Seismotectonic implications of the Chile Oceanic ridge subduction beneath the Patagonian Andes

Abstract

The Chile oceanic ridge intersects the South America trench, forming the Chile Triple Junction (CTJ) at the Taitao Peninsula latitude (~46º 20´), on the western margin of the Patagonian Andes. The subduction of sea-fl oor-spreading centers from the Chile seismic ridge beneath Patagonia produces a set of thermo-mechanical eff ects on the overriding plate, as already evidenced by several studies. However, the eff ects of ridge subduction on the seismicity distribution and the related tectonic stress regime have been poorly investigated. To address this issue, we compilated and analyzed a database of seismic events, and available intraplate earthquakes focal mechanisms provided by the GCMT catalog merged with events recorded by local temporary seismic networks (Lange et al. 2008, Agurto et al. 2012, Sielfeld et al. 2019). We observe that the distribution of the intraplate crustal seismicity along the Patagonian Andes is disrupted by a 450-470 km long gap without signifi cant seismic activity (Fig. 1), coinciding with the location of the asthenospheric slab window beneath Patagonia. Besides, the calculated stress tensors from intraplate earthquake focal mechanisms depict notably diff erent tectonic regimes north and south of the Chile Triple Junction. North of the CTJ, a strike-slip tectonic stress regime prevails consistent with long- and short-term dextral shearing along the Liquiñe-Ofqui fault system, while E-W compression takes place south of the CTJ, in the southernmost foreland of the southern Patagonian Andes.