Browsing by Author "Wesson, Robert L."

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    The giant 1960 tsunami in the context of a 6000-year record of paleotsunamis and coastal evolution in south-central Chile
    Matos-Llavona, Pedro, I; Ely, Lisa L.; MacInnes, Breanyn; Dura, Tina; Cisternas, Marco A.; Bourgeois, Joanne; Bruce, David; DePaolis, Jessica M.; Dolcimascolo, Alexander; Horton, Benjamin P.; Melnick, Daniel; Nelson, Alan R.; Szeliga, Walter; Wesson, Robert L. (Wiley, 2022-03-24)
    The tsunami associated with the giant 9.5 M-w 1960 Chile earthquake deposited an extensive sand layer above organic-rich soils near Queule (39.3 degrees S, 73.2 degrees W), south-central Chile. Using the 1960 tsunami deposits, together with eye-witness observations and numerical simulations of tsunami inundation, we tested the tsunami inundation sensitivity of the site to different earthquake slip distributions. Stratigraphically below the 1960 deposit are two additional widespread sand layers interpreted as tsunami deposits with maximum ages of 4960-4520 and 5930-5740 cal BP. This >4500-year gap of tsunami deposits preserved in the stratigraphic record is inconsistent with written and geological records of large tsunamis in south-central Chile in 1575, 1837, and possibly 1737. We explain this discrepancy by: (1) poor preservation of tsunami deposits due to reduced accommodation space from relative sea-level fall during the late Holocene; (2) recently evolved coastal geomorphology that increased sediment availability for tsunami deposit formation in 1960; and/or (3) the possibility that the 1960 tsunami was significantly larger at this particular location than other tsunamis in the past >4500 years. Our research illustrates the complexities of reconstructing a complete stratigraphic record of past tsunamis from a single site for tsunami hazard assessment.
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    Holocene relative sea-level change along the tectonically active Chilean coast
    Garrett, E. Spencer; Melnick, Daniel; Dura, Tina; Cisternas, Marco; Ely, Lisa L.; Wesson, Robert L.; Jara-Munoz, Julius; Whitehouse, Pippa L. (2020-05-15)
    We present a comprehensive relative sea-level (RSL) database for north, central, and south-central Chile (18.5 degrees S - 43.6 degrees S) using a consistent, systematic, and internationally comparable approach. Despite its latitudinal extent, this coastline has received little rigorous or systematic attention and details of its RSL history remain largely unexplored. To address this knowledge gap, we re-evaluate the geological context and age of previously published sea-level indicators, providing 78 index points and 84 marine or terrestrial limiting points spanning from 11 ka to the present day. Many data points were originally collected for research in other fields and have not previously been examined for the information they provide on sea-level change. Additionally, we describe new sea-level data from four sites located between the Gulf of Arauco and Valdivia. By compiling RSL histories for 11 different regions, we summarise current knowledge of Chilean RSL. These histories indicate mid Holocene sea levels above present in all regions, but at highly contrasting elevations from similar to 30 m to <5 m. We compare the spatiotemporal distribution of sea-level data points with a suite of glacial isostatic adjustment models and place first-order constraints on the influence of tectonic processes over 10(3)-10(4) year timescales. While seven regions indicate uplift rates <1 m ka(-1), the remaining regions may experience substantially higher rates. In addition to enabling discussion of the factors driving sea-level change, our compilation provides a resource to assist attempts to understand the distribution of archaeological, palaeoclimatic, and palaeoseismic evidence in the coastal zone and highlights directions for future sea-level research in Chile. (C) 2020 Elsevier Ltd. All rights reserved.
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    Stratigraphic evidence of two historical tsunamis on the semi-arid coast of north-central Chile
    DePaolis, Jessica M.; Dura, Tina; MacInnes, Breanyn; Ely, Lisa L.; Cisternas, Marco; Carvajal, Matias; Tang, Hui; Fritz, Hermann M.; Mizobe, Cyntia; Wesson, Robert L.; Figueroa, Gino; Brennan, Nicole; Horton, Benjamin P.; Pilarczyk, Jessica E.; Corbett, D. Reide; Gill, Benjamin C.; Weiss, Robert (Pergamon-Elsevier, 2021-07-21)
    On September 16, 2015, a Mw 8.3 earthquake struck the north-central Chile coast, triggering a tsunami observed along 500 km of coastline, between Huasco (28.5°S) and San Antonio (33.5°S). This tsunami provided a unique opportunity to examine the nature of tsunami deposits in a semi-arid, siliciclastic environment where stratigraphic and sedimentological records of past tsunamis are difficult to distinguish. To improve our ability to identify such evidence, we targeted one of the few low-energy, organic-rich depositional environments in north-central Chile: Pachingo marsh in Tongoy Bay (30.3°S). We found sedimentary evidence of the 2015 and one previous tsunami as tabular sand sheets. Both deposits are composed of poorly to moderately sorted, gray-brown, fine-to medium-grained sand and are distinct from underlying and overlying organic-rich silt. Both sand beds thin (from ∼20 cm to <1 cm) and fine landward, and show normal grading. The older sand bed is thicker and extends over 125 m further inland than the 2015 tsunami deposit. To model the relative size of the tsunamis that deposited each sand bed, we employed tsunami flow inversion. Our results show that the older sand bed was produced by higher flow speeds and depths than those in 2015. Anthropogenic evidence along with 137Cs and 210Pb dating constrains the age of the older tsunami to the last ∼110 years. We suggest that the older sand bed was deposited by the large tsunami in 1922 CE sourced to the north of our study site. This deposit represents the first geologic evidence of a pre-2015 tsunami along the semi-arid north-central Chile coast and highlights the current and continuing tsunami hazard in the region.