DUCTILITY IN FAULT GOUGE FROM A NORMAL-FAULT SYSTEM, DEATH-VALLEY, CALIFORNIA - A MECHANISM FOR FAULT-ZONE STRENGTHENING AND RELEVANCE TO PALEOSEISMICITY

Fault gouge along the Badwater Turtleback fault system displays abunda nt evidence for mesoscopic ductility, as foliation, isolated and/or ro tated inclusions, and isoclinal folds, Fault-gouge thicknesses also va ry dramatically, At the outcrop scale, gouge thicknesses can range fro m 0 to > 1 m, and at the 100 m scale, they can range from 0 to > 5 m, Because these variations are closely associated with other ductility-r elated features, they probably also formed because of ductile flow, Du ctile flow appears to locally strengthen the fault zone by severe atte nuation of the gouge and by transport of inclusions, Where gouge pinch es out to zero thickness, hanging-wall rock rests directly on footwall rock, a condition that produces an overall stronger fault zone as wel l as stick-slip behavior in laboratory tests, Transport of inclusions within the gouge zone may create local inclusion ''jams'' which may al so have a strengthening effect, The presence of these stronger portion s of the fault zone may give indirect evidence for ancient seismicity on the fault.