Title

Sedimentological and stratigraphic evidence for paleotsunami events at Quidico, Chile

Presenter Information

Isabel Hong

Document Type

Oral Presentation

Location

SURC Room 140

Start Date

15-5-2014

End Date

15-5-2014

Keywords

Sedimentology, Tsunami, Chile

Abstract

We utilized geomorphic, microfossil, sedimentological, and stratigraphic methods to investigate the history of past earthquakes and tsunamis at Quidico, Chile (38.1°S, 73.2°W). The study area lies within the transition zone between two recent subduction-zone earthquakes: the great 1960 Mw 9.5 earthquake to the south and the 2010 Mw 8.8 Maule earthquake to the north. Despite Chile’s growing need to better understand its earthquake and tsunami hazards, there are few studies aimed at establishing the geologic record of these events throughout time. A combination of pits, cores, and riverbank exposures provide stratigraphic evidence of six to seven, laterally-continuous sand layers at Quidico. The sand units display landward thinning and disappear completely from the stratigraphy approximately 1 km inland from the coast, characteristic of tsunami deposits. Intervening sediment layers consists of organic-rich silts and peat. All of the sand units contain sediments of similar mineral compostion and unimodal grain size distribution (120-316 μm), contrasting with the broader, bimodal distribution of sediment sizes in the organic-rich silts and peat (3-171 μm). Preliminary microfossil analysis indicates a slightly more marine diatom assemblage in the first buried sand layer than in the organic-rich silt units above and below it, indicating a marine incursion. AMS radiocarbon dates of Scirpus seeds found in units below each sand layer indicate an 800 year history of tsunami deposition at Quidico. Correlating this record with additional geologic studies and historic accounts of earthquakes and tsunamis throughout the region will collectively advance our understanding of seismic hazards in south-central Chile.

Faculty Mentor(s)

Ely, Lisa

Additional Mentoring Department

Geological Sciences

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May 15th, 1:30 PM May 15th, 1:50 PM

Sedimentological and stratigraphic evidence for paleotsunami events at Quidico, Chile

SURC Room 140

We utilized geomorphic, microfossil, sedimentological, and stratigraphic methods to investigate the history of past earthquakes and tsunamis at Quidico, Chile (38.1°S, 73.2°W). The study area lies within the transition zone between two recent subduction-zone earthquakes: the great 1960 Mw 9.5 earthquake to the south and the 2010 Mw 8.8 Maule earthquake to the north. Despite Chile’s growing need to better understand its earthquake and tsunami hazards, there are few studies aimed at establishing the geologic record of these events throughout time. A combination of pits, cores, and riverbank exposures provide stratigraphic evidence of six to seven, laterally-continuous sand layers at Quidico. The sand units display landward thinning and disappear completely from the stratigraphy approximately 1 km inland from the coast, characteristic of tsunami deposits. Intervening sediment layers consists of organic-rich silts and peat. All of the sand units contain sediments of similar mineral compostion and unimodal grain size distribution (120-316 μm), contrasting with the broader, bimodal distribution of sediment sizes in the organic-rich silts and peat (3-171 μm). Preliminary microfossil analysis indicates a slightly more marine diatom assemblage in the first buried sand layer than in the organic-rich silt units above and below it, indicating a marine incursion. AMS radiocarbon dates of Scirpus seeds found in units below each sand layer indicate an 800 year history of tsunami deposition at Quidico. Correlating this record with additional geologic studies and historic accounts of earthquakes and tsunamis throughout the region will collectively advance our understanding of seismic hazards in south-central Chile.