NEAR-SURFACE FOLDING ALONG AN ACTIVE FAULT - SEISMIC OR ASEISMIC

The Meers fault in southwestern Oklahoma has been active in recent tim es. The most recent movement occurred about 1100 years ago in the late Holocene. During the faulting, the Quaternary age alluvial deposits a long the fault were folded as well as ruptured. In some places, almost all of the deformation is accommodated by ductile folding of these de posits. Having this type of deformation with no record of an earthquak e associated with the Meers fault during historical times raises the q uestion whether the present scarp was formed seismically by earthquake event(s), or aseismically by slow deformation (aseismic fault creep). Triaxial shear tests with various shear rates were run to determine t he conditions for brittle, ductile and brittle-ductile transition type failures. Relationships between ductility, moisture content, strain-r ate, shear-rate or failure time, and confining stress were determined. The results show that under the possible field conditions that existe d during the faulting, the ductile folding of these deposits is possib le, indicating the Meers fault scarp could have been created contempor aneously with earthquake event(s). (C) 1998 Elsevier Science B.V. All rights reserved.