Seismotectonics of the Coso Range–Indian Wells Valley region, California: Transtensional deformation along the southeastern margin of the Sierran microplate

Abstract

Space-based geodetic observations show that the Coso Range and Indian Wells Valley lie along the southeastern margin of the Sierra Nevada–Central Valley (i.e., “Sierran”) microplate, which moves ~13–14 mm/yr northwest with respect to stable North America. Detailed kinematic analysis of seismicity indicates that active crustal extension in the Coso Range occurs in a right-lateral transtensional regime along the eastern border of the Sierran microplate. The Airport Lake fault in the northern Indian Wells Valley and the Owens Valley fault are the major strike-slip faults along the eastern margin of the Sierran microplate south and north, respectively, of the Coso Range. Patterns of seismogenic deformation and Quaternary faulting indicate that dextral shear passes through the Coso Range in a right-releasing stepover between the Airport Lake and Owens Valley faults. Extension within the stepover region is accommodated in part by opening of CosoWash as a pull-apart basin. The stepover is bounded on the east by a blind, northwest-striking dextral fault that is well expressed by patterns of microseismicity. Comparison with analogue sandbox models of pull-apart basins suggests that the Coso stepover is a relatively immature structure, consistent with models for a westward step in the locus of dextral shear along the eastern margin of the Sierran microplate to the IndianWells Valley and Owens Valley in the past 2–3 m.y.