bluuebunny/crossref_metadata_2025_split huggingface dataset:
An absolute method of vertical seismometer calibration by reference to a falling mass with application to the measurement of the gain
Authors: Canuteson Eric , Zumberge Mark , Hanson Jeffrey 
Published: September 2021

Abstract
We measure the gain of a vertical seismometer by simultaneously recording the output of the seismometer and repeatedly measuring the displacement between the seismometer and a free-falling mass in a vacuum. The falling object provides an inertial reference frame. By comparing the ground motion measured by the seismometer with the independent record of displacement between the seismometer and inertial space, we obtain the gain. It is an absolute measurement of the gain relative to the local Lorentz reference frame. Bootstrap error estimates show that a high precision in the estimate of the gain can be obtained with a small number of individual drops. The method derived can be extended to multi-parameter searches of the vertical response function. The technique is also shown to reduce noise in absolute gravity measurements due to ground noise. Finally, we discuss the potential for replacing vibration isolation schemes in absolute gravity systems with digital noise reduction.
Static stress changes and earthquake triggering during the 1954 Fairview Peak and Dixie Valley earthquakes, central Nevada
Authors: Caskey S. J. , Wesnousky S. G. 
Published: September 2021

AbstractThe 16 December 1954 Dixie Valley (MS 6.8) earthquake followed the Fairview Peak (MS 7.2) earthquake by only 4 min and 20 sec. A three-dimensional model of the two dip-slip fault systems based on recent detailed field studies shows the ruptures were separated by a 6-km step in surface trace. A boundary-element approach shows that the static stress changes imposed by rupture of the Fairview Peak earthquake are in the correct sense to explain the northward propagation of faulting along four distinct faults that comprise the Fairview Peak earthquake and the subsequent triggering of the Dixie Valley earthquake. The location of rupture end points at sites where static stresses change sign is also used to suggest that static stress changes may play a role in controlling the extent of fault ruptures. We also observe that the largest coseismic surface displacements tend to correlate with those sections of the faults showing the largest positive stress change from preceding ruptures.
An evaluation of generalized likelihood ratio outlier detection to identification of seismic events in western China
Authors: Taylor Steven R. , Hartse Hans E. 
Published: September 2021

AbstractThe generalized likelihood ratio outlier detection technique for seismic event identification is evaluated using synthetic test data and frequency-dependent Pg/Lg measurements from western China. For most seismic stations that are to be part of the proposed International Monitoring System (IMS) for the Comprehensive Test Ban Treaty (CTBT), there will be few or no nuclear explosions in the magnitude range of interest (e.g., mb &lt; 4) on which to base an event-identification system using traditional classification techniques. Outlier detection is a reasonable alternative approach to the seismic discrimination problem when no calibration explosions are available. Distance-corrected Pg/Lg data in seven different frequency bands ranging from 0.5 to 8 Hz from the Chinese Digital Seismic Station WMQ are used to evaluate the technique. The data are collected from 157 known earthquakes, 215 unknown events (presumed earthquakes and possibly some industrial explosions), and 18 known nuclear explosions (1 from the Chinese Lop Nor test site and 17 from the East Kazakh test site). A feature selection technique is used to find the best combination of discriminants to use for outlier detection. Good discrimination performance is found by combining a low-frequency (0.5 to 1 Hz) Pg/Lg ratio with high-frequency ratios (e.g., 2 to 4 and 4 to 8 Hz). Although the low-frequency ratio does not discriminate between earthquakes and nuclear explosions well by itself, it can be effectively combined with the high-frequency discriminants. Based on the tests with real and synthetic data, the outlier detection technique appears to be an effective approach to seismic monitoring in uncalibrated regions.
Slip history of the 1994 Sanriku-Haruka-Oki, Japan, earthquake deduced from strong-motion data
Authors: Nakayama Wataru , Takeo Minoru 
Published: September 2021

Abstract
We analyzed the seismic waves of the 1994 Sanriku-Haruka-Oki earthquake (Mw = 7.7), which occurred in the aftershock area of the 1968 Tokachi-Oki earthquake (Mw = 8.2). Applying a multiple-time window inversion scheme to near-source strong-motion data, we obtained a detailed spatiotemporal rupture process and compared it with that of the Tokachi-Oki earthquake. The fault geometry is constructed based on the aftershock distribution. The obtained rupture model is consistent with the CMT solution even for a non-double-couple component. The total seismic moment is 4.0 × 1020 N-m. Large slips are concentrated in three asperities: the first asperity centers about 40 km south and 50 km west from the hypocenter with a maximum slip of 4.4 m, the second one centers about 60 km west from the hypocenter with a maximum slip of 2.2 m, and the third one lies about 110 km west from the hypocenter with a maximum slip of 2.6 m. The obtained moment rate and the duration on the first and second asperities are lower and much longer than those on the third asperity, respectively. The first asperity does not overlap with an area of large slip during the Tokachi-Oki earthquake, but the second or third seem to overlap with or be adjacent to the asperity of the Tokachi-Oki earthquake. Our inversion result also shows an abrupt change of the rupture velocity (from 1.8 to 3.0 km/sec) at the central part of the fault plane. A difference of the seismic coupling between the oceanic and the continental lithospheres at the trenchward side and at the landward side of the 143° E meridian seems to affect the rupture process of this earthquake.
Frequency response of a strainmeter
Authors: Lomnitz Cinna 
Published: September 2021

AbstractThe amplification of a strainmeter is frequency dependent. As the wavelength λ approaches the length L of the strainmeter, the amplitude vanishes, because the two extremes of the strainmeter are in phase. The sign of the response is inverted at zero crossings such that λ = L/n, n = 1, 2,…. Between L &lt; λ &lt; 2L, the amplitude of an incoming signal may be reduced by 60% or more. Filtering of the output may worsen the problem. Thus, strainmeters may be poorly suited for certain research purposes, including surface-wave studies and first-motion studies. The output of long-base strainmeters sited on low-velocity materials (such as the 732-m-long strainmeters at Piñon Flat Observatory) may require correction for amplitude distortion.
Evidence for stability in coda Q associated with the Egion (central Greece) earthquake of 15 June 1995
Authors: Tselentis G-Akis 
Published: September 2021

AbstractOne hundred seventy-two seismograms, recorded at one seismological station located close to the source region of the Egion (Ms = 6.2) 15 June 1995 earthquake, were used to measure values of Q from the decay of the earthquake coda. The collected data were compared between events that occurred before and after the main event. The analysis showed no significant temporal variation in the value of coda Q for the region.
Ground-motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor
Authors: Konno Katsuaki , Ohmachi Tatsuo 
Published: September 2021

AbstractThe spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.
Dynamic stress changes during earthquake rupture
Authors: Day Steven M. , Yu Guang , Wald David J. 
Published: September 2021

AbstractWe assess two competing dynamic interpretations that have been proposed for the short slip durations characteristic of kinematic earthquake models derived by inversion of earthquake waveform and geodetic data. The first interpretation would require a fault constitutive relationship in which rapid dynamic restrengthening of the fault surface occurs after passage of the rupture front, a hypothesized mechanical behavior that has been referred to as “self-healing.” The second interpretation would require sufficient spatial heterogeneity of stress drop to permit rapid equilibration of elastic stresses with the residual dynamic friction level, a condition we refer to as “geometrical constraint.” These interpretations imply contrasting predictions for the time dependence of the fault-plane shear stresses. We compare these predictions with dynamic shear stress changes for the 1992 Landers (M 7.3), 1994 Northridge (M 6.7), and 1995 Kobe (M 6.9) earthquakes. Stress changes are computed from kinematic slip models of these earthquakes, using a finite-difference method. For each event, static stress drop is highly variable spatially, with high stress-drop patches embedded in a background of low, and largely negative, stress drop. The time histories of stress change show predominantly monotonic stress change after passage of the rupture front, settling to a residual level, without significant evidence for dynamic restrengthening. The stress change at the rupture front is usually gradual rather than abrupt, probably reflecting the limited resolution inherent in the underlying kinematic inversions. On the basis of this analysis, as well as recent similar results obtained independently for the Kobe and Morgan Hill earthquakes, we conclude that, at the present time, the self-healing hypothesis is unnecessary to explain earthquake kinematics.
Correcting regional seismic discriminants for path effects in western China
Authors: Hartse H. E. , Flores R. A. , Johnson P. A. 
Published: September 2021

AbstractThe effect of path on regional seismic wave propagation can be significant. In an effort to improve discriminant performance, we explore the effect of path upon Pg/Lg ratios. Our primary objective is to find path corrections that reduce scatter within earthquake and explosion ratio populations, while at the same time increasing the separation between the two populations. We emphasize the 1.5- to 3-Hz and 2- to 4-Hz bands, as Pg and Lg in these bands can often be observed at smaller magnitudes and greater distances than higher-frequency bands, which have previously been shown to be reliable discriminants. For data, we use 271 earthquakes from northwest China, 25 nuclear explosions from the Kazakh test site (KTS), and one nuclear explosion from the Lop Nor test site recorded at station WMQ. We also use 185 earthquakes from the same region and seven nuclear explosion from the Lop Nor test site recorded at station AAK. Event-station distances range from 200 to 1400 km, earthquake magnitudes range between mb 2.5 and 6.2, and explosion magnitudes range between mb 4.5 and 6.5. In addition to ratio-distance trends, we examine Pg/Lg ratio-parameter trends related to topography, basin thickness, and crustal thickness. The parameters we consider are mean, roughness, gradient mean, and gradient roughness of the topography, basin thickness, and crustal thickness along each event-station path. We also consider the same parameters after weighting by path length. Through linear regressions, we found path corrections that reduce scatter within event populations, and we also found path corrections that increase the separation between earthquakes and KTS explosions recorded at WMQ. We obtained the best improvement in discrimination performance at WMQ by removing the trends of topography roughness, mean topography, and the gradient of basin thickness after weighting the parameters by path length. For AAK, we found that removing the trends of mean topography and the basement roughness improved discrimination performance over the uncorrected case. However, unlike WMQ, weighting these parameters by path length degraded discriminant performance. Because we see no predictable or repeatable trends for “adjacent” central Asian stations and overlapping regions of interest, we recommend an even more empirical approach to correcting for the effect of path. Where earthquakes are abundant, such as the Tian Shan, contouring a grid of ratio residuals (for each band of interest) may be a simpler method of finding appropriate path corrections.
A global test of a time-frequency small-event discriminant
Authors: Hedlin Michael A. H. 
Published: September 2021

Abstract
The Comprehensive nuclear-Test-Ban Treaty (CTBT), which was recently adopted by the UN General Assembly and signed by President Clinton, has lowered the testing yield limit to zero and raised the profile of small earthquakes and mining blasts. Because relatively small events are very common, there is a strong need for automated algorithms that can be used to screen out the events that are obviously chemical or natural and identify those few curious enough to warrant closer scrutiny. The primary objective of this article is to assess the utility of high-frequency spectral modulations for the discrimination of mining blasts from earthquakes and single explosions at near-regional distances. Mining blasts commonly yield spectral modulations that are independent of time and the recording component. This article describes an automated discriminant that looks for these delay-fire diagnostics in data recorded on one or three components by single stations, arrays, or regional networks. Distinct deployments in central Asia, Europe, and North America are used to assess the transportability of the approach. The discriminant tests give misclassification probabilities, estimated with multivariate statistics, ranging from 0.5 to 3.5%. Discrimination using time-frequency expansions does not rely on expert interpretation but is quite routine.
The article explores likely causes of the occasional discrimination outliers. Factors that can eliminate spectral modulations from a delay-fired event include attenuation, detonation anomalies (where deviations from the designed, regular, shot sequence occur), and waveform variability. Some natural events and single explosions will exhibit spectral modulations that most likely result from propagation resonance. Data from Kyrgyzstan and Nevada is used to illustrate these effects; however, inadequate ground truth information and lack of calibration explosions in most of these datasets keeps definitive conclusions, regarding why the method will sometimes fail, out of reach. These observations underscore the need to train this algorithm to most effectively deal with these processes and pair it with other, complementary, discriminants to allow accurate characterization of all small events.
Self-consistent retrieval of source parameters using mantle waves
Authors: Gouget Karine , Ihmlé Pierre F. , Campos Jaime , Montagner Jean-Paul 
Published: September 2021

AbstractThe large number of high-quality stations from global networks (e.g., IRIS, GEOSCOPE) allows for rapid and robust recovery of source parameters of large earthquakes. We present a self-consistent analysis of surface waves in terms of directivity parameters. The boxcar is often used to recover source parameters but is rarely a faithful representation of an event's time function. We demonstrate that more reliable estimates of directivity parameters can be obtained when we take into account the source time function (STF) of the event. A low-frequency STF is obtained from first (R1) and second (R2) orbit Rayleigh waves in the range 2 to 15 mHz, with a spectral synthesis and inversion method. We measure the differential amplitudes between data and 3D synthetics. We use the R1/R2 ratio of differential amplitudes to invert, in a single narrow-frequency band, for the event's apparent rupture azimuth and velocity. For the Mw 8.1 Chile 1995 event, data are consistent with unilateral southward propagation, with a velocity of about 2.4 km/sec. For the Mw 7.9 Mexico 1995 earthquake, the rupture propagated toward the NW at about 2.0 km/sec. Our low-frequency estimates agree with broadband studies of both events and can be retrieved rapidly on a routine basis after a large earthquake.
Attenuation relationship for estimation of peak ground horizontal acceleration using data from strong-motion arrays in India
Authors: Sharma M. L. 
Published: September 2021

Abstract
An attenuation relationship for peak horizontal ground accelerations for Himalayan region in India has been developed. The data base consists of 66 peak ground horizontal accelerations from five earthquakes recorded by strong-motion arrays in India. The present analysis uses a two-step stratified regression model. The attenuation relationship proposed is
log ( A ) = − 1.072 + 0.3903 M − 1.21 log ( X + e 0.5873 M ) ,
where A is the peak ground acceleration (g), M is the magnitude, and X is the hypocentral distance from the source. The residual sum of squares is 0.14. Comparison with other such attenuation relationships have been made. The proposed relationship giving lesser values at shorter distances compared to other relationships needs further investigation with a larger data set. The attenuation relationship needs upgradation when more data become available in future.
A physical model of the effect of a shallow weak layer on strong ground motion for strike-slip ruptures
Authors: Brune James N. , Anooshehpoor Abdolrasool 
Published: September 2021

AbstractWe report results of foam rubber modeling of the effect of a shallow weak layer on ground motion from strike-slip ruptures. Computer modeling of strong ground motion from strike-slip earthquakes has in some cases involved somewhat arbitrary assumptions about the nature of slip along the shallow part of the fault (e.g., fixing the slip to be zero along the upper 2 km of the fault plane). Fault-slip inversion studies indicate that the high-frequency radiation from the shallow part of strike-slip faults is typically less than that for the deeper parts of the fault. In many cases, faults (1) may be weak along the upper few kilometers of the fault zone and may not be able to maintain high levels of shear strain required for high dynamic energy release during earthquakes and (2) may have different constitutive relations for fault slip, for example, slip strengthening. The object of this article is to present results of physical modeling using a shallow weak layer, in order to support the physical basis for assuming a long rise time and a reduced high-frequency pulse for the slip on the shallow part of faults. A weak zone was modeled by inserting weak plastic layers of a few inches in width into the foam rubber model. The long-term strength of the weak layer is about an order of magnitude less than the rest of the model. The transient strength is velocity strengthening with the strength estimated to be about three times higher at slip velocities typical of dynamic slip events. It appears a 2-km-deep, weak zone along strike-slip faults could indeed reduce the high-frequency energy radiated from shallow slip and that this effect can best be represented by superimposing a small-amplitude, short rise-time pulse at the onset of a much longer rise-time slip. For the 15-cm weak zone, the average pulse amplitude is reduced by a factor of about 0.4. The reduction factor for the 20-cm case is about 0.2. For the 30-cm case, it is about 0.1. From these results, we can see that the thicker the weak layer, the more difficult it is for a short rise-time acceleration pulse to push its way through the weak layer to the surface. The velocity strengthening property of the weak layer further damps the slip motion and increases the rise time. These results support reducing the high-frequency radiation from shallower parts of strike-slip faults in modeling studies if it is known that the shallow part of the fault is weak or has not stored up a large shear stress.
Using safety inspection data to estimate shaking intensity for the 1994 Northridge earthquake
Authors: Thywissen Katharina , Boatwright John 
Published: September 2021

Abstract
We map the shaking intensity suffered in Los Angeles County during the 17 January 1994, Northridge earthquake using municipal safety inspection data. The intensity is estimated from the number of buildings given red, yellow, or green tags, aggregated by census tract. Census tracts contain from 200 to 4000 residential buildings and have an average area of 6 km2 but are as small as 2 and 1 km2 in the most densely populated areas of the San Fernando Valley and downtown Los Angeles, respectively. In comparison, the zip code areas on which standard MMI intensity estimates are based are six times larger, on average, than the census tracts. We group the buildings by age (before and after 1940 and 1976), by number of housing units (one, two to four, and five or more), and by construction type, and we normalize the tags by the total number of similar buildings in each census tract. We analyze the seven most abundant building categories. The fragilities (the fraction of buildings in each category tagged within each intensity level) for these seven building categories are adjusted so that the intensity estimates agree. We calibrate the shaking intensity to correspond with the modified Mercalli intensities (MMI) estimated and compiled by Dewey et al. (1995); the shapes of the resulting isoseismals are similar, although we underestimate the extent of the MMI = 6 and 7 areas. The fragility varies significantly between different building categories (by factors of 10 to 20) and building ages (by factors of 2 to 6). The post-1940 wood-frame multi-family (≧5 units) dwellings make up the most fragile building category, and the post-1940 woodframe single-family dwellings make up the most resistant building category.
Quick and reliable determination of magnitude for seismic early warning
Authors: Wu Yih-Min , Shin Tzay-Chyn , Tsai Yi-Ben 
Published: September 2021

AbstractThis article reports efforts toward using real-time earthquake monitoring by the Taiwan Central Weather Bureau to meet the needs of seismic early warning. Twenty-three sets of strong-motion data from moderate earthquakes (ML &gt; 5.0) in the Taiwan area are used to demonstrate the feasibility of this goal. For earthquakes larger than ML 5, epicenters can be reliably determined in about 15 sec after the arrival of the P wave at the nearest station. The earthquake magnitude ML cannot be determined in the same time frame due to incomplete recording of shear waves at some stations. However, the magnitude based on the first 10 sec of signal (ML10) can be related to ML as follows:M L = 1.28 * M L 10 − 0.85 ± 0.13 .Our results show that the real-time strong-motion system routinely used by the Central Weather Bureau can be used to determine epicenters and magnitudes in about 30 sec after occurrence of earthquakes in Taiwan. Such information hopefully can be used to reduce damage to society.