Spectral discrimination between NTS explosions and Western United States earthquakes at regional distances

Abstract Spectral ratio disciminants are applied to 72 Western United States earthquakes and 64 NTS explosions recorded at four broadband seismic stations surrounding NTS. The ratio of the energy in the 1- to 2- and 6- to 8-Hz bands for Pn, Pg, and Lg is calculated and a simple distance correction applied to the data. The spectral ratio appears to have potential as a disciminant at relatively small magnitudes (3.0 < mb < 4.5) and single station misclassification probabilities for detected phases range from 4 to 33 per cent, with Lg showing the best performance followed by Pg and Pn. Below mb 4.5 to 5.0, the earthquakes are observed to have more high-frequency energy than the explosions for all three phases. This observation may be due to actual source differences or to depth-dependent effects of attenuation on the shallow explosions and deeper earthquakes. At higher magnitudes, the two populations merge and discrimination is poor. Overburied explosions are characterized by the existence of more high-frequency energy than those at standard containment depths and are often misclassified. The Brune dislocation source model is shown to satisfactorily fit the earthquake spectral ratios plotted as a function of mb for reasonable stress drops. However, the Mueller-Murphy explosion source model has problems predicting the decrease in the explosion spectral ratio observed at higher magnitudes (mb > 4.5 to 5.0). This may be due to uncertainties in the apparent source-time function for explosions. These complications may be due to changes in the dynamic response of the material in the near-source region as a function of overburden pressure, effects of secondary sources, or to variations in regional phase excitation with depth.

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Source comparisons between nuclear and chemical explosions detonated at Rainier Mesa, Nevada Test Site

Bulletin of the Seismological Society of America ◽

10.1785/bssa0890020409 ◽

1999 ◽

Vol 89 (2) ◽

pp. 409-422 ◽

Cited By ~ 3

Author(s):

Brian W. Stump ◽

D. Craig Pearson ◽

Robert E. Reinke

Keyword(s):

Source Region ◽

Spectral Ratio ◽

Test Site ◽

Source Model ◽

Transverse Component ◽

Propagation Path ◽

Cube Root ◽

Nevada Test Site ◽

Spectral Difference ◽

Receiver Array

Abstract A series of nuclear [MINERAL QUARRY (MQ), HUNTERS TROPHY (HT)] and chemical [NON-PROLIFERATION EXPERIMENT (NPE) and NPECAL] explosions were detonated in the same geological material at Rainier Mesa, Nevada Test Site. These sources were extensively instrumented with the same near-source, free-surface instrumentation array. The data from these explosions allow the establishment of empirical source scaling relations as well as investigation of possible chemical and nuclear source differences. Even in the near-source region at common receivers, the data display propagation path effects resulting from slight differences in source locations. These effects are effectively taken into account by smoothing the source comparisons across the different stations in the receiver array. As many as 30 individual waveforms from each source are used in this smoothing process. Comparison of HT and NPE at near-source distances indicates that within the bandwidth of the data (0.36 to 100 Hz), there is no apparent spectral difference between the nuclear and single-fired chemical source. The smoothed spectral ratio between the NPE and NPE CAL is consistent with the long-period source spectral difference (104), corner frequencies (2 to 3 Hz/NPE and 40 to 60 Hz/NPE CAL), and high-frequency decay (ƒ−2) similar to the Mueller-Murphy source model for wet tuff after modifying the cavity radius to scale as the cube root of yield. Comparison of the two nuclear sources, HT and MQ, indicates that at long periods, the HT/MQ ratio is 0.4 to 0.6 with the spectra from the two explosions merging above 5 Hz, which is consistent with the 0.3 magnitude difference observed for the two sources. In all the source comparisons, the spectral ratios of the transverse components of motion are indistinguishable from those produced by either the vertical or radial components. This fact argues that the transverse component of motion from an explosion is generated at very close-in distances, in this case on the order of 1 to 2 km. These observations are in agreement with some type of linear scattering mechanism.

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Source parameter analysis from strong motion records of the Friuli, Italy, earthquake sequence (1976-1977)

Bulletin of the Seismological Society of America ◽

10.1785/bssa0770041127 ◽

1987 ◽

Vol 77 (4) ◽

pp. 1127-1146

Author(s):

Giuseppe De Natale ◽

Raul Madariaga ◽

Roberto Scarpa ◽

Aldo Zollo

Keyword(s):

Frequency Domain ◽

Stress Drop ◽

High Frequency ◽

Epicentral Distance ◽

Strong Motion ◽

Source Model ◽

Parameter Analysis ◽

Corner Frequency ◽

Spectral Parameters ◽

Single Station

Abstract Time and frequency domain analyses are applied to strong motion data recorded in Friuli, Italy, during 1976 to 1977. An inversion procedure to estimate spectral parameters (low frequency level, corner frequency, and high frequency decay) has been applied to displacement spectra using a simple earthquake source model with a single corner frequency. The data were digitized accelerograms from ENEA-ENEL portable and permanent networks. Instrument-corrected SH waves were selected from a set of 138 three-component, hand-digitized records and 28 automatically digitized records. Thirty-eight events with stations having 8 to 32 km epicentral distance were studied. Different stress drop estimates were performed showing high values (200 to 300 bars, on the average) with seismic moments ranging from 2.8 × 1022 to 8.0 × 1024 dyne-cm. The observation of systematic higher values of Brune stress drop (obtained from corner frequencies) with respect to other time and frequency domain estimates of stress release, and the evidence on time series of multiple rupture episodes suggest that the observed corner frequencies are most probably related to subevent ruptures rather than the overall fault size. Seven events recorded at more than one station show a good correlation between rms, Brune, and dynamic stress drops, and a constant scaling of this parameter as a function of the seismic moment. When single station events are also considered, a slight moment dependence of these three stress drop estimates is observed differently. This may be explained by an inadequacy of the ω−2 high-frequency decay of the source model or by high-frequency attenuation due to propagation effects. The high-frequency cutoff of acceleration spectra indicates the presence of an Fmax in the range of 5 to 14 Hz, except for the stations where local site effects produce spectral peaks.

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Source spectral characteristics of Miramichi earthquakes: Results from 115 P-wave observations

Bulletin of the Seismological Society of America ◽

10.1785/bssa0790010015 ◽

1989 ◽

Vol 79 (1) ◽

pp. 15-30

Author(s):

Kin-Yip Chun ◽

Richard J. Kokoski ◽

Gordon F. West

Keyword(s):

High Frequency ◽

Dynamic Range ◽

Spectral Characteristics ◽

Sampling Rate ◽

Spectral Ratio ◽

P Wave ◽

P Waves ◽

Single Station ◽

Source Scaling ◽

Source Models

Abstract Source scaling relation is studied over the magnitude (mN) range 2.6 to 5.4 using P waves generated by 31 tightly clustered earthquakes in New Brunswick, Canada. The recording stations, six in total, have a 60-points/sec sampling rate and a dynamic range of about 100 dB. They are located at regional distance (188 to 448 km), with a wide azimuthal coverage. The data interpreted consist of 115 spectral ratio curves (2-20 Hz), each obtained in a manner that allows effective cancellation of the effects caused by source radiation pattern, path attenuation, geometrical spreading, instrument error, and variability in site function. The data selected in this study differ from the single-station records used in a previous source-scaling study of Miramichi earthquakes (Chael, 1987) in having: 1) broader distance coverage; 2) greater recording dynamic range; 3) higher Nyquist frequency; and 4) larger data size. We conclude from the observed spectral ratios that source models having an ω−2 high-frequency fall-off (ω-square model) are strongly favored by the data over those having an ω−3 high-frequency fall-off (ω-cube model) and that stress drop increases with moment at a rate proposed earlier by Nuttli (1983a, b).

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Discrimination of Small Earthquakes and Buried Single-Fired Chemical Explosions at Local Distances (<150 km) in the Western United States from Comparison of Local Magnitude (ML) and Coda Duration Magnitude (MC)

Bulletin of the Seismological Society of America ◽

10.1785/0120200188 ◽

2020 ◽

Author(s):

Keith D. Koper ◽

Monique M. Holt ◽

Jonathan R. Voyles ◽

Relu Burlacu ◽

Moira L. Pyle ◽

...

Keyword(s):

United States ◽

High Frequency ◽

Characteristic Curve ◽

Moment Tensor ◽

Western United States ◽

Local Magnitude ◽

Underground Nuclear Explosions ◽

Nuclear Explosions ◽

Duration Magnitude ◽

Chemical Explosions

ABSTRACT Seismologists distinguish underground nuclear explosions from more commonly occurring earthquakes using moment tensor inversion, high-frequency P/S amplitude ratios, mb:Ms comparisons, and P-pP differential travel times. These methods are generally successful for large seismic events (M>3–4) well recorded at regional-to-teleseismic distances (>150 km); however, it is unclear whether they can be modified to work for small events (M<3) well recorded only at local distances (<150 km). Here, we evaluate a recently proposed, local-distance seismic source discriminant—the difference between local magnitude (ML) and coda duration magnitude (MC)—using seismograms of earthquakes and buried, single-fired chemical explosions recorded in three regions of the western United States. The quantity ML–MC was previously found to be sensitive to source depth, effectively discriminating mine blasts, induced earthquakes, and very shallow tectonic earthquakes from deeper crustal earthquakes. In this study, we report the first evaluation of ML–MC as a depth discriminant using data from buried, single-fired explosions that, unlike the seismic sources studied earlier, are good analogs for underground nuclear explosions. We find that even when using generic, uncalibrated methods of assigning magnitudes, ML–MC separates single-fired explosions and earthquakes. The area under the receiver operating characteristic curve is 0.92 for 19 explosions and 14 earthquakes in Washington, 0.90 for 22 explosions and 90 earthquakes in Wyoming, and 0.99 for three explosions and 149 earthquakes in Nevada. ML:MC comparisons have the potential to enhance discrimination based on high-frequency P/S amplitudes ratios—which perform less well at local than regional distances—because the two metrics have complementary sensitivities.

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Writing Time in Metaphors

10.3366/edinburgh/9781474423939.003.0004 ◽

2018 ◽

Author(s):

Jennifer J. Smith

Keyword(s):

United States ◽

The United States ◽

Western United States ◽

Entire System ◽

Language And Culture ◽

Space Race ◽

Do So

Coherence of place often exists alongside irregularities in time in cycles, and chapter three turns to cycles linked by temporal markers. Ray Bradbury’s The Martian Chronicles (1950) follows a linear chronology and describes the exploration, conquest, and repopulation of Mars by humans. Conversely, Louise Erdrich’s Love Medicine (1984) jumps back and forth across time to narrate the lives of interconnected families in the western United States. Bradbury’s cycle invokes a confluence of historical forces—time as value-laden, work as a calling, and travel as necessitating standardized time—and contextualizes them in relation to anxieties about the space race. Erdrich’s cycle invokes broader, oppositional conceptions of time—as recursive and arbitrary and as causal and meaningful—to depict time as implicated in an entire system of measurement that made possible the destruction and exploitation of the Chippewa people. Both volumes understand the United States to be preoccupied with imperialist impulses. Even as they critique such projects, they also point to the tenacity with which individuals encounter these systems, and they do so by creating “interstitial temporalities,” which allow them to navigate time at the crossroads of language and culture.

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