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San Andreas Fault damage at SAFOD viewed with fault‐guided waves
Author(s) -
Li YongGang,
Malin Peter E.
Publication year - 2008
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 - 10.1029/2007gl032924
Subject(s) - geology , seismology , borehole , seismometer , fault (geology) , seismic wave , amplitude , tapering , fault trace , geophysics , geotechnical engineering , physics , computer graphics (images) , quantum mechanics , computer science
Highly damaged rocks within the San Andreas fault zone at Parkfield form a low‐velocity waveguide for seismic waves, giving rise to fault‐guided waves. Prominent fault‐guided waves have been observed at the San Andreas Fault Observatory at Depth (SAFOD) site, including a surface array across the fault zone and a borehole seismograph placed in the SAFOD well at a depth of ∼2.7 km below ground. The resulting observations are modeled here using 3‐D finite‐difference methods. To fit the amplitude, frequency, and travel‐time characteristics of the data, the models require a downward tapering, 30–40‐m wide fault‐core embedded in a 100–200‐m wide jacket. Compared with the intact wall rocks, the core velocities are reduced by ∼40% and jacket velocities by ∼25%. Based on the depths of earthquakes generating guided waves, we estimate that the low‐velocity waveguide along the fault at SAFOD extends at least to depths of ∼7 km, more than twice the depth reported in pervious studies.