bluuebunny/crossref_metadata_2025_split huggingface dataset:
Earthquake site response estimation: A weak-motion case study
Authors: Field E. H. , Jacob K. H. , Hough S. E. 
Published: September 2021

AbstractUsing weak-motion recordings of aftershocks of the 1989 Loma Prieta earthquake recorded in Oakland, California, near the failed Nimitz Freeway, two methods have been applied to estimate the site response of an alluvium site and three mud-over-alluvium sites. The first estimate is the traditional spectral ratio, and the second utilizes the cross spectrum. Recordings obtained at a nearby bedrock site are used as estimates of the sediment site input motions. While the two site response estimates produce similar peaks and troughs, there is an approximate factor of 2 difference in amplitudes. This discrepancy is evidence that there is a much greater level of noise than would be expected from the pre-event ambient noise. We interpret this as signal-generated noise produced by scattering from heterogeneities, which causes the true sediment site input to differ significantly from the bedrock site recording. Given this level of noise, the cross-spectrum estimate suffers a severe downward bias (by a factor of 2 in this study) and should probably not be used when the input motion is estimated from a bedrock site recording. The spectral-ratio estimates are relatively unbiased, but the level of noise introduces a large degree of uncertainty. Therefore, inferences about site response from individual spectral ratios should probably be avoided. On the other hand, ensemble averages of the estimates significantly reduce the scatter to reveal resonances that agree quite well in frequency and overall shape with those of one-dimensional models whose parameters were determined independently. A discrepancy of higher observed amplitudes than predicted by theory remains unexplained but most likely results from the effects of boundary layer topography, which are not accounted for by the simple one-dimensional models.
Aftershock stress release along active fault planes of the 1984 Round Valley, California, earthquake sequence applying a time-domain stress drop method
Authors: Smith Kenneth D. , Priestley Keith F. 
Published: September 2021

AbstractThe 23 November 1984 ML 5.8 Round Valley earthquake is one in a series of moderate (ML ≈ 6) earthquakes to have occurred in the Bishop-Mammoth Lakes, California, area since 1978. This earthquake and its aftershock sequence occurred within a dense seismic network, and hypocentral location quality is excellent. In a previous study, we determined that the Round Valley sequence involved faulting on a conjugate set of fault planes; one, a near-vertical plane striking N30°E, the mainshock fault plane showing principally left-lateral strike-slip motion, and another subperpendicular to the mainshock fault plane striking N40°W and dipping 55°NE, exhibiting dominantly right-lateral strike slip. This conjugate fault plane conforms to a postulated extension of the Hilton Creek fault and is the only significant activity on this structure in the 12-year Bishop-Mammoth Lakes earthquake sequence. Source dimensions and stress drops for 87 aftershocks (ML 2.8 to 4.2) of the Round Valley sequence have been determined using an adaptation of the initial P-wave pulse width time-domain deconvolution technique of Frankel and Kanamori (1983). The aftershock sequence is confined to a limited volume of crust. We have shown that site and instrument effects and not whole-path attenuation control the minimum pulse widths for this limited region. The determination of a site minimum pulse width, rather than a minimum pulse width for each source receiver pair as in the Frankel and Kanamori study, makes the deconvolution procedure practical for processing the large numbers of events in an aftershock sequence. With the large data set available for the Round Valley aftershock sequence, patterns of the stress drop along the active fault planes can be seen in detail. Source radii systematically increase with magnitude from about 100 m for events near magnitude 3.0 to 500 m for events near magnitude 4.0. Static stress drops range from 10 to 200 bars and are not strongly correlated with magnitude or depth. The stress release pattern reveals a broad stress drop low (Δσ ≈ 10 bars) for aftershocks within the mainshock fault plane that is consistent with other evidence of the rupture surface of the Round Valley mainshock. Higher stress release occurs above and below the mainshock rupture surface and on the shallower, conjugate fault plane. Further distant from the rupture surface of the mainshock, stress drops decrease to average values. On the conjugate fault surface, stress drops are seen to be high in areas that may be interpreted as “off-fault” clusters with respect to the mainshock rupture surface.
Discrimination of explosions from simultaneous mining blasts
Authors: Smith Albert T. 
Published: September 2021

Abstract
Large mining blasts can complicate the identification and discrimination of small underground nuclear explosions and may offer evasion opportunities. Mining blasts typically show a unique spectral signature: spectral reinforcements associated with time-delayed detonations between adjacent shot holes or rows of shots. Discrimination of a nuclear detonation that is simultaneous with a mining blast must depend upon recognizing significant spectral or waveform abnormalities within seismic signals from the mining blasts. In this investigation, large, simultaneous detonations within mining blasts are simulated for observed explosions from the Mesabi Range in Minnesota and for a series of quarry blasts at the Kaiser Permanente Quarry in Cupertino, California, which included a simultaneous detonation conducted by Lee et al. (1989). The Mesabi explosions are examples of large, ripple-fired blasts with known blast patterns (Smith, 1989).
The models suggest that a large, single, deeply buried explosion dominates the waveform signature if it contains more than 5 to 15% of the total explosive in the mining blast. Spectral signatures of these combined explosions still show periodicities characteristic of ripple firing; however, their amplitude is greatly reduced. Inclusion of a deep simultaneous shot accentuates the high-frequency spectrum. If single explosions are sufficiently close to the combined quarry blast, their application as empirical Green's functions can isolate the simultaneous explosion within the blast. If empirical Green's functions are within 0.5 km of quarry blasts, individual explosions can be retrieved if delays are 100 msec between shot holes and signals extend to 40 Hz. Identification of large, simultaneous detonations within a blast may depend upon knowledge of the mine's blasting practices and its variability from blast to blast.
Tomography without rays
Authors: Ammon Charles J. , Vidale John E. 
Published: September 2021

Abstract
We present two new techniques for the inversion of first-arrival times to estimate velocity structure. These travel-time inversion techniques are unique in that they do not require the calculation of ray paths. First-arrival times are calculated using a finite-difference scheme that iteratively solves the eikonal equations for the position of the wavefront. The first inversion technique is a direct extension of linearized waveform inversion schemes. The nonlinear relationship between the observed first-arrival times and the model slowness is linearized using a Taylor series expansion and a solution is found by iteration. For a series of two-dimensional numerical tests, with and without random noise, this travel-time inversion procedure accurately reconstructed the synthetic test models. This iterative inversion procedure converges quite rapidly and remains stable with further iteration. The second inversion technique is an application of simulated annealing to travel-time topography. The annealing algorithm is a randomized search through model space that can be shown to converge to a global minimum in well-posed problems. Our tests of simulated annealing travel-time topography indicate that, in the presence of less than ideal ray coverage, significant artifacts may be introduced into the solution. The linearized inversion scheme outperforms the nonlinear simulated annealing approach and is our choice for travel-time inversion problems. Both techniques are applicable to a variety of seismic problems including earthquake travel-time tomography, reflection, refraction/wide-angle reflection, borehole, and surface-wave phase-velocity tomography.
Stratigraphic evidence for seven meters of dextral slip on the San Andreas fault during the 1857 earthquake in the Carrizo Plain
Authors: Grant Lisa B. , Sieh Kerry 
Published: September 2021

Abstract
The smallest geomorphic offsets along a 35 km section of the San Andreas fault in the Carrizo Plain vary from 7 to 10 m. Our three-dimensional excavation of alluvial deposits a few km southeast of Wallace Creek confirms that at least 6.6 to 6.9 m of dextral slip occurred there during the latest large earthquake, in 1857. Dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range A.D. 1305 to 1623. The 3-m range in smallest offsets along this portion of the fault may reflect either a 3-m variation in slip along the San Andreas in 1857, or 2 to 3 m of slip during an event prior to 1857. Observations made after the recent Landers earthquake are compatible with the hypothesis of large, local variations in slip during a single earthquake, but do not explain the cause of such variations. Off-fault dextral rotations would be one plausible explanation. However, paleoseismic data in the Carrizo Plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m, an amount of slip which would be several times too small to fit a time-predictable model.
Direct boundary element method for dynamics in a half-space
Authors: Nowak Paul S. , Hall John F. 
Published: September 2021

Abstract
An application of the direct boundary element method for solving the response of a linearly elastic half-space with a canyon cut into the surface is presented. This approach uses source solutions for an undamped half-space where the resulting singular integral equations are solved directly without adding any artificial damping. Solutions for the displacements on the canyon surface reveal an artificial resonance phenomenon when solving the exterior problem in the frequency domain. The use of an additional source loading in the boundary element method is shown to eliminate these resonances and yield accurate results. A method for solving the Rayleigh waves generated on the surface of the half-space caused by the canyon is shown.
Crustal anisotropy from local observations of shear-wave splitting in West Bohemia, Czech Republic
Authors: Vavryčuk Václav 
Published: September 2021

Abstract
The results of a systematic study of shear-wave splitting, observed in the three-component digital seismograms of about 400 local microearthquakes that occurred during the 1985/1986 West-Bohemian earthquake swarm are presented. Two shear phases, polarized nearly perpendicularly in horizontal projection, were observed at all five stations of the local seismic network for most of the events. The polarization of the faster shear wave is aligned in the WNW-ESE direction, regardless of the mechanism and hypocenter location of the individual events, and coincides with the direction of the maximum horizontal compressive tectonic stress in the region. These effects are interpreted in terms of effective anisotropy of the upper crust in the region. The maximum delay time between the split shear waves is 0.15 sec and corresponds to 6% anisotropy.
Directional variation of the delay time was observed at the nearest station (epicentral distance ≈ 5 km). This variation was compared with functions predicted by theoretical models of cracked media to resolve which model is the most appropriate for crustal anisotropy. Surprisingly, no agreement could be found for Hudson's model of dry or water-filled parallel cracks that is widely used by many authors. A successful fit was obtained for Schoenberg — Douma's model of a medium with parallel fractures. The fracture normal pointed N31°E, and the optimum fracture parameters were EN = 0.4 and ET = 0.02. The theoretically calculated fractures are aligned parallel to the tectonic stress direction and do not correspond to any real tectonic lines in the region.
Site effect evaluation using spectral ratios with only one station
Authors: Lermo Javier , Chávez-García Francisco J. 
Published: September 2021

AbstractThe spectral ratio technique is a common useful way to estimate empirical transfer function to evaluates site effects in regions of moderate to high seismicity. The purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station. The technique, originally proposed by Nakamura to analyze Rayleigh waves in the microtremor records, is presented briefly and it is discussed why it may be applicable to study the intense S-wave part in earthquake records. Results are presented for three different cities in Mexico: Oaxaca, Oax., Acapulco, Gro., and Mexico City. These cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city. Each time we compare the results of Nakamura's technique with standard spectral ratios. In all three cases the results are very encouraging. We conclude that, if site effects are caused by simple geology, a first estimate of dominant period and local amplification level can be obtained using records of only one station.
Estimation of strong ground motions in meizoseismal region of the 1976 Tangshan, China, earthquake
Authors: Dan K. , Ishii T. , Ebihara M. 
Published: September 2021

AbstractThe 1976 Tangshan, China, earthquake of MS 7.8 killed 242,000 persons, seriously injured 164,000 persons, and caused direct property losses totaling 8 billion Yuan Ren Min Bi (US $4.3 billion). Few investigations have been performed to estimate the characteristics of the strong ground motions in the meizoseismal region of this earthquake using either seismological or earthquake engineering approaches.In this paper, the observed far-field accelerograms of the mainshock are simulated by using the records of the second largest aftershock of MS 6.9 as Green's functions in order to obtain appropriate fault models for the mainshock. The strong ground motions in the meizoseismal region of the mainshock are then estimated by using these fault models and the records of several aftershocks with a magnitude of about 5 which were observed at temporary stations in the damaged area. The results indicate that large horizontal acceleration responses over 1000 cm/sec2 and vertical acceleration responses over 2000 cm/sec2 acted on the structures with natural periods shorter than 0.1 sec in the wide meizoseismal region having a length of 90 km.
Seismic wave-field observations at a dense, small-aperture array located on a landslide in the Santa Cruz Mountains, California
Authors: Xu Zhengyu , Schwartz Susan Y. , Lay Thorne 
Published: September 2021

Abstract
A rectangular (4 by 5) array of short-period three-component seismometers with 15-m spacing was deployed to record several U.S. Geological Survey calibration explosions detonated around the Santa Cruz Mountains. The array was located at a site where an earlier station had recorded frequency-dependent polarized site resonances for aftershocks of the 1989 Loma Prieta earthquake. The site is on a hillside believed to be a landslide structure, with the near surface consisting of poorly sorted sediments and weathered rocks with dipping subsurface layers. The primary objective was to explore the site effects in this complex three-dimensional soft-rock environment, characteristic of much of the Loma Prieta source region. The direct P waves from four nearby (15 to 20 km) explosions at easterly azimuths from the array show counterclockwise arrival azimuth anomalies of 30° to 50°. These deflections are attributed to the presence of more than one dipping velocity contrast beneath the array, with dips of from 10° to 50° and dip directions generally toward the south. One such boundary may correspond to the landslide slip surface, and the presence of dipping velocity contrasts underlying the site is probably responsible for some of the observed directional site resonance. A slowness vector analysis demonstrates that arrivals early in the P coda have similar azimuthal anomalies, while later scattered arrivals come from many azimuths. Particle motions indicate that the more coherent arrivals in the coda are comprised of scattered P waves and Rayleigh waves, probably associated with scattering from the rough topography in the region. The coda displays greater spatial coherency along the hill strike than down the slope, consistent with a wedge-shaped landslide. The overall wave-field spatial coherence, CCC(f, Δx), decreases with increasing frequency, f, and spatial offset, Δx, and on average can be well represented by CCC(f, Δx) = e−cfΔx, with c = 0.6 km−1 Hz−1 for the vertical P wave in the first 1-sec window. This behavior is comparable to that found for previously studied hard-rock locations.
The great Mexican earthquake of 19 June 1858: Expected ground motions and damage in Mexico City from a similar future event
Authors: Singh S.  K. , Ordaz M. , Pérez-Rocha L.  E. 
Published: September 2021

Abstract
The description of the great earthquake of 19 June 1858 is unusual: damage and high intensities were reported both in the state of Michoacan and in Mexico City. Although a coastal epicenter for this earthquake cannot be ruled out, the reports agree better with an intermediate-depth (about 50 km), normal-faulting event in the subducted Cocos plate. A careful examination of the reports of this event and other normal-faulting events below the Mexican altiplano suggests that a likely location is 18.0 °N, 100.8 °W, near the epicenter of the 6 June 1964 (M7.3, H = 55 km) event. This location is 220 km SW of the city. The magnitude of the earthquake is estimated to be about 7.7. We synthesize expected ground motions in CU, a hill-zone site in the city, from an event similar to that of 1858, using records from the 23 May 1994 earthquake (18.0 °N, 100.6 °W, H = 50 km, M5.7) as an empirical Green's function and stress parameter, Δσ, of 50, 160, and 300 bar. The expected peak horizontal acceleration in CU of Δσ = 160 bar is about 30 gals. Similar acceleration was recorded in CU during the 1985, Michoacan earthquake (M8.0). We compute expected ground motions at many sites in Mexico City using empirical transfer functions and random vibration theory and compare these motions and the expected damage in the city with those from the 1985 Michoacan earthquake. Results show that the overall expected damage during the postulated earthquake is ⅔ and 1⅓ of that during the Michoacan earthquake for Δσ = 160 and 300 bar, respectively. A greater percentage of low-rise construction, which constitute about 80% of the total in the city, will be damaged during the postulated earthquake than during the Michoacan earthquake. The expected ground motions for Δσ = 50 bar are smaller at all periods than those from the Michoacan earthquake. As the present building code for Mexico City contemplates coastal earthquakes of magnitude greater than 8.0, the case of Δσ = 50 bar is not of interest in this article. This preliminary study suggests a need for a more careful evaluation of expected ground motion in the Valley of Mexico from the postulated earthquake and its impact on the current design spectra of the city.
Northridge earthquake rupture models based on the global positioning system measurements
Authors: Shen Zheng-Kang , Ge Bob X. , Jackson David D. , Potter David , Cline Michael , Sung Li-yu 
Published: September 2021

AbstractWe use global positioning system (GPS) data to study the rupture mechanism of the 1994 Northridge earthquake in southern California. We include data from 62 observation sites, of which two (Palos Verdes and Jet Propulsion Lab) are permanent GPS geodetic array (PGGA) sites. We use a grid-search scheme to study the range of single- and dual-plane, uniform and varied slip models consistent with the data. We find that in order to fit the geodetic data with a fault model whose primary fault patch is confined to a plane through the aftershocks, a secondary fault plane is required above the primary fault plane. The moment release of the secondary fault can be as large as 1.9 × 1018 N-m, 14% of the moment release of the primary fault. This result implies significant deformation in the shallow crust associated with the mainshock. Our preferred model has a 14 × 14 array of dislocation patches on a plane through the main aftershock cluster and a 5 × 6 array of patches in the hanging wall west of the epicenter. We estimate the displacements on the patches by linear inversion with a first-order smoothness constraint. The estimated displacements on the main fault for this model are confined to a simple region between depths of 5 and 18 km, in the interior of the modeled fault surface. The mainshock lies at the bottom of the aftershock zone, near which about 1-m slip is shown on our modeled fault surface. The maximum slip on the fault surface is about 2.2 m, located at 34.28° N, 118.55° W, and 12.4 km at depth. The seismic moment release estimate of 1.34 ± 0.15 × 1019 N-m on the main fault at the 95% confidence is consistent with the estimate from strong-motion studies.
Contribution of seismic tomography in moment-tensor inversions using teleseismic surface-wave spectra
Authors: Dufumier Hugues , Trampert Jeannot 
Published: September 2021

Abstract
The knowledge of lateral heterogeneities is crucial for path corrections in moment tensor inversions using surface waves. After some attempts to use regionalized Earth models for very long-period surface-wave moment-tensor inversions, recent tomographic Earth models offer the possibility to make short-period path corrections and therefore retrieve more reliable moment tensors for teleseismic earthquakes. First we try to evaluate the precision required for path corrections in comparison with source effects. Some selected Earth models are tested to evaluate how their results compare to those using multiple-frequency filtering techniques. Some real cases illustrate the sensitivity of moment-tensor solutions to the different path corrections, and it appears clearly that regionalized Earth models and tomographic models deduced from long-period data alone (greater than 150 sec) cannot lead to trustworthy broadband moment-tensor inversions. Recent tomographic models using phase velocities at much shorter periods (40 to 200 sec) offer a precision comparable to that of the multiple-frequency filtering technique. Both methods lead to acceptable source mechanisms, using a small number of stations, in more than two cases out of three. The use of recent global tomographic models based upon shorter-period surface waves might thus be a useful alternative to heavy multiple-frequency filtering techniques to automate source studies, especially for rapid determinations using a small number of stations.