Near-surface folding along an active fault: seismic or aseismic?

The Meers fault in southwestern Oklahoma has been active in recent times. The most recent movement occurred about 1100 years ago in the late Holocene. During the faulting, the Quaternary age alluvial deposits along the fault were folded as well as ruptured. In some places, almost all of the deformation is accommodated by ductile folding of these deposits. Having this type of deformation with no record of an earthquake associated with the Meers fault during historical times raises the question 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 the conditions for brittle, ductile and brittle-ductile transition type failures. Relationships between ductility, moisture content, strain-rate, shear-rate or failure time, and confining stress were determined. The results show that under the possible field conditions that existed during the faulting, the ductile folding of these deposits is possible, indicating the Meers fault scarp could have been created contemporaneously with earthquake event(s). (C) 1998 Elsevier Science B.V. All rights reserved.