bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Ghir earthquake of April 10, 1972 in the Zagros Mountains of southern Iran: seismotectonic aspects and some results of a field reconnaissance
Authors: Dewey James W. , Grantz Arthur 
Published: September 2021

Abstract
The southern Iran earthquake of April 10, 1972 (Ms = 6.9) killed more than 5,000 people in the region of Ghir, Fars Province, in the folded belt of the Zagros Mountains. Aftershocks of the earthquake, relocated with respect to the hypocenter of the main shock by the method of joint hypocenter determination, and the radiation pattern of P and S waves suggest that the earthquake occurred on a west-northwest-striking reverse fault. This fault had a moderate dip and a strike that was parallel to the local trend of the folds and thrust faults of the Zagros folded belt, which are of latest Cenozoic (Pliocene and Quaternary) age. The inferred fault rupture of the main shock propagated approximately 35 km east-southeast from its epicenter, terminating in the epicentral region of a Ms = 5.6 earthquake that occurred on September 14, 1968. The zone of heaviest damage to adobe structures follows closely the trend indicated by the relocated epicenters of the main shock and principal aftershocks. Beyond 25 km from this trend, damage to adobe structures was negligible.
Earthquake modeling by stick-slip along precut surfaces in stressed foam rubber
Authors: Brune James N. 
Published: September 2021

AbstractStick-slip along precut surfaces in stressed foam rubber is similar to earthquake faulting, stick-slip in rock specimens, and theoretical predictions. An additional feature is the common occurrence of multiple events. A significant amount of slip occurs as fault creep.For simple one-slip events on a long fault, the peak particle velocities near the center of the fault average about half the value Δσβ/μ, with Δσβ/μ apparently being a good upper bound. The variation is probably due to focusing by rupture propagation. On a circular fault, the peak values average 3 to 4 times less, partly a result of a greater amount of fault creep, and probably, partly a result of focusing by rupture propagation. Total stress drops are typically about 10 to 20 per cent of the absolute stress, and during individual events about 80 to 90 per cent of the released strain energy is dissipated as friction.For multiple events the cumulative source time function is usually much longer than the source dimension divided by the shear-wave velocity. Thus, the far-field spectrum would have the shape for fractional stress drop, but the low-frequency spectral corner would not correspond to the fault dimension; thus, the inferred stress drops would be too low. Multiple events may explain some anomalously low inferred stress drops for small earthquakes and may partly explain the success of surface-wave excitation as a method of distinguishing underground nuclear explosions from earthquakes. Foam rubber models may be used to study strong motion around various types of faults and, thus, aid in the problem of microzonation.
Area-based tests of long-term seismic hazard predictions
Authors: Ward Steven N. 
Published: September 2021

Abstract
This article develops several area-based tests of long-term seismic hazard predictions. The tests stem from the hypothesis that the observed fractional area of hazard exceedence should follow in proportion to the region's predicted likelihood of exceedence. For example, a prediction is successful if roughly 30% of the area mapped as having a 30% likelihood of exceeding some hazard threshold in a certain time interval, actually does suffer this level of shaking. Although tests of earthquake predictions are always equivocal, the success or failure of a forecast hazard map can be argued strongly from a statistical assessment of the hundreds of individual point predictions comprising the map. The specific forecasts to be examined are the 30-yr probabilities of peak ground acceleration exceedence that were presented by Ward (1994) for southern California. In lieu of a lengthy historical set of recorded peak accelerations, observational data for the tests were derived from the 150-yr earthquake catalog and standard attenuation relationships. In all cases, the observed hazard ratios were highly correlated with the predictions. Within 95% confidence bounds, the observed levels of hazard coincided with the predicted hazard from models that included a low-magnitude cutoff of M = 5.5 to 6, approximately the same limit as enlisted in the earthquake catalog. I propose a pass/fail criterion for acceleration hazard maps and I suggest that all seismic hazard predictions submit to area-based tests.
Measurements of intrinsic and scattering seismic attenuation in the crust
Authors: Del Pezzo Edoardo , Ibanez Jesus , Morales José , Akinci Aybige , Maresca Rosalba 
Published: September 2021

Abstract
Intrinsic and scattering attenuation parameters, Qi and QS, have been measured in three different tectonic areas for local and shallow earthquakes located close to the receiver. The approach developed by Wennerberg (1993), which takes into account the numerical correction of the coda-Q parameter for the multiple scattering formulation of Zeng, was used to infer from the estimates of coda Q and direct S-wave Q the intrinsic (Qi) and scattering (QS) Q values. Results for 1 to 12 Hz range show that Qi is comparable to QS for the Etna volcano and for the Campi Flegrei area, while Qi for the tectonically active area of Granada is lower than QS. Coda Q is close to intrinsic Q, suggesting that, at least in the crust, coda Q is a good estimate of the intrinsic Q. Volcanic areas show a reasonable higher degree of heterogeneity, if compared with the nonvolcanic area of Granada.
Correlation of seismicity and water level in the Açu reservoir—an example from Northeast Brazil
Authors: Ferreira Joaquim M. , Oliveira Ronaldo T. De , Assumpção Marcelo , Moreira José A. M. , Pearce Robert G. , Takeya Mário K. 
Published: September 2021

Abstract
Seismic monitoring of the Açu reservoir (31-m depth, 2.4 × 109 m3 in volume), in Rio Grande do Norte State, Northeastern Brazil, started in 1987 about 2 years after impoundment. The largest earthquake so far (magnitude 2.8) occurred in August 1994. From 1987 to 1989, the monthly number of induced events had a clear correlation with the water level, with a 3-month delay, and the activity occurred mainly inside the reservoir. Although no preimpoundment monitoring had been carried out, the correlation of the water level and the seismicity strongly suggests the activity was induced by pore pressure diffusion. Since 1990, the activity migrated toward the border of the reservoir, and the number of events no longer correlated with the water level. A seismographic network was deployed around the reservoir during two field campaigns (1989 and 1990/91), showing that the activity occurred preferentially with strike-slip mechanisms on NE oriented faults. The E-W orientation of the P axes, parallel to the regional maximum horizontal stress, and the presence of many NE trending faults and fractures in the Precambrian basement near the reservoir, suggest that the probably induced seismicity was a typical case of water pore pressure facilitating earthquake occurrence in pre-existing zones of weakness under high regional stresses.
Search of a worldwide catalog for earthquakes triggered at intermediate distances
Authors: Lomnitz Cinna 
Published: September 2021

Abstract
An anomalous increase of seismicity was recorded at intermediate distances from the Landers, California, earthquake of 28 June 1992 (M = 7.3). Several authors have suggested that enhanced activity was triggered at distances of up to 17 fault lengths. We test a 90-year catalog of shallow world earthquakes (M &gt; 7) for evidence of this effect. It is found that triggering is present even at these high magnitude levels. The pattern of enhanced activity comprises two concentric regions: (a) the aftershock region and (b) the region of triggered seismicity at distances of 300 to 1000 km. The two regions are activated together; they are separated by a ring-shaped gap at a distance of around 300 km. This “Mexican Hat” pattern is attributed to recovery flows generated by the stress drop of the earthquake in a steady-state convecting system.
Horizontal-to-vertical spectral ratio and geological conditions: The case of Garner Valley Downhole Array in southern California
Authors: Theodulidis N. , Bard P.-Y. , Archuleta R. , Bouchon M. 
Published: September 2021

AbstractThe aim of the present article is to further check the use of the horizontal-to-vertical (h/v) spectral ratio, which has been recently suggested as an indicator of site effects. The data set consists of 110, three-component, high sensitivity accelerograms, recorded at five different depths by the Garner Valley Downhole Array (GVDA), in southern California, with peak ground accelerations 0.0002 g ≦ ag ≦ 0.04 g, magnitudes 3.0 ≦ ML ≦ 4.6, and hypocentral distances 16 km ≦ R ≦ 107 km. First, the stability of the (h/v) spectral ratio is investigated by computing the mean for the whole data set in different depths. The (h/v) spectral ratio on the surface is compared with the surface-to-depth standard spectral ratio, with theoretical S-wave transfer functions derived from the vertical geotechnical profile, as well as with the (h/v) spectral ratio of synthetic accelerograms generated by the discrete wavenumber method. Both theoretical and experimental data show a good stability of the (h/v) spectral ratio shape, which is in good agreement with the local geological structure and is insensitive to the source location and mechanism. However, the absolute level of the (h/v) spectral ratio depends on the wave field and is different from the surface-to-depth spectral ratio. Consequently the (h/v) spectral ratio technique provides only partially the information that can be obtained from a downhole array. But surface-to-depth ratios may also be misleading because they combine effects at surface and at depth.
RMS response of a one-dimensional half-space toSH
Authors: Day Steven M. 
Published: September 2021

AbstractWe examine the extent to which the response of a perfectly elastic half-space to an SH-wave incident from below can be characterized when knowledge about the elastic structure is limited to the near surface. Elastic properties are modeled as piecewise continuous functions of the depth coordinate. It is found that the site amplification function can be determined with a frequency resolution that depends inversely on the depth to which the elastic structure is known. Specifically, certain spectral averages of the site amplification function, concentrated over bandwidth Δƒ, depend only on the elastic structure down to a two-way travel-time depth of 1/Δƒ. These spectral averages are entirely independent of the elastic properties at greater depth. Equivalently, when the incident motion has a bandlimited white power spectrum of bandwidth Δƒ, the site amplification of the root mean square (rms) ground motion depends only on the elastic structure down to a two-way travel-time depth of 1/Δƒ. When the bandwidth is sufficiently large, the following corollary applies: the rms surface ground motion equals the rms incident motion multiplied by 2√Ib/I0, where I0 and Ib are shear impedances at the ground surface and basement depth, respectively. This result provides justification for a procedure conventionally used to correct stochastic estimates of earthquake ground motion to account for local site effects. The analysis also clarifies the limitations of that conventional procedure.The results define specific site-response parameters that can be computed from knowledge of shallow structure alone and may thereby contribute to improved understanding of the physical basis for, and limitations of, site classification schemes that are based on average S-wave velocity at shallow depth. While the analytical results are rigorous only for infinite Q, numerical experiments indicate that similar results apply to models with finite, frequency-independent Q. The practical utility of the results is likely to be limited primarily by the degree of lateral heterogeneity present near sites of interest and the degree to which the sites respond nonlinearly to incident ground motion.
Seismogram synthesis for multi-layered media with irregular interfaces by global generalized reflection/transmission matrices method. III. Theory of 2DP-SVcase
Authors: Chen Xiaofei 
Published: September 2021

AbstractIn this third article of a series study attempting to present a new method of seismogram synthesis for irregular multi-layered media problem, I shall present the theoretical development for the 2D P-SV case. Following the similar procedures developed for solving the SH problem presented in an earlier article (Chen, 1990), I first set up the basic matrix equations starting from the basic boundary integral equations, then introduce and determine the global generalized reflection/transmission (R/T) matrices, and finally solve the basic matrix equations by using the global generalized R/T matrices. It can be demonstrated that for the case of horizontally layered media (a special case of the general model), the general solution derived in this study naturally becomes identical to that of the generalized reflectivity method, which is directly developed for horizontally layered media. Therefore, this new method can be viewed as an extension of the generalized reflectivity method to the case of irregular multi-layered media. For the problems of seismic ground motion and irregular topography, I derive the simplified formulas. This new method can provide an efficient, accurate, and unified algorithm to calculate the synthetic seismograms for a variety of the laterally heterogeneous media.
Propagation characteristics ofLgacross the Tibetan Plateau
Authors: McNamara D. E. , Owens T. J. , Walter W. R. 
Published: September 2021

AbstractWe present the results of a study on the propagation of Lg within the Tibetan Plateau. We analyze over 1200 seismograms for Lg propagation from 185 local and regional earthquakes recorded at distances from 150 to 2000 km, 52 of which are located within the Tibetan Plateau. Although the propagation of Lg has been observed across most of Asia, Lg has not been observed for paths crossing the Tibetan Plateau. We analyze paths that cross the plateau boundaries and paths contained entirely within the Tibetan Plateau. Lg is generated within the Tibetan Plateau and can propagate to epicentral distances of at least 600 km. For events located outside of the Tibetan Plateau, Lg is either absent or severely diminished for paths that cross both the Himalayan and Kunlun ranges, confirming that the margins of the plateau weaken Lg transmission.Based on the observations from our qualitative analysis, we invert Lg amplitudes for event/station paths that are confined to the Tibetan Plateau to estimate the quality factor, Q. The inversion yields a frequency-dependent Q function:Q ( f ) = ( 366 ± 37 ) f ( 0.45 ± 0.06 ) ( 0.5 ≦ f ≦ 16 H z ) .Similar observations in other areas indicate that frequency-dependent apparent Q within the Tibetan Plateau is well below that expected for a typical continental interior. Instead, it has a frequency dependence that is characteristic of a tectonically active region.
Use of empirical Green's functions, spectral ratios, and kinematic source models for simulating strong ground motion
Authors: Haddon R. A. W. 
Published: September 2021

AbstractGround motions for large and moderately large earthquakes at short and moderate distances are particularly important for seismic hazard estimation in eastern North America (ENA). Very few direct observations of such ground motions have been obtained, however, because of the sparsity of recording sites and the relatively low rates of occurrence of large earthquakes inside the region. Estimation of strong ground motion must therefore rely heavily on theoretical models to extend empirical results obtained from small earthquakes and from the few larger ones for which reliable data are available. Because of the generally large distances between recording stations, the main source of useful data comes from Lg wave trains observed at relatively large distances. For the two largest earthquakes to have occurred near populated regions of southeastern Canada during the past decade, spectral ratios of the Lg wave trains of the mainshocks, with respect to those of their aftershocks, are found to depend almost entirely upon the source radiation characteristics of the sources alone. This result is utilized to derive elastodynamically-based kinematic rupture models that are consistent with the empirical spectral ratio data. Such models provide a firm physical basis from which to infer the most probable spectral characteristics for future large earthquakes in the region. In converse application, it is shown that spectral ratios obtained from such models, along with empirical seismograms from small earthquakes, can be used to accurately simulate strong ground motions at short and moderate (as well as large) distances. As such small-event seismograms are relatively plentiful, the problem of reliable strong ground motion estimation is therefore reduced to that of obtaining reliable representative source spectral models. The solution of this latter problem must continue to depend upon whatever empirical data are available and upon appropriately detailed theoretical modeling.
Analysis of spectral ratios for estimating ground motion in deep basins
Authors: Dravinski M. , Ding G. , Wen K.-L. 
Published: September 2021

Abstract
Use of Nakamura's spectral ratio (horizontal versus vertical components) is investigated theoretically for deep sedimentary basins by considering semi-circular and semi-spherical valleys. The ratio is evaluated from the steady-state surface response for different incident waves. Based on this ratio, both the resonant frequencies and ground motion amplification are determined. The results based on Nakamura's ratio are compared with those based on the sediment-to-bedrock spectral ratios (Kagami's ratio).
The results show that for both two- and three-dimensional models, Nakamura's technique predicts well the fundamental resonant frequency, but it could not determine higher resonant frequencies of the basins. The error in Nakamura's estimate of the fundamental resonant frequency increases for stations near the valley center. For alluvial valleys considered in this article, Nakamura's ratio failed to predict accurately surface ground-motion amplification.
Improving teleseismic event locations using a three-dimensional Earth model
Authors: Smith Gideon P. , Ekström Göran 
Published: September 2021

Abstract
A comparison is made between seismic event locations derived from standard spherically symmetric Earth models (JB, PREM, IASP91) and a recent Earth model (S&P12/WM13) that incorporates large-scale lateral heterogeneity of P- and S-wave velocities in the mantle. Events with known hypocentral coordinates are located in the different Earth models using standard methods. Two sets of events are considered: a data set of 26 explosions, including primarily nuclear weapons test explosions and peaceful nuclear explosions in the United States and former USSR; and a published data set of 82 well-located earthquakes with a more even global distribution. IASP91 and PREM are shown to offer similar errors in event location and origin time estimates with respect to the JB model. The three-dimensional (3D) model S&P12/WM13 offers improvement in event locations over all three one-dimensional (1D) models with, or without, station corrections. For the explosion events, the average mislocation distance is reduced by approximately 40%; for the earthquakes, the improvements are smaller. Corrections for crustal thickness beneath source and receiver are found to be of similar magnitude to the mantle corrections, but use of station corrections together with the three-dimensional mantle model provide the best locations.
A new regional hypocenter location method
Authors: Xie Zhi , Spencer Terry W. , Rabinowitz Philip D. , Fahlquist Davis A. 
Published: September 2021

AbstractA new regional hypocenter location method is presented in this article to address location problems associated with sparse station distributions and lack of velocity information. For an arbitrary slowness structure, an unknown parameter, slowness deviation, is introduced to construct a more precise slowness model than a homogeneous slowness model. By incorporating a genetic algorithm, the new method yields reasonable solutions for epicenters and origin times both inside and outside the seismic network. The synthetic data tests indicate that outside the network the new method gives excellent results for epicenter locations compared with Geiger's method, even when Geiger's method is used with the true velocity structure. The relocation of the Loma Prieta mainshock and 26 aftershocks occurring within the first 24 h after the mainshock by using the new hypocenter location method places the aftershocks an average of 2.29 km to the southwest of the locations published by the Northern California Earthquake Data Center. The new locations are in better agreement with the geodetic measurements.
A comparison of the high-frequency (&gt;1 Hz) surface and subsurface noise environment at three sites in the United States
Authors: Young Christopher J. , Chael Eric P. , Withers Mitchell M. , Aster Richard C. 
Published: September 2021

AbstractSurface and subsurface high-frequency (&gt;1 Hz) noise data were recorded using nearly identical instrumentation at three widely separated sites in the United States (Amarillo, Texas; Datil, New Mexico; and Pinedale, Wyoming) for extended periods of time under varying wind conditions. While the sites are geologically distinct, the near-surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site. Noise levels seen at or near the surface (5 m or less) are much higher (up to 30 dB) and much more variable (power range up to 44 dB) than those seen at depth (the smallest range was 9 dB for 1951 m at Amarillo). The greatest gains in noise level reduction are realized within the first 100 m and probably much shallower (&lt; ∼ 10 m). Regardless of the wind profile or local lithology, all sites show an excellent correlation between increased noise levels and higher wind speed, even at significant depths (367 m at Amarillo). Wind-generated noise is broadband (at least 15 to 60 Hz) and apparently nonlinear, increasing dramatically when a wind speed threshold is exceeded (3 to 4 m/sec within a few meters of the surface; as high as 8 m/sec at a depth of a few hundred meters). It is possible to be essentially completely shielded from the wind-generated component of seismic noise by deploying instruments at sufficient depth, but we observed this only for the two deepest deployments (1219 and 1951 m, both at Amarillo). Reducing the wind profile at the surface, however, can yield similar reductions for a much smaller cost. Cultural or “workday” noise, if present (depending on the remoteness of the site), is typically much weaker (10 dB or less) than wind noise but may propagate very effectively to great depths and therefore could be of concern for very deep deployments where wind is not a factor.