ALBERT

Description: Compilation and synthesis of neotectonic data from the Great Basin region (western U.S.), based on 173 published studies for 171 faults across the region, offer an unprecedented view into the spatiotemporal evolution of strain release in continental domains, at time scales of 1 k.y. to 1 m.y. The results indicate a mean vertical surface displacement for normal faulting earthquakes of 2 m (approximately two-thirds of events in the 1–3 m range). The distribution of earthquake recurrence intervals is more scattered, with a mode of 1–3 k.y., a mean of 11 k.y., and 15% of recurrence intervals 〉20 k.y. While strike-slip faults nearest the plate boundary show relatively steady slip rates through time, northern Great Basin normal faults have had marked temporal slip-rate variations in the Quaternary. Since 15 ka, strain release has been concentrated near the margins (fault slip rates to 1–2 mm/yr), with the central region being nearly inactive. However, over the past 150 k.y., finite deformation is more evenly distributed as faults show more uniform slip rates (0.2–0.3 mm/yr) consistent with their long-term rates. The paleo-earthquake distribution since ca. 60 ka shows two kinematic patterns: local clusters (episodes of events repeated on a single fault) and regionally distributed faulting (episodes of events distributed across several parallel faults, each with a single event). We thus propose a model for northern Great Basin normal faults where they alternate between (1) transient fast periods (1–2 mm/yr) lasting ~50 k.y., characterized by local clusters; and (2) transient slow periods (0.05–0.1 mm/yr) lasting 200–400 k.y., characterized by regional distributed faulting.