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

Gail M. Atkinson; David M. Boore

doi:10.1785/0120130136

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

Gail M. Atkinson·David M. Boore

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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/R 1.3 to a transition distance of 50 km, with a geometric spreading of 1/R 0.5 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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Source-reported bounding extent: 34° to 54° latitude; -90° to -55° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeX RIS

Gail M. Atkinson, David M. Boore. 2013-11-26. The attenuation of Fourier amplitudes for rock sites in eastern North America. https://doi.org/10.1785/0120130136

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