bluuebunny/crossref_metadata_2025_split huggingface dataset:
Site amplification at five locations in San Francisco, California: A comparison ofSwaves, codas, and microtremors
Authors: Seekins Linda C. , Wennerberg Leif , Margheriti Lucia , Liu Hsi-Ping 
Published: September 2021

AbstractWe compare microtremor data to weak-motion S-wave and coda recordings at sites in San Francisco in order to clarify the range of applicability of microtremor data to ground-motion prediction. We also compare S-wave results to coda results. For each type of data, we compute spectral ratios of motions from two soil/rock station pairs and from an uphole/downhole pair in the Marina district. We compute horizontal/vertical ratios (Nakamura's method) at a soil site, a rock site, and the surface and borehole instruments. In the station-pair analyses, microtremor data show amplifications at the same fundamental frequency as S waves, but the frequencies of other peaks do not agree. The amplification at frequencies higher than 2 Hz is greater in the microtremor data. Station-pair ratios of coda data generally show spectral peaks occurring at the same frequencies, but with levels varying from one to four times the amplification from S-wave ratios. Nakamura's method of analyzing microtremors agrees better with S-wave station-pair results than the microtremor station-pair method over a limited frequency band that varies from station to station.
Statistical estimation of seismic hazard parameters: Maximum possible magnitude and related parameters
Authors: Pisarenko V. F. , Lyubushin A. A. , Lysenko V. B. , Golubeva T. V. 
Published: September 2021

AbstractThe problem of statistical estimation of earthquake hazard parameters is considered. The emphasis is on estimation of the maximum regional magnitude, Mmax, and the maximum magnitude, Mmax(T), in a future time interval T and quantiles of its distribution. Two estimators are suggested: an unbiased estimator with the lowest possible variance and a Bayesian estimator. As an illustration, these methods are applied for the estimation of Mmax and related parameters in California and Italy.
Real-time seismology at UC Berkeley: The Rapid Earthquake Data Integration project
Authors: Gee Lind S. , Neuhauser Douglas S. , Dreger Douglas S. , Pasyanos Michael E. , Uhrhammer Robert A. , Romanowicz Barbara 
Published: September 2021

AbstractThe Rapid Earthquake Data Integration project is a system for the fast determination of earthquake parameters in northern and central California based on data from the Berkeley Digital Seismic Network and the USGS Northern California Seismic Network. Program development started in 1993, and a prototype system began providing automatic information on earthquake location and magnitude in November of 1993 via commercial pagers and the Internet. Recent enhancements include the exchange of phase data with neighboring networks and the inauguration of processing for the determination of strong-motion parameters and seismic moment tensors.
Analysis of high-frequency Pg/Lg ratios from NTS explosions and western U.S. earthquakes
Authors: Taylor Steven R. 
Published: September 2021

Abstract
The high-frequency Pg/Lg discriminant is studied between frequencies of 0.5 and 10 Hz using 294 NTS explosions and 114 western U.S. earthquakes recorded at four broadband seismic stations operated by Lawrence Livermore National Laboratory. The stations are located at distances of about 200 to 400 km from the Nevada Test Site (NTS). Event magnitudes ranged from about 2.5 to 6.5, and propagation paths for the earthquakes range from approximately 175 to 1300 km. The discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased. Because of propagation effects, it is important to apply distance corrections directly to the amplitude ratios or to the magnitude-corrected amplitudes prior to computing the ratios. Multivariate discrimination analysis using both maximum-likelihood Gaussian classifiers and a backpropagation neural network show that approximately 95% of the events can be correctly identified. Both classification procedures were designed to handle missing data filled in using a nearest-neighbor algorithm. Except for a few notable exceptions, most of the earthquake misclassifications occur for mb &lt; 4, which is expected for events having reduced signal-to-noise ratios. All of the explosion misclassifications occur for mb &lt; 4, suggesting a source or near-source effect rather than an effect of poor signal-to-noise ratio. The explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb/Ms or Love-wave energy. The main drawback of the Pg/Lg discriminant is that, because of signal-to-noise considerations and propagation effects, the number of measurements are reduced considerably at higher frequencies. It is expected that the problem will be amplified as magnitudes are reduced and event-receiver distances are increased.
Mapping shallow heterogeneity with teleseismic P to Rg scattered waves
Authors: Revenaugh Justin , Mendoza Hal 
Published: September 2021

Abstract
Over 9000 records of teleseismic P-wave coda from the Southern California Seismic Network are used to map lateral variations in P to Rg scattering strength and the group velocity of scattered Rg. Building on the results of Revenaugh (1995a), we use the correlation of scattering strength and topographic roughness as an indicator of model fit to estimate group-velocity dispersion over five frequency bands between 0 and 3 Hz. Rg group velocity displays normal dispersion, decreasing from 2.7 ± 0.3 km/sec for frequencies between 0 and 0.6 Hz to a low of 2.2 ± 0.4 km/sec for the 2.0 to 3.0 Hz band. Lateral heterogeneity is introduced by assuming Rg velocity is a function of local topographic roughness. Grid-search/migration analysis yields group velocities of 2.2 and 2.85 km/sec for “smooth” and “rough” terrain, respectively, and a 150-m threshold for the local standard deviation of topography distinguishing “smooth” from “rough”. The map of scattering strength approximates topographic roughness throughout southern California, implying that teleseismic P-wave coda duration and relative amplitude level depend strongly on near-surface (&lt;3 km) geology.
Toward real-time estimation of regional moment tensors
Authors: Pasyanos Michael E. , Dreger Douglas S. , Romanowicz Barbara 
Published: September 2021

Abstract
Recent advances in broadband station coverage, continuous telemetry systems, moment-tensor procedures, and computer data-processing methods have given us the opportunity to automate the two regional moment-tensor methods employed at the UC Berkeley Seismographic Station for events in northern and central California. Preliminary solutions are available within minutes after an event has occurred and are subsequently human reviewed. We compare the solutions of the two methods to each other, as well as the automatic and revised solutions of each individual method. Efforts are being made to establish robust criteria for determining accurate solutions with human review and to fully automate the moment-tensor procedures into the already-existing automated earthquake-location system.
Seismic hazard estimate from background seismicity in southern California
Authors: Cao Tianqing , Petersen Mark D. , Reichle Michael S. 
Published: September 2021

AbstractWe analyzed the historical seismicity in southern California to develop a rational approach for calculating the seismic hazard from background seismicity of magnitude 6.5 or smaller. The basic assumption for the approach is that future earthquakes will be clustered spatially near locations of historical mainshocks of magnitudes equal to or greater than 4. We analyzed the declustered California seismicity catalog to compute the rate of earthquakes on a grid and then smoothed these rates to account for the spatial distribution of future earthquakes. To find a suitable spatial smoothing function, we studied the distance (r) correlation for southern California earthquakes and found that they follow a 1/rµ power-law relation, where µ increases with magnitude. This result suggests that larger events are more clustered in space than smaller earthquakes. Assuming the seismicity follows the Gutenberg-Richter distribution, we calculated peak ground accelerations (PGA) for 10% probability of exceedance in 50 yr. PGA estimates range between 0.25 and 0.35 g across much of southern California. These ground-motion levels are generally less than half the levels of hazard that are obtained using the entire seismic source model that also includes geologic and geodetic data. We also calculated the overall uncertainty for the hazard map using a Monte Carlo method and found that the coefficient of variation is about 0.24 ± 0.01 for much of the region.
A Monte Carlo approach in estimating uncertainty for a seismic hazard assessment of Los Angeles, Ventura, and Orange counties, California
Authors: Cramer Chris H. , Petersen Mark D. , Reichle Michael S. 
Published: September 2021

AbstractMaps of uncertainty and parametric sensitivity in ground motion have been produced for three southern California counties using a Monte Carlo approach. The uncertainty in hazard is estimated by random sampling a logic tree that has the uncertainty in most parameters described by a normal distribution. The nine parameters varied in the uncertainty analysis are those related to the estimation of recurrence rates for earthquakes on faults using geologic information, the ground-motion attenuation relations, the relations available for estimating the magnitude-frequency distribution of earthquakes on faults, and the inclusion or exclusion of blind thrusts in the Los Angeles area. Besides simultaneously varying all nine parameters for a Monte Carlo series of runs to obtain the overall uncertainty in ground motion for a fixed annual probability, each of the nine parameters were varied separately while the others were held fixed to determine the sensitivity of each parameter on this uncertainty. The total uncertainty in shaking levels corresponding to a fixed annual probability is up to ±50% at the 95% confidence level. The parameters that most influence the uncertainty in the hazard estimates from geologic information are (1) maximum magnitude, (2) choice of attenuation relations, (3) the magnitude-frequency distribution, and (4) slip rate.
Automatic seismic event recognition and later phase identification for broadband seismograms
Authors: Tong Cheng , Kennett Brian L. N. 
Published: September 2021

AbstractKnowledge of the patterns of frequently observed seismic phases associated with specific distances and depths have been well developed and applied by seismologists (see, e.g., Richter, 1958; Kulhánek, 1990). However, up till now, the expertise of recognizing seismic event patterns for teleseisms has not been translated into automatic processing procedure. A new approach is developed to automate this kind of heuristic human expertise in order to provide a means of improving preliminary event locations from a single site.An automatic interpretation system exploiting three-component broadband seismograms is used to recognize the pattern of seismic arrivals associated with the presence of a seismic event in real time accompanied by an identification of the individual phases. For a single station, such a real-time analysis can be used to provide a preliminary estimation of the location of the event. The inputs to the interpretation process are a set of features for detected phases produced by another real-time phase analyzer. The combinations of these features are investigated using a novel approach to the construction of an expert system. The automatic system exploits expert information to test likely assumptions about phase character and hence epicentral distance and depth. Some hypotheses about the nature of the event will be rejected as implausible, and for the remainder, an assessment is given of the likelihood of the interpretation based on the fit to the character of all available information.This event-recognition procedure provides an effective and feasible means of interprating events at all distances, and characterizing information between hundreds of different possible classes of patterns even when the observation is incomplete. The procedure is based on “assumption trees” and provides a useful tool for classification problems in which a number of factors have to be identified. The control set of expert knowledge used in testing hypotheses is maintained separately from the computational algorithm used in the assumption search; in consequence, the information base can be readily updated.
A composite source model of the 1994 Northridge earthquake using genetic algorithms
Authors: Zeng Yuehua , Anderson John G. 
Published: September 2021

AbstractThe 17 January 1994 Northridge earthquake (Mw 6.7) occurred on a buried thrust fault in the northwest Los Angeles metropolitan area. We investigate the source process of this earthquake using the CSMIP strong motion records and a composite source model developed by Zeng et al. (1994a) for realistic earthquake strong ground motion prediction. Our previous studies demonstrated the realism of the synthetic strong motions generated from the composite source model by comparing them with observed records from earthquakes in many areas of the world. This article addresses an inverse study of the problem to find a specific composite source model for the Northridge earthquake. This is done by adjusting the location of a suite of composite subevents, using genetic algorithms (Holland, 1975), to best match the observed waveforms. A test run of the genetic algorithm on synthetic data sets finds a very good convergence of the approach. We reduce largely the intensive computation time by identifying subevents with major contribution to the waveform fit. Our result for the 1994 Northridge earthquake indicates a complex earthquake rupture process with three large slip zones: one at the hypocenter and the other two to the west of the hypocenter. We then use this model to compute the high-frequency strong-motion velocity and acceleration. The results show that the composite source model provides a very realistic broadband source description for the Northridge earthquake.
On some microearthquakes near Tarbela reservoir during three low water stands
Authors: Kalpna  , Chander R. 
Published: September 2021

Abstract
Detailed 3D stress analyses with a simulated model of Tarbela reservoir indicate that most nearby seismogenic faults inferred from observations of preimpoundment seismicity in the region should be stabilized even when the reservoir has low water levels during dry seasons. We hypothesize that the hypocenters of some microearthquakes occurring close to the reservoir during dry seasons of 1977, 1980, and 1981 were located on those of the above faults that are destabilized by accumulation of broadly north-south horizontal compressive stresses of plate tectonic origin. An order of magnitude analysis shows that the rate of accumulation of these stresses may be sufficiently rapid to overcome the stability imparted to the seismogenic faults by the Tarbela reservoir.
Location and source parameters of the 19 June 1994 (MW = 5.0) offshore Petrolia, California, earthquake
Authors: Braunmiller Jochen , Leitner Beate , Nábělek John , Tréhu Anne M. 
Published: September 2021

Abstract
The MW = 5.0, 19 June 1994 offshore Petrolia, California, earthquake was well recorded by nine ocean-bottom hydrophones (OBH) and seismometers (OBS), providing an opportunity to precisely locate an earthquake in the tectonically active Mendocino triple junction region. Adding the offshore data improves the azimuthal station coverage and essentially removes the epicenter's sensitivity to the choice of inversion parameters and velocity models. The hypocentral parameters, assuming an oceanic upper-mantle velocity of 7.9 km/sec, are 10:39:33.2 UTC for origin time, 40.376° N latitude, 124.441° W longitude, and a depth of 18.8 km. The moment-tensor solution obtained by modeling of low-frequency regional waveforms indicates predominantly strike-slip faulting with a north-south-trending P axis, as is typical for Gorda plate earthquakes, and confirms the depth estimate from the P-wave travel-time data.
Characteristics of nonlinear response of deep saturated soil deposits
Authors: Ni Shean-Der , Siddharthan Raj V. , Anderson John G. 
Published: September 2021

Abstract
Recent EPRI seismic design guidelines call for dynamic soil properties (shear modulus ratio and damping) and liquefaction strength curves to be characterized as a function of the effective vertical stress (or depth). A modified version of the DESRA2 constitutive model for saturated soil has been applied to study the nonlinear seismic response including liquefaction of medium dense soil deposits of various thicknesses. The results of the stress-dependent soil properties model show lower deamplification and higher first-mode (resonant) frequency than that of the stress-independent soil properties model. By using the stress-dependent model with impulse base excitation, the nonlinear behavior of various soil deposits has been investigated under a variety of conditions. The results show that (1) the saturated soil deposit has a smaller surface amplitude and significantly lower resonant frequency than the unsaturated soil deposit of the same thickness; (2) for the saturated soil conditions, the larger the base excitation, the lower the surface amplification and the resonant frequency; (3) the deep soil deposits show lower surface amplification and resonant frequency compared to the response of shallow deposits; (4) when shallow and deep deposits are compared, the shallow deposits develop much higher residual pore-water pressure; and (5) the amplification and residual pore-water-pressure response of deposits deeper than 100 m or so are very similar. The application of the method has also been illustrated using a strong synthetic base excitation applied to the base at a site near Reno. The results in general are consistent with those computed using the impulse loading. The study reveals that the response predicted from the conventionally used stress-independent soil properties model is unconservative for deep deposit.
The effect of the crust on the estimation of mantleQfrom spectral ratios of multipleScSphases
Authors: Isse Takehi , Nakanishi Ichiro 
Published: September 2021

AbstractTo estimate Qscs, previous studies used the spectral ratios of multiple ScS phases calculated for specific time windows. They assumed that the spectral ratios had linear relation with frequency. However, the spectral ratios very often did not seem to be linear, and the error bars were very large for frequencies higher than about 0.05 Hz.We have performed numerical experiments to search for the cause of these anomalies and found that they are caused by the multiple reflection in the crust under the surface bounce point of ScS2. A method of suppressing the anomalies is to start the time of the time window at 40 sec prior to the theoretical arrival times of the multiple ScS phases. In numerical tests, the difference between the correct and estimated values of Qscs is only 0 to 5% using this method, but it is 10 to 50% in the conventional method. We find that the crustal effect is more important in the estimation of Qscs than background noise, which has been readily handled in previous studies using standard stacking techniques.
The paradox of the expected time until the next earthquake
Authors: Sornette D. , Knopoff L. 
Published: September 2021

AbstractWe show analytically that the answer to the question, (can it be that) “The longer it has been since the last earthquake, the longer the expected time till the next?” depends crucially on the statistics of the fluctuations in the interval times between earthquakes. The periodic, uniform, semi-Gaussian, Rayleigh, and truncated statistical distributions of interval times, as well as the Weibull distributions with exponent greater than 1, all have decreasing expected time to the next earthquake with increasing time since the last one, for long times since the last earthquake; the lognormal and power-law distributions and the Weibull distributions with exponents smaller than 1 have increasing times to the next earthquake as the elapsed time since the last increases, for long elapsed times. There is an identifiable crossover between these models, which is gauged by the rate of fall-off of the long-term tail of the distribution in comparison with an exponential fall-off. The response to the question for short elapsed times is also evaluated. The lognormal and power-law distributions give one response for short elapsed times and the opposite for long elapsed times. Even the sampling of a finite number of intervals from a Poisson distribution will lead to an increasing estimate of time to the next earthquake for increasing elapsed time since the last one.
The 14 September 1995 (M= 7.3) Copala, Mexico, earthquake: A source study using teleseismic, regional, and local data
Authors: Courboulex F. , Santoyo M. A. , Pacheco J. F. , Singh S. K. 
Published: September 2021

AbstractWe analyze source characteristics of the 14 September 1995, Copala, Mexico, earthquake (M = 7.3) using teleseismic, regional, and local seismograms. In the analysis of the teleseismic and the regional seismic waves, we apply the empirical Green's function (EGF) technique. The recording of an appropriate aftershock is taken as the EGF and is used to deconvolve the mainshock seismogram, thus obtaining an apparent far-field source-time function at each station. The deconvolution has been done using surface waves. For teleseismic data, we apply a spectral deconvolution method that enables us to obtain 37 apparent source-time functions (ASTFs) at 29 stations. In the analysis of the regional broadband seismograms, we use two different aftershocks as EGF, and the deconvolution is performed in the time domain with a nonlinear method, imposing a positivity constraint, and the best azimuth for the directivity vector is obtained through a grid-search approach.We also analyze two near-source accelerograms. The traces are inverted for the slip distribution over the fault plane by applying a linear inversion technique. With the aid of a time-window analysis, we obtain an independent estimation of the source-time function and a more detailed description of the source process.The analysis of the three datasets permits us to deduce the main characteristics of the source process. The rupture initiated at a depth of 16 km and propagated in two directions: updip along the plate interface toward 165° N and toward 70° N. The source duration was between 12 and 14 sec, with the maximum of energy release occurring 8 sec after the initiation of the rupture. The estimated rupture dimension of 35 × 45 km is about one-fourth of the aftershock area. The average dislocation over the fault was 1.4 m (with a maximum dislocation of 4.1 m located 10 km south of the hypocenter), which gives roughly 1 MPa as the average static stress drop.