Holocene activity and seismogenic capability of intraplate thrusts: Insights from the Pampean Ranges, Argentina

Abstract Trench excavations across the El Molino fault in the southeastern Pampean Ranges of central-western Argentina have revealed a deformation zone composed of opposite-verging thrusts that deform a succession of Holocene sediments. The west-verging thrusts place Precambrian basement over Holocene proximal scarp-derived deposits, whereas the east-verging thrusts form an east-directed fault-propagation fold that deforms colluvium, fluvial and aeolian deposits. Ages for exposed fault-related deposits range from 7.1 ± 0.4 to ~0.3 ka. Evidence of surface deformation suggests multiple rupture events with related scarp-derived deposits and a minimum of three surface ruptures younger than 7.1 ± 0.4 ka, the last rupture event being younger than 1 ka. Shortening rates of ~0.7 ± 0.2 mm/a are near one order of magnitude higher than those estimated for the faults bounding neighboring crustal blocks and are considered high for this intraplate setting. These ground-rupturing crustal earthquakes are estimated to be of magnitude M w  ≥ 7.0, a significant discrepancy with the magnitudes M w