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Multi‐scale compressional wave velocity structure of the San Gregorio Fault zone
Author(s) -
Gettemy G. L.,
Tobin H. J.,
Hole J. A.,
Sayed A. Y.
Publication year - 2004
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 - 10.1029/2003gl018826
Subject(s) - geology , seismology , hypocenter , fault (geology) , slip (aerodynamics) , induced seismicity , physics , thermodynamics
Understanding fault architecture at multiple scales is crucial to delineate in situ fault zone physical properties and rupture dynamics through modeling and geophysical imaging/monitoring. An exposure of the active large‐offset, strike‐slip San Gregorio Fault at Moss Beach, CA provides a unique field site to relate the well‐mapped fault zone architecture with compressional wave velocity ( V p ) structure measured at centimeter to meter scales. Laboratory ultrasonic velocities of fault zone samples, adjusted for fluid‐related frequency and structural dispersion, indicate that (i) a seismic velocity reduction of ∼30% characterizes the central smectite‐rich clay gouge relative to the rocks 100 m away in the relatively undeformed host rocks, and (ii) the across‐fault velocity profile trends for the seismic to ultrasonic bandwidth correlate almost exactly to the previously mapped macroscale fault zone structure. These results highlight the value of conducting multiscaled investigations when measuring fault zone properties defined by physical elements at multiple scale lengths.