HR: 1340h
AN: S53B-0205    [Abstracts]
TI: Seismic Attenuation Anisotropy in the Crust Beneath ANZA (Southern California)
AU: * Martynov, V G
EM: vladik@epicenter.ucsd.edu
AF: V.G. Martynov, Cecil H. & Ida M. Green Institute of Geophysics & Planetary Physics, 0225, Scripps Institution of Oceanography, La Jolla, CA 92093-0225 United States
AU: Vernon, F L
EM: vernon@epicenter.ucsd.edu
AF: V.G. Martynov, Cecil H. & Ida M. Green Institute of Geophysics & Planetary Physics, 0225, Scripps Institution of Oceanography, La Jolla, CA 92093-0225 United States
AU: Kilb, D L
EM: dkilb@epicenter.ucsd.edu
AF: V.G. Martynov, Cecil H. & Ida M. Green Institute of Geophysics & Planetary Physics, 0225, Scripps Institution of Oceanography, La Jolla, CA 92093-0225 United States
AB: We present a method to study crustal anisotropy using polarization-dependence attenuation of {\it S}-coda waves. We have tested our algorithm on band-passed ( 2 - 4 Hz ) waveforms of a {\it M$_{L}$} = 5.1 local crustal earthquake ( {\it h} = 18.7 km ) recorded by the ANZA broadband network in southern California. We analyzed the records of 10 stations, of which 7 are $<$ 20 km away. For all stations {\it S}-coda waves with a polarization direction of $184\deg$ ( from North ) have the maximum value of the quality factor {\it Q$_{c}$} ( or the smallest attenuation ). This orientation is in agreement with the axes of the maximum compression obtained from fault mechanism analysis ( http://www.trinet.org/shake/9718013/zhu.html ) and results of seismogenic deformation field ( Unruh {\it et al}., 1996, {\it JGR} ) in southern California. The polarization directions with the biggest values of {\it Q$_{c}$} orient in a plane with the strike $159\deg$ and dip $74\deg$. This result suggests that the cracks are oriented $\sim$ NWN - SES and they are responsible for the induced attenuation anisotropy in the crust beneath ANZA. The cracks are parallel the maximum compressional stress. We found the coefficient of attenuation anisotropy at 3 Hz equals 9%.
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting