Assessing giant tsunamigenic subduction earthquakes in the Northern Chile Seismic Gap during the last two millennia

Wednesday, 17 December 2014
Gabriel Vargas Easton1, Sergio Ruiz2, Felipe Leyton3, Rachel Abrahami1, Jacobus Le Roux1, Silvio Pantoja4, Carina Lange4, Eduardo Contreras Reyes2 and Jaime A Campos2, (1)University of Chile, Departamento de Geología, CEGA, Santiago, Chile, (2)University of Chile, Departamento de Geofísica, Santiago, Chile, (3)University of Chile, CSN, Santiago, Chile, (4)University of Concepcion, Departamento de Oceanografía, COPAS, Concepcion, Chile
Marine sedimentary records off Northern Chile provide a new view about the occurrence of large subduction earthquakes along the hyperarid convergent margin of the Central Andes. From high resolution geochronology and sedimentology of laminated series accumulated on narrow shelf, we observed that anomalous structures such as slumps and discontinuities overlaid by turbidite deposits record the last giant Mw~8.8 earthquake and tsunami occurred on 1877 in the region. Once compared with the reanalysis of historical chronicles and seismological data, we suggest that only large magnitude events produce ground accelerations generating slumping or discontinuities.

The analysis of long (ca. 5.5 m) sediment cores together with high resolution seismic subbottom profile data allow us to infer the occurrence of several giant earthquakes in the last ca. 1600 years, with a mean recurrence in the order of 400 years. Under this scope, the Mw8.1 occurred this year off Pisagua-Iquique region, as other previous historic events (Mw7.7, Tocopilla, 2007; Mw7.6, Iquique, 1933), seem to be moderate earthquakes into a larger seismic cycle.