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Paleoseismic inferences from a high-resolution marine sedimentary record in northern Chile (23°S) .

Abstract : The active margin of northern Chile is characterized by strong seismic events which induce gravity instability for sedimentary sequences located along the outer forearc of the Andean range. Even though the narrow continental platform of this area limits the accumulation of marine sediments, a detailed paleoceanographic reconstruction, using high-resolution sedimentological and geochronological techniques, of a Holocene sedimentary sequence in Mejillones bay (23°S) provides important tools to infer the occurrence of past great subduction earthquakes and/or associated tsunamis. From the analyses of short cores retrieved in this shallow marine basin, we infer the occurrence of two strong seismic events during historical times. The first one, dated between the years 1409 and 1449 AD, produced an angular unconformity and associated lenticular coarse-grained deposits generated after local reworking of shallower material. The second one, dated between the years 1754 and 1789 AD, caused slumping, erosive processes and local reworking of material. The analysis of seismic profile data acquired in this bay allowed the recognition of a major slump deposit within the upper sedimentary sequence, tentatively dated as of Middle Holocene age. This event might record the greatest earthquake (and tsunami) affecting the basin within the last few thousand years. We interpret that destabilization of sediments occurs most probably in response to local reactivation of faults within the Mejillones peninsula during strong earthquakes, especially the Mejillones fault.
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Submitted on : Saturday, April 29, 2006 - 8:07:28 AM
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Gabriel Vargas, Luc Ortlieb, Emmanuel Chapron, Jorge Valdés, Carlos Marquardt. Paleoseismic inferences from a high-resolution marine sedimentary record in northern Chile (23°S) .. Tectonophysics, Elsevier, 2005, 399 (1-4), pp.381-398. ⟨10.1016/j.tecto.2004.12.031⟩. ⟨hal-00023572⟩



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