High-frequency imaging of elastic contrast and contact area with implications for naturally observed changes in fault properties

Journal of Geophysical Research
By: , and 

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Abstract

During localized slip of a laboratory fault we simultaneously measure the contact area and the dynamic fault normal elastic stiffness. One objective is to determine conditions where stiffness may be used to infer changes in area of contact during sliding on nontransparent fault surfaces. Slip speeds between 0.01 and 10 µm/s and normal stresses between 1 and 2.5 MPa were imposed during velocity step, normal stress step, and slide-hold-slide tests. Stiffness and contact area have a linear interdependence during rate stepping tests and during the hold portion of slide-hold-slide tests. So long as linearity holds, measured fault stiffness can be used on nontransparent materials to infer changes in contact area. However, there are conditions where relations between contact area and stiffness are nonlinear and nonunique. A second objective is to make comparisons between the laboratory- and field-measured changes in fault properties. Time-dependent changes in fault zone normal stiffness made in stress relaxation tests imply postseismic wave speed changes on the order of 0.3% to 0.8% per year in the two or more years following an earthquake; these are smaller than postseismic increases seen within natural damage zones. Based on scaling of the experimental observations, natural postseismic fault normal contraction could be accommodated within a few decimeter wide fault core. Changes in the stiffness of laboratory shear zones exceed 10% per decade and might be detectable in the field postseismically.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title High-frequency imaging of elastic contrast and contact area with implications for naturally observed changes in fault properties
Series title Journal of Geophysical Research
DOI 10.1002/2014JB011014
Volume 119
Issue 7
Year Published 2014
Language English
Publisher American Geophysical Union
Contributing office(s) Earthquake Science Center
Description 21 p.
First page 5855
Last page 5875