Bulletin of the Seismological Society of America
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Bulletin of the Seismological Society of America; February 1995; v. 85; no. 1; p. 237-253
© 1995 Seismological Society of America
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Sharrock, D. S.
Right arrow Articles by Douglas, A.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Observations of Q from the northwest Pacific subduction zone recorded at teleseismic distances

D. S. Sharrock, I. G. Main and A. Douglas

Department of Geology and Geophysics Grant Institute University of Edinburgh, Edinburgh EH9 3JW United Kingdom
AWE Blacknest, Brimpton, Reading, Berkshire RG7 4RS United Kingdom

Abstract

Twenty-seven earthquakes in the northwest Pacific, with mb greater double equals 5.4, are used to study upper-mantle attenuation. The data were recorded at seismometer arrays in Australia, Canada, India, and Scotland. The short-period instruments used in the arrays are sufficiently broadband, and the signal-to-noise enhancement resulting from beamforming the data is good enough, that seismic noise is above system noise out to between 3 and 5 Hz, and in some cases to 8 Hz. The instrument response has been removed and a power law ({omega}–2) farfield source correction has been assumed and applied. The remaining fall-off in the spectra above 1 Hz (which is above the corner frequency fc) is assumed to be due to attenuation, including losses due both to anelasticity and to scattering. An {omega}–3 spectral fall-off, preferred by some, would result in lower estimates of attenuation. Conservative estimates of the average attenuation along the whole path have been made from the spectral fall-off. Despite the imperfect knowledge of the source spectra, the high sensitivity of spectral amplitudes to attenuation at high frequencies yields quite reliable and stable attenuation estimates. The scatter in the data is small, resulting in estimates of mean t* (tAV*) with an average standard error of only 21%, where tAV* is defined as the ratio of the travel time T to the effective mean quality factor QAV. Only 14 of the 64 measurements show a tAV* above 0.5 sec within the given error bounds. All estimates of tAV* and QAV refer to P-wave attenuation only. The results for tAV* from the northwest Pacific subduction zone cannot be explained simply by the traditional high-Q subducting slab in a low-Q upper mantle. A low-Q region in the uppermost 100 km (approximately) of the subduction zone has been identified. Source-corrected tAV* yield upper-mantle QAV estimates of about 1200 for predominantly oceanic paths (Australia and India) and 1500 for mixed continental and oceanic paths (Canada and Scotland).




This article has been cited by other articles:


Home page
 Bulletin of the Seismological Society of AmericaHome page
A. Katsumata
Comparison of magnitudes estimated by the Japan Meteorological Agency with moment magnitudes for intermediate and deep earthquakes
Bulletin of the Seismological Society of America, June 1, 1996; 86(3): 832 - 842.
[Abstract] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 1995 by the Seismological Society of America.