Subduction of an extinct rift and its role in the formation of submarine landslides in NW South America

Abstract

AbstractOn the eastern margin of the Panama Basin, the Nazca oceanic plate converges towards the continental plate of South America at approximately 53 mm a−1. Subduction processes are accompanied by the presence of anomalous bathymetric elements including the Sandra Ridge. This east–west-orientated ridge is catalogued as an aborted rift derived from a magmatic spreading axis that was active between 12 and 9 Ma. Seismic activity within this structure is considered evidence of fault reactivation and tectonism. Once the structure reached the subduction trench several submarine landslides were triggered. Run-out lengths of these submarine landslides are perpendicular to the convergence of the structure with some units spreading and forming a wide fan that reaches tens of kilometres to the north and south of the trench. The area affected by the three main landslides varies between 130 and 300 km2 approximately, with relatively superficial earthquakes (<33 km) and with magnitudes that reach up to Mw 7.2. The morphology of the landslides suggests a retrogressive nature with younger events proximal to shore. This paper presents estimates of the age of these landslides and discusses sources of uncertainty regarding these times of occurrence.