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.

Regional Lg attenuation for the continental United States

1997 ◽  
Vol 87 (3) ◽  
pp. 606-619 ◽  
Author(s):  
Harley M. Benz ◽  
Arthur Frankel ◽  
David M. Boore
Keyword(s):  
United States ◽  
Frequency Band ◽  
Southern California ◽  
Basin And Range ◽  
Northeastern United States ◽  
Basin And Range Province ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
Central United States ◽  
Q Function

Abstract Measurements 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 >1.5 Hz due to larger microseismic noise levels at the lower frequencies.

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.

High-frequency refraction and diffraction in general media

1963 ◽  
Vol 255 (1058) ◽  
pp. 341-387 ◽  
Keyword(s):  
Circular Cylinder ◽  
High Frequency ◽  
Final Section ◽  
Homogeneous Medium ◽  
Stratified Medium ◽  
Parabolic Cylinder ◽  
Universal Formula ◽  
First Approximation ◽  
The Difference ◽  
High Frequency Waves

The working hypothesis of this paper is that the effect of an opaque boundary on the propagation of high-frequency waves in a general medium is to produce a wave reflected according to the laws of geometrical optics together with a field which to a first approximation depends upon the difference between the curvatures of a tangent ray and the boundary. In order to determine the latter field the model of a medium, whose properties vary linearly, above a straight boundary is employed. A first approximation to the field with this model is found, together with an estimate of the error. The formula for the field is then cast into a form which is invariant under a conformal mapping. Since the difference in curvatures of a tangent ray and the boundary is invariant it is suggested that the field is applicable for all media and boundaries provided that certain conditions imposed in deriving the approximation are fulfilled. As a check the predictions of the formula are compared with independent calculations on (i) a stratified medium above a straight boundary, (ii) a circular cylinder in a homogeneous medium, (iii) a parabolic cylinder in a homogeneous medium, (iv) a circular cylinder in a circularly stratified medium. In all cases the two calculations are in agreement. In a final section the results are extended to phenomena which are aperiodic in time. The proposed universal formula is simple to apply, requiring only the calculation of rays in the medium.

Comparison of In-the-Ear and Over-the-Ear Hearing Aid Fittings

1986 ◽  
Vol 51 (4) ◽  
pp. 362-369 ◽  
Author(s):  
Donna M. Risberg ◽  
Robyn M. Cox
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Comparative Evaluation ◽  
Speech Intelligibility ◽  
Hearing Aid ◽  
Hearing Aid Fitting ◽  
The Difference ◽  
Functional Gain ◽  
The Relationship

A custom in-the-ear (ITE) hearing aid fitting was compared to two over-the-ear (OTE) hearing aid fittings for each of 9 subjects with mild to moderately severe hearing losses. Speech intelligibility via the three instruments was compared using the Speech Intelligibility Rating (SIR) test. The relationship between functional gain and coupler gain was compared for the ITE and the higher rated OTE instruments. The difference in input received at the microphone locations of the two types of hearing aids was measured for 10 different subjects and compared to the functional gain data. It was concluded that (a) for persons with mild to moderately severe hearing losses, appropriately adjusted custom ITE fittings typically yield speech intelligibility that is equal to the better OTE fitting identified in a comparative evaluation; and (b) gain prescriptions for ITE hearing aids should be adjusted to account for the high-frequency emphasis associated with in-the-concha microphone placement.

Monitoring air quality in class I wilderness areas of the northeastern United States using lichens and bryophytes

2016 ◽  
Author(s):  
Alison C. Dibble ◽  
James W. Hinds ◽  
Ralph Perron ◽  
Natalie Cleavitt ◽  
Richard L. Poirot ◽  
...  
Keyword(s):  
United States ◽  
Air Quality ◽  
Class I ◽  
Northeastern United States ◽  
Wilderness Areas
Sign in / Sign up

Export Citation Format

Share Document