Erratum to “The high-frequency shape of the source spectrum for earthquakes in Eastern and Western Canada”

1998 ◽  
Vol 88 (2) ◽  
pp. 633-634
Keyword(s):  
High Frequency ◽  
Source Spectrum ◽  
Western Canada

The high-frequency shape of the source spectrum for earthquakes in eastern and western Canada

1996 ◽  
Vol 86 (1A) ◽  
pp. 106-112 ◽  
Author(s):  
Gail M. Atkinson
Keyword(s):  
High Frequency ◽  
Fourier Spectrum ◽  
Response Spectrum ◽  
Ground Motions ◽  
Source Spectrum ◽  
Western Canada ◽  
Eastern Canada ◽  
Ground Acceleration ◽  
Kappa Effect ◽  
Key Parameter

Abstract The high-frequency shape of the earthquake spectrum strongly influences the amplitude of the peak ground acceleration and of the response spectrum at frequencies of 10 Hz and greater. A key parameter for the description of high-frequency ground motions is “kappa,” which is the decay slope of the Fourier spectrum of acceleration at near-source distances (Anderson and Hough, 1984; note Anderson and Hough originally referred to this parameter as kappa (0)). Kappa may be attributed to site effects (fmax; Hanks, 1982), source processes (Papageorgiou and Aki, 1983), or both. Seismographic data place weak but significant constraints on kappa values. On average, there is no resolved kappa effect on spectra recorded at rock sites in eastern Canada, in the frequency range f ≦ 30 Hz. Four firm-soil sites in southwestern Ontario also show no kappa effect. An implied upper bound for kappa is 0.004 (or lower bound of 30 Hz for fmax). By contrast, source spectra from earthquakes in the Cascadia region, recorded on hard-rock sites in southwestern British Columbia (B.C.), appear to be well described by a kappa of 0.011 ± 0.002. The B.C. spectra are thus intermediate to the eastern case, with zero apparent kappa, and the typical California case, for which kappa is about 0.04.

New evidence of high frequency of antler wounding in cervids

1986 ◽  
Vol 64 (2) ◽  
pp. 380-384 ◽  
Author(s):  
Valerius Geist
Keyword(s):  
Field Observation ◽  
High Frequency ◽  
Western Canada ◽  
Field Observations ◽  
Opt Out ◽  
Combat Injuries ◽  
New Evidence

Seventy-two tanned, dehaired hides of four species of cervids from western Canada were examined for evidence of injuries. Combat injuries were segregated from injuries incurred from other sources. Forty-six of 55 males 1.5 years of age and older were scarred, as were 14 of 15 females. Of 15 males 1.5 years of age, 7 showed no scars, nor did two 6-month-old male fawns. Only 1of 22 male cervids over 2.5 years of age showed no combat scars. The frequency of wounding in males was 0–225, and in females0–18 per individual. About three-quarters of the scars were on the neck and haunches, about equally divided between these areas. The longest healed scar measured 420 mm; about 20% of the scars exceeded 100 mm in length. Field observations greatly underestimate wounding in cervids. A few males appear to opt out of rutting, but opt in when opportunity allows. The "dove" strategy is rare, but evidence from hides indicates that it does exist, confirming field observation.

A Comparison of Eastern North American ground Motion Observations with Theoretical Predictions

1990 ◽  
Vol 61 (3-4) ◽  
pp. 171-180 ◽  
Author(s):  
Gail M. Atkinson
Keyword(s):  
Stochastic Model ◽  
Ground Motion ◽  
North American ◽  
High Frequency ◽  
Ground Motions ◽  
Source Spectrum ◽  
Regression Analyses ◽  
Specific Effects ◽  
Model Predictions ◽  
Theoretical Predictions

Abstract Theoretical predictions of eastern North American (ENA) ground motion parameters based on a stochastic model (Boore and Atkinson, 1987; Atkinson and Boore, 1990) are evaluated in light of recent data, including data from the 1988 Saguenay, Quebec earthquake. The evaluation is based on visual comparisons of predicted and observed ground motion amplitudes, and on regression analyses of the data. Data are consistent with the theoretical model on average, although high-frequency ground motions from the Saguenay earthquake are underpredicted. It is hypothesized that differences between the observations and the stochastic model predictions may be explained by the presence of two corner frequencies in the source spectrum. Any single earthquake may exhibit ground motions significantly higher or lower than predicted due to local or earthquake-specific effects not accounted for in predictions of ‘average’ motions.

Stress Drops and Directivity of Induced Earthquakes in the Western Canada Sedimentary Basin

2019 ◽  
Vol 109 (5) ◽  
pp. 1635-1652 ◽  
Author(s):  
Joanna M. Holmgren ◽  
Gail M. Atkinson ◽  
Hadi Ghofrani
Keyword(s):  
Stress Drop ◽  
Sedimentary Basin ◽  
Source Parameters ◽  
Corner Frequency ◽  
Source Spectrum ◽  
Western Canada ◽  
Induced Earthquakes ◽  
Western Canada Sedimentary Basin ◽  
Stress Drops ◽  
Canada Sedimentary Basin

Abstract The Western Canada sedimentary basin (WCSB) has experienced an increase in seismicity during the last decade due primarily to hydraulic fracturing. Understanding the ground motions of these induced earthquakes is critical to characterize the increase in hazard. Stress drop is considered an important parameter in this context because it is a measure of the high‐frequency content of the shaking. We use the empirical Green’s function (EGF) method to determine S‐wave corner frequencies and stress drops of 87 earthquakes of moment magnitude (M) 2.3–4.4 in the WCSB. The EGF method is an effective technique to isolate earthquake source effects by dividing out the path and site components in the frequency domain, using a smaller collocated earthquake as an EGF. The corner frequency of the target event is determined for an assumed spectral ratio shape, from which the stress drop is computed. Assuming a fixed velocity, we find that the average stress drop for induced earthquakes in the WCSB for small‐to‐moderate events is 7.5±0.5  MPa, with a total range from 0.2 to 370 MPa. However, because of the dependence of stress drop on model conventions and constants, we consider the absolute stress‐drop value meaningful only for comparison with other results using the same underlying models. By contrast, corner frequency is a less‐ambiguous variable with which to characterize the source spectrum. The range of corner frequencies obtained in this study for events of M 4.0±0.5 is 1.1–5.8 Hz. Significant rupture directivity is observed for more than one‐third of the earthquakes, with station corner frequencies varying by about a factor of 4 with azimuth. This emphasizes the importance of having suitable station coverage to determine source parameters. We model directivity where evident using a Haskell source model and find that the rupture azimuths are primarily oriented approximately north–south throughout the region.

Seismic source spectrum of microearthquakes

1992 ◽  
Vol 82 (6) ◽  
pp. 2391-2409
Author(s):  
Yoshihisa Iio
Keyword(s):  
Wave Velocity ◽  
High Frequency ◽  
Hard Rock ◽  
Ground Surface ◽  
Seismic Source ◽  
P Wave ◽  
Source Spectrum ◽  
Anelastic Attenuation ◽  
P Wave Velocity ◽  
Source Spectra

Abstract The seismic source spectra of microearthquakes having seismic moments between 1014 and 1018 dyne cm were investigated by using local recordings from an excellent hard-rock site. The P-wave velocity near the site was estimated as about 6 km/sec, even immediately below the ground surface. The effect of anelastic attenuation was thought to be very small, since predominant frequencies of greater than 100 Hz were detected in seismograms recorded at focal distances greater 10 km. Many seismograms with S-P times of less than 0.6 sec were observed. The first cycle of the P-wave velocity seismogram was used in this study. The waveforms after the first cycle are likely formed near the site, since their periods are exactly the same for earthquakes that have different source processes. In the high-frequency portion of the estimated displacement source spectra, the slopes of the fall-off have values much greater than 2. The source process of microearthquakes is assumed to be very slow and smooth.

Source and scatering effects on the spectra of small local earthquakes

1981 ◽  
Vol 71 (6) ◽  
pp. 1687-1700
Author(s):  
Keiiti Aki
Keyword(s):  
High Frequency ◽  
Rayleigh Scattering ◽  
Wave Spectrum ◽  
Structural Difference ◽  
Forward Scattering ◽  
Source Spectrum ◽  
Small Scale ◽  
S Wave ◽  
Data Set ◽  
Scattering Effect

Abstract In order to separate the scattering effect from the source effect on high-frequency seismic waves, the spectra of S and coda waves are studied simultaneously for 900 small earthquakes (magnitude 3 to 4) in the Kanto region, Japan. The observed S-wave spectrum is the source spectrum modified by the attenuation and forward-scattering effect, while the coda spectrum is the source spectrum modified by the attenuation and back-scattering effect. From previous studies (Aki, 1980a, b) on the same data set, we know about the attenuation effect. Comparing the S-wave spectrum with the coda spectrum, we find that our data are consistent with the source spectrum with corner frequencies 3 to 6 Hz, and high-frequency decay ω−1 to ω−2, and support the hypothesis that scattering is the major cause of attenuation of S waves in the lithosphere, in which the small-scale Rayleigh scattering (Q−1 ∝ f3) applies to frequencies lower than 3 Hz and the large-scale scattering (Q−1 ∝ f0∼−1) to higher frequencies. The high-frequency decay of the source spectrum appears to be somewhat steeper for shallower earthquakes. We found that two areas with significantly different tectonic features shared similar attenuation and source effects, but showed very different envelopes of seismograms due to different forward-scattering effects. The forward-scattering effect may be the most sensitive to the structural difference.

Variation in the serum proteins of the red-backed mice Clethrionomys rutilus and C. gapperi and its taxonomic significance

1972 ◽  
Vol 50 (2) ◽  
pp. 217-227 ◽  
Author(s):  
Raymond P. Canham ◽  
David G. Cameron
Keyword(s):  
Rocky Mountains ◽  
High Frequency ◽  
Gel Electrophoresis ◽  
Serum Proteins ◽  
Western Canada ◽  
Starch Gel Electrophoresis ◽  
Common Boundary ◽  
Southern Alberta ◽  
Starch Gel ◽  
Clethrionomys Rutilus

Starch gel electrophoresis revealed the existence of four transferrins, five albumins, and 17 α-globulins in the serum of red-backed mice from nine locations in western Canada. Two of the transferrins and one of the albumins occurred in populations of both Clethrionomys rutilus and C. gapperi, but every population sampled contained at least one of the remainder of these proteins at a moderately high frequency. Populations of the two species near the boundary between their ranges of distribution could also be distinguished by the frequencies of the shared transferrins and albumins. Eight of the α-globulins were found only in C. gapperi, and two only in C. rutilus. Populations of the two species could not invariably be distinguished by means of these proteins: the same seven α-globulins were present in both species near their common boundary in the Northwest Territories, although only one was shared by populations on either side of the boundary in the Rocky Mountains of British Columbia. Several α-globulins were found only in samples of C. gapperi from southern Alberta. Differences between populations with respect to the α-globulins present, as well as to the frequencies of certain transferrins and α-globulins, were probably the result of differences in the environmental conditions to which the populations were subject.

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