Propagation of high-frequency (4- to 50-Hz) P waves in the northeastern United States

1995 ◽  
Vol 85 (4) ◽  
pp. 1244-1248
Author(s):  
Eric P. Chael ◽  
Patrick J. Leahy ◽  
Jerry A. Carter ◽  
Noël Barstow ◽  
Paul W. Pomeroy
Keyword(s):  
United States ◽  
Decay Rate ◽  
High Frequency ◽  
P Wave ◽  
Wave Spectra ◽  
Northeastern United States ◽  
P Waves ◽  
Geometric Spreading ◽  
Frequency Independent

Abstract We have measured the decay rate of high-frequency (4- to 50-Hz) P waves in the northeastern United States. We analyzed signals from 28 explosions of a 1988 USGS/AFGL/GSC refraction survey recorded at distances between 30 and 400 km. Over this range, the decay rate steadily increases from Δ−2 at 10 Hz to Δ−4 at 45 Hz. If one assumes geometric spreading of Δ−1.3, then the remaining decay is consistent with a nearly frequency-independent Q of about 1000. The results provide a useful parameterization for predicting P-wave spectra at near-regional ranges.

Short-period P-wave attenuation along various paths in North America as determined from P-wave spectra of the SALMON nuclear explosion

1976 ◽  
Vol 66 (5) ◽  
pp. 1609-1622 ◽  
Author(s):  
Zoltan A. Der ◽  
Thomas W. McElfresh
Keyword(s):  
United States ◽  
North America ◽  
Wave Attenuation ◽  
Nuclear Explosion ◽  
P Wave ◽  
Western United States ◽  
Source Spectrum ◽  
Wave Spectra ◽  
Short Period ◽  
Q Values

abstract Average Q values were determined for ray paths to various LRSM stations from the SALMON nuclear explosion by taking ratios of observed P-wave spectra to the estimated source spectrum. Most Q values for P-wave paths throughout eastern North America are in the range 1600 to 2000 while those crossing over into the western United States are typically around 400 to 500. These differences in Q for intermediate distances can sufficiently explain the differences in the teleseismic event magnitudes observed, 0.3 to 0.4 magnitude units, in the western versus the eastern United States, if one assumes that the low Q layer under the western United States is located at depths less than 200 km.

Network-averaged teleseismic P-wave spectra for underground explosions. Part II. Source characteristics of Pahute Mesa explosions

1989 ◽  
Vol 79 (1) ◽  
pp. 156-171
Author(s):  
John R. Murphy
Keyword(s):  
Frequency Band ◽  
P Wave ◽  
Spectral Amplitude ◽  
Model Parameters ◽  
Scaling Analysis ◽  
Wave Spectra ◽  
Amplitude Data ◽  
Short Period ◽  
Frequency Independent ◽  
Averaged Model

Abstract A source scaling analysis is presented based on network-averaged, teleseismic P-wave spectra determined from short-period data recorded from a sample of 20 Pahute Mesa explosions. These explosions, which were all detonated below the water table in saturated tuff/rhyolite emplacement media, cover a range of announced yields from 155 to 1300 kt. The spectra were analyzed using a simple set of source and propagation models consisting of a Mueller/Murphy source coupling model, a conventional, frequency-independent t* model of anelastic attenuation and a “quasi-linear” description of the surface-reflected pP phase. It is demonstrated that these models can account for virtually all the observed spectral variability over the frequency band extending from 0.5 to 2.0 Hz, down to a level which is close to that associated with measurement uncertainty. In particular, the use of network averaged model parameters of t* = 0.75 sec, an average pP/P-amplitude ratio of about 0.4 and an average source medium velocity of 3.5 km/sec reduces the spectral amplitude data from these explosions to an essentially frequency-independent constant value with an associated standard error of estimate which averages to only about 20 per cent over this frequency band.

Relation between P- and S-wave corner frequencies in the seismic spectrum

1974 ◽  
Vol 64 (6) ◽  
pp. 1621-1627 ◽  
Author(s):  
J. C. Savage
Keyword(s):  
High Frequency ◽  
Body Wave ◽  
Fault Model ◽  
P Wave ◽  
Corner Frequency ◽  
Rupture Propagation ◽  
S Wave ◽  
P Waves ◽  
Fault Surface ◽  
S Waves

abstract A comprehensive set of body-wave spectra has been calculated for the Haskell fault model generalized to a circular fault surface. These spectra are used to show that in practice the P-wave corner frequency (ƒp) may exceed the S-wave corner frequency (ƒs) when near-sonic or transonic rupture propagation obtains. The explanation appears to be that in such cases ƒs is so large that it is not identified within the recorded band, but rather a secondary corner is mistaken for ƒs. As a consequence of failing to detect the true asymptotic trend, the high-frequency falloff of the spectrum with frequency is substantially less for S waves than for P waves. This explanation appears to be consistent with the demonstration by Molnar, Tucker, and Brune (1973) that ƒp may exceed ƒs.

Spectral and magnitude characteristics of anomalous Eurasian earthquakes

1977 ◽  
Vol 67 (2) ◽  
pp. 463-478
Author(s):  
So Gu Kim ◽  
Otto W. Nuttli
Keyword(s):  
Focal Mechanism ◽  
Rayleigh Waves ◽  
Main Shock ◽  
Focal Depth ◽  
P Wave ◽  
Wave Spectra ◽  
P Waves ◽  
Aftershock Sequences ◽  
Short Period ◽  
Amplitude Spectra

Abstract A number of main shock-aftershock sequences in the Eurasian interior contain some aftershocks whose mb:MS values are close to those of underground explosions. This paper is concerned with a study of the amplitude spectra of the P waves and Rayleigh waves for earthquakes of those main shock-aftershock sequences. It is found that for any given sequence studied, there is little if any variation in focal depth or focal mechanism. This rules out variations in these quantities as being the cause of anomalous mb:MS values. A study of the P-wave spectra establishes that one or both of the corner periods of anomalous earthquakes are smaller than those of non-anomalous earthquakes of the same moment. Thus the cause of anomalous mb:MS values of the earthquakes studied is a relative enrichment of the short-period portion of the spectrum of the anomalous events, which cannot be attributed to focal depth or focal mechanism.

Fault plane solutions for northeastern United States earthquakes

1981 ◽  
Vol 71 (6) ◽  
pp. 1875-1882
Author(s):  
Jay J. Pulli ◽  
M. Nafi Toksöz
Keyword(s):  
United States ◽  
New York ◽  
New England ◽  
Fault Plane ◽  
Local Stress ◽  
P Wave ◽  
Northeastern United States ◽  
Stress Concentrations ◽  
Fault Plane Solutions ◽  
Entire Area

Abstract Fault plane solutions for eight earthquakes occurring in the northeastern United States have been determined using P-wave first motions and a computer algorithm for picking all valid solutions. The predominant mechanism in the area is thrust faulting, however the direction of the P axis is not consistent throughout the entire area. In central New England (Maine-New Hampshire), the P axis trends nearly E-W. In southeastern New England, the P axis trends N-S to NE-SW. In the Adirondacks region of New York, the P axis trends NE-SW as previously reported by Yang and Aggarwal (1981). Although the stress distribution appears to be complicated, as in the Central United States (Street et al., 1974), an underlying E-W compressive stress may exist in the New England area. These small earthquakes may represent the response to local stress concentrations.

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).

ML measurements for northeastern United States earthquakes

1982 ◽  
Vol 72 (4) ◽  
pp. 1367-1378
Author(s):  
John E. Ebel
Keyword(s):  
United States ◽  
High Frequency ◽  
Southern California ◽  
Northeastern United States ◽  
The Difference ◽  
High Frequency Waves ◽  
Magnitude Determination

abstract Local magnitudes (ML) are reported for 56 northeastern United States and Canadian earthquakes using records from a pair of Wood-Anderson torsion instruments which have operated at Weston Observatory since 1967. Corrections to the Richter ML formula are computed to take into account the difference in attenuation between southern California and the northeastern United States. The corrected ML values for these events were compared to the previously reported magnitudes which had been calculated either from the Nuttli (1973) mbLg formula applied to 5- to 10-Hz waves (called MN) or from a coda magnitude formula (Mc). In general, the ML determinations tend to underestimate the MN and Mc values by about 0.4 magnitude units. This confirms the fact that the MN scale is not appropriate when applied to high-frequency waves, as it is in the northeastern United States. The reason for this appears to be in the relation of the period of the wave used in the magnitude determination to the corner period of the earthquake and earth response.

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