Listric thrusts in the western Transverse Ranges, California

Some of the main faults accommodating current shortening in the,western Tra nsverse Ranges are probably listric because (1) they are associated with pr ogressive tilting, and (2) they may be preexisting normal faults that accom modated Miocene extension. These faults have been reactivated in the Plioce ne-Quaternary transpressive regime. We propose a listric thrust model where slip is proportional to backlimb dip. This model requires relatively littl e fault slip to account for progressive tilting and for wide (in the dip di rection) and gently dipping backlimbs. In contrast, widely applied fault-be nd fold and fault-propagation fold models relate fault slip to limb width a lone and typically predict more shortening by the blind thrusts that can he accounted for by folding in the cover above them, We trace the southern-mo st structural high in the Transverse Ranges from the Santa Monica Mountains through the southern Santa Barbara Channel. The north-dipping backlimb of this anticline is 20-30 km wide acid 220 km long; its presence suggests a v ery large north dipping thrust that could generate very large earthquakes. The slip rate for this fault, however, is substantially lower for a listric thrust model than for a single-step ramp-flat model.