bluuebunny/crossref_metadata_2025_split huggingface dataset:
Source processes of large earthquakes along the Xianshuihe fault in southwestern China
Authors: Zhou Huilan , Liu Hsui-Lin , Kanamori Hiroo 
Published: July 2021

abstractThe Xianshuihe fault is one of the most active faults in southwestern China. Recently, three large earthquakes occurred along it in 1967 (Ms = 6.1), 1973 (Ms = 7.5), and 1981 (Ms = 6.8).The 1981 event occurred near the central portion of the fault zone. Modeling of the body and surface waves indicates pure left-lateral strike-slip motion on a vertical fault striking N40°W consistent with the surface trend of the Xianshuihe fault. Two major ruptures are suggested for this source, with a total moment of 1.3 ×1026 dyne-cm. The 1973 event occurred about 65 km northwest of the 1981 event and ruptured about 90 km bilaterally along the fault. The body-wave synthetics indicate three main ruptures during faulting within 43 sec, with a total moment of 1.8 ×1027 dyne-cm. The mechanisms are similar to the 1981 event, and the average slip is determined to be 3.8 m. The largest aftershock (Ms = 5.9) occurred 1 day after the main event with a normal-fault mechanism striking almost perpendicular to the surface breakage. The 1967 event occurred at the northwestern end of the fault zone, with a strike of N65°E. It had a nearly normalfault mechanism with a seismic moment of 4.5 ×1025 dyne-cm. The largest aftershock (Ms = 5.1) occurred 7 hr later with a similar focal mechanism.The primary faulting along the Xianshuihe fault is left-lateral strike-slip, but the normal faulting with strike direction about perpendicular to the Xianshuihe fault trace is common, especially in the northwestern segment. The faulting pattern in this region is consistent with the regional stress field caused by the India-Tibet collision. The normal event which is not on the major fault seems to have more frequent foreshocks and aftershocks than those on the main fault.
Spatial attenuation of theLgwave in the Central United States
Authors: Dwyer John J. , Herrmann Robert B. , Nuttli Otto W. 
Published: July 2021

abstractThe spatial attenuation of the Lg wave in the Central United States is studied in the time domain in the frequency range of 1 to 10 Hz. Fitting Lg amplitudes according to the relationA = A o r − 5 / 6 exp ( − γ r ) ,γ varies between 0.0007 ± 0.0001 km−1 at 1 Hz and 0.0029 ± 0.0005 km−1 at 10 Hz (standard errors given). Relating γ to Qβ by the relationγ = π f / Q β U ,these results imply a frequency dependence for Qβ given byQ β ( f ) = Q β ( 1 H z ) f ( 04 ± 015 ) .This result extends Singh's (1981) estimate of 0.1 to 0.3 for the exponent of frequency dependence for the frequency range to 0.5 to 2 Hz for coda waves observed in the Central United States.Bandpassed microearthquake data were also used to estimate source spectrum shapes and seismic moments. Incorporating these results with those of Street et al. (1975), the seismic moment-magnitude scaling for the Central United States is found to belog 10 M o = 16.44 ± 0.18 + ( 1.26 ± 0.05 ) m b L gfor the magnitude range 1.8 ≦ mbLg ≦ 4.9.
A study of the 20 January 1982 earthquake near Great Nicobar Island, India
Authors: Agrawal P. N. 
Published: July 2021

abstract
An earthquake of MS = 6.3 occurred on 20 January 1982 near the east coast of Great Nicobar Island (in the Bay of Bengal), India and caused great panic among the inhabitants. Ground Fissures and damage to civil engineering structures was also caused. A study comprised of the recording of aftershocks and their migration, the preparation of an isoseismal map, and the compilation of other damage data is presented. Some recommendations have been made to permit suitable safeguards in future development.
Digitization noise and accelerograph pen offset associated with Japanese accelerograms
Authors: Crouse C. B. , Matuschka Trevor 
Published: July 2021

abstractGround-motion accelerograms recorded in Japan between 1956 and 1978 were recently processed. Preprocessing studies of the accelerograms were required that consisted of: (1) evaluation of the long-period digitization noise in the accelerograms, and (2) correction for initial offset of the recording pen in the SMAC accelerograph. Long-period digitization noise present in each accelerogram was identified from the Fourier Amplitude Spectrum of the uncorrected accelerogram. Similar investigations with United States accelerograms recorded on 70-mm film revealed that the noise in both sets of data had similar characteristics. In nearly all cases, the noise spectrum was proportional to the period, which suggested that fatigue and carelessness of the operator during digitization may have been responsible for the observed period dependence. Correction for initial pen offset was necessary for some Japanese accelerograms because the pen arm was not parallel to the direction of movement of the recording paper. To account for pen offset, values of the initial pen rotation were assumed, and the accelerograms were corrected using a simple algorithm. Our best estimate of the true offset was based not only on the offset which best removed the slanted appearance, but also the offset inferred from the original accelerogram.
Source parameters and scaling laws of the 1978 Swabian Jura (southwest Germany) aftershocks
Authors: Scherbaum Frank , Stoll Dieter 
Published: July 2021

AbstractThe 3 September 1978, Swabian Jura (southwest Germany) earthquake (MWA = 5.7) was followed by a large number of aftershocks which have been recorded with a local network of five portable seismic stations. The seismic moments, fault radii, and the static stress drops have been determined from the SH displacement spectra using the Brune (1970) source model. The data set is consistent with the Gutenberg-Richter energy-magnitude relation.Below a Wood-Anderson magnitude of about 4, the corner frequencies increase only slowly with decreasing magnitudes. No corner frequency higher than 15 Hz has been observed in the magnitude range down to 0.8. Correspondingly, the high-frequency decay slopes show a strong increase when the corner frequencies are approaching the maximum frequency. This prevents the use of slope data for Q determinations.In terms of the Madariaga (1977) crack model, the data show a strong influence of source complexities on the smaller events.
Wave propagation in a three-dimensional circular basin
Authors: Lee Jia-Ju , Langston Charles A. 
Published: July 2021

AbstractWave propagation in a three-dimensional circular basin model is studied by using a ray technique which employs the method of principal curvature for geometric spreading calculation. Three components of ground motion are calculated at surface stations assuming incident plane P and SH waves with various incidence angles. Computed results show that seismic energy is substantially enhanced in the central region of the basin while it diverges rapidly toward the edge of the basin. Compared to a two-dimensional basin with the same cross section, amplitudes are larger for stations in the central region and smaller for stations near the edge. Waveforms and amplitudes can change drastically between two nearby stations due to caustics and geometric focusing for different paths. It is found, for the particular basin geometry and velocity contrast used, that the first multiple P wave and other particular phases experience two caustics near the basin center which are associated with the principal curvatures of the wave front. This results in the reversal of the polarity of the waveform. As incidence angle increases, later arrivals at near-edge stations and the stations in the diagonal direction are more strongly developed from the curved boundary of the basin, but amplitudes of ground motions generally decrease as incidence angle increases. In general, wave responses strongly depend on the incidence angle and station location. These results have important implications for site amplification of strong ground motions since wave behavior is so complex even for this simple idealized structure.
Nongeometric arrivals due to highly concentrated sources adjacent to plane interfaces
Authors: Daley P. F. , Hron F. 
Published: July 2021

Abstract
A high-frequency approximation for nongeometrical arrivals due to highly concentrated sources adjacent to the interfaces between two different elastic media has been developed following their detection in the real field data by Gutowski et al. (1982). In our approach, the “★” waves are associated with secondary saddle-point contributions of the contour of integration circumventing branch points in the integral representation of transmitted wave field. Our formulas are presented in a simple form suitable for an easy incorporation into any ray synthetic seismogram computation. The range of validity of our approximations is discussed and their accuracy tested by comparing the pertinent ray seismograms with their equivalents produced by the Alekseev-Mikhailenko method. A good match between both sets of seismograms suggests that our high-frequency approximations for “★” waves are well justified as are our formulas derived for the head wave-like arrivals driven by the “★” waves, and seen in the full wave field seismograms and detected in real data as well.
The viscoelastic reflection/transmission problem: Two special cases
Authors: Krebes E. S. 
Published: July 2021

AbstractIn the general problem of plane wave reflection and transmission at a boundary separating two linear viscoelastic media, the mathematical formulas for the reflection and transmission coefficients, the transmission angle, the attenuation vector, etc., are not easily interpretable because they cannot easily be expressed in terms of the basic input parameters (Q, incidence angle, etc.). To gain further insight, we study two special cases in which mathematical simplifications occur. No low-loss approximations are involved. In the first case, the incident wave is homogeneous, and the Q values of the two layers are equal, and we find, among other things, that the reflection and transmission coefficients are the same as the ones for perfect elasticity (they do not involve complex velocities, etc., and are independent of Q). In the second special case, the degree of inhomogeneity of the incident wave approaches its upper limit, and we find that the reflection and transmission coefficients approach constant (complex) values independent of the incidence angle, and that there is almost no ray-bending (refraction) upon transmission of the incident wave through the boundary.
Microearthquakes and the nature of the creeping-to-locked transition of the San Andreas fault zone near San Juan Bautista, California
Authors: Bakun William H. , McLaren Marcia 
Published: July 2021

AbstractEighteen digital event recorders were deployed during May-June 1981 along the creeping-to-locked transition of the San Andreas fault zone near San Juan Bautista, California, as a supplement to the U.S. Geological Survey's central California seismic network. Analysis of 18 well-recorded microearthquakes (0.7 ≦ ML ≦ 2.8) located along the transition confirms the complexity of the crust and fault-zone structure of the transition region. Seismic-wave site amplification is 2 to 10 times greater at sites between the San Andreas and Sargent fault traces, consistent with other evidence for lower velocities in the upper 3 km of crust there. Routine mislocation of epicenters 2 to 4 km northeast of the Sargent fault are consistent with greater P-wave velocity northeast of the Sargent fault. Microearthquake source parameters are consistent with a more segmented and splayed fault geometry toward the northwest locked end of the transition. P-wave nodal planes for 10 microearthquakes located to the northwest, 9 on the Sargent fault, and 1 near the San Andreas, are oriented more westerly than nodal planes commonly obtained for the frequent moderate-size earthquakes on the creeping section of the San Andreas fault to the southeast. Static stress drop, dynamic stress drop, and apparent stress estimates all increase with seismic moment, with the apparent stress and dynamic stress drops equal to about 3 and 20 per cent, respectively of the static stress drop. Average fracture energies, calculated assuming complete stress drop, generally increase with source size (seismic moment, rupture area, seismic slip, etc.) from 7 to 3000 J/m2; the two events with anomalously low fracture energies occurred on the creeping section of the San Andreas fault.
Use of seismoscope records to determineMLand peak velocities
Authors: Boore David M. 
Published: July 2021

AbstractMore information about ground motion can be extracted from seismoscope records than a single point on a response spectrum. To demonstrate this, the relation between seismoscope response and Wood-Anderson instrument output and peak horizontal ground velocity has been studied by simulating the various responses for a range of distances and magnitudes. The simulations show that the relation used by Jennings and Kanamori (1979) to convert from peak seismoscope readings to the peak response of a Wood-Anderson instrument has a distance- and magnitude-dependent systematic error. The error is negligible, however, for modern seismoscopes at distances of a few tens of kilometers. At several hundred kilometers, the relation underestimates the Wood-Anderson response by as much as a factor of two. The spread in Jennings and Kanamori's estimate of ML for the 1906 San Francisco earthquake, recorded on seismoscopes having relatively low natural frequencies (0.26 and 0.5 Hz), is reduced by the results in this paper—the upper value, from a seismoscope in Carson City, Nevada, at 290 km from the fault, going from ML = 7.2 to ML = 7.0 and the lower value, from Yountville, California (R ≈ 60 km), going from about 6.3 to 6.4. About 0.3 units of the remaining spread may be due to local geologic site conditions. If the 0.3 units is distributed equally between the Yountville and Carson City recordings, the estimates of ML for the San Francisco earthquake then become 6.5 and 6.8, somewhat lower than Jennings and Kanamori's final estimates of 634 to 7. Although the error in using the relation of Jennings and Kanamori to estimate Wood-Anderson response was at most a factor of 1.6 for the 1906 earthquake, the error can be substantially larger for smaller earthquakes recorded on similar low frequency seismoscopes.The relation between Wood-Anderson and seismoscope response used by Jennings and Kanamori can be combined with an empirical relation between peak horizontal velocity and Wood-Anderson response to predict peak velocity from seismocope recordings. The simulations show that this relation (vmax = 8.1Awa, where vmax is the peak horizontal velocity in centimeters/second and Awa is one-half the range of the Wood-Anderson motion in meters) forms a lower bound for estimates of peak velocity from seismoscope recordings. The relation is good for stations within about 100 km of earthquakes with moment magnitudes of about 4.5 to 6.5, and it underestimates peak velocity by factors up to 2 or 3 for larger earthquakes at distances within 100 km. An application of the simulation method to the 1976 Guatemala earthquake (moment magnitude = 7.6) results in 37 cm/sec as a lower bound to vmax, with 66 cm/sec as a more likely value, from the seismocope recording in Guatemala City (approximately 25 km from the Motagua fault).
Seismic moments, local magnitudes, and coda-duration magnitudes for earthquakes in central California
Authors: Bakun William H. 
Published: July 2021

AbstractOnscale seismograms recorded at stations in the U.S. Geological Survey's (USGS) central California seismic network (CALNET) have been used to estimate the seismic moment M0 and local magnitude ML for earthquakes of 1 ≦ ML ≦ 4 located on the San Juan Bautista and Parkfield sections of the San Andreas fault, the Coyote Lake section of the Calaveras fault, the Sargent fault, and near Livermore. These data, together with M0 and ML estimates for 4 ≦ ML ≦ 6 earthquakes in these areas, cannot be fit with a single linear log M0-versus-ML relation. Rather, the data are consistent with log M0 = 1.5 ML + 16 for 3 ≲ ML ≲ 6, with log M0 = 1.2 ML + 17 for 1 1/2 ≲ ML ≲ 3 1/2 and with a slope of ⅔ to 1 fro 1/2 ≲ ML ≲ 1 1/2.Whereas USGS coda duration magnitude MD is consistent with ML for 1 1/2 ≲ ML ≲ 3¼, MD is larger than ML at ML ≲ 1 1/2 and smaller than ML at ML ≳ 3¼. Log M0 can be estimated to a precision of 0.2 for 1 ≦ MD ≦ 3 1/2 earthquakes in central California by applying log M0 = 1.2 MD + 17 to the MD that have been routinely published by the USGS.
Reconnaissance seismic refraction-reflection surveys in northwestern New Mexico
Authors: Jaksha Lawrence H. , Evans David H. 
Published: July 2021

AbstractA velocity model of the crust in northwestern New Mexico has been constructed from an interpretation of direct, refracted, and reflected seismic waves. The model suggests a sedimentary section about 3 km thick with an average P-wave velocity of 3.6 km/sec. The crystalline upper crust is 28 km thick and has a P-wave velocity of 6.1 km/sec. The lower crust below the Conrad discontinuity has an average P-wave velocity of about 7.0 km/sec and a thickness near 17 km. Some evidence suggests that velocity in both the upper and lower crust increases with depth. The P-wave velocity in the uppermost mantle is 7.95 ± 0.15 km/sec. The total crustal thickness near Farmington, New Mexico, is about 48 km (datum = 1.6 km above sea level), and there is evidence for crustal thinning to the southeast.
Short- and long-period subevents of the 4 February 1965 Rat Islands earthquake
Authors: Mori Jim 
Published: July 2021

AbstractShort- and long-period records of the P wave of the 1965 Rat Islands earthquake were analyzed to locate subevents within the main rupture. Four subevents were identified on the short-period records in the first 100 sec and on the two long-period records in the first 30 sec. The short-period subevents cluster in an area 100 km south of the initial epicenter which appears to be off of the main fault plane, an area in which two larger aftershocks have relatively high stress drops. The long-period subevents are located 90 km west of the initial epicenter. The times and locations of the first short- and long-period subevents indicate they were triggered by a front moving near the P-wave velocity.
Experimental study of soil-structure interaction at an accelerograph station
Authors: Crouse C. B. , Liang George C. , Martin Geoffrey R. 
Published: July 2021

AbstractForced harmonic vibration tests, using eccentric mass shakers, were conducted at the Jenkinsville, South Carolina, accelerograph station to determine the effect of soil-structure interaction on the motions recorded during four small magnitude earthquakes. The station consisted of a 4′ × 4′ × 2′ concrete pad that was embedded in a stiff clayey to medium sandy silt with a shear-wave velocity estimated at 500 fps. A five-foot-high wooden hut was attached to the pad and provided shelter to the SMA-1 accelerograph, which was bolted directly to the pad. The real parts of complex foundation impedance functions, which were obtained by solving the equations of motion for the vibration tests, were generally similar to the theoretical impedance functions for an embedded rectangular foundation. However, the imaginary parts, which are a measure of the foundation damping, were closer to the theoretical prediction for a surface foundation. The tests also showed that the soil-pad-hut system had two strongly coupled translational and rocking modes of vibration in the frequency range of 1 to 60 Hz. The first mode occurred at approximately 11 Hz (N40°W direction) and 17 Hz (N50°E direction) and involved mostly the response of the hut, while the second mode occurred at approximately 50 Hz in both directions and involved mostly the response of the concrete pad. Approximate transfer functions between the motions recorded at the station during the earthquakes and the free-field motions were computed from the experimental data. These functions showed significant amplification in the frequency band 20 to 50 Hz with a maximum amplification of 3 occurring at 50 Hz. Some measurable amplification also was observed at the fundamental natural frequencies in both directions. Calculations based on the transfer functions indicated that the average response spectra of the recorded earthquake motions were amplified by an average of about 30 per cent for frequencies greater than 15 Hz. These results suggest that careful attention must be given to the design of accelerograph stations if they are to record true ground motions over a wide frequency range.
Direct observation of rupture propagation during the 1979 Imperial Valley earthquake using a short baseline accelerometer array
Authors: Spudich Paul , Cranswick Edward 
Published: July 2021

AbstractThe 1979 Imperial Valley, California, earthquake (Ms = 6.9) was recorded on the El Centro differential array, a 213-m-long linear array of 5 three-component digital accelerometers 5.6 km from the nearest tectonic surface rupture. Although absolute time was not recorded on the array elements, a relative time base was established using the main shock hypocentral P wave and the P and S waves from a later aftershock. A cross-correlation technique was used to measure the difference in arrival times of individual seismic waves in a moving 0.6 to 1.2 sec window at each array element, which would then be converted into the wave's slowness (1/velocity) along the array. When applied to the main shock vertical and horizontal accelerograms, results from both components of motion indicated that the early arriving energy came from a source to the south of the array, and the source of the energy moved rapidly to the north of the array during the strong shaking. The ground motions at the array elements were well correlated for about the first 11 sec of motion. These observations suggest that we have observed the initiation of rupture south of the array and its subsequent propagation along the fault to a position north of the array in about 10 sec, and that the energy was radiated from a fairly compact region around the rupture front. If the observed vertical and horizontal ground motions are assumed to be caused by P and S waves, respectively, then the observed slownesses show irregularities which can be interpreted as implying that the observed high-frequency ground motions originated at irregularly distributed regions on the fault surface, or that the rupture velocity was variable, or both. One possible interpretation of the data suggests that the rupture proceeded at near P-wave velocity over a 7-km-long section of fault. Average rupture velocities of about 2.7 to 3.2 km/sec at 8 km depth are consistent with the data, and 2.8 km/sec is weakly preferred under the assumption that rupture propagates at a fixed fraction of the shear velocity. The large vertical pulse, which had a peak acceleration of 1.7 g at E06, was emitted from the portion of the fault extending 25 to 30 km northwest of the hypocenter near Meloland overpass, and not from the point on the fault closest to the differential array. Nothing can be said about fault behavior southeast of the hypocenter.