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The attenuation of Fourier amplitudes for rock sites in eastern North America

Bulletin of the Seismological Society of America

By:
and
DOI: 10.1785/0120130136

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Abstract

We develop an empirical model of the decay of Fourier amplitudes for earthquakes of M 3–6 recorded on rock sites in eastern North America and discuss its implications for source parameters. Attenuation at distances from 10 to 500 km may be adequately described using a bilinear model with a geometric spreading of 1/R1.3 to a transition distance of 50 km, with a geometric spreading of 1/R0.5 at greater distances. For low frequencies and distances less than 50 km, the effective geometric spreading given by the model is perturbed using a frequency‐ and hypocentral depth‐dependent factor defined in such a way as to increase amplitudes at lower frequencies near the epicenter but leave the 1 km source amplitudes unchanged. The associated anelastic attenuation is determined for each event, with an average value being given by a regional quality factor of Q=525f 0.45. This model provides a match, on average, between the known seismic moment of events and the inferred low‐frequency spectral amplitudes at R=1  km (obtained by correcting for the attenuation model). The inferred Brune stress parameters from the high‐frequency source terms are about 600 bars (60 MPa), on average, for events of M>4.5.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The attenuation of Fourier amplitudes for rock sites in eastern North America
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120130136
Volume
104
Issue:
1
Year Published:
2014
Language:
English
Publisher:
Seismological Society of America
Contributing office(s):
Earthquake Science Center
Description:
16 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
513
Last page:
528
Number of Pages:
16
Country:
Canada;United States