HR: 17:25h
AN: S44B-06    [Abstracts]
TI: Seismic Attenuation Observations: Signals and Artifacts
AU: * Lawrence, J F
EM: jfl77@ucsd.edu
AF: Stanford University, Department of Geophysics 397 Panama Mall Mitchell Building 360 Stanford University, Stanford, CA 94305-2215, United States
AU: * Lawrence, J F
EM: jfl77@ucsd.edu
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography University of California, San Diego IGPP 0225 9500 Gilman Drive, La Jolla, CA 92093-0225, United States
AU: Thorne, M S
EM: mthorne@gi.alaska.edu
AF: Arctic Region Supercomputing Center, University of Alaska, Geophysical Institute 903 Koyukuk Drive P.O. Box 757320, Fairbanks, AK 99775-7320, United States
AU: Shearer, P M
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography University of California, San Diego IGPP 0225 9500 Gilman Drive, La Jolla, CA 92093-0225, United States
AB: In this study we estimate to what degree seismic velocity heterogeneity contaminates seismic attenuation measurements for body waves. Comparisons between anelastic attenuation (per cycle energy loss) and seismic velocity can be used to infer temperature or chemical heterogeneity in the Earth. Unfortunately, many observations of seismic attenuation may not represent true anelastic attenuation if proper precautions are not taken. By measuring the seismic attenuation for attenuation-free 2.5D axisymetric synthetic S waves we can estimate how much elastic velocity heterogeneity contaminates attenuation observations. We perform multiple tests representing varying idealized and seismically observed structures in the Earth. While all S-wave attenuation measurements for seismic waves that travel through a heterogeneous body are contaminated to some degree, the severity of the contamination can be greatly reduced by taking three steps: (1) Determine differential attenuation for as many phase pair combinations as possible to increase reliability and redundancy. (2) Properly align/window each wave prior to measuring differential attenuation. (3) Only accept attenuation measurements for highly correlated (R² > 0.9) wave pairs. These three steps minimize the observed contamination in synthetic S waves, even for cases of severe velocity heterogeneity. We have developed a fast and easy interactive tool for measuring differential attenuation with large seismic networks (e.g., EarthScope) following the three criteria listed above. Application of this program to USArray broadband data for both P and S waves provides sufficient data to invert for spatial variations in the quality factor Q. We present these attenuation results for the Western United States.
DE: 5144 Wave attenuation
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7270 Tomography (6982, 8180)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting