Isostatic uplift of denuded footwall rocks beneath a shallowly-dipping detachment fault is thought to cause upwards arching of the detachment and may cause the shallow past of the fault to be abandoned. This theory predicts that as fault slip continues, the hinge zone between steep, active and shallow, inactive parts of the fault will migrate through the footwall. Alternative models predict different strain paths will be recorded in the footwall rocks. This study will test the hypothesis of a migrating hinge zone by examining the strain state in footwall rocks beneath three detachment faults from different tectonic settings: Beaver Dam Mountains, Utah; Whipple Mountains, California; and Brenner Line, eastern Alps. The results will allow assessment of the migrating hinge models and will have broad applicability to extensional zones in a variety of tectonic environments.
