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Tsunami Hazards, Modeling, and the Sedimentary Record

See also:

• Tsunami and Earthquake Research at the USGS: http://walrus.wr.usgs.gov/tsunami
• Information on Tsunamis: http://walrus.wr.usgs.gov/tsunamis.html
• Notes From the Field: http://walrus.wr.usgs.gov/news/field.html

Overview

The 11 March 2011 Tohoku-oki tsunami underscores that the US is at risk from a deadly, devastating tsunami. The extent of risk is not known. However, the 2009 Samoa tsunami, geologic evidence in the Pacific Northwest and to a lesser degree the Caribbean, historical records in Hawaii, and Alaska, and modeling studies for California and the US East Coast, all indicate that there is significant risk to the US from tsunamis. The effect of a tsunami at a coast, and the resulting risk, is the result of processes that control its generation, propagation, and inundation. Although potential tsunami sources (e.g., underwater earthquakes, landslides) can be identified, it is difficult, if not impossible, to predict with any certainty the largest possible tsunami that will impact an area based solely on current knowledge of source character and tsunami generating capacity. This is borne out by the 11 March 2011 tsunami that was larger in many regions in Japan than the largest historical or predicted tsunami. However, the geologic record did portend that a mega-tsunami would hit eastern Japan. The geologic record revealed that on average every 1000 years a mega-tsunami similar to the one on 11 March hits northeastern Japan.

Basic research to develop the geologic record of paleotsunamis and improve the ability to interpret that record is needed to mitigate tsunami risk in the US.

Objectives

The objectives of this project are to improve understanding of tsunamis, to develop techniques to assess the threat they pose, and to develop the paleotsunami record using sedimentary deposits. See tasks for specific research objectives.

What could be more relevant than research that can save lives? This project does exactly that by increasing the understanding of tsunami hazard in the US. This understanding informs mitigation of tsunami hazard in numerous ways including allowing development and refinement of evacuation plans, coastal zoning, and tsunami education.

Approach

Our strategy is to apply knowledge and skill gained from past CMG tsunami projects to paleotsunami deposit studies in locations with a known, but not well defined, tsunami hazard. Because the ability to identify and interpret paleotsunami deposits is still an emerging science, by necessity our approach includes targeted studies that develop methods for utilizing tsunami deposits in hazard assessment. These studies increase the value of the location-based paleotsunami studies. The locations of the paleotsunami studies are driven primarily by tsunami hazard potential, but also partially by opportunities to collaborate with researchers both inside and outside of the USGS. This collaboration leverages CMG resources and expertise. Paleotsunami studies will be phased, with initial investigations and more detailed, focused investigations in areas where paleotsunamis deposits are found to assess tsunami hazard. Detailed studies may include tsunami generation, propagation, and inundation modeling and source evaluation components.

Tasks and SubTasks

• California Paleotsunami Studies
  • Phase 1: Initial assessment work tasks.
    1. Canvas existing tsunami deposit information in California utilizing the new California Tsunami Deposit Database.
    2. Select 9 to 11 sites (possibly including Crescent City, Morro Bay, Point Mugu, Pillar Point, Elkhorn Slough and Bolinas Bay) of potential tsunami deposits based on:
       1. projected large run-ups from existing modeling results (CGS database), and
       2. favorable locations for tsunami deposit accumulation and preservation based on in-office evaluation using GIS imagery/DEMs, digital ortho/stereo/oblique photography, GoogleEarth, and historic T-sheets (topographic maps).
    3. Conduct initial assessment of 9 to 11 sites to collect cores to determine the potential of tsunami deposits.
    4. Perform cursory laboratory analyses (fossil, grain-size analysis).
    5. Write preliminary findings report.
  • Phase 2: Detailed site work tasks (pending positive outcome of Phase 1.
    1. Select three to five most likely sites for positive results and perform more detailed core/trench campaign.
    2. Collect and send in samples for laboratory work including radiocarbon dating, grain-size, fossil, and geochemical analyses.
    3. Comparison of tsunami deposit locations and ages to numerical modeling data and to events from the eastern Aleutians tsunami source region.
    4. Write/publish report.
• Alaska Paleotsunami Reconnaissance
  • The objectives of this project include:
    1. Conduct reconnaissance field investigations of the earthquake and tsunami geologic record in the eastern Aleutian Islands, west of Kodiak Island
    2. Develop field techniques and logistics for extended field operations in remote Alaska settings
    3. Collect samples of modern microfossils along coastal and estuarine transects to document species assemblages
    4. Collect samples of ash deposits to include in archives for stratigraphic correlations
• Identification and Interpretation of Paleotsunamis
  • The objective of this task is to improve the ability to identify and interpret paleotsunami deposits. By doing so, the utility of tsunami deposits in tsunami hazard assessment is increased. Analysis of tsunami deposits holds the potential, once the relations between deposit and flow are established, to estimate paleotsunami flow height, speed, and other characteristics that result in loss of life and property.

Cooperators California Geological Survey/POC: Wilson, Rick California State University, Humboldt/POC: Hemphill-Haley, Eileen Georgia Tech/POC: Fritz, Hermann National Oceanic and Atmospheric Administration (NOAA)/NOAA/Pacific Marine Environmental Laboratory, Center for Tsunami Inundation Mapping Efforts/POC: Titov, Vasily Australian Research Center, University of New South Wales, Sydney, Australia/POC: Goff, Jame Chiba Institute of Technology, Japan/POC: Goto, Kazuhis Institute of Geology, Adam Mickiewicz University, Pozna, Poland/POC: Szczuciski, Witold Nishimura, Yuichi Tohoku University/POC: Sugawara, Daisuke Federal Emergency Management Agency (FEMA)/Department of Homeland Security, American Samoa/POC: John, Goeke National Park Service (NPS)/POC: Beavers, Rebecca Samoa National Park/POC: Reynolds, Mike

From Apotsos et al., 2011, doi:10.1007/s00024-011-0291-5