Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005geoji.160..695l&link_type=abstract
Geophysical Journal International, Volume 160, Issue 1, pp. 695-706.
Astronomy and Astrophysics
Astronomy
7
Attenuation, Borehole, Crust, Q, Seismic Anisotropy, Shear Wave Splitting
Scientific paper
Seismograms from local aftershocks of the 1999 Chi-Chi, Taiwan, earthquake recorded at a 200-m-deep downhole station CHY of the Taiwan Central Weather Bureau Seismic Network (CWBSN) have clear direct upgoing shear waves and their surface-reflected downgoing phases. Measurements of time difference between the direct and reflected phases of the fast and slow components of split shear waves show approximately 8 per cent velocity anisotropy in the top 200 m of the crust. The phase velocities extracted from the direct and reflected waveforms display clear evidence of attenuation-related dispersion. Taking the dispersion and geometrical spreading factor into account, we estimate the Q value of the shear waves by fitting calculated results to the observed reflected waveforms. The amplitude spectral density ratios between the direct and reflected phases are approximately linear within the frequency range 2-15 Hz. This allows us also to estimate the Q value from the slope of the amplitude spectral ratio (in dB Hz-1) in this range. The estimated Q values with both methods, based on a set of similar waveforms and additional 156 high-quality records, are 61-68 for the fast components and 43-52 for the slow components. The observed attenuation anisotropy may be, similarly to velocity anisotropy, a manifestation of microcracks alignment and their response to in situ stress. Strong attenuation anisotropy (23-30 per cent in this study) along with attenuation-related dispersion in the shallow crust can affect significantly the properties of shear waves and should be taken into account in studies employing surface and shallow borehole records of shear waveforms.
Ben-Zion Yehuda
Liu Yunfeng
Teng Ta-Liang
No associations
LandOfFree
Near-surface seismic anisotropy, attenuation and dispersion in the aftershock region of the 1999 Chi-Chi earthquake does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Near-surface seismic anisotropy, attenuation and dispersion in the aftershock region of the 1999 Chi-Chi earthquake, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Near-surface seismic anisotropy, attenuation and dispersion in the aftershock region of the 1999 Chi-Chi earthquake will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1358990