Premium
Fault‐zone attenuation of high‐frequency seismic waves
Author(s) -
Blakeslee Sam,
Malin Peter,
Alvarez Marcos
Publication year - 1989
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl016i011p01321
Subject(s) - attenuation , seismology , geology , fault (geology) , amplitude , seismic wave , active fault , geophysics , optics , physics
We have developed a technique to measure seismic attenuation within an active fault‐zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave‐propagation within the fault‐zone. This empirical approach eliminates common source, propagation, instrument and near‐surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault‐zone, at Parkfield California. Over the 1‐40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault‐zone propagation distance correlates with the severity of attenuation. Assuming a constant Q attenuation operator, the S‐wave quality factor within the fault‐zone at a depth of 5‐6 kilometers is 31 (+7,−5). If fault‐zones are low‐Q environments, then near‐source attenuation of high‐frequency seismic waves may help to explain phenomenon such as f max . Fault‐zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault‐zones. Specific asperities can be monitored for precursory changes associated with the evolving stress‐field within the fault‐zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.