Recent crustal deformation in southern California deduced from the restoration of folded and faulted strata

A rigid element method of restoration (UNFOLD) is used to restore competent folded and faulted layers of the Ventura and Los Angeles basins to their i nitial horizontal state. Comparison of initial (undeformed) state with pres ent (deformed state) allows one to estimate both the finite crustal deforma tion and its associated horizontal displacement field (relative to an arbit rary fixed line). Including data from the Santa Barbara Channel basin, the total finite displacement field for the western Transverse Ranges and vicin ity (within the Pacific plate) is inferred from this map restoration and is modeled as a double fan closure. This model implies a 10 degrees clockwise rotation of the northern boundary of the western Transverse Ranges and a 5 degrees counterclockwise rotation of its northeast boundary. Lateral varia tion of the deformation reveals the heterogeneity of the subsurface deforma tion. Most of the major thrusts appear to initiate as en echelon structures along the left-lateral northern margin and the right-lateral northeastern margin of the studied area. The resulting deformation and displacement valu es closely match those derived by other geological methods (section balanci ng techniques or fault slip measurements) and by geophysical methods (geode tic, paleomagnetic, and focal mechanism data). Map restoration thus is a me thod that can independently quantify both local and regional deformation in cluding folds and faults. This method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused.