Browsing by Author "Dura, Tina"

Now showing 1 - 16 of 16
  • Thumbnail Image
    Changing impacts of Alaska-Aleutian subduction zone tsunamis in California under future sea-level rise
    Dura, Tina; Garner, Andra J.; Weiss, Robert; Kopp, Robert E.; Engelhart, Simon E.; Witter, Robert C.; Briggs, Richard W.; Mueller, Charles S.; Nelson, Alan R.; Horton, Benjamin P. (Springer Nature, 2021-12-08)
    The amplification of coastal hazards such as distant-source tsunamis under future relative sea-level rise (RSLR) is poorly constrained. In southern California, the Alaska-Aleutian subduction zone has been identified as an earthquake source region of particular concern for a worst-case scenario distant-source tsunami. Here, we explore how RSLR over the next century will influence future maximum nearshore tsunami heights (MNTH) at the Ports of Los Angeles and Long Beach. Earthquake and tsunami modeling combined with local probabilistic RSLR projections show the increased potential for more frequent, relatively low magnitude earthquakes to produce distant-source tsunamis that exceed historically observed MNTH. By 2100, under RSLR projections for a high-emissions representative concentration pathway (RCP8.5), the earthquake magnitude required to produce >1 m MNTH falls from ~Mw9.1 (required today) to Mw8.0, a magnitude that is ~6.7 times more frequent along the Alaska-Aleutian subduction zone.
  • Thumbnail Image
    Comparing UAV and Pole Photogrammetry for Monitoring Beach Erosion
    Gonzales, Jack Joseph (Virginia Tech, 2021-09-14)
    Sandy beaches are vulnerable to extreme erosion during large storms, as well as gradual erosion processes over months and years. Without monitoring and adaptation strategies, erosion can put people, homes, and other infrastructure at risk. To effectively manage beach resources and respond to erosion hazards, coastal managers must have a reliable means of surveying the beach to monitor erosion and accretion. These elevation surveys typically incorporate traditional ground-based surveying methods or lidar surveys flown from large, fixed-wing aircraft. While both strategies are effective, advancements in photogrammetric technology offers a new solution for topographic surveying: Structure from Motion (SfM). Using a set of overlapping aerial photographs, the SfM workflow can generate accurate topographic surveys, and promises to provide a fast, inexpensive, and reliable method for routine beach surveying. Unmanned aerial vehicles (UAVs) are often successfully employed for SfM surveys but can be limited by poor weather ad government regulations, which can make flying difficult or impossible. To circumvent these limitations, a digital camera can be attached to a tall pole on a mobile platform to obtain aerial imagery, avoiding the restrictions of UAV flight. This thesis compares these two techniques of image acquisition for routine beach monitoring. Three surveys were conducted at monthly intervals on a beach on the central South Carolina coast, using both UAV and pole photogrammetry. While both methods use the same software and photogrammetric workflow, the UAV produced better results with far fewer processing artifacts compared to pole photogrammetry.
  • Thumbnail Image
    Diatom-based reconstructions of earthquake-induced paleoenvironmental change in coastal Alaska and Washington, USA
    DePaolis, Jessica (Virginia Tech, 2024-01-30)
    Great (Mw >8.5) earthquakes occur over long temporal intervals that extend beyond current historical (written and oral) records along most subduction zone coastlines often leading to the underestimation of magnitude, recurrence, and spatial extent of these events. Paleoseismic studies target low energy depositional environments that record primary and secondary evidence of earthquake occurrence within the coastal stratigraphy over much longer temporal scale, thus improving our understanding of the behavior of subduction zone earthquakes. Diatoms preserved within coastal stratigraphic records are sensitive to earthquake-induced environmental change and are useful bioindicators in paloesiesmology studies. The two studies in this dissertation employ diatoms to create novel approaches to investigate behavior and recurrence of earthquakes along two subductions zones: Alaska-Aleutian subduction zone and the Cascadia subduction zone. In these chapters we use diatoms to explore 1) the potential for combined slip along the Patton Bay splay fault system and the eastern Alaska-Aleutian subduction zone within Prince William Sound, Alaska, and 2) lacustrine turbidite source mechanisms in Ozette Lake, Washington to potentially improve the spatial and temporal earthquake record for the northern Cascadia subduction zone. This work has implications for improving our earthquake chronologies along subduction zone coastlines and making important contributions to coastal hazards assessments.
  • Thumbnail Image
    Expanding the stratigraphic record of tsunami inundation along the semi-arid, siliciclastic coast of north-central Chile
    DePaolis, Jessica M. (Virginia Tech, 2019-09-17)
    On September 16, 2015, a Mw 8.3 earthquake struck offshore of the north-central Chile coast with a fault-rupture length of approximately 150 km. The earthquake triggered a tsunami that impacted 500 km of coastline from Huasco (28.5°S) to San Antonio (33.5°S), registering as much as 4.5 m on the tide gauge at Coquimbo (30.0°S) with run-up heights >10 m at a few exposed locations between Limarí (30.7°S) and Coquimbo. The tsunami provided an invaluable opportunity to examine the nature of tsunami deposit evidence in a semi-arid, siliciclastic environment, where settings suitable for the preservation of tsunami sedimentation are scarce, thereby improving our ability to identify such evidence in the geologic record. Using before-and-after-tsunami satellite imagery and post-tsunami coastal surveys, we targeted one of the few low-energy depositional terrestrial environments in the tsunami-affected area that had a high potential to preserve the 2015 tsunami deposit and older events: the Pachingo marsh in Tongoy Bay (30.3°S). We employed field and laboratory methods to document the 2015 tsunami deposit and discovered sedimentological evidence of previous tsunami inundation of the site. The 2015 tsunami deposit and an older sand bed ~10 cm lower in the stratigraphy exhibit similar sedimentological characteristics. Both sand beds are composed of poorly to moderately sorted, gray-brown, fine- to medium-grained sand and are distinct from underlying and overlying organic-rich silty sediments. The sand beds are thinner (from ~20 cm to <1 cm) and finer (from medium- to fine-grained sand) at more inland locations, and fine upward. However, the older sand bed extends over 150 m farther inland than the 2015 tsunami deposit. To explore the differences in the offshore ruptures that generated the tsunamis that deposited each sand bed, we employed an inverse sediment transport model (TSUFLIND). Our field survey, sedimentological data, and modeling results infer that the older sand bed preserved at the Pachingo marsh field site was produced by a larger tsunami than the 2015 tsunami. Anthropogenic evidence (copper smelter waste) along with Cs137 and Pb210 dating constrains the magnitude and age of the older sand bed to the last 130 years. Based on historical analysis of recent tsunamis that impacted the Pachingo marsh region, we infer a widespread tsunami in 1922 is the best candidate for depositing the older sand bed at our site, providing first geologic evidence of pre-2015 tsunami inundation along the north-central Chile coast.
  • Thumbnail Image
    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.
  • Thumbnail Image
    High-latitude sedimentation in response to climate variability during the Cenozoic
    Varela Valenzuela, Natalia Ines (Virginia Tech, 2024-01-03)
    Here we investigate sedimentological responses to past climate change in shallow to deep marine depositional environments. Our primary study spans from the Late Pliocene to the Pleistocene (3.3 to 0.7 Ma), and features results from two International Ocean Discovery Program (IODP) Sites U1525 and U1524. Each of these sites is discussed in separate chapters here (Chapters 1 and 2). This interval experienced the change from the warming of the Late Pliocene, known as the Mid-Piacenzian Warming Period, to the Pleistocene cooling. This shift significantly impacted the expansion of the West Antarctic Ice Sheet, sea ice/polynya formation, and, notably, the genesis of Antarctic Bottom Water (AABW), a crucial component of the global thermohaline circulation. In Chapter 1, we propose that turbidite currents, arising from the formation of dense shelf water (DSW) in the Ross Sea (a precursor to AABW), leave a distinct record in the levees of Hillary Canyon. This canyon acts as a conduit, channeling DSW into the deep ocean and contributing to AABW production. By analyzing turbidite beds based on their frequency, thickness, and grain size, we gain insights into the historical occurrence and magnitude of these currents. Furthermore, we explore the influence of factors such as shelf availability and sea ice/polynya formation within the broader climate context of AABW formation. Chapter 2 shifts its focus to the sedimentological variability from shelf-to-slope along Hillary Canyon. This chapter examines the turbidite record associated with AABW formation within the shared timeframe (2.1 to 0.7 million years ago) between IODP Sites U1524 and U1525, and the impact of along slope currents and other processes in the sedimentary deposition and transport. The second study interval (Chapter 3), focuses on the regional sedimentological response proximal to a hydrothermal vent complex associated with the Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma), a global warming event during which thousands of Gt C was released into the ocean-atmosphere on Kyr timescales. IODP Site U1568, strategically located near the hydrothermal vent complex and part of a broader drilling transect in the Modgunn Arch, North Atlantic, is the main study subject. This site's proximity to the vent complex offers a distinctive environment for refining our understanding of stratigraphy and sedimentology within the PETM. We achieve this through a comprehensive analysis of grain size and composition, coupled with a comparison to XRF data. Our findings show that the timing between the onset of the PETM and the response of the sedimentary system to the warming, reflected in the grain size coarsening after the start of the PETM, is not synchronous. Notably, the transition from a marine to a more terrestrial composition predates this shift in grain size, aligning with the PETM onset instead.
  • Thumbnail Image
    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.
  • Thumbnail Image
    Measuring, modelling and projecting coastal land subsidence
    Shirzaei, Manoochehr; Freymueller, Jeffrey; Tornqvist, Torbjorn E.; Galloway, Devin L.; Dura, Tina; Minderhoud, Philip S. J. (2021-01)
    Measuring coastal subsidence is essential to evaluating hazards associated with sea-level rise. This Review discusses the processes driving coastal subsidence, space-borne and land-based measurement techniques, as well as models for simulating observed subsidence and predicting future trends. Coastal subsidence contributes to relative sea-level rise and exacerbates flooding hazards, with the at-risk population expected to triple by 2070. Natural processes of vertical land motion, such as tectonics, glacial isostatic adjustment and sediment compaction, as well as anthropogenic processes, such as fluid extraction, lead to globally variable subsidence rates. In this Review, we discuss the key physical processes driving vertical land motion in coastal areas. Use of space-borne and land-based techniques and the associated uncertainties for monitoring subsidence are examined, as are physics-based models used to explain contemporary subsidence rates and to obtain future projections. Steady and comparatively low rates of subsidence and uplift owing to tectonic processes and glacial isostatic adjustment can be assumed for the twenty-first century. By contrast, much higher and variable subsidence rates occur owing to compaction associated with sediment loading and fluid extraction, as well as large earthquakes. These rates can be up to two orders of magnitude higher than the present-day rate of global sea-level rise. Multi-objective predictive models are required to account for the underlying physical processes and socio-economic factors that drive subsidence.
  • Thumbnail Image
    Model Development and Monte-Carlo Methods for the Simulation and Analysis of Coastal Impacts of Barrier Island Breach During Hurricanes
    Jeffries, Catherine Renae (Virginia Tech, 2024-05-07)
    Barrier islands can protect the mainland from flooding during storms through reduction of storm surge and dissipation of storm generated wave energy. However, the protective capability is reduced when barrier islands breach and a direct hydrodynamic connection between the water bodies on both sides of the barrier island is established. Breaching of barrier islands during large storm events is complicated, involving nonlinear processes that connect water, sediment transport, dune height, and island width among other factors. In order to assess the impacts barrier island breaching has on flooding on the mainland, we modified a storm surge model, GeoClaw, to impose a Gaussian bell-curve on the barrier island that opens during a hurricane simulation and deepened over time. We added a new method of generating storm surge with storm forcing inputs in the form of wind and pressure fields to expand GeoClaw's current utilization of best track information so that storm forcing from planetary boundary layer models can also be utilized in simulations. We created a statistical method to assess the sensitivity of mainland storm-surge to barrier island breaching by randomizing the location, time, and extent of a breach event across the barrier island at Moriches, NY. My results show that total mainland inundation is affected by the changes in location, size, timing and numbers of breaches. Total inundation has a logarithmic relationship with total breach area and breach location is an important predictor of inundation and bay surge. The insights from this study can help prepare shoreline communities for the differing ways that breaching affects the mainland coastline. The model updates created can also allow others to use this framework to study differing regions. Understanding which mainland locations are vulnerable to breaching, planners and coastal engineers can design interventions to reduce the likelihood of a breach occurring in areas adjacent to high flood risk.
  • Thumbnail Image
    Modeling Coastal Environmental Change and the Tsunami Hazard
    Weiss, Robert; Dura, Tina; Irish, Jennifer L. (Frontiers, 2022-05-02)
    The hazard from earthquake-generated tsunami waves is not only determined by the earthquake's magnitude and mechanisms, and distance to the earthquake area, but also by the geomorphology of the nearshore and onshore areas, which can change over time. In coastal hazard assessments, a changing coastal environment is commonly taken into account by increasing the sea-level to projected values (static). However, sea-level changes and other climate-change impacts influence the entire coastal system causing morphological changes near- and onshore (dynamic). We compare the run-up of the same suite of earthquake-generated tsunamis to a barrier island-marsh-lagoon-marsh system for statically adjusted and dynamically adjusted sea level and bathymetry. Sea-level projections from 2000 to 2100 are considered. The dynamical adjustment is based on a morphokinetic model that incorporates sea-level along with other climate-change impacts. We employ Representative Concentration Pathways 2.6 and 8.5 without and with treatment of Antarctic Ice-sheet processes (known as K14 and K17) as different sea-level projections. It is important to note that we do not account for the occurrence probability of the earthquakes. Our results indicate that the tsunami run-up hazard for the dynamic case is approximately three times larger than for the static case. Furthermore, we show that nonlinear and complex responses of the barrier island-marsh-lagoon-marsh system to climate change profoundly impacts the tsunami hazard, and we caution that the tsunami run-up is sensitive to climate-change impacts that are less well-studied than sea-level rise.
  • Thumbnail Image
    Monte Carlo Simulation of Barrier-Island Systems and Tsunami Hazards
    Irish, Jennifer L.; Weiss, Robert; Dura, Tina (Coastal Engineering Research Council, 2023-09-01)
    Robust characterization of the future tsunami hazard is critically important for resilient planning and engineering in coastal communities prone to tsunami inundation. The hazard from earthquake-generated tsunami waves is not only determined by the earthquake's characteristics and distance to the earthquake area, but also by the geomorphology of the nearshore and onshore areas, which can change over time. In coastal hazard assessments, a changing coastal environment is commonly taken into account by increasing the sea-level to projected values (static). However, sea-level changes and other climate-change impacts influence the entire coastal system causing morphological change (dynamic). Here, we present the modeling framework and results initially published in Weiss et al. (2022), which employs within a Monte Carlo framework the barrier island-marsh, lagoon- marsh evolution model of Lorenzo-Trueba and Mariotti (2017) and the tsunami model Geoclaw (e.g., LeVeque et al. 2011). We compare the runup of the same suite of earthquake-generated tsunamis to a barrier system for statically adjusted and dynamically adjusted sea level and bathymetry over the period from 2000 to 2100. We employ Representative Concentration Pathways 2.6 and 8.5 without and with treatment of Antarctic ice-sheet processes (e.g., Kopp et al. 2017) as different sea-level projections.
  • Thumbnail Image
    Quantifying the Role of Vulnerability in Hurricane Damage via a Machine Learning Case Study
    Szczyrba, Laura Danielle (Virginia Tech, 2020-06-10)
    Pre-disaster damage predictions and post-disaster damage assessments are challenging because they result from complicated interactions between multiple drivers, including exposure to various hazards as well as differing levels of community resiliency. Certain societal characteristics, in particular, can greatly magnify the impact of a natural hazard, however they are frequently ignored in disaster management because they are difficult to incorporate into quantitative analyses. In order to more accurately identify areas of greatest need in the wake of a disaster, both the hazards and the vulnerabilities need to be carefully assessed since they have been shown to be positively correlated with damage patterns. This study evaluated the contribution of eight drivers of structural damage from Hurricane Mar'ia in Puerto Rico, leveraging machine learning algorithms to determine the role that societal factors played. Random Forest and Stochastic Gradient Boosting Trees algorithms analyzed a diverse set of data including wind, flooding, landslide, and vulnerability measures. These data trained models to predict the structural damage caused by Hurricane Mar'ia in Puerto Rico and the importance of each predictive feature was calculated. Results indicate that vulnerability measures are the leading predictors of damage in this case study, followed by wind, flood, and landslide measures. Each predictive variable exhibits unique, often nonlinear, relationships with damage. These results demonstrate that societal-driven vulnerabilities play critical roles in damage pattern analysis and that targeted, pre-disaster mitigation efforts should be enacted to reinforce household resiliency in socioeconomically vulnerable areas. Recovery programs may need to be reworked to focus on the highly impacted vulnerable populations to avoid the persistence, or potential enhancement, of preexisting social inequalities in the wake of a disaster.
  • Thumbnail Image
    Repeated Coseismic Uplift of Coastal Lagoons Above the Patton Bay Splay Fault System, Montague Island, Alaska, USA
    DePaolis, Jessica M.; Dura, Tina; Witter, Robert C.; Haeussler, Peter J.; Bender, Adrian; Curran, Janet H.; Corbett, D. Reide (American Geophysical Union, 2024-05)
    Coseismic slip on the Patton Bay splay fault system during the 1964 Mw 9.2 Great Alaska Earthquake contributed to local tsunami generation and vertically uplifted shorelines as much as 11 m on Montague Island in Prince William Sound (PWS). Sudden uplift of 3.7–4.3 m caused coastal lagoons along the island's northwestern coast to gradually drain. The resulting change in depositional environment from marine lagoon to freshwater muskeg created a sharp, laterally continuous stratigraphic contact between silt and overlying peat. Here, we characterize the geomorphology, sedimentology, and diatom ecology across the 1964 earthquake contact and three similar prehistoric contacts within the stratigraphy of the Hidden Lagoons locality.We find that the contacts signal instances of abrupt coastal uplift that, within error, overlap the timing of independently constrained megathrust earthquakes in PWS—1964 Common Era, 760–870 yr BP, 2500–2700 yr BP, and 4120– 4500 yr BP. Changes in fossil diatom assemblages across the inferred prehistoric earthquake contacts reflect ecological shifts consistent with repeated draining of a lagoon system caused by >3 m of coseismic uplift. Our observations provide evidence for four instances of combined megathrust‐splay fault ruptures that have occurred in the past ∼4,200 years in PWS. The possibility that 1964‐style combined megathrust‐splay fault ruptures may have repeated in the past warrants their consideration in future seismic and tsunami hazards assessments.
  • Thumbnail Image
    Seismic Sources in the Aleutian Cradle of Tsunamis
    Witter, Rob; Briggs, Rich; Dura, Tina; Engelhart, Simon; Nelson, Alan (2022-10-01)
  • Thumbnail Image
    Stratigraphic and microfossil evidence of repeated late Holocene tsunami inundation at Sitkalidak Island, Alaska
    Prater, Alexa Brianne (Virginia Tech, 2021-09-28)
    Seismic hazard models for Alaska require estimates of the size and frequency of prehistoric megathrust earthquakes. However, observations that place limits on the size of subduction paleoearthquakes along the Alaska-Aleutian subduction zone are scarce. To help place bounds on the along-strike extent of prehistoric Alaska-Aleutian subduction ruptures, we present stratigraphic and microfossil evidence of repeated tsunami inundation over the last ~400 years at Sitkalidak Island, located 0.5 km off the coast of south-central Kodiak Island. Peat cores collected from an estuary in southern Sitkalidak Island reveal three anomalous, laterally continuous sand beds with sharp upper and lower contacts preserved within a coastal peat sequence. The microfossil and lithostratigraphic characteristics of the sand beds, including the presence of anomalous marine planktonic diatoms, high fragmentation of diatoms, and upward fining sand sequences, indicate high-energy marine incursions consistent with tsunami inundation. Radiocarbon dating constrains the deposition of the sand beds to AD 1964, AD 1788, and ~400 cal yr B.P. The peat core stratigraphy and dates are consistent with tidal wetland stratigraphic records observed at sites ~90 km to the west at Sitkinak Island, and ~80 km to the east at Middle Bay, Kodiak Island. Diatom results from Sitkalidak Island suggest decimeter-scale subsidence during the deposition of the 1964 CE and 1788 CE sand bed. Deformation concurrent with the 1964 and 1788 ruptures along with the presence of a sand bed associated with the ~400 cal yr BP rupture at Sitkalidak help better define the western and eastern rupture limits, and thus the permissible maximum magnitudes, of past Alaska-Aleutian subduction zone ruptures.
  • Thumbnail Image
    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.