bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismic codaQand scaling law of the source spectra at the Aeolian Islands, southern Italy
Authors: Del Pezzo E. , Ferulano F. , Giarrusso A. , Martini M. 
Published: July 2021

abstractThe model developed by Aki and Chouet for the coda wave generation and propagation has been used to calculate the quality factor Q for the zone of the Aeolian Islands, southern Italy, in the frequency range of 1 to 12 Hz, and the scaling properties of the seismic spectrum in the magnitude range of 0.4 to 4.7.The Q found for the Aeolian area has a frequency dependence of the form Q = qfv. The absolute values of Q seem to be dependent on the station and location of the seismic events, confirming the strong lateral heterogeneities in the geological structure beneath the Aeolian Arc. A temporal variation has been noted in the Q calculated at Vulcano station (VPL) in a period of 3 weeks soon after the occurrence of a main shock of ML = 5.5 located near the station.The scaling behavior of this sequence is similar to that obtained in two areas of California and one portion of Japan, with a corner frequency that remains constant with an increasing seismic moment between magnitudes 1 and 4. It differs substantially from the scaling properties of the Hawaian earthquakes that show a linear pattern, without an increase of the stress drop with magnitude. The fact that Vulcano is an active volcano seems not to influence the scaling properties of the seismic sequence localized very near it. It probably indicates that the aftershocks used for calculating the scaling law are generated out of the volcanic complex Lipari-Vulcano, in a zone with a good capability of accumulating the stress.
Seismic quiescence, stress drops, and asperities in the New Hebrides arc
Authors: Wyss M. , Habermann R. E. , Heiniger Ch. 
Published: July 2021

abstract
The rate of occurrence of earthquakes shallower than 100 km during the years 1963 to 1980 was studied as a function of time and space along the New Hebrides island arc. Systematic examination of the seismicity rates for different magnitude bands showed that events with mb &lt; 4.8 were not reported consistently over time. The seismicity rate as defined by mb ≧ 4.8 events was examined quantitatively and systematically in the source volumes of three recent main shocks and within two seismic gaps. A clear case of seismic quiescence could be shown to have existed before one of the large main shocks if a major asperity was excluded from the volume studied. The 1980 Ms = 8 rupture in the northern New Hebrides was preceded by a pattern of 9 to 12 yr of quiescence followed by 5 yr of normal rate. This pattern does not conform to the hypothesis that quiescence lasts up to the mainshock which it precedes. The 1980 rupture also did not fully conform to the gap hypothesis: half of its aftershock area covered part of a great rupture which occurred in 1966. A major asperity seemed to play a critical role in the 1966 and 1980 great ruptures: it stopped the 1966 rupture, and both parts of the 1980 double rupture initiated from it. In addition, this major asperity made itself known by a seismicity rate and stress drops higher than in the surrounding areas. Stress drops of 272 earthquakes were estimated by the MS/mb method. Time dependence of stress drops could not be studied because of changes in the world data set of Ms and mb values. Areas of high stress drops did not correlate in general with areas of high seismicity rate. Instead, outstandingly high average stress drops were observed in two plate boundary segments with average seismicity rate where ocean floor ridges are being subducted. The seismic gaps of the central and northern New Hebrides each contain seismically quiet regions. In the central New Hebrides, the 50 to 100 km of the plate boundary near 18.5°S showed an extremely low seismicity rate during the entire observation period. Low seismicity could be a permanent property of this location. In the northern New Hebrides gap, seismic quiescence started in mid-1972, except in a central volume where high stress drops are observed. This volume is interpreted as an asperity, and the quiescence may be interpreted as part of the preparation process to a future large main shock near 13.5°S.
A regional magnitude scale for Brazil
Authors: Assumpção Marcelo 
Published: July 2021

abstractAn empirical amplitude-distance curve is determined for earthquakes registered at regional distances in conterminous Brazil. This curve is the basis of a regional magnitude scale, mR, using the maximum amplitude in the whole P-wave train with periods in the range 0.1 to 1.0 sec. In the distance range 200 ≦ R ≦ 1500 km, we findm R = log ⁡ ( A / T ) + 2.3 log ⁡ R − 1.48.This scale gives much better agreement with the teleseismic mb magnitudes than the values calculated using the regional Q factors of Gutenberg and Richter (1956). It is shown that, despite using a wide range of periods, mR should be a good estimate of the 1-sec teleseismic mb in the range 2 ≦ mb &lt; 5.
Two methods to improve location estimates—preliminary results
Authors: Chang A. C. , Shumway R. H. , Blandford R. R. , Barker B. W. 
Published: July 2021

abstractPreliminary test results of two new seismic epicenter location methods show that the methods are quite effective in reducing location errors.The first method assumes that a large part of the travel-time residuals is caused by differences between the actual structures at source and receiver, and the standard structure used in the program. To correct for both regions, tables of the differences between the half-way travel times from source to bottoming layer using the Herrin model, and various regional models, were computed. In application, the total travel-time correction for each source-to-station path is the sum of the down-ray correction of the source region and the up-ray correction of the receiver region. Resulting location errors are much smaller (about half) than the errors using the ordinary location method.The second method considers the possibility that stations in close proximity may be measuring essentially the same travel-time residual, leading to a consistent stochastic bias. The assumption that the bias is stochastic can be modeled in terms of a correlation matrix for the residuals which varies according to the separation between two stations. The method adjusts the weighting of travel-time residuals in accordance with their overall intercorrelation matrix so that a large cluster of stations will not exert an inordinate effect on the estimated location. It thus becomes unnecessary to “balance” networks. Correlation coefficients estimated with 186 station residuals from LONGSHOT, were 0.7 for the O° to 5° distance range, 0.3 for the 5° to 10° range, and 0 for distances greater than 10°. For ease of computation, 184 stations were separated into nine geographical groupings. It was necessary to smooth the resulting correlation matrix to ensure a positive definite matrix. The LONGSHOT location error with the smoothed correlation matrix was reduced to 3.2 km, and the computational confidence intervals include the true location.
A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes
Authors: Barker Jeffery S. , Langston Charles A. 
Published: July 2021

abstractTeleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.
Variability in ground motions: Root mean square acceleration and peak acceleration for the 1971 San Fernando, California, earthquake
Authors: McCann Martin W. , Boore David M. 
Published: July 2021

abstractData from the 1971 San Fernando, California, earthquake provided the opportunity to study the variation of ground motions on a local scale. The uncertainty in ground motion was analyzed by studying the residuals about a regression with distance and by utilizing the network of strong-motion instruments in three local geographic regions in the Los Angeles area. Our objectives were to compare the uncertainty in the peak ground acceleration (PGA) and root mean square acceleration (RMSa) about regressions on distance, and to isolate components of the variance. We find that the RMSa has only a slightly lower logarithmic standard deviation than the PGA and conclude that the RMSa does not provide a more stable measure of ground motion than does the PGA (as is commonly assumed). By conducting an analysis of the residuals, we have estimated contributions to the scatter in high-frequency ground motion due to phenomena local to the recording station, building effects defined by the depth of instrument embedment, and propagation-path effects. We observe a systematic decrease in both PGA and RMSa with increasing embedment depth. After removing this effect, we still find a significant variation (a standard deviation equivalent to a factor of up to 1.3) in the ground motions within small regions (circles of 0.5 km radius). We conclude that detailed studies which account for local site effects, including building effects, could reduce the uncertainty in ground motion predictions (as much as a factor of 1.3) attributable to these components. However, an irreducible component of the scatter in attenuation remains due to the randomness of stress release along faults during earthquakes. In a recent paper, Joyner and Boore (1981) estimate that the standard deviation associated with intra-earthquake variability corresponds to a factor of 1.35.
Three-dimensional ray tracing and the method of principal curvature for geometric spreading
Authors: Lee Jia-Ju , Langston Charles A. 
Published: July 2021

abstractA three-dimensional ray method is used to compute three components of ground motion for complex structures involving curved boundaries. The method of principal curvature is developed to compute geometrical spreading of rays. This method, commonly used in electromagnetic wave propagation problems, employs phase matching at model interfaces and analysis of the wave front surface metric as the ray propagates throughout the model. It is an elegant way to examine the characteristics of three-dimensional caustics. Results computed for a two-dimensional canonical basin model with a plane SH-wave source are compared and are found to be in good agreement with those previously obtained by other independent numerical methods. Relaxing the restriction that the incident wave be perpendicular to the basin symmetry axis gives rise to large amplitude vertical and radial motions for incident SH waves and large tangential motions for incident P waves. As in the two-dimensional case, seismic energy is geometrically focused in the central region of the basin but strong later arrivals from the curved boundaries are not well developed in the three-dimensional case. The method is of direct use in analyzing three-dimensional crustal structure from off-azimuth P to S and S to P conversions.
Body-wave amplitude and travel-time correlations across North America
Authors: Lay Thorne , Helmberger Donald V. 
Published: July 2021

abstractRelationships between travel-time and amplitude station anomalies are examined for short- and long-period SH waves and short-period P waves recorded at North American WWSSN and Canadian Seismic Network stations. Data for two azimuths of approach to North America are analyzed. To facilitate intercomparison of the data, the S-wave travel times and amplitudes are measured from the same records, and the amplitude data processing is similar for both P and S waves. Short-period P- and S-wave amplitudes have similar regional variations, being relatively low in the western tectonic region and enhanced in the shield and mid-continental regions. The east coast has intermediate amplitude anomalies and systematic, large azimuthal travel-time variations. There is a general correlation between diminished short-period amplitudes and late S-wave arrival times, and enhanced amplitudes and early arrivals. However, this correlation is not obvious within the eastern and western provinces separately, and the data are consistent with a step-like shift in amplitude level across the Rocky Mountain front. Long-period S waves show no overall correlation between amplitude and travel-time anomalies.
Seismicity in the St. Elias region of northwestern Canada and southeastern Alaska
Authors: Horner Robert B. 
Published: July 2021

abstractLow-level monitoring in the St. Elias region between September 1978 and March 1981 has identified two principal zones of seismicity that are consistent with the historical pattern of seismicity at higher magnitude levels. The most active zone follows the plate boundary along the coast of southeast Alaska. A recurrence relation based on completeness over varying time intervals is log(N ≧ M) = −0.74M + 3.77. A less active zone is observed generally following the Duke River and Dalton segments of the Denali fault system through the southwest Yukon. Instead of continuing into Chatham Strait, this trend of seismicity turns south into the Glacier Bay region to connect with the Fairweather fault north of Cross Sound. The seismicity and high rate of uplift observed in the Glacier Bay region is probably the result of convergence across the Fairweather fault north of Cross Sound. The recurrence relation for the Denali zone is log(N ≧ M) = −0.90M + 3.77. A similiar recurrence curve is found for activity with magnitudes down to about 2.0 observed over the 39-month low-level monitoring program. The rate of activity in the Denali zone appeared to decrease for a period of about 1 yr following the 28 February 1979, M 7.2 St. Elias earthquake. The rate of aftershock activity was also found to vary, with the b value decreasing throughout the sequence. Only minor seismicity is observed northeast of the Denali fault system in the southwest Yukon and east of Chatham Strait in northwest British Columbia. A prominent cluster east of Juneau near the British Columbia border may be related to volcanic activity.A 5-week microearthquake survey over a 40-km segment of the Denali fault system found activity in a highly faulted zone about 15 km wide at depths of less than about 15 km. A composite P-nodal solution indicates motion on either east-west or north-south striking planes, neither of which are consistent with the general trend of the Denali system in the area. An average slip rate of no more than about 1 mm/yr is estimated from the seismicity for the Denali fault system through the southwest Yukon. An estimate of the minimum present accumulated elastic strain suggests the potential for a magnitude 612 earthquake.
Uncertainties in probabilistic seismic hazard assessment as a function of probability level: A case history for Vancouver, British Columbia
Authors: Atkinson Gail M. , Charlwood Robin G. 
Published: July 2021

abstractThe stability of probabilistic methods of evaluating expected strong ground motion levels is examined as a function of probability level. A case history for Vancouver, British Columbia, is used to show that when input parameters are screened on the basis of compatibility with low probability calculations, robust (±25 per cent) results are obtained for probabilities in the range of 10−2 to 10−4 per annum. There is no inherent loss of stability with decreasing probability.Probabilistic approaches are not in conflict with deterministic approaches, since deterministic data can be incorporated into the analysis. The usefulness of the probabilistic approach lies in providing a framework for evaluating uncertainties.
Seismicity of the Teton-southern Yellowstone region, Wyoming
Authors: Doser Diane I. , Smith Robert B. 
Published: July 2021

AbstractEpicenter patterns, focal depths, and focal mechanisms for earthquakes occurring between 1973 and 1981 in the Teton-Jackson Hole-southern Yellowstone region are presented in this study. Available earthquake information recorded prior to 1980 was combined with the results obtained from two microearthquake surveys operated in 1980 and 1981. Earthquakes used in this joint analysis met rigid standards for location accuracy, and hence the resulting data set provides the most complete, accurate and up-to-date information on seismicity in this region.The majority of earthquakes in the region do not appear to be associated with mapped traces of Quaternary faults. The Teton fault appears to be active at the small earthquake level along some of its segments, although several segments, including the north-central segment which exhibits the greatest prehistoric displacement, appear to be quiescent. Seismicity in the Gros Ventre Range may be related to reactivation of older basement structures. Fault plane solutions in the region show predominately normal faulting with extension in an east-west to northwest-southeast direction.Geologic seismic moment rates of 1.1 × 1024 dyne-cm/yr for the Teton region and 4.0 × 1023 dyne-cm/yr for the Teton fault were estimated using available geologic information on mapped faults. From the limited available data, a return period of 130 to 155 yr for a magnitude 6.5 to 7.5 earthquake is predicted for the Teton region, while the Teton fault has a predicted return period of 800 to 1800 yr for a magnitude 7.5 earthquake. A regional strain rate of 6.9 × 10−9/yr is also obtained.
Rupture complexity of the 1970 Tonghai and 1973 Luhuo earthquakes, China, from P-wave inversion, and relationship to surface faulting
Authors: Zhou Hui-lan , Allen Clarence R. , Kanamori Hiroo 
Published: July 2021

Abstract
The source processes of the 4 January 1970, Tonghai earthquake (Ms = 7.5) and the 6 February 1973, Luhuo earthquake (Ms = 7.5) in southwestern China were investigated using an inversion technique on the very complex body waves. The two earthquakes were associated with 48 and 90 km of surficial strike-slip rupture, respectively, and the distribution of displacement with distance along the fault was well documented by field studies of both events. The source process for both earthquakes comprised three to four subevents with different moments and rupture durations. These calculated parameters agree well with the field observations and aftershock distributions, particularly in the total rupture length and in the amount and asymmetry of fault displacements relative to the locations of the main epicenters.
Short-periodLgmagnitudes: Instrument, attenuation, and source effects
Authors: Herrmann Robert B. , Kijko Andrzej 
Published: July 2021

AbstractThe applicaton of the Nutli (1973) definition of the mbLg magnitude to instruments and wave periods other than the short-period WWSSN seismograph is examined. The basic conclusion is that the Nuttli (1973) definition is applicable to a wider range of seismic instruments if the log10(A/T) term is replaced by log10A. For consistency and precision, the notation mbLg should be applied only to magnitudes based upon 1.0 Hz observations. The mbLg magnitude definition was constrained to be consistent with teleseismic P-wave mb estimates from four Central United States earthquakes. In general, for measurements made at a frequency f, the notation mLg(f) should be used, wherem L g ( f ) = 2.94 + 0.833 log ⁡ 10 ( r / 10 ) + 0.4342 γ r + log ⁡ 10 A ,and r is the epicentral distance in kilometers, γ is the coefficient of anelastic attenuation, and A is the reduced ground amplitude in microns. Given its stability when estimated from different instruments, the mLg(f) magnitude is an optimum choice for an easily applied, standard magnitude scale for use in regional seismic studies.
Rayleigh wave scattering at various wedge corners
Authors: Fujii Kazunari , Takeuchi Shozaburo , Okano Yukio , Nakano Masayoshi 
Published: July 2021

AbstractA system of model experiment is constructed in order to measure the reflection and transmission coefficients of Rayleigh wave at wedge comers with the wedge angle from 39° to 154°. The measurement is performed according to the change of each 1° in wedge angle. A theoretical result is also derived about these coefficients, which is numerically calculated and, practically, recognized to be almost exact. Within the range of wedge angle in which the theoretical calculation can be performed, both experimental and theoretical results coincide very well with each other, and hence, the experimental result will be considered reliable even outside of this range. For a few different values of Poisson ratio of medium, the curves denoting variations of the coefficients are theoretically obtained, and a characteristic feature of Rayleigh wave scatterings at wedge corners is pointed out.
Observations of hard-rock site effects
Authors: Tucker B. E. , King J. L. , Hatzfeld D. , Nersesov I. L. 
Published: July 2021

AbstractDifferences were measured in seismograms recorded at eight proximate hardrock sites: five in tunnels and three on outcrops on hills. Tunnel sites affected the amplitude of incident signals by as much as a factor of three, at frequencies inversely proportional to the depth of the site into the tunnel. For example, the maximum effect of a site 12 m deep was at 25 Hz while that of a site 85 m deep was at 11 Hz. Most of the observed tunnel effects could be explained in terms of interference between the incident and surface-reflected waves. Rock outcrop sites on hills affected the amplitude of incident signals by as much as a factor of eight, at frequencies inversely proportional to the dimension of the hill, and more for horizontally than for vertically polarized signals. Hard-rock site effects typically varied by no more than a factor of three for input signals from different earthquakes, having widely different azimuth and incident angles.