bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention of Youth Involvement in Religious and Cult Organizations via the Online Space
Authors: Mironova O.I.
Published: July 2021

The results of an empirical study related to the problem of preventing the involvement of modern youth in religious and cult organizations through the Internet are presented in the article. An effective tool for preventing the involvement of young people in religious and cult organizations through the Internet space is a specially developed author's program aimed at developing critical thinking, skills to resist manipulation, increasing the level of self-esteem and harmonizing family relations - it is assumed in the research hypothesis. 30 young people included in the control and experimental groups, 15 people in each, acted as respondents. The study included two measurements carried out before and after the implementation of the author's program. The methodology used was "Exposure to manipulation", "Study of general self-esteem", "Critical thinking", "The psychological climate of the family." The effectiveness of the author's program was proved thanks to the comparative analysis of the experimental group before and after the corrective action and the comparative analysis of the experimental and control groups after the experiment.
Diagnostic imaging in patients with mucopolysaccharidosis: important imaging patterns
Authors: Yarmola Igor I. , Anikin Anatoly V. , Fomina Lyubov E.
Published: July 2021

Background: The need for systematization, generalization and analysis of structural changes in various organs and systems that occur in patients with mucopolysaccharidosis (MPS). MPS is a rare disease, therefore, there is a lack of structured information in Russian publications in the field of radiology. Aims: The purpose of the study is to summarize our own experience, identifying the incidence of changes in various organs and describing the most significant changes and their causes. Identification of more informative and safe diagnostic methods of various organs, taking into account the specificity of changes in MPS. Methods: Retrospectively, 303 children with MPS of different types were examined (the sample included 70 cases verified by the laboratory studies and molecular genetics), the revision of tomograms and radiographs was carried out for the studies from 2015 to 2021. All the patients underwent MRI of the brain and cervical spine, X-ray of the skeletal bones. Results: The analysis of the obtained images revealed the most common changes, such as dysostosis (in 100%; 70 patients), stenosis of the spinal canal at the craniovertebral level (73%; 51 patients), atrophy (47%; 33 patients) and focal lesions of the brain substance (67%; 47 patients), hydrocephalus (28%; 20 patients), expansion of the perivascular spaces (70%; 58 patients). The pathophysiological mechanisms of the occurrence of structural changes have been analyzed and described. Conclusions: The assessment and comparison of various diagnostic methods for different organs and systems has demonstrated that MRI is the most informative imaging method for the assessment of the craniovertebral junction. Given the lower radiation exposure compared to computed tomography, it is preferable to use digital radiography for examining the bones of the extremities.
Earthquake prediction: What we have learned and what we should do now
Authors: Evernden Jack F.
Published: July 2021

abstract

Adopting out of necessity a definition of “earthquake prediction” which stresses short-term warnings (months, weeks, day, and hours), I must conclude that either we are doing the wrong things or such predictions may be impossible. Assuming the former, I recommend major emphasis on direct or nearly direct measurements of stress/strain change in or across fault zones in the immediate vicinity of strong points or “asperities” (how do you find asperities?). This recommendation presupposes essentially total emphasis of the United States' program in California. Even if this recommendation is unpalatable, it is certain that resources now available require a total reanalysis of the present program and a consequent reallocation of funds.
Parametric study of near-field ground motions for oblique-slip and dip-slip dislocation models
Authors: Anderson John G. , Luco J. Enrique
Published: July 2021

abstract

The near-field motion on the surface of a uniform half-space for oblique-slip and dip-slip faults has been studied by the use of a dislocation model. The fault is modeled by an infinitely long buried dislocation of finite width; rupture propagates horizontally along the fault and past the observation points with a constant rupture velocity lower than the Rayleigh wave velocity. In addition to those parameters which control peak amplitudes near a vertical, strike-slip fault (depth of the top of the fault, horizontal rupture velocity), the dip of the fault plays an important role. The slip direction and the angle between the rupture front and the down-dip direction of the fault also become increasingly important in determining amplitudes of peak ground motions as the dip of the fault decreases from vertical to shallow angles. In some regions near a thrust fault, peak amplitudes are significantly greater than the largest values near a vertical, strike-slip fault.
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

abstract

The 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 < 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

abstract

An 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 find

m 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 < 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

abstract

Preliminary 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

abstract

Teleseismic 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

abstract

Data 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

abstract

A 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

abstract

Relationships 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

abstract

Low-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

abstract

The 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

Epicenter 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

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

The 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, where

m 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

A 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

Differences 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.
Observed variations of earthquake motion across a sediment-filled valley
Authors: King J. L. , Tucker B. E.
Published: July 2021

The response to earthquake motion of a site in one sediment-filled valley was observed to depend strongly on frequency and the position of the site within the valley and weakly on the input signal's azimuth and incidence angles. The observed input motion was weak, varying between 10−5 and 10−3g. Measurements of ground velocity were made on profiles across and along the valley and simultaneously on two nearby rock sites. The valley was 400 m wide and 700 m long, with a maximum sediment thickness of 60 m. The average seismic impedance contrast between the sediments and underlying basement rock was about 6:1.

Ratios of Fourier spectra from soil sites to spectra from nearby rock sites showed apparent site amplifications of as much as a factor of ten, depending strongly on frequency and the distance of the site from the valley edge. The scatter in spectral ratios for earthquakes with different azimuths and angles of incidence was about a factor of two; thus local site effects that changed the amplitude of incident motion by a factor of two or more could be identified in the records of most earthquakes. Ground motion at valley-edge and mid-valley sites, separated by less than 100 m, differed by as much as a factor of five. This difference could cause large differential motion in structures spanning these sites.

A theoretical, flat layer model of sediment response predicts the average behavior of the middle of the valley but not that of the valley edge. The lowest frequency responance apparently involves the sediments across the width of the valley, not just the vertical column of soil beneath each site.
Study of the 6 June 1977 Lorca (Spain) earthquake and its aftershock sequence
Authors: Mezcua J. , Herraiz M. , Buforn E.
Published: July 2021

On 2 May 1977, a portable array of five stations was installed for the reconnaisance of the Alhama de Murcia fault in southern Spain. During this survey on 6 June 1977, a 4.2 mb (Lg) shock took place within the array and was followed by a long series of aftershocks. Due to the good quality of the records, a comprehensive study of location, magnitude, seismic moment, focal mechanism, and related parameters has been carried out. In the seismic moment calculation, we have used the coda wave analysis, which also gives information about Q values of approximately 320 and 617 for body and surface waves, respectively. In evaluating the focal mechanisms of the sequence, we have used a joint treatment which permits us to separate the two types of faulting involved in the rupture process. Finally, to interpret these results in terms of the tectonics of the region, the focal mechanism of the earthquake of 5 March 1981, which occurred in a neighboring area, has also been studied.
Earthquake frequency and prediction
Authors: Liu Zheng-rong
Published: July 2021

The coefficient p in n(t) = n1t−p, where n(t) is the daily count of earthquakes and n1 is the number of earthquakes on the first day following a larger earthquake, is ≦1 for foreshock sequences, ≳1 for double-main shock sequences, and »1 for aftershock sequences with a single largest earthquake. For p »1, the magnitude of the largest aftershock and the cutoff time of the aftershocks can be estimated. These observations are the basis for an earthquake prediction technique successfully used in the Peoples Republic of China (PRC).
An experiment in the retrieval of depth and source mechanism of large earthquakes using very long-period Rayleigh wave data
Authors: Romanowicz Barbara , Guillemant Philippe
Published: July 2021

The possibility of obtaining an estimate of depth for large earthquakes from low-frequency mantle wave data alone is investigated using moment tensor formalism.

After illustrating the sensitivity to depth of the eigenfunctions in the period range of 160 to 350 sec, we give several examples of application of the two-step inversion procedure proposed earlier for shorter period Rayleigh wave data (Romanowicz, 1982). We find that for earthquakes below a depth of about 50 km, we are able to resolve depth even when a spherically symmetric average Earth model is used for propagation corrections. This is particularly interesting in the case of large subduction zone earthquakes for which an estimate of the vertical extent of faulting can thus be obtained, independently of aftershock studies, in a very fast and simple manner which does not involve any synthetic seismogram calculations or lateral heterogeneity modeling.

For shallower earthquakes, especially those with one steeply dipping nodal plane, the resolution of depth is less precise. Taking lateral heterogeneity into account by using available regionalized phase velocities improves the results marginally. We anticipate that accounting more accurately for the low-order harmonics in the worldwide phase velocity distribution should prove most helpful, since these interfere the most with the theoretical radiation patterns of earthquakes. The determination of depth depends more critically on the source process time, which has to be accounted for especially for horizontally propagating faults.
Seismicity and waveforms of the microearthquakes before and after the Shizuoka-Seibu earthquake, central Japan
Authors: Ishida Mizuho , Ohtake Masakazu
Published: July 2021

Investigating the foreshock-main shock-aftershock sequence of the Shizuoka-Seibu earthquake (M = 2.8, 16 January 1981), central Japan, we found evidence that suggests high stress conditions for the foreshock period. The source dimension of the main shock was roughly estimated to be about 0.5 × 0.2 km2. The m value of the Ishimoto-lida's formula was 1.87 for foreshocks and 2.37 for aftershocks.

Waveforms of the foreshocks, main shock, and aftershocks were similar to each other. However, the amplitude ratio of the low (0.9 to 0.8 Hz) to high (3.5 to 10 Hz) frequency band was different between the foreshocks and aftershocks. The ratio for the foreshocks was lower than that for the aftershocks, indicating that the foreshocks contain more high-frequency energy than the aftershocks. The Shizuoka-Seibu sequence included a larger number of foreshocks (70) compared to aftershocks (43). This characteristic, in contrast with large earthquakes, was found common to small-sized earthquakes occurring in the neighborhood areas. These observations can be interpreted based on the asperity model.
Stochastic slip-predictable model for earthquake occurrences
Authors: Kiremidjian Anne S. , Anagnos Thalia
Published: July 2021

A slip-predictable stochastic model is presented based on Markov renewal theory. Times between successive events are assumed to be Weibull-distributed with an increasing hazard rate. The model forecasts probabilities of earthquake occurrences conditional on the time of occurrence of the last event. The hazard along the Middle America Trench, Mexico, where data has suggested slip-predictable behavior, is obtained for illustrative purposes. Comparisons of this model with the Poisson model show that probability forecasts are underestimated with the Poisson model when there has been a seismic gap. The slip-predictable stochastic model presented in this paper represents a considerable improvement over the existing seismic hazard analysis methods. However, further testing of the model is necessary prior to wider application.
The effects of tectonic release on short-periodPwaves from NTS explosions
Authors: Lay Thorne , Wallace Terry C. , Helmberger Don V.
Published: July 2021

The first cycle (ab amplitude) of teleseismic short-period P waves from underground nuclear explosions at Pahute Mesa (NTS) show a systematic azimuthal amplitude pattern that can possibly be explained by tectonic release. The amplitudes vary by a factor of three, with diminished amplitudes being recorded at azimuths around N25°E. This azimuthal pattern has a strong sin(2φ) component and is observed, to varying degrees, for 25 Pahute Mesa events, but not for events at other sites within the NTS. Events that are known to have large tectonic release have more pronounced sin(2φ) amplitude variations. A synthesis of long-period body and surface wave investigations of tectonic release for Pahute Mesa events shows that, in general, the nonisotropic radiation is equivalent to nearly vertical, right-lateral strike-slip faulting trending from N20°W to due north. Long-period P waves at upper mantle distances demonstrate that there is a significant high-frequency component to the tectonic release. Using the long-period constraints on orientation, moment, and frequency content of the tectonic release, the expected short-period P wave effects are predicted. For models in which the downgoing P wave from the explosion triggers tectonic release within a few kilometers below the shot point, a factor of 2.5 amplitude variation with azimuth is predicted for the short-period ab amplitudes, with the lowest amplitudes expected near N25°E. Rather subtle azimuthal variations in the waveforms are expected, particulary for downward propagating ruptures, which is consistent with the absence of strong variations in the data. The occurrence of the azimuthal pattern, albeit with varying strength, for all of the Pahute Mesa events suggests a tectonic release model in which the shatterzone surrounding the explosion cavity is extended preferentially downward by driving a distributed network of faults and joints underlying the Mesa several kilometers beneath the surface. In this model, all events could have a component of tectonic release which would reflect the regional stress regime, although there may be slight spatial and temporal variations in the tectonic release contribution. Some events may trigger slip on larger throughgoing faults as well. While it is shown that tectonic release can affect teleseismic short-period signals significantly, and may contribute to the Pahute Mesa amplitude pattern, other possible explanations are considered.
Seismicity changes prior to several great earthquakes in the circum-Pacific area
Authors: Acharya Hemendra
Published: July 2021

Spatio-temporal variation in earthquake activity, prior to several post-1950 earthquakes with magnitude ≧ 8.0 in the circum-Pacific area, has been examined in order to identify a common precursory pattern. Strain energy ΣE released in the rupture zone of these great earthquakes was computed for every year between 1910 and the time of the great earthquake. An examination of strain energy release as a function of time shows that maximum strain energy Σ(EB) is released in the rupture zone at a time which depends on the magnitude (M) of the subsequent great earthquake. The ratio of strain energy ΣEM released in the great earthquake to the strain energy ΣEB varies between 3 and 30, i.e., this burst of activity is equivalent to a single earthquake of magnitude between 12 to 2 units less than the magnitude of the great earthquake. The amount of maximum deformation and the time at which it occurs appears to depend on the magnitude of the great earthquake.
Estimates of magnitudes and short-period wave attenuation of Chinese earthquakes from Modified Mercalli intensity data
Authors: Chen Peishan , Nuttli Otto W.
Published: July 2021

Intensity data for Chinese earthquakes are used to estimate the body-wave magnitude, mb, of selected historical earthquakes and to estimate Q0, the 1-sec period Q value of Lg waves for various geographical areas of China. In order to derive the necessary empirical relation between the intensity distribution and mb, data are used from recent earthquakes, for which instrumentally obtained mb values as well as isoseismal maps are available. Average Qo values are approximately 175 for the mountainous regions of southwest China, 550 for southeastern China, and 150 for Taiwan. These values agree qualitatively with those obtained by Evernden (1983) and Chen et al. (1983), who utilized a different method of analysis of the intensity data
A two-state Poisson model for seismic hazard estimation
Authors: Bender Bernice
Published: July 2021

Most seismic hazard analyses assume that earthquakes have a Poisson distribution and that data from recorded earthquakes can be used to predict future seismic activity in a region. Historic catalogs, however, may show different earthquake occurrence rates for regions that are geologically similar, suggesting, on a local scale at least, temporal variations in seismicity. The simple two-state model presented here allows a region to have both seismically “active” and “inactive” states; in this model, earthquakes have a Poisson distribution during both states, but occur at a higher rate when the region is “active.” The probability of changing from one state to the other at any time is constant. The two-state model reduces to the usual Poisson model if the region is always “active” or if the rate is the same for both states.
Analysis of upper mantle structure using wave field continuation ofPwaves
Authors: Walck Marianne C. , Clayton Robert W.
Published: July 2021

Wave field continuation transforms seismic record section data directly into velocity-depth space, simultaneously providing an estimate of model nonuniqueness. This inversion, previously used for reflection and refraction data, converts readily to spherical earth problems through simple adjustments in each of the two linear transformations: the slant stack and downward continuation. Because the time resolution inherent in the data transforms to depth resolution in the model space, this method is extremely useful for analysis of data compatibility with preexisting models and direct comparison between data sets, as well as the complete inversion of raw data for structure. Wave field inversion demands densely sampled, digital data, and assumes source coherency and lateral homogeneity along the profile.

We test this technique for upper mantle analysis using a previously studied, large, array-recorded data set representative of structure beneath the Gulf of California. We compare slant stacks and downward continuations of both synthetic and data record sections to illustrate the method's resolution capability. Wave field continuation proves particularly useful in comparing entire data sets to various models; even subtle structural differences are resolvable given good data quality.
Historical seismicity and rates of crustal deformation along the margins of the Ordos block, north China
Authors: Wesnousky S. G. , Jones L. M. , Scholz C. H. , Deng Qidong
Published: July 2021

Earthquakes in China show an empirical relation between seismic moment (M0) and the areal distribution of Modified Mercalli intensities VI and VIII (log M0 = 16.66 + 0.91 log AVIII and log M0 = 14.35 + 1.16 log AVI, where A and M0 are measured in squared kilometers and Newton-meter, respectively). The empirical relations may be used to estimate M0 for historical earthquakes in China to within a factor of three, on average, when sufficient isoseismal data exist. This observation and an extensive collection of isoseismal maps are used to estimate M0 for large earthquakes that occurred along the margins of the Ordos block during the last 700 yr. Focal parameters of the historical events are inferred from the orientation and displacements across Quaternary faults. Average rates of crustal deformation are then estimated from the 700-yr historical record with formulas that relate the occurrence rate of seismic moment in a region to rates of crustal strain. The Shanxi and northern Ningxia graben systems are situated along the eastern and northwestern edges of the Ordos block, respectively. Normal faults in the two systems trend northeasterly and are characterized by a component of right-lateral slip. The deformation resulting from slip during earthquakes in each of the respective fault systems is estimated at about 0.5 to 1.0 mm/yr of both right-lateral shear and north by northwest extension. The Weihe graben system bounds the southern edge of the Ordos block, strikes easterly and conjugate to the Shanxi and northern Ningxia fault systems, and exhibits left-lateral normal fault displacements. The average rate of deformation across Weihe is described by about 1.0 mm/yr of north by northwest extension and 1.5 mm/yr left-lateral east-west shear. The Hetao fault system delineates the northern edge of the Ordos block and displays Quaternary faults similar in orientation and mechanism to that observed in Weihe. Although mapped faults in Hetao exhibit evidence of Quaternary displacement, crustal deformation rates are not estimated because there exists no historical record of large earthquakes in the area. In southern Ningxia, at the southwest boundary of the Ordos block, deformation occurs by slip on left-lateral strike-slip faults oriented in an easterly azimuth and thrust faults with strikes ranging from southeast to south. The average deformation rate in southern Ningxia is found to be about 4.0 mm/yr of east by northeast contraction and 10.0 mm/yr of left-lateral shear. Deformation of each of the fault systems is consistent with a regional compressive stress that trends northeast and results in an average of about 3.0 mm/yr each of contraction at N70°E and extension of N160°E across the entire region. Inasmuch as uncertainties in estimates of M0 for historical earthquakes are about a factor of three, a similar uncertainty is attached to rates of crustal strain determined in this manner.
TheMLscale in central California
Authors: Bakun William H. , Joyner William B.
Published: July 2021

Nine hundred fifty-seven maximum zero-to-peak Wood-Anderson amplitudes A (synthesized or recorded) from 40 horizontal-component seismographs (20 sites) with 0 ≲ Δ ≲ 400 km for 106 earthquakes with 18 ≦ log M0 ≦ 22.3 in central California have been fit in a least-squares sense using the parametric form log A ij = − n log R ij − K R ij − ∑ l = 1 40 S l δ ij + ∑ k = 1 106 C k δ ik where Aij = A (mm) for earthquake i on seismograph component j, δik = Kronecker delta, R = hypocentral distance, and n, K, Sl, and Ck are variables determined by regression analysis. The Ck are a magnitude measure, and the Sl are station corrections constrained to have zero average. We find n = 1.018 ± 0.107 and K = 0.00291 ± 0.00070 km−1. Setting n = 1, appropriate for body-wave propagation in homogeneous media, yields K = 0.00301 ± 0.00036 km−1. Following Richter's definition of an ML = 3 earthquake as one for which A = 1 mm at Δ = 100 km and S1 = 0, we express the local magnitude ML as ML = log A − log A0, where -log A0 = n log (R/100) + K (R − 100) + 3. For 30 ≲ Δ ≲ 475 km, the -log A0 values using n = 1 and K = 0.00301 km−1 are within 0.15 of Richter's values for southern California. For Δ ≲ 30 km, Richter's values are significantly smaller than those obtained here, a result consistent with recent studies of −log A0 for southern California. Our results suggest that the ML scale as commonly used underestimates the sizes of small shocks that are predominantly recorded at Δ ≲ 30 km.