bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of the hanging wall and footwall on ground motions recorded during the Northridge earthquake
Authors: Abrahamson N. A. , Somerville P. G. 
Published: September 2021

AbstractSystematic differences in ground motion on the hanging wall and footwall during the Northridge earthquake are evaluated using empirical data. An empirical model for the hanging-wall effect is developed for the Northridge earthquake. This empirical model results in up to a 50% increase in peak horizontal accelerations on the hanging wall over the distance range of 10 to 20 km relative to the median attenuation for the Northridge earthquake. In contrast, the peak accelerations on the footwall are not significantly different from the median attenuation over this distance range. Recordings from other reverse events show a similar trend of an increase in the peak accelerations on the hanging wall, indicating that this systematic difference in hanging-wall peak accelerations is likely to be observed in future reverse events.
Lifeline utilities performance in the 17 January 1994 Northridge, California, earthquake
Authors: Lund Le Val 
Published: September 2021

Abstract
Lifelines performed an important role in emergency response and restoring the community after the 17 January 1994 Northridge earthquake. Telecommunications, radio, and electronic media played a valuable role in directing emergency response for essential services, directing the repairing of damaged lifelines and informing the public of vital information. Water supply was necessary where available for public fire protection. Highways and roads were used to move rescue, repair, fire, and medical teams and their supplies and equipment to the damaged areas. Although the Northridge earthquake was severe, the lifeline disruption represented a relatively small percentage of inconvenience to the total population served within the total earthquake impact area. The 1994 Northridge event showed improvement in the seismic performance of lifeline facilities and equipment installed and built, under modern seismic codes, since the 1971 San Fernando earthquake.
Shallow crustal structure from short-period Rayleigh-wave dispersion data in southwestern Taiwan
Authors: Chung Jen-Kuang , Yeh Yeong Tein 
Published: September 2021

Abstract
Strong ground motions in the period range of 1 to 5 sec observed in Taiwan in a dense network during the Tapu earthquake (ML = 5.8) of 15 December 1993 were dominated by fundamental-mode Rayleigh waves. The shallow crustal structure beneath this network was determined from the group velocity dispersion data using standard inversion techniques. Results show that an alluvial layer with a thickness of only about 160 m exists over the sedimentary structure in the western coastal plain. A clear lateral variation in the shear-wave velocity along a cross section perpendicular to the western structural grain (Ho, 1982) was resolved.
For the purpose of retrieving the ground motions to confirm the proposed model, forward modeling with a two-dimensional finite-element method was used and agreed well with the observed seismograms when slightly lower velocities than those of the inversions were used. It is concluded that the velocity model estimated using group velocity data cannot definitively correspond to the real one at such short distances and in such a complex structure. On the basis of quantitative simulations, a very soft surface layer must be crucial in the interpretation of the slow wave trains with long duration and the rare prograde particle motions. The results suggest that these surface waves may be generated by the conversion of body waves at the boundary of the western coastal plain and foothills.
RegionalLgattenuation for the continental United States
Authors: Benz Harley M. , Frankel Arthur , Boore David M. 
Published: September 2021

AbstractMeasurements of the Fourier amplitude spectra of Lg phases recorded at high frequency (0.5 to 14.0 Hz) by broadband seismic stations are used to determine regional attenuation relationships for southern California, the Basin and Range Province, the central United States, and the northeastern United States and southeastern Canada. Fourier spectral amplitudes were measured every quarter octave from Lg phases windowed between 3.0 and 3.7 km sec−1 and recorded in the distance range of 150 to 1000 km. Attenuation at each frequency is determined by assuming a geometrical spreading exponent of 0.5 and inverting for Q and source and receiver terms. Both southern California and the Basin and Range Province are well described by low Lg Q and frequency-dependent attenuation. Lg spectral amplitudes in southern California are fit at low frequencies (0.625 to 0.875 Hz) by a constant Lg Q of 224 and by a frequency-dependent Lg Q function Q = 187−7+7f0.55(±0.03) in the frequency band 1.0 to 7.0 Hz. The Basin and Range Province is characterized by a constant Lg Q of 192 for frequencies of 0.5 to 0.875 Hz and by the frequency-dependent Lg Q function Q = 235−11+11f0.56(±0.04) in the frequency band 1.0 to 5.0 Hz. A change in frequency dependence above 5.0 Hz is possible due to contamination of the Lg window by Pn and Sn phases. Lg spectral amplitudes in the central United States are fit by a mean frequency-independent Lg Q of 1291 for frequencies of 1.5 to 7.0 Hz, while a frequency-dependent Lg Q of Q = 1052−83+91(f/1.5)0.22(±0.06) fits the Lg spectral amplitudes for the northeastern United States and southeastern Canada over the passband 1.5 to 14.0 Hz. Attenuation measurements for these areas were restricted to frequencies &gt;1.5 Hz due to larger microseismic noise levels at the lower frequencies.
Bandpass filtering to reduce noise on seismograms: Is there a better way?
Authors: Douglas A. 
Published: September 2021

Abstract
Short-period (SP) P waves at low signal-to-noise ratios (S/Ns) usually appear as signals of about 1 Hz or higher frequencies riding on background noise with frequencies of 0.5 Hz or less. Often bandpass filtering is used to further attenuate the noise relative to the signal to improve the S/N. However, bandpass filtering introduces significant distortion into the signal. Here the use of optimum filters is described, such filters being constructed using autocorrelation functions of the signal and noise derived from noise and signal models. The autocorrelation of the impulse response of the recording system is used to describe the signal. For the noise, a tapered cosine wave is used that has the frequency of the main noise component. To compute the filter, the relative sizes of the signal and noise correlations should be proportional to the square of the S/N. Now, the noise can be estimated by subtracting the estimated signal from the observed seismogram. This property can be used to decide by trial and error on the S/N. The optimum S/N is found by gradually reducing the trial ratio starting from too high a value, until the noise has the amplitude expected and there is no evidence of significant signal in the noise estimate. Examples are given showing how the method can lift observed signals off the background noise with less distortion to the signal than usually occurs with bandpass filtering.
Inversion ofRgwaveforms recorded in southern Spain
Authors: Navarro Manuel , Corchete Victor , Badal José , Canas José A. , Pujades Luis , Vidal Francisco 
Published: September 2021

AbstractGroup velocity dispersion measurements of Rg waves generated either by blasts or by local earthquakes are used to investigate the shallow crustal structure of Almería (southern Spain). In principle, the usable frequency range of 250 to 2000 mHz allows determination of structures to depths of about 4 km. For this purpose, the main operations are a detailed dispersion analysis of high-frequency Rayleigh waves propagating along very short paths and the inversion of Rg-wave group velocities. A total of 21 seismic events were studied. These events had small magnitudes (2.0 to 2.5 approximately) and very shallow focal depths (about 100 m) and were taken from a set of 214 events that occurred in 1991 during a Spanish-Italian seismic experiment. The events were recorded at seven single-component stations belonging to the Regional Seismic Network of Andalucía at approximate distances of between 15 and 57 km from the source. These events were grouped into six seismic sources according to specific criteria. We used digital filtering techniques providing a significant improvement in signal-to-noise ratio to determine ray-path group velocities, and we inverted dispersion data via generalized inversion. In order to obtain refined dispersion data, we have carried out a further regionalization of group velocities, and thus six small subregions have been resolved in group velocities. The highest group velocity values, from 1.93 to 2.25 km sec−1, correspond to the Filabres mountain range, which is an area containing materials of the Nevado-Filábride complex of Paleozoic and Triassic age. On the other hand, low velocity values, between 1.39 and 1.56 km sec−1, correspond to the Alhamilla mountain range, which belongs to the Alpujárride complex and contains conglomerates of the Cambrian and Tortonian periods. The velocities obtained for the neogene-quaternary basin of the Andarax river, with materials of the Tortonian and Pliocene periods, are also very low, between 1.35 and 1.68 km sec−1. We inverted the regionalized group velocities in order to obtain the shear velocity structure of the region for depths down to 4 km. According to the regional Earth models that we obtained, we find clear variations in velocity both laterally and vertically for several zones with different composition. The Filabres mountain range shows high shear velocity values: 2.14 to 2.83 km sec−1. In the opposite end, we have the Andarax basin that presents the lowest shear velocity values, consistent with its sedimentary structure: 1.56 to 2.55 km sec−1. Intermediate shear-wave velocities characterize the remaining regions: the Tabernas-Sorbas basin, the Gádor mountain range, and the volcanic region of Nijar-Cape of Gata. Although the relationship between lateral changes in Rg dispersion and geologic structure may not be straightforward, in this study, we have observed a correlation between those changes and the sharply contrasting geology between adjacent geological formations.
Empirical observations regarding reverse earthquakes, blind thrust faults, and quaternary deformation: Are blind thrust faults truly blind?
Authors: Lettis William R. , Wells Donald L. , Baldwin John N. 
Published: September 2021

AbstractActive thrust faults pose a significant seismic hazard worldwide. Many of these faults include “blind” thrusts, where the propagating fault tip does not reach the Earth's surface, and “buried” faults, where the geomorphic expression of the fault is obscured by subsequent sedimentation and/or erosion. This raises the issue of whether conventional geologic, geomorphic, and paleoseismic methods can be used to identify and characterize thrust faults for the assessment of seismic hazards or whether these faults sometimes are truly “blind.” We compiled a data base of 148 worldwide moderate- to large-magnitude thrust/reverse earthquakes to evaluate whether or not the event occurred on a fault that could have been identified prior to the earthquake on the basis of recognizable Quaternary surface deformation (i.e., a pre-existing fault or fold). Analysis of the data shows that interplate reverse earthquakes almost always are associated with pre-existing Quaternary deformation that was or could have been recognized prior to the earthquake. In particular, most interplate reverse earthquakes are associated with an active reverse fault at the surface and/or an active anticline. In contrast, intraplate reverse earthquakes seldom occur on faults associated with pre-existing recognizable surface deformation. We conclude that thrust faults can be detected in interplate regions with careful Quaternary geologic and geomorphic mapping; furthermore, the absence of Quaternary surface deformation can be used to infer the absence of an underlying active blind thrust fault in interplate tectonic settings. However, the data show that Quaternary geologic mapping techniques alone likely are insufficient to characterize blind thrusts in intraplate regions. In these areas, inclusion of a floating or random earthquake may be necessary to assess earthquake hazards.
Attenuation of coda waves at the Cerro Prieto geothermal field, Baja California, Mexico
Authors: Domínguez Tonatiuh , Rebollar Cecilio J. , Fabriol Hubert 
Published: September 2021

AbstractWe analyzed coda waves from 22 local events recorded by a temporary network of seismic stations deployed in the Cerro Prieto geothermal field of Baja California, Mexico, to estimate coda attenuation Qc in the frequency range 6 to 24 Hz. We used Sato's (1977) single scattering model for a coda window of 12.5 ± 2.5 sec beginning at twice the S-wave travel time. All events analyzed were located within the exploitation area with depths up to 6 km and source-to-receiver distances less than 8 km. At frequencies of 3, 4, and 5 Hz, rms amplitudes of coda to S waves showed no clear decay or even negative Qc values. This could be due to the inability of the theory to fit the data at low frequencies as it was suggested by Fehler et al. (1992). Within the range of variation, five of the seven stations showed similar Qc values that ranged from about 200 at 6 Hz to about 490 at 24 Hz. Assuming a power-law dependence of the form Qc (ƒ) = Q0ƒη, we estimated a value of Q0 = 111.5 ± 23 and a frequency dependence η of 0.41 ± 0.1. We found site effects at two stations that were located close to hot springs and mud pools.
Bias in surface-wave magnitudeMsdue to inadequate distance corrections
Authors: Rezapour Mehdi , Pearce Robert G. 
Published: September 2021

AbstractWe investigate bias in surface-wave magnitude using the complete ISC and NEIC datasets from 1978 to 1993. We conclude that although there are some small differences between the ISC and NEIC magnitudes, there is no major difference between these agencies for this presentation of the global dataset. The frequency-distance plot for reported surface-wave amplitude observations exhibits detailed structure of the body-wave amplitude-distance curve at all distances; the influence of the surface-wave amplitude decay with distance is much less apparent. This censoring via the body waves represents a large deficit in the number of potentially usable surface-wave amplitude observations, particularly in the P-wave shadow zone between Δ = 100° and 120°. We have obtained two new modified Ms formulas based upon analysis of all ISC data between 1978 and 1993. In the first, the conventional logarithmic dependence of the distance correction is retained, and we obtainM s e = log ( A / T ) max + 1.155 log ( Δ ) + 4.269 .In the second, we make allowance for the theoretically known contribution of dispersion and geometrical spreading, to obtainM s t = log ( A / T ) max + 1 3 log ( Δ ) + 1 2 log ( sin Δ ) + 0.0046 Δ + 5.370.Comparison of these formulas with other work confirms the inadequacy of the distance-dependence term in the Gutenberg and Prague formulas, and we show that our first formula, as well as that of Herak and Herak, gives less bias at all epicentral distances to within the scatter of the observed dataset. Our second formula provides an improved overall distance correction, especially beyond Δ = 145°. We show evidence that Airy-phase distance decay predominates at shorter distances (Δ≦30°), but for greater distances, we are unable to resolve whether this or non-Airy-phase decay predominates. Assuming 20-sec surface waves with U = 3.6 km/sec, we obtain a globally averaged apparent Q−1 of 0.00192 ± 0.00026 (Q ≈ 500). We argue that our second formula not only improves the distance correction for surface-wave magnitudes but also promotes the analysis of unexplained amplitude anomalies by formally allowing for those contributions that are theoretically predictable. We conclude that there remains systematic bias in station magnitudes and that this includes the effects of source depth, different path contributions, and differences in seismometer response. For intermediate magnitudes, Mts shows less scatter against log M0 than does Ms calculated using the Prague formula.
Estimates of regional and local strong motions during the great 1923 Kanto, Japan, earthquake (Ms8.2). Part 2: Forward simulation of seismograms using variable-slip rupture models and estimation of near-fault long-period ground motions
Authors: Sato Toshiaki , Graves Robert W. , Somerville Paul G. , Kataoka S. 
Published: September 2021

AbstractThis article addresses the forward simulation of regional and local strong motions from the 1923 Kanto, Japan, earthquake (Ms 8.2), using two variable-slip rupture models: the Wald and Somerville (1995) slip model (WS slip model) derived from geodetic and teleseismic data and a resampled version of the Takeo and Kanamori (1992) slip model (TK slip model) that was obtained from the forward simulation of the Ewing seismoscope record at Hongo (HNG, epicentral distance R = 60 km). Green's functions are calculated using flat-layered velocity models for specific source-receiver paths, which were developed in our first article (Sato et al., 1998). For regional stations Sendai (R = 350 km) and Gifu (R = 220 km), the WS slip model provides a much better match to the waveform data than the TK slip model. For local station HNG, the first 40 sec of the N77°E Imamura seismogram is successfully reproduced by both of the slip models, although the arrivals are delayed in the TK slip model. The large-amplitude long-duration, long-period (13 sec) later phases in the southwest-component Ewing seismogram are not reproduced by either of the slip models. Our results suggest that the WS slip model gives a better representation of the overall rupture process of the 1923 event than the TK slip model does. Near-fault long-period ground motions calculated at several stations using the WS slip model suggest that the motions at HNG were not the largest in the Tokyo metropolitan area during the 1923 event. In addition, we estimate that the ground motions near the southern margin of the fault plane were significantly larger than the recorded near-fault motions of recent magnitude 7 earthquakes, such as Northridge and Kobe, for periods longer than several seconds. This suggests that design codes based on the experience of these recent events may not adequately describe the long-period response expected during a magnitude 8 earthquake.
An intensity survey of households affected by the Northridge, California, earthquake of 17 January 1994
Authors: Dengler L. A. , Dewey J. W. 
Published: September 2021

AbstractFollowing the Northridge, California, earthquake of 17 January 1994, the Humboldt Earthquake Education Center (HEEC) conducted a telephone survey of approximately 6000 adults from within the felt region to study the earthquake's effects on individual households. We tabulate human responses to the earthquake and observations of the earthquake's effects on inanimate objects from the HEEC survey as a function of independently assigned U.S. Geological Survey Modified Mercalli (USGS MM) intensity for the same communities. Human responses and subjective judgments about the severity of shaking, when averaged over a large number of samples, are useful discriminants of the levels of strong ground motion up to those associated with USGS MM intensity VII, notwithstanding that individual human responses and subjective judgments are notoriously unreliable. A threshold of strong ground motion corresponds to USGS MM intensity of about VII, above which over 40% of respondents described the earthquake as “violent” and most people reported difficulty standing, furniture displaced, and some damage to their homes. Even at intensities VIII and IX, however, relatively few people (about 15%) described their reaction as “panic” and only about 12% reported major damage to their homes. The HEEC phone-survey data show that, in communities of low to moderate shaking, USGS MM intensities estimated from a single postal questionnaire are quite robust. At USGS MM intensity of V and below, 88% of USGS MM intensities determined from postal questionnaires are within one intensity unit of intensities determined from the more numerous HEEC telephone survey data for the same community. We introduce the concept of a community decimal intensity scale (CDI) based on telephone-survey data and calibrated to agree on average with the USGS MM intensities. The CDIs are more regularly distributed than the USGS MM intensities and show much less scatter when plotted as a function of epicentral distance. CDIs show promise as a tool for comparing regional attenuation, for delineating variations in shaking strength within areas mapped as a single MM zone, and for rapid preliminary intensity estimates utilizing electronic media.
The effect of the earthquake radiation pattern on mb—A study using aftershocks in the 1976 Gazli sequence
Authors: Bowers David , Douglas Alan 
Published: September 2021

Abstract
We use published focal mechanisms to estimate radiation coefficients to four short-period arrays recording teleseismic P from 38 aftershocks in the 1976 Gazli, Uzbekistan, earthquake sequence. We divide the observed P-wave amplitude by its radiation coefficient to estimate the P-wave amplitude that would be observed if it was from the maximum of the double-couple radiation pattern. We use this new P-wave amplitude to calculate a P-wave magnitude, mCb, that is independent of the P-radiation pattern if the focal mechanisms are without error. Analysis of variance shows that the random error in mCb is reduced relative to that in the original P-wave magnitudes mCb and that this reduction is statistically significant at the 11% level. Further, analysis of variance demonstrates that the radiation coefficients calculated from the focal mechanisms contain error but that this error is probably not large enough to mask the detection of the radiation effect in mOb. Published averages of the logarithm of P-radiation coefficients allow an assessment of the differences in network-averaged mb due to the radiation pattern of point earthquake and explosion sources. Network-averaged mb from a vertical strike-slip earthquake can differ from an explosion of similar scalar moment by as much as 1.0 m.u. (magnitude units). However, this difference can be as little as 0.2 m.u. if the earthquake mechanism is 30° dip slip. We argue that, if mb is required to be independent of the earthquake mechanism, the most appropriate network average is mCb − 0.48.