published: September 2021

abstract
The upper mantle P-wave velocity structure of the region of Japan has been studied in great detail from travel times of 107 earthquakes with focal depths varying from 40 to 600 km, using a new analytical method given by Kaila (1969). In southwestern Japan the P-wave velocity is found to be 7.88 km/sec at a 40-km depth, and it remains almost constant to a depth of 255 km. For northeastern Japan the velocity, determined as 7.88 km/sec at 40 km, increases linearly with moderate gradient to 8.14 km/sec at a 175-km depth. On the other hand, for central Japan the P-velocity is found to be 7.92 km/sec at a 40-km depth, and increases linearly with a high-velocity gradient to 8.33 km/sec at a depth of 180 km. Then, there is a slight decrease in the velocity gradient, but the velocity still increases linearly to 8.52 km/sec at a depth of 365 km. At this transition depth, there is a first-order velocity discontinuity—the velocity increasing from 8.52 to 9.10 km/sec. Below this depth, velocity again increases linearly from 9.10 to 9.99 km/sec at a depth of 600 km. Probable causes for these lateral-velocity inhomogeneities in the upper mantle of the Japan region are discussed.
Graphs have been drawn to show the variation with depth of Δ*, the epicentral distance to the inflection point, (Δ2 − Δ1), ptrue = ∂T/∂Δ and ap = (T − pΔ) at the inflection point, the latter acting as a calibration curve for earthquake focal-depth determination in Japan. Using this calibration curve, focal depths are redetermined for all of the earthquakes under study for central Japan, and the same are compared with the values reported in the International Seismological Summaries.
Long-period body-wave propagation from 4° to 13°
Authors: Helmberger Donald V. 
Published: September 2021

Abstract
Numerical seismograms are computed for a compressional pulse in a layered model. The simpler models consist of a fluid layer over a fluid half-space, a fluid layer over a solid half-space, and a solid layer over a solid half-space. Restricted portions of the theoretical response for a layered model approximating the Earth are constructed. Synthetic seismograms are generated using the pressure pulse appropriate for NTS events and the long-period instrument response. The interplay between the PL wave, the refracted wave along the lid, and the arrival from the base of the low-velocity zone is displayed. A detailed comparison between the synthetics and observations indicates a prominent low-velocity zone with appreciable seismic absorption. Observed regional wave-shape characteristics are displayed and a reconnaissance map of lateral variations along the top of the mantle presented.
The July 8, 1971 Chilean earthquake
Authors: Eisenberg A. , Husid Raul , Luco Juan E. 
Published: September 2021

Abstract
Observations on the destructive 1971 Chilean earthquake show that the epicenter and focal mechanism might be different from the one in 1965 in the same region. Field study shows that almost all damage was confined to poorly-built structures or to those that were not earthquake-resistant. Local high intensities are well correlated with the soil characteristics of alluvial valleys. Analyses of accelerograms at Santiago, about 140 km from the epicenter, show, as in 1965, rather high (15 to 17 per cent of g) values of ground accelerations for that distance.
Magnitude from short-period P-wave data
Authors: Veith K. F. , Clawson G. E. 
Published: September 2021

abstract
An empirical surface-focus amplitude-distance curve, based on approximately 2400 short-period P-wave amplitudes from 43 large explosions at 19 different sites, and a corresponding curve based on geometrical spreading in the Herrin earth model are developed. The relative amplitude differences are inverted to obtain the Q structure of the mantle. Theoretical, deep-focus, amplitude-distance curves incorporating geometric spreading and attenuation are developed. Corresponding distance and depth amplitude-correction P factors are given for computing magnitude (mp). The correction factors are evaluated and are shown to provide a significantly improved basis for computing magnitude relative to the presently used Q factors which yield mb. Values of mp were normalized to be equal on the average to values of mb for a surface source; differences in attenuation factors generally make mb larger than mp for deep earthquakes.