Near-source effects on regional seismograms: An analysis of the NTS explosions PERA and QUESO

1991 ◽  
Vol 81 (6) ◽  
pp. 2371-2394
Author(s):  
Steven R. Taylor ◽  
John T. Rambo ◽  
Robert P. Swift
Keyword(s):  
Shock Wave ◽  
High Frequency ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Spectral Ratio ◽  
Corner Frequency ◽  
Burial Depth ◽  
Wave System ◽  
Spectral Ratios ◽  
Remarkable Similarity

Abstract A comparative analysis of two closely spaced Nevada Test Site explosions, PERA and QUESO, is made to study the effects of near-source phenomena on regional-wave excitation. Although the two explosions were of similar size, burial depth, and only separated by 4 km, the 1 to 2 and 6 to 8 Hz regional-wave spectral ratio for QUESO is anomalously low (a factor of 10 smaller than that of PERA). Examination of the regional and close-in spectra for each event shows a remarkable similarity and suggests that QUESO has less low-frequency and more high-frequency energy than PERA. These observations may be caused by a 564 m3, funnel-shaped region filled with unconsolidated sand and a possible void directly above the QUESO detonation point. Close-in observations suggest that this region may have partially decoupled the up-going energy from QUESO, resulting in a reduction of the low-frequency energy. The high-frequency enhancement for QUESO may be due to the rapid loss of energy to nonlinear effects such as greater pore collapse and fracturing in the anomalous region. This resulted in the radiation of more impulsive, shorter-duration waveforms producing a higher corner frequency and less-rapid high-frequency spectral decay for QUESO. For PERA, the loss of energy to a two-wave system occurred more slowly and over a larger volume, resulting in a broader source pulse typical of explosions in porous materials. Comparison of shock radius versus time data suggests that the shock wave was strongly affected in the anomalous zone a few meters above the QUESO device. One-dimensional finite-difference calculations with and without a partial decoupling region within 8 m of the device are consistent with the observations. Although spallation was reduced for QUESO, simulations using a finite spall model indicate that the spall spectral peak should be centered at about 3 to 7 Hz and probably did not significantly contribute to the reduced spectral ratio. The remarkable similarity of the PERA/QUESO spectral ratios taken at distances of 90 m and 400 km suggests that the spectral characteristics of explosions are established in close proximity to the source. Although depth-dependent effects of attenuation acting at small strains may enhance the differences in spectral ratios between NTS explosions and western U.S. earthquakes, these effects are probably secondary to the high-pressure, high strain-rate dynamic material response to the radiated explosion shock wave. These observations point out the importance of up-going energy on the generation of regional phases from explosions. Because of reduced overburden pressures above the detonation point, large nonlinear deformations predominate in this region and appear to affect all of the signals except perhaps the very initial part of the Pn waveform.

Spectral characteristics of regional phases recorded at Noress

1988 ◽  
Vol 78 (2) ◽  
pp. 708-725
Author(s):  
Anne Suteau-Henson ◽  
Thomas C. Bache
Keyword(s):  
Soviet Union ◽  
Nuclear Explosion ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Spectral Ratio ◽  
Spectral Ratios ◽  
Data Set ◽  
Nuclear Explosions ◽  
The Soviet Union ◽  
Mine Blasts

Abstract The spectral characteristics of Pn and Lg are studied for regional events recorded at the NORESS array in Norway. The emphasis is on the potential value of spectral ratios for identifying events as earthquake, chemical explosions, and nuclear explosions. The events studied include a suite of explosions from the Titania Mine in southwest Norway, a suite of events of unknown source type from a site offshore about 90 km from this mine, suites of explosions from several mines in the Soviet Union about 1000 km from NORESS, events from several locations along the 90° azimuth from NORESS, an apparent earthquake in the North Atlantic, and a nuclear explosion (PNE) at a range of 1560 km. The event identification issues addressed are as follows: (1) Can earthquakes and explosions be identified based on the ratio of high- and low-frequency energy in their signal spectra? (2) Do spectral ratios separate mine blasts from earthquakes for all source areas? (3) Will spectral ratio discriminants be effective for identifying decoupled underground nuclear explosions? We conclude that spectral ratios can sometimes separate events. An example is separation of the Titania mine blasts from the events at the nearby offshore locations, although we cannot be sure how much this is due to path differences. However, in general, spectral ratios vary as much within classes of events as they do among different classes. The PNE in our data set allows the simulation of spectra from a decoupled nuclear explosion by simply applying the frequency-dependent decoupling factor to the observed Pn spectrum for this event. After applying a distance correction, the spectrum for this simulated decoupled nuclear explosion is similar to those for the Soviet Union mine blasts in our data set.

Two-parameter scaling of source spectra: Love waves from deep-focus Bonin Islands earthquakes

1977 ◽  
Vol 67 (2) ◽  
pp. 285-300
Author(s):  
R. James Brown
Keyword(s):  
Body Wave ◽  
Scaling Law ◽  
Spectral Ratio ◽  
Love Waves ◽  
Corner Frequency ◽  
Spectral Ratios ◽  
Bonin Islands ◽  
Deep Focus ◽  
Two Parameter ◽  
Fault Length

Abstract Starting with the one-parameter scaling law of Aki, a two-parameter expression is developed to model the source factor of the far-field spectrum from a dislocation fault source for both ω−2 and ω−3 high-frequency asymptotic types. Aki's assumption of similarity is relaxed in two respects: it is neither here assumed that wD0 ∞ L2 (L = fault length, w = fault width, D0 = average dislocation) nor that kT = v kL (kT−1 = correlation time, kL−1 = correlation length, v = velocity of rupture propagation), the latter being equivalent to allowing for Brune's fractional stress drop. From this two-parameter model a four-parameter model of spectral ratio is obtained and fitted to observed spectral ratios by computer optimization of the four parameters. Observed spectral ratios have been determined from the Love waves recorded at NORSAR from six deep-focus Bonin Islands earthquakes using a common-path method. From the optimal values of the four parameters, values are determined for corner frequency (f ≈ 0.2 Hz for m 6.0; f ≈ 0.3 Hz for m = 5.3; m = PDE body-wave magnitude), relative fault length, relative seismic moment (and magnitudes), and p, the slope of the corner-frequency locus. Values found for p are all greater than 3 and such p, in combination with an ω−3 scaling law, can yield a reasonable m:M relation, i.e., with no ceiling imposed on m. A slightly better fit is obtained by starting with an ω−3 model than with ω−2.

scholarly journals Acoustical study on spectral characteristics of teachers’ English vocalization

2021 ◽  
Vol 257 ◽  
pp. 02027
Author(s):  
Yao Xiao ◽  
Yue-Zhe Zhao
Keyword(s):  
Frequency Band ◽  
High Frequency ◽  
Sound Pressure ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Sound Intensity ◽  
English Teaching ◽  
Female Teachers ◽  
Acoustical Study ◽  
Second Peak

With the increase of English teaching courses, the specific vocal characteristics of teachers in English teaching are studied and used as the basic data for the design of teachers’ spatial acoustics. In order to study this problem, three different English voice materials were read in a anechoic room under three sound intensity levels: large, medium and small, respectively, so as to analyse the equivalent continuous sound pressure level (SPL) and frequency characteristic curves of male and female teachers at 0.3m. In the low frequency band, the SPL increases as the frequency increases. In the mid-frequency band, the SPL reaches the first peak, then decreases briefly as the frequency increases, then increases again to the second peak, and then decreases again briefly as the frequency increases. Then increase again to the third peak. In the high frequency band, the SPL decreases as the frequency increases.

scholarly journals Spectral characteristics of satellite links at ka band in the southern tropical region of India

2017 ◽  
Vol 7 (1.1) ◽  
pp. 631
Author(s):  
Sravya Velaga ◽  
Jagadeesh Korrapati ◽  
Chaithanya Krishna B ◽  
Vandana Matti ◽  
K Ch. Sri Kavya ◽  
...  
Keyword(s):  
High Frequency ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Radiowave Propagation ◽  
Tropical Region ◽  
Multimedia Services ◽  
System Availability ◽  
Ka Band ◽  
Frequency Bands ◽  
Satellite Links

The objective of this study was to perform a spectral analysis of the Ka band propagation channel. Now a day, because of the expanding interest of the end users for multimedia services which require vast bandwidth, and because of the immersion of low frequency bands, for example, L, S, C bands, and Ku band in close future, satellite media transmission systems are moving to higher frequency bands. In such high frequency bands, the presence of the atmosphere strongly affects radiowave propagation and attenuation effects become so severe that system availability would not be sufficient if systems were designed in a conventional way with a static propagation margin. 

scholarly journals Spectral Characteristics of the Response of the Meridional Overturning Circulation to Deep-Water Formation

2005 ◽  
Vol 35 (10) ◽  
pp. 1813-1825 ◽  
Author(s):  
Julie Deshayes ◽  
Claude Frankignoul
Keyword(s):  
High Frequency ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Meridional Overturning Circulation ◽  
Thermocline Depth ◽  
Deep Water Formation ◽  
Meridional Transport ◽  
Overturning Circulation ◽  
Water Formation ◽  
Meridional Overturning

Abstract The response of the upper limb of the meridional overturning circulation to the variability of deep-water formation is investigated analytically with a linear, reduced-gravity model in basins of simple geometry. The spectral characteristics of the model response are first derived by prescribing white-noise fluctuations in the meridional transport at the northern boundary. Although low-frequency basin modes are solutions to the eigenproblem, they are too dissipative to be significantly excited by the boundary forcing, and the thermocline depth response has a red spectrum with no prevailing time scale other than that of a high-frequency equatorial mode, only flattening at the millennial time scale because of vertical diffusivity. The meridional transport is asymmetric about the equator because the northern part of the basin is directly influenced by the boundary forcing while the southern part is mostly set in motion by long Rossby waves. This results in the equator acting as a low-pass filter for the Southern Hemisphere, which clarifies the so-called buffering effect of the equator. In a basin connected by a southern circumpolar channel, the thermocline depth and the transport spectra are redder than in the forced basin and, when a somewhat more realistic stochastic forcing derived from general circulation model simulations is considered, the variability is strongly reduced at high frequency. The linear model qualitatively explains several features of the low-frequency variability of the meridional overturning circulation in climate models, such as its red spectrum and its larger intensity in the North Atlantic Ocean.

Selective loss of high-frequency oscillations in phrenic and hypoglossal activity in the decerebrate rat during gasping

2006 ◽  
Vol 291 (5) ◽  
pp. R1414-R1429 ◽  
Author(s):  
Vitaliy Marchenko ◽  
Robert F. Rogers
Keyword(s):  
Power Distribution ◽  
High Frequency ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
High Amplitude ◽  
Medial Branch ◽  
Adult Rats ◽  
Time Frequency ◽  
High Frequency Oscillations ◽  
Nerve Recordings

Respiratory motor outputs contain medium-(MFO) and high-frequency oscillations (HFO) that are much faster than the fundamental breathing rhythm. However, the associated changes in power spectral characteristics of the major respiratory outputs in unanesthetized animals during the transition from normal eupneic breathing to hypoxic gasping have not been well characterized. Experiments were performed on nine unanesthetized, chemo- and barodenervated, decerebrate adult rats, in which asphyxia elicited hyperpnea, followed by apnea and gasping. A gated fast Fourier transform (FFT) analysis and a novel time-frequency representation (TFR) analysis were developed and applied to whole phrenic and to medial branch hypoglossal nerve recordings. Our results revealed one MFO and one HFO peak in the phrenic output during eupnea, where HFO was prominent in the first two-thirds of the burst and MFO was prominent in the latter two-thirds of the burst. The hypoglossal activity contained broadband power distribution with several distinct peaks. During gasping, two high-amplitude MFO peaks were present in phrenic activity, and this state was characterized by a conspicuous loss in HFO power. Hypoglossal activity showed a significant reduction in power and a shift in its distribution toward lower frequencies during gasping. TFR analysis of phrenic activity revealed the increasing importance of an initial low-frequency “start-up” burst that grew in relative intensity as hypoxic conditions persisted. Significant changes in MFO and HFO rhythm generation during the transition from eupnea to gasping presumably reflect a reconfiguration of the respiratory network and/or alterations in signal processing by the circuitry associated with the two motor pools.

scholarly journals 6-Hour to 1-Year Variance of Five Global Precipitation Sets

2007 ◽  
Vol 11 (11) ◽  
pp. 1-29 ◽  
Author(s):  
Alex C. Ruane ◽  
John O. Roads
Keyword(s):  
High Frequency ◽  
Spectral Characteristics ◽  
Power Spectra ◽  
Low Frequency ◽  
Tropical Rainfall Measuring Mission ◽  
Seasonal Migration ◽  
Low Frequency Variability ◽  
Precipitation Estimation ◽  
The Indian Ocean ◽  
Global Precipitation

Abstract Three-hourly time series of precipitation from three high-resolution precipitation products [Tropical Rainfall Measuring Mission (TRMM) algorithm 3B-42, the Climate Prediction Center’s morphing method (CMORPH), and the Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks (PERSIANN)] and two reanalyses are examined for their frequency characteristics using broad and narrow variance categories. After isolating the diurnally forced peaks (at 24, 12, 8, and 6 h), the power spectra are divided into comprehensive broad bands comprising the annual (∼80 days–1 yr), intraseasonal (20 to ∼80 days), slow (6–20 days) and fast (36 h–6 days) synoptic, and high-frequency (6–36 h) periods. Global maps accounting for 100% of precipitation’s variance are analyzed to identify unique regional behaviors. Annual variability is strongest over regions affected by the seasonal migration of the intertropical convergence zone, as well as over monsoonal regions. The intraseasonal band displays off-equatorial evidence of the Madden–Julian oscillation (MJO), particularly in the Indian Ocean, but the MJO’s rainfall is partially manifested in the slow synoptic band and at higher frequencies. The fast synoptic band is particularly strong over the oceans, while high-frequency variability is enhanced over land by more extreme surface gradients. Diurnal variance is strongest at low latitudes and is pronounced over regions with well-known diurnal circulations, including mountains and coastlines. Interproduct and intermodel differences also indicate biases of the precipitation product algorithms and convective parameterizations, including a strong bias toward low-frequency variability in the relaxed Arakawa–Schubert parameterization employed by one of the reanalyses, as well as increased white-spectral characteristics over land in the precipitation products.

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

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).

Insights into downhole array spectra of hydraulic-fracturing induced seismicity in the Horn River Basin, British Columbia

2020 ◽  
Author(s):  
Adam Klinger ◽  
Max Werner
Keyword(s):  
British Columbia ◽  
Hydraulic Fracturing ◽  
Stress Drop ◽  
High Frequency ◽  
Source Parameters ◽  
Low Frequency ◽  
Corner Frequency ◽  
Downhole Array ◽  
Horn River Basin ◽  
Downhole Arrays

<p>Hydraulic fracturing underpins tight shale gas exploration but can induce seismicity. During stimulations, operators carefully monitor the spatio-temporal distribution and source parameters of seismic events to be able to respond to any changes and potentially reduce the chances of fault reactivation. Downhole arrays of geophones offer unique access to (sub) microseismic source parameters and can provide new insights into the processes that induce seismicity. For example, variations in stress drop might indicate changes in the seismic response to injection (e.g. pore pressure variations). However, borehole arrays of geophones and the high frequencies of small events also present new challenges for source characterization. Stress drop depends on the corner frequency, a parameter with great uncertainty that is sensitive to attenuation, especially for (sub-) microseismicity. Here, we explore the behavior of microseismic spectra measured along borehole arrays and the effect of attenuation on estimates of corner frequency. We examine a dataset of over 90,000 microseismic events recorded during hydraulic fracturing in the Horn River Basin, British Columbia. We only see clear phase arrivals for events M<sub>w</sub> > -1 and restrict our initial analysis to a subsample of M<sub>w</sub>> 0 events that vary in space and time.</p><p>Our first observation is that some stations in the borehole array show an unexpected increase in the displacement energy from the low frequency to the corner frequency in the P and SH phases as well as high-frequency energy spikes inconsistent with a smooth Brune source model. A shorter time window that only captures the direct arrival results in a flatter low frequency plateau and reduces the amplitude of the pulses but compromises the resolution. The spikes may be caused by high frequency coda energy. We also find that corner frequency estimates decrease with decreasing station depth along the array in both the P and SH phases, a likely result of high frequency attenuation along the downhole array. The findings suggest Brune corner frequencies of moment magnitudes < 0.5 may not be resolvable even with downhole arrays at close proximity. Our results will eventually contribute to a better characterization of microseismic source parameters measured in borehole arrays.</p><p> </p>

Determination of Site Response in Anchorage, Alaska, on the Basis of Spectral Ratio Methods

2002 ◽  
Vol 18 (1) ◽  
pp. 85-104 ◽  
Author(s):  
A. Martirosyan ◽  
U. Dutta ◽  
N. Biswas ◽  
A. Papageorgiou ◽  
R. Combellick
Keyword(s):  
Shear Wave ◽  
Shear Wave Velocity ◽  
High Frequency ◽  
Site Response ◽  
Low Frequency ◽  
Spectral Ratio ◽  
Frequency Range ◽  
The West ◽  
Site Coefficients ◽  
Average Shear

This paper deals with the site response (SR) in the Anchorage basin in south-central Alaska. The investigation is based on the analysis of seismograms of 114 earthquakes recorded by 22 weak-motion stations and 46 earthquakes recorded by 19 strong-motion stations in the study area. We have computed SR for 41 sites, using standard spectral ratio and horizontal-to-vertical spectral ratio methods in the frequency range from 0.5 to 11 Hz. Based on these results, we have calculated band-average site response values in two frequency ranges: low frequency (from 0.5 to 2.5 Hz) and high frequency (from 3 to 7 Hz). There is a good correlation between SR values and surficial geology of the Anchorage area in the low-frequency range. SR values increase by a factor of three from the foothills of the Chugach Mountains in the east to the west towards the deeper part of the basin. The highest site response values (SR>2.5) in the same frequency range are observed in the west-central part of the city, which is underlain by cohesive facies of the Bootlegger Cove formation. The SR has a good correlation with the uppermost 30-m time-average shear-wave velocity with a correlation coefficient of 0.82. Moreover, the low-frequency SR values are close to the NEHRP site coefficients for 1 sec. However, high-frequency SR values lack correlation with 30-m average shear-wave velocity and short-period NEHRP site coefficients.

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