Deformation partitioning • Large-scale at obliquely converging or diverging boundaries (~60% of plate boundaries have some transcurrent component of motion) • Small-scale at fault bends and step-overs
Partitioning between discontinuous & continuous or distributed deformation • Distributed (e.g., a zone of closely spaced fractures) and/or continuous (e.g., folds, flow) deformation is common between faults in a system
Extensional plate margins • Note changing length of San Andreas fault system as subduction of mid-ocean rifts along North and Central America continues
Transcurrent margins and major faults • Fracture zones extend from transform faults • Major strike-slip or transcurrent faults transfer slip between trenches • Major strike-slip faults (Anatolian, Altyn Tagh) accomplish extrusion
Why Study Reverse Faults? • Host the largest, and potentially most destructive earthquakes (subduction zone thrusts). Low dip requires that faults have large surface area in brittle "seismogenic zone" and that this surface area is close to ground surface where we live. • Associated with mountain building and collisional tectonics. Low-angle faults with big displacements have been known since 1800's (Lapworth). • Large displacements and mechanical paradoxes. • Influence positions of ore deposits (high-angle reverse faults) and hydrocarbons (thrusts).
Initiating subduction • Generally will reactivate pre-existing structures, such as rift-related features preserved on passive margins (producing continental arc) or transform faults in mid-ocean ridges (producing island arc)