bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variability of ground motions in southern California—data from the 1995 to 1996 Ridgecrest sequence
Authors: Scrivner Craig W. , Helmberger Donald V. 
Published: August 2021

AbstractSeismograms from the 1995 to 1996 Ridgecrest, California, earthquake sequence, recorded by the TriNet digital seismic network, provide high-quality waveforms from sites throughout southern California, including sites in markedly heterogeneous areas like the Los Angeles area sedimentary basins. Synthetic seismograms calculated by the reflectivity method with various 1D models are used as a baseline to measure the variability of amplitudes throughout southern California. Regardless of the model used, there is greater variability in the amplitudes from basin site records than from rock site records. Rock, soil, and basin sites are all rather insensitive to radiation pattern nodes at the three frequency bands investigated: 0.1 to 0.2 Hz, 0.2 to 0.4 Hz, and 0.4 to 0.8 Hz. This complicates the analysis because the nodes create singularity points in the distribution of ratios of observed and synthetic amplitudes. When stations near nodal planes are removed, the surface waves observed at most rock sites have peak amplitudes within a factor of 2 of synthetic waveform amplitudes. Peak amplitude of the surface waves observed at the soil and basin stations are more variable, with the bulk of the distribution of data/synthetic amplitude ratios less than 3 and a few outliers greater than 5. These outliers occur at the higher frequency bands. Soil and basin sites are also more often larger than the synthetics (higher median values). Most outliers can be explained by applying a water level of 50% to the radiation pattern. This reduces the scatter in the distributions to about the same extent as removing data within 10° of nodes. Thus, most of the outliers are sites that are insensitive to the nodes, not sites that are larger than the overall data distribution.
An automated local and regional seismic event detection and location system using waveform correlation
Authors: Withers Mitchell , Aster Richard , Young Christopher 
Published: August 2021

AbstractWe report on the development of an automated Local Waveform Correlation Event Detection System (LWCEDS) and its application to the New Mexico Tech Seismic Network. LWCEDS is an adaptation of a global system, WCEDS, a matched filtering algorithm for global Comprehensive Test Ban Treaty (CTBT) monitoring applications developed at Sandia National Laboratories and New Mexico Tech. Although the current CTBT monitoring system is based on teleseismic phase detection, effort is being placed on research to highlight specific areas of the globe for which local and regional seismic networks could be employed. An automated waveform correlation regional location system could also serve as a rapid alert and automated location system by providing magnitude and hypocenter information within a few minutes of the occurrence of a hazardous earthquake.In the LWCEDS algorithm, processed waveforms are correlated with theoretical travel-time envelopes, and a grid search is performed to identify the space-time solutions that yield the highest correlations. High correlation indicates that an event has occurred and that a good approximation to the correct origin time and hypocenter has been determined; explicit phase identification is not required. To avoid the large computational expense of calculating a complete correlation for each grid point, we use a laterally homogeneous velocity model and reformulate the problem into a single matrix multiplication and matrix assessment for each time step. LWCEDS has been successfully tested on a suite of local and regional seismic events selected to span the range of expected event quality. Preliminary results from our sparse network show typical epicentral errors of less than 3 km for local events and, with notable exceptions, to within 10 to 20 km for regional events. Similar results were obtained during an on-line experiment conducted to generate daily bulletins during the time period from 3 December 1996 through 7 January 1997. Data from 156 triggers were processed, including 33 teleseisms, 102 regional events (includes explosions), and 21 local earthquakes. Results from this expanded test set are encouraging but reveal the need for a method to mask or flag various electronic and telemetry spikes.
An artificial neural network approach for broadband seismic phase picking
Authors: Zhao Yue , Takano Kiyoshi 
Published: August 2021

AbstractThis article presents a method for picking broadband seismic phases by using backpropagation neural networks (BPNNs) as detectors. By combining the results from three BPNN detectors—long term, mid-term, and short term—the method combines the features of short term's higher accuracy and long term's lower false alarm rate. We demonstrate that proper pre- and postprocessing of the data can help to improve the system's performance. The determination of the architecture and parameters for BPNNs is also discussed in this article. The devised BPNN detector is applied to 1254 broadband seismograms of the IRIS network to determine the first arrival, which is expected to be used in tomographic studies of the mantle structure. The results show that the first arrival can be identified for more than 95% of the 1254 seismograms. The automatically picked travel times have a reasonable accuracy; more than 85% have an error of less than 1 sec, and about 80% have an error of less than 0.5 sec.
Lateral propagation effects observed at Parkway, New Zealand. A case history to compare 1D versus 2D site effects
Authors: Chávez-García Francisco J. , Stephenson William R. , Rodríguez Miguel 
Published: August 2021

AbstractThe importance of 2D or 3D site effects has been shown by theoretical studies. However, there is a lack of observational evidence of site effects due to lateral heterogeneities. We have evaluated 1D and 2D site effects in the data obtained by a dense seismograph array that operated for more than 2 months in the alluvial basin of Parkway, New Zealand. 1D site effects were evaluated using three independent techniques: spectral ratios relative to a reference station, spectral ratios of horizontal relative to vertical ground motion, and a generalized inversion scheme. Site effects due to lateral heterogeneity were investigated in detail for two events using frequency-wavenumber analysis. Our results show that it is not possible to separate 1D from 2D site effects using frequency-domain techniques. This explains the scatter obtained from standard 1D data analysis: the 1D resonance peaks will be more or less contaminated with laterally propagating waves for different events.
The calculation of expected loss using probabilistic seismic hazard
Authors: Cao Tianqing , Petersen Mark D. , Cramer Chris H. , Toppozada Tousson R. , Reichle Michael S. , Davis James F. 
Published: August 2021

AbstractThe formulas for the estimation of expected loss from probabilistic seismic hazard are presented systematically by using the basics of calculating expected values and the concept of distributing the total loss between the insurer and the insured. The conversion from acceleration to intensity and then to loss factor (the ratio of damage value to the property value) is applied in the calculation. The seismic hazard used in the loss calculation is for four locations in California. These locations are representative of high and low hazards in California and of the two most populated areas in northern and southern California. The calculated loss values show a strong dependence on the hazard and the soil conditions. The deaggregation of total loss with respect to intensity, acceleration, and loss factor shows that a greater portion of the total loss in the high-hazard region is from large intensities and accelerations compared with the low-hazard region. The deaggregation with respect to loss factor reveals that most of the loss is from loss factors below 15-20%, even for the high-hazard regions. This result has a significant impact on the amount of the loss that is greater than the deductible. The calculation of loss to the insurer shows that a mere 5% deductible reduces the loss to the insurer by 40-50% for a high-hazard region and by more than that for a low-hazard region. Underinsurance and inflation have the effect of increasing the loss to the insurer but are less significant than the effect of deductible in reducing the loss to the insurer. These calculations suggest that updating the relation converting ground motion to loss factor is critical. In addition, the correction for soil condition needs to be calibrated with more recent strong-motion and earthquake damage data.
Numerical evaluation of the effect of cross-coupling of different components of ground motion in site response analyses
Authors: Paolucci Roberto 
Published: August 2021

AbstractThe effect of cross-coupling between the three components of ground motion in the evaluation of site-response functions, such as standard spectral ratios (SSRs) and horizontal-to-vertical spectral ratios (HVSRs), is analyzed in this article. Numerical analyses of the seismic response of fully 3D geological structures, namely, a real topographic irregularity and an ideal stratigraphic inclusion, have been carried out to obtain a 3D transfer function in the form of a 3 × 3 matrix. Each element of this matrix contains the frequency response in the ith direction due to an input motion in the jth direction. A synthetic set of acceleration time histories at the surface of the geological irregularity has been created by convolution with the 3D transfer function, using as input motion different real multicomponent strong-motion accelerograms recorded at stiff-soil or rock sites. The SSRs and HVSRs are calculated and compared with the theoretical 3D transfer function in order to highlight the effect of cross-coupling terms. These are found to generate a rather large dispersion in the site-response functions, as well as response peaks that could be misleading in the interpretation of both numerical and observed spectral ratios.
Two-dimensional linear and nonlinear wave propagation in a half-space
Authors: Xu Heming , Day Steven M. , Minster Jean-Bernard H. 
Published: August 2021

AbstractWe examine a staggered pseudospectral method to solve a two-dimensional wave propagation problem with arbitrary nonlinear constitutive equations, and evaluate a general image method to simulate the traction-free boundary condition at the surface. This implementation employs a stress-velocity formulation and satisfies the free surface condition by explicitly setting surface shear stress to zero and making the normal stress antisymmetric about the free surface. Satisfactory agreement with analytical solutions to Lamb's problem is achieved for both vertical point force and explosion sources, and with perturbation solutions for nonlinearly elastic wave propagation within the domain of validity of such solutions. The Rayleigh wave, however, suffers much more severe numerical dispersion than do body waves. At four grids per wavelength, the relative error in the Rayleigh-wave phase velocity is 25 times greater than the corresponding error in the body-wave phase velocity. Thus for the Rayleigh wave, the pseudospectral method performs no better than a low-order finite difference method.A substantial merit of the image approach is that it does not assume any particular rheology, the method is readily applicable even when stresses are not analytically related to kinematic variables, as is the case for most nonlinear models. We use this scheme to investigate the response of a nonlinear half-space with endochronic rheology, which has been fit to quasi-static and dynamic observations. We find that harmonics of a monochromatic source are generated and evolve with epicentral range, and energy is transferred from low to higher frequencies for a broadband source. This energy redistribution characteristic of the propagation is strain-amplitude dependent, consistent with laboratory experiments. Compared with the linear response, the nonlinear response of an endochronic layer near the surface shows a deamplification effect in the intermediate-frequency band and an amplification effect in the higher-frequency band. The computational method, with modifications to accommodate realistic nonlinear soil characteristics, could be applied to estimate earthquake strong ground motions and path effects.
Seismic threshold monitoring for continuous assessment of global detection capability
Authors: Kværna Tormod , Ringdal Frode 
Published: August 2021

AbstractContinuous seismic threshold monitoring is a technique that has been developed over the past several years to assess the upper magnitude limit of possible seismic events that might have occurred in a geographical target area. The method provides continuous time monitoring at a given confidence level. In this article we expand upon previous work to apply the method to a global network of seismic stations and give examples of applications from a prototype system that will be installed at the International Data Center for monitoring the Comprehensive Nuclear Test Ban Treaty.Using a global grid of 2562 geographical aiming points, we computed site-specific threshold traces for each grid point and applied spatial interpolation to obtain full global coverage. For each grid point, the procedure is in principle to “focus” the network by tuning the frequency filters and array beams using available information on signal and noise characteristics at each station-site combination. Standard global P-phase attenuation relationships and travel-time tables (IASP91) are used in this initial implementation, but the system lends itself easily to applying station-site-specific corrections (magnitudes, travel times, etc.) to each seismic phase.We give examples of two main types of applications based on data from a worldwide seismic network: (a) an estimated continuous global threshold level and (b) an estimated continuous global detection capability. The first application provides a continuous view of the global seismic “background field” as calculated from the station data, with the purpose of assessing the upper magnitude limit of any seismic event that might have occurred anywhere on Earth. The second application introduces detection thresholds for each station and provides a simplified estimate, continuously in time, of the n-station detection capability of the network. The latter approach naturally produces higher threshold values, with the difference typically being 0.5-1 magnitude unit. We show that both these approaches are useful especially during large earthquakes, where conventional capability maps based on statistical noise and signal models cannot be applied.In order to illustrate the usefulness of combining global monitoring with site-specific monitoring for areas of special interest, we consider a large earthquake aftershock sequence in Kamchatka and its effect on the threshold trace in a very different region (the Novaya Zemlya nuclear test site). We demonstrate that the effects of the aftershock signals on the thresholds calculated for Novaya Zemlya are modest, partly because of the emphasis on high-frequency signals. This indicates that threshold monitoring could provide significantly improved seismic monitoring during aftershock sequences compared with conventional methods, for which the large number of detected phases tends to saturate the phase association process.
Seismic signal detection by fractal dimension analysis
Authors: Tosi Patrizia , Barba Salvatore , De Rubeis Valerio , Di Luccio Francesca 
Published: August 2021

AbstractWe introduce a new detection algorithm with improved local and regional seismic signal recognition. The method is based on the difference between seismic signals and background random noise in terms of fractal dimension D. We compare the new method extensively with standard methods currently in use at the Seismic Network of the Istituto Nazionale di Geofisica. Results from the comparisons show that the new method recognizes seismic phases detected by existing procedures, and in addition, it features a greater sensitivity to smaller signals, without an increase in the number of false alarms. The new method was tested on real continuous data and artificially simulated high-noise conditions and demonstrated a capability to recognize seismic signals in the presence of high noise. The efficiency of the method is due to a radically different approach to the topic, in that the assertion that a signal is fractal implies a relationship between the spectral amplitude of different frequencies. This relationship allows, for the fractal detector, a complete analysis of the entire frequency range under consideration.
Active faulting in the Gulf of Aqaba: New knowledge from theMW 7.3 earthquake of 22 November 1995
Authors: Klinger Yann , Rivera Luis , Haessler Henri , Maurin Jean-Christophe 
Published: August 2021

AbstractOn 22 November 1995 the largest earthquake instrumentally recorded in the area, with magnitude MW 7.3, occurred in the Gulf of Aqaba. The main rupture corresponding to the strike-slip mechanism is located within the gulf of Aqaba, which forms the marine extension of the Levantine fault, also known as the Dead Sea fault. The Levantine fault accommodates the strike-slip movement between the African plate and the Arabian plate. The Gulf of Aqaba itself is usually described as the succession of three deep pull-apart basins, elongated in the N-S direction. Concerning historical seismicity, only two large events have been reported for the last 2000 years, but they are still poorly constrained. The seismicity recorded since installation of regional networks in the early 1980s had been characterized by a low background level punctuated by brief swarmlike activity a few months in duration. Three swarms have already been documented in the Gulf of Aqaba in 1983, 1990, and 1993, with magnitudes reaching at most 6.1 (MW). We suggest that the geometry of the rupture for the 1995 event is related to the spatial distribution of these previous swarms. Body-wave modeling of broadband seismograms from the global network, along with the analysis of the aftershock distribution, allow us to propose a well-constrained model for the rupture process. Northward propagation of the rupture has been found. We have demonstrated that three successive subevents are necessary to obtain a good fit between observed and synthetic wave forms. The total seismic moment released was 7.42 × 1019 N-m. The location of the subsevents shows that the three stages of the rupture involve three different segments within the gulf. Substantial surface breakage showing only normal motion (up to 20 cm) affecting beachrock was observed along the Egyptian coast. We show that these ruptures are only a secondary feature and are in no case primary ruptures. The stress tensor derived from striations collected in quaternary sediments shows radial extension. This result supports landsliding of the beach terraces under the action of the earthquake shaking.
Using waveform similarity to constrain earthquake locations
Authors: Menke William 
Published: August 2021

AbstractWe demonstrate that the numerical value of the cross-correlation between P or S waveforms, commonly computed to determine differential travel times for earthquake relocation, itself contains useful information about the relative location of the events. This information can be used to supplement traditional travel-time inversions (especially when few stations are available) and to investigate the heterogeneity that underlies the multiple scattering process.
Integration of high-resolution seismic and aeromagnetic data for earthquake hazards evaluations: An example from the Willamette Valley, Oregon
Authors: Liberty Lee M. , Trehu Anne M. , Blakely Richard J. , Dougherty Martin E. 
Published: August 2021

AbstractAeromagnetic and high-resolution seismic reflection data were integrated to place constraints on the history of seismic activity and to determine the continuity of the possibly active, yet largely concealed Mount Angel fault in the Willamette Valley, Oregon. Recent seismic activity possibly related to the 20-km-long fault includes a swarm of small earthquakes near Woodburn in 1990 and the magnitude 5.6 Scotts Mills earthquake in 1993. Newly acquired aeromagnetic data show several large northwest-trending anomalies, including one associated with the Mount Angel fault. The magnetic signature indicates that the fault may actually extend 70 km across the Willamette Valley to join the Newberg and Gales Creek faults in the Oregon Coast Range. We collected 24-fold high-resolution seismic reflection data along two transects near Woodburn, Oregon, to image the offset of the Miocene-age Columbia River Basalts (CRB) and overlying sediments at and northwest of the known mapped extent of the Mount Angel fault. The seismic data show a 100-200-m offset in the CRB reflector at depths from 300 to 700 m. Folded or offset sediments appear above the CRB with decreasing amplitude to depths as shallow as were imaged (approximately 40 m). Modeling experiments based on the magnetic data indicate, however, that the anomaly associated with the Mount Angel fault is not caused solely by an offset of the CRB and overlying sediments. Underlying magnetic sources, which we presume to be volcanic rocks of the Siletz terrane, must have vertical offsets of at least 500 m to fit the observed data. We conclude that the Mount Angel fault appears to have been active since Eocene age and that the Gales Creek, Newberg, and Mount Angel faults should be considered a single potentially active fault system. This fault, as well as other parallel northwest-trending faults in the Willamette Valley, should be considered as risks for future potentially damaging earthquakes.
Pregnancy and marriage among teenage schoolgirls in rural western Kenya; a secondary analysis of a menstrual solution feasibility COHORT study
Authors: Nyothach Elizabeth , Ambrose Eleanor , Van Eijk Anna M. , Obor David , Mason Linda , Oduor Clifford , Zulaika Garazi , Laserson Kayla F. , Phillips Howard Penelope A. 
Published: August 2021

Background: Adolescent pregnancy increases the risk of adverse health outcomes, social stigma, loss of education and employment, and early marriage. Research characterising at risk girls will inform targeting of effective interventions.Methods: Risk characteristics for adolescent pregnancy were evaluated in schoolgirls aged 14-16 years as a secondary analysis in a longitudinal study evaluating menstrual products in 30 primary schools in rural western Kenya. Characteristics of participants were collected at baseline and follow-up. Descriptive and multivariate analysis were conducted.Results: Of 766 girls enrolled into the study, aged 14-16 years and followed over a school year, 53 (7%) were or became pregnant, with three (6%) neonatal deaths reported. Girls with the lowest compared with the highest socio-economic status had 2.5-fold higher risk of pregnancy (13.1% vs 5.0%: adjusted risk ratio (aRR) 2.48, confidence limits 1.32-4.64). Girls reporting early menarche (<13 years) had a 2.5-fold higher risk of pregnancy (aRR 2.61, 1.38-4.92), while those happy in school had a reduced risk (aRR 0.60, 0.34-1.04). Age, presence of parents, and being harassed by boys or men were not associated with pregnancy risk. Twenty-two girls (2.9%) married by the study end. Marriage was significantly associated with pregnancy (aRR 13.44, 5.50-32.83) and a history of sex at baseline (3.15, 1.55-6.38). All but two girls dropped out of school when pregnant with only five girls returning after delivery.Conclusions:Pregnancy leading to school dropout and child marriage remains an urgent public health concern among teenage girls in rural Kenya. Interventions are needed to enable schoolgirls to reach their educational potential.