Late Quaternary accelerated coastal uplift and crustal faulting in Mejillones peninsula at the southern edge of the Northern Chile subduction seismic gap

Abstract:

The Mejillones peninsula (23ºS) is an anomalous geomorphologic and tectonic feature along the subduction margin of the Central Andes, characterized by Quaternary uplifted littoral ridges, marine terraces and active crustal faults. It lies at the southern edge of the Northern Chile seismic gap, where the last large event Mw~8.8 occurred on 1877. The peninsula has been regarded like a tectonic boundary for large earthquakes, where strong interaction between surface, crustal and interplate deformation associated to the subduction of the Nazca beneath the South American plates occur.

Geochronological and geomorphologic results including the analysis of Digital Elevation Model, differential GPS data and submarine subbottom seismic profiles (3.5 kHz), evidence an acceleration of the coastal uplift (from ca. 0.2 m/ka up to ca. 1 m/ka) and crustal normal faulting (slip rate in the order of 0.6 m/ka) processes in the last ~40 ka, with respect to the Middle and Late Pleistocene, according previous results. Onshore and offshore observations revealed a scissor-shape deformation along the Mejillones Fault, with increasing slip rate offshore. Accelerated coastal uplift phenomenon in the last ~40 ka should evidence increased earthquake production along the subduction contact, implying also an acceleration of the seismogenic activity along crustal normal faults, and should result in the current coastal cliff formation.