Normal fault corrugation: implications for growth and seismicity of activenormal faults

Large normal faults are corrugated. Corrugations appear to form from overla pping or en echelon fault arrays by two breakthrough mechanisms: lateral pr opagation of curved fault-tips and linkage by connecting faults. Both mecha nisms include localized fault-parallel extension and eventual abandonment o f relay ramps. These breakthrough mechanisms produce distinctive hanging wa ll and footwall geometries indicative of fault system evolution,From such g eometries, we can estimate the positions of tilted relay ramps or ramp segm ents and ramp internal deformation in;incompletely exposed or poorly imaged fault systems. We examine the evolution of normal fault corrugations at Fi sh Slough (California), Yucca Mountain (Nevada), and Pleasant Valley (Nevad a), in the Basin and Range province. We discuss how evolution of the Pleasa nt Valley and Yucca Mountain systems relates to seismicity. For example, th e 1915 Pleasant Valley earthquake produced four en echelon ruptures that ap peared as overlapping segments of a single immature fault at depth. At Yucc a Mountain, we argue that an enchelon array, which includes the Solitario C anyon and Iron Ridge faults, should be considered a single source, such tha t western Yucca Mountain could experience up to a M-w 6.9 earthquake compar ed to M-w 6.6 estimates for the largest individual segment, (C) 1999 Elsevi er Science Ltd. All rights reserved.