Offset and evolution of the Gowk fault, S.E. Iran: a major intra-continental strike-slip system

We use drainage reconstructions to estimate long-term offsets on the Gowk fault, an oblique right-lateral strike-slip fault in eastern Iran, on which there have been a number of recent large earthquakes. A 3 km horizontal offset is inferred from well-preserved geomorphology. We further identify a total cumulative offset of ∼12 km, which produces a simple reconstruction of geomorphology across the fault, filling in pull-apart basins, restoring rivers to linear courses across the fault trace and aligning structural and bed-rock features. The probable age of the Gowk fault, and K–Ar dating of offset basalts north of the study region, suggest an overall slip rate of ∼1.5–2.4 mm/year. This is small compared with the overall 10–20 mm/year of shear expected between central Iran and Afghanistan and the deficit is likely to have been accommodated on other faults east of the Gowk fault. Drainage displaced by dextral movement leads to the development of a series of basins along the fault and a longitudinal topographic profile that resembles an asymmetric saw-tooth. The geomorphic evolution of the fault zone at the surface includes both normal and reverse faulting components, reflecting a probable ramp-and-flat structure in cross-section. This interpretation is consistent with evidence from the analysis of seismological, radar and surface rupture data in recent earthquakes.