CONCENTRATED SLIP ZONES WITH SUBSIDIARY SHEARS - THEIR DEVELOPMENT ON3 SCALES IN THE CERRO-BRASS FAULT ZONE, APPALACHIAN VALLEY AND RIDGE

Concentrated slip zones bound subsidiary shears at three scales within the Cerro Brass Fault, which cuts Cambrian dolomites of the Nittany A nticlinorium, Pennsylvania. On the outcrop scale thrust faults along b oth Cerro Brass fault zone boundaries acted as concentrated slip zones bounding subsidiary shears developed along original bedding planes. T he outcrop scale subsidiary shears are zones of concentrated slip boun ding hand-specimen-scale subsidiary shears. In turn, the hand-specimen -scale subsidiary shears are concentrated slip zones bounding even sma ller-scale subsidiary shears. Subsidiary shears in Cerro Brass fault z one are analogous to subsidiary shears (i.e. R(1) and R(2)) commonly f ound in laboratory gouge-friction experiments. The orientations of sub sidiary shears at the outcrop and hand-specimen scales define a 'Riede l within Riedel' geometry in which the original bedding played the rol e of R(1) shears at the outcrop scale and, at the same time, operated as boundary faults at a smaller scale. The presence of subsidiary shea rs on more than one scale suggests that the Coulomb failure theory is not sufficient to explain their origin.