Inference of trishear-faulting processes from deformed pregrowth and growth strata

Near surface strata deformed by propagation of a fault situated underneath these strata hold explicit records of fault activities. The delicate deformed strata exposed in investigation trenches for paleoseismologic study conform to fault-propagation folds growing above a blind thrust. Growth strata deposited subsequently across the coseismic fold scarps are preserved by onlap and unconformities. Information from these sedimentary and folding processes was used in conjunction with inverse modeling using the trishear model technique proposed by Allmendinger (Allmendinger, R.W., 1998. Inverse and forward numerical modeling of trishear fault-propagation folds. Tectonics 17, 640–656) in estimating the times and amounts of slips. This methodology becomes necessary especially when the extent of a deformed profile is insufficiently exposed to observation or the location of the fault tip is invisible. The proposed method can deal with growth strata that can be selectively removed during fold restoration. terpretations on the deformation history obtained by inverse analysis and trench investigation were then compared. The combination of these two approaches seemed to enhance and complement each other and allows a better and more complete understanding of the trishear-faulting processes and is useful in seismic hazard assessment.