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Quantitative Evaluation of Tsunami Hazard to the U.S. Atlantic Coast: Daniel Brothers
Project Title: Quantitative Evaluation of Tsunami Hazard to the U.S. Atlantic Coast
Mendenhall Fellow: Daniel Brothers, (508) 457-2293, dbrothers@usgs.gov
Duty Station: Woods Hole, MA
Start Date: November 16, 2009
Education: Ph.D. Scripps Institution of Oceanography, 2009
Research Advisor: Uri ten Brink, (508) 457-2396, utenbrink@usgs.gov

Project Description

In the United States, tsunamis resulting from offshore earthquakes, landslides, and volcanic activity are rare events, but our ability to forecast when and where tsunamis will strike is limited. During the last 30 years, advances in seafloor mapping technology and improved understanding of the geologic processes that shape continental margins have led to better constraints on the tsunami–related risks to the U.S. East Coast (for example, Chaytor and others, 2009; Geist and others, 2009; ten Brink and others, 2009a, b; Twichell and others, 2009). Several approaches to quantitatively estimate the probability of tsunamis have been developed, but their accuracy depends in large part on observations of landslide size distribution, recurrence interval, and the geotechnical parameters of the seafloor (McAdoo and others, 2000). Building on ongoing research at the U.S. Geological Survey (USGS), I am using a suite of existing marine geophysical data and data that will be acquired in 2010 and 2011 to quantitatively examine the distribution, style, and age of submarine landslides along the East Coast. I will study the operative processes that lead to submarine landsliding at the temporal and spatial scales in which they occur.

The distribution of submarine landslides along the Atlantic margin appears to be strongly related to their proximity to continental glaciers, as sediment accumulation rates were extremely high during the Quaternary. The margin can be divided into three sub-regions: a northern glacially influenced region, a central fluvially influenced region, and a southern region with limited direct input of continental sediment during the Quaternary (Booth and others, 1993). New multibeam bathyemetry data collected by the University of New Hampshire and the USGS have helped identify a total of 48 distinct areas affected by submarine slides in the region between Geroges Bank and the Blake Spur (figs. 1, 2) and as much as 33 percent of the seafloor off southern New England is covered by landslides.

Distribution of landslide types along the U.S. Atlantic continental slope and rise   Figure 1. Distribution of landslide types along the U.S. Atlantic continental slope and rise (modified from ten Brink and others, 2008). Red box is approximate location of figure 2.

Toward the southern study region, glacial activity has less influence, with only 13 percent of the area south of Cape Hatterus covered by landslides. Here the sources appear to be related to salt dome tectonics (Popenoe and others, 1993) or pore pressure changes due to gas hydrate stability (Hornbach and others, 2004; Maslin and others, 2004); however, the average depth of headwall scarps in this region is 1,630 m (ten Brink and others, 2008), significantly deeper than the 200- to 600-m depth at which hydrates are most susceptible to decomposition during lowered sea level. Ultimately, the ages of the landslides on the U.S. Atlantic margin are poorly known due to an absence of reliable dating, which limits our interpretations of the feedback and response mechanisms. Of those that have been dated, most are older than 7,000 yr BP (ten Brink and others, 2008).

Bird's-eye view of continental slope and rise near Hudson Canyon   Figure 2. Bird's-eye view of continental slope and rise near Hudson Canyon. Note the landslide head-scarps and lobate deposits along the rise.

Broader Impacts
The results of this research will be used to make hazard assessments and update vulnerability maps along the East Coast. Gravity-driven seafloor instabilities exert a significant influence on the evolution of continental margin morphology and stratigraphy. In order to understand continental margin evolution, along both active and passive margins, we need to study underwater landsliding and other instability generated downslope processes. They control the timing, location, volume and mechanism by which sediment is transferred from shallow to deep water. All physiographic provinces along continental margins appear to be susceptible to seafloor instability, but we still do not know why one area will fail while neighboring areas remain intact (Pratson, 2001).

References
Booth, J.S., O'Leary, D.W., Popenoe, P., and Danforth, W.W., 1993, U.S. Atlantic continental slope landslides: Their distribution, general attributes, and implications, in Schwab, W.C., Lee, H.J., and Twichell, D.C., eds., Submarine landslides: Selected studies in the U.S. Exclusive Economic Zone: U.S. Geological Survey Bulletin, v. 2002, p. 14–22.

Chaytor, J.D., ten Brink, U.S., Solow, A.R., and Andrews, B.D., 2009, Size distribution of submarine landslides along the US Atlantic margin: Marine Geology, v. 264, p. 16–27.

Geist, E.L., Lynett, P.J., and Chaytor, J.D., 2009, Hydrodynamic modeling of tsunamis from the Currituck landslide: Marine Geology, v. 264, p. 41–52.

Hornbach, M.J., Saffer, D.M., and Holbrook, W.S., 2004, Critically pressured free-gas reservoirs below gas-hydrate provinces: Nature, v. 427, p. 142–144.

Maslin, M., Owen, M., Day, S., and Long, D., 2004, Linking continental-slope failures and climate change: Testing the clathrate gun hypothesis: Geology, v. 32, p. 53–56.

McAdoo, B.G., Pratson, L.F., and Orange, D.L., 2000, Submarine landslide geomorphology, US continental slope: Marine Geology, v. 169, p. 103–136.

Popenoe, P., Schmuck, E.A., and Dillon, W.P., 1993, The Cape Fear Landslide: Slope failure associated with salt diapirism and gas hydrate decomposition, in Schwab, W.C., Lee, H.J., and Twichell, D.C., eds., Submarine landslides: Selected studies in the U.S. Exclusive Economic Zone: U.S. Geological Survey Bulletin, v. 2002, p. 40–53.

Pratson, L.F., 2001, A perspective on what is known and not known about seafloor instability in the context of continental margin evolution: Marine and Petroleum Geology, v. 18, p. 499–501.

ten Brink, U.S., Barkan, R., Andrews, B.D., and Chaytor, J.D., 2009a, Size distributions and failure initiation of submarine and subaerial landslides: Earth and Planetary Science Letters, v. 287, p. 31–42.

ten Brink, U.S., Lee, H.J., Geist, E.L., and Twichell, D., 2009b, Assessment of tsunami hazard to the US East Coast using relationships between submarine landslides and earthquakes: Marine Geology, v. 264, p. 65–73.

ten Brink, U.S., Twichell, D., Geist, E.L., Chaytor, J.D., Locat, J., Lee, H.J., Buczkowski, B., and Barkan, R., 2008, Evaluation of tsunami sources with the potential to impact the U.S. Atlantic and Gulf coasts: U.S. Geological Survey Administrative Report to the U.S. Nuclear Regulatory Commission, p. 300.

Twichell, D.C., Chaytor, J.D., ten Brink, U.S., and Buczkowski, B., 2009, Morphology of late Quaternary submarine landslides along the US Atlantic continental margin: Marine Geology, v. 264, p. 4–15.

 

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