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Seismically invisible fault zones: Laboratory insights into imaging faults in anisotropic rocks
Author(s) -
Kelly C. M.,
Faulkner D. R.,
Rietbrock A.
Publication year - 2017
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 - 10.1002/2017gl073726
Subject(s) - anisotropy , fault gouge , geology , fault (geology) , schist , protolith , seismology , geophysical imaging , petrology , orientation (vector space) , seismic anisotropy , mica , geophysics , metamorphic rock , geometry , paleontology , physics , mathematics , quantum mechanics , mantle (geology)
Phyllosilicate‐rich rocks which commonly occur within fault zones cause seismic velocity anisotropy. However, anisotropy is not always taken into account in seismic imaging and the extent of the anisotropy is often unknown. Laboratory measurements of the velocity anisotropy of fault zone rocks and gouge from the Carboneras fault zone in SE Spain indicate 10–15% velocity anisotropy in the gouge and 35–50% anisotropy in the mica‐schist protolith. Greater differences in velocity are observed between the fast and slow directions in the mica‐schist rock than between the gouge and the slow direction of the rock. This implies that the orientation of the anisotropy with respect to the fault is key in imaging the fault seismically. For example, for fault‐parallel anisotropy, a significantly greater velocity contrast between fault gouge and rock will occur along the fault than across it, highlighting the importance of considering the foliation orientation in design of seismic experiments.