As the population continues to migrate toward the coastlines, the societal impacts of these hazards are expected to grow. Recent giant earthquakes that spawned pan-oceanic tsunamis have revealed the vulnerability of U. S. coasts to such natural disasters. The highest priorities for regional active margin field studies are in direct response to the aftermath of the 2011 Japan 9.0 earthquake and tsunami: 1) a re-assessment of the hazards of earthquake, landslides and tsunamis to coastal nuclear power plants located along active strike-slip fault zones in California, and 2) an assessment of the eastern Aleutian-Alaska subduction zone to determine whether conditions exist along the megathrust that are similar to Japan, which could result in the generation of a giant earthquake and tsunami that would pose a thrust to ports and harbors along the West Coast. Results of these studies will available to and have a direct impact on the re-licensing of the nuclear facilities. The Aleutian-Alaska studies will also contribute significantly to the Multihazard Demonstration Project tsunami scenario and planned 2014 emergency management exercise.
Above, 3-D perspective view of shaded relief bathymetry offshore Chenega village, Alaska. Shaded patches of seafloor depict areas that experienced dramatic changes in water depth between 1957 and 2014. Read the article in Earth and Planetary Science Letters.
Map showing AUV-collected multibeam data (color scale) from a section of the La Jolla Canyon where the water depth ranges from 636 to 772 m. From: Paull, et al., 2013, Marine Geology v.335
The USGS Coastal and Marine Geology program (CMGP) provides expertise to the nation in understanding hazards related to offshore earthquakes, landslides and tsunamis the U.S. and territorial coasts. As the recent 2011 Japan giant earthquake and tsunami have brought to light, there is still much we do not understand about conditions that lead to these unusually large events. All U.S. and territorial coastlines are vulnerable to both remote and remote hazards. This project focuses on regional geologic studies of active margins that are considered to be most at risk based on:
These field studies are an integral part of a coordinated CMGP effort to understand hazards and to develop scientifically sound contributions to forecasts of loss of life, infrastructure, and property from catastrophic geologic events associated with coastal and marine geologic processes.
Colored shaded relief panels of 2m resolution AUV bathymetry for (a) the upper section and (b) lower section of the Palos Verdes fault survey area, offshore Southern California. From: Brothers et al., Journal of Geophysical Research: Solid Earth v. 120
The strategy for this project is to focus resources on specific geographic areas that are considered by consensus to be the most at risk for earthquakes, landslides or tsunamis. This approach allows flexibility to refocus efforts in response to actual catastrophic events, or needs for model validation or the development of specific hazard assessment products. The project is separated into 5 tasks based primarily on geography and differing tectonic regimes:
3-D perspective view of shaded relief bathymetry offshore Chenega village. Shaded patches of seafloor depict areas that experienced dramatic changes in water depth between 1957 and 2014. Read more in the USGS Newsroom.
Minutes after the 1964 magnitude-9.2 Great Alaska Earthquake began shaking, a series of tsunami waves swept through the village of Chenega in Prince William Sound, destroying all but two of the buildings and killing 23 of the 75 inhabitants. Fifty years later, scientists from the U.S. Geological Survey revealed the likely cause of the tsunami, a large set of underwater landslides. The scientists used detailed seafloor images not only clear up a decades-old mystery, but also underscore the tsunami hazard that submarine landslides can pose in fjords around the world where communities and ports are commonly located.
Read the entire USGS News Release from February 1, 2016.
Shaded relief bathymetry draped draped by slope gradient (warm colors= steep; cool colors = gentle). Submarine headwall and sidewall scarps delineate several large landslide evacuation zones and their associated deposits along the floor of Santa Cruz Basin. Slides face the mainland shoreline of Santa Monica and Redondo Beach. Red line is a seismic reflection profile (click to view).
To better understand offshore earthquake and tsunami hazards, USGS scientists from the Pacific Coastal and Marine Science Center (PCMSC) and the Woods Hole Coastal and Marine Science Center ran a multichannel seismic survey off southern California in late November. Led by PCMSC, the research cruise was a collaborative effort between USGS, Scripps Institution of Oceanography, and University of California, Santa Cruz. It produced detailed images of
The three faults—San Clemente fault, Catalina fault, and San Diego Trough fault—combined accommodate 10–15% of the North America-Pacific plate motion (5–7 mm/yr). Results of the survey will contribute to probabilistic hazards models for metropolitan Los Angeles and San Diego. For more information, contact Danny Brothers.
Map showing regional geography, locations of seismic-reflection profiles (faint blue lines), outer boundary of multibeam bathymetric mapping (yellow line), significant faults (thick black lines), fault sections (A through H), and locations of the more detailed maps. From: Johnson and Watt, 2012, Geosphere v.8
Brothers, D.S., Conrad, J.E., Maier, K.L., Paull, C.K., McGann, M., and Caress, D.W., 2015, The Palos Verdes Fault offshore southern California: Late Pleistocene to Present tectonic geomorphology, seascape evolution and slip-rate estimate based on AUV and ROV surveys: Journal of Geophysical Research: Solid Earth, v. 120 no. 7, pp. 4734–4758, doi:10.1002/2015jb011938
Brothers, D.S., Haeussler, P.J., Liberty, L., Finlayson, D., Geist, E., Labay, K., and Byerly, M., 2016, A submarine landslide source for the devastating 1964 Chenega tsunami, southern Alaska: Earth and Planetary Science Letters, v. 438, pp. 112–121, doi: 10.1016/j.epsl.2016.01.008
Dartnell, P., Driscoll, N.W., Brothers, D., Conrad, J.E., Kluesner, J., Kent, G., and Andrews, B., 2015, Colored shaded-relief bathymetry, acoustic backscatter, and selected perspective views of the inner continental borderland, Southern California: U.S. Geological Survey Scientific Investigations Map 3324, 3 p., doi:10.3133/sim3324.
Hartwell, S.R., Finlayson, D.P., Dartnell, P., and Johnson, S.Y., 2013, Bathymetry and Acoustic Backscatter—Estero Bay, California: U.S. Geological Survey Open-File Report 2013–1225, doi:10.3133/ofr20131225
Johnson, S.Y., Hartwell, S.R., Dartnell, P., 2014, Offset of Latest Pleistocene Shoreface Reveals Slip Rate on the Hosgri Strike-Slip Fault, Offshore Central California: Bulletin of the Seismological Society of America, v. 104 no. 4, pp. 1650–1662, doi:10.1785/0120130257.
Johnson, S.Y., and Watt, J.T., 2012, Influence of fault trend, bends, and convergence on shallow structure and geomorphology of the Hosgri strike-slip fault, offshore Central California: Geosphere, v. 8, no. 6, 25 p., doi:10.1130/GES00830.1
Langenheim, V.E., Watt, J.T., and Denton, K.M., 2012, Magnetic map of the Irish Hills and surrounding areas, San Luis Obispo County, central California: U.S. Geological Survey Open-File Report 2012-1080, scale 1:24,000
Miller, J.J., von Huene, R., and Ryan, H.F., 2014, The 1946 Unimak tsunami earthquake area—Revised tectonic structure in reprocessed seismic images and a suspect near-field tsunami source: U.S. Geological Survey Open-File Report 2014–1024, 19 p., doi: 10.3133/ofr20141024
Paull, C.K., Caress, D.W., Lundsten, E., Gwiazda, R., Anderson, K., McGann, M., Conrad, J.E., Edwards, B.D., and Sumner, E.J., 2013, Anatomy of the La Jolla Submarine Canyon system: offshore southern California: Marine Geology, v. 335, p. 16-34, doi:10.1016/j.margeo.2012.10.003
Ryan, H.F., Conrad, J.E., Paull, C.K., and McGann, M., 2012, Slip rate on the San Diego Trough fault zone, inner California Borderland, and the 1986 Oceanside earthquake swarm revisited: Bulletin of the Seismological Society of America, v. 102, n. 6, p. 2300-2312, doi:10.1785/0120110317, download PDF, 2.7 MB
Ryan, H.F., Draut, A.E., Keranen, K., Scholl, D.W., 2012, Influence of the Amlia fracture zone on the evolution of the Aleutian Terrace forearc basin, central Aleutian subduction zone: Geosphere, v. 8 no. 6, pp. 1254–1273, doi:10.1130/Ges00815.1.
Ryan, H., von Huene, R., Scholl, D., and Kirby, S., 2012, Tsunami hazards to U.S. coasts from giant earthquakes in Alaska: Eos, Transactions, v. 93 no. 19, doi:10.1029/2012eo190001
Ryan, H.F., von Huene, R., Wells, R.E., Scholl, D.W., Kirby, S., and Draut, A.E., 2012, History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland, in Dumoulin, J.A., and Dusel-Bacon, C., eds., Studies by the U.S. Geological Survey in Alaska, 2011: U.S. Geological Survey Professional Paper 1795-A, 31 p.
Sliter, R. Johnson, S.Y., Watt, J.T., Scheirer, D.S., Allwardt, P. and Triezenberg, P.J., 2013, High-resolution seismic-reflection and marine-magnetic data from offshore central California--San Gregorio to Point Sur: U.S. Geological Survey Open-File Report 2013-1071
ten Brink, U.S., Chaytor, J.D., Geist, E.L., Brothers, D.S., Andrews, B.D., 2014, Assessment of tsunami hazard to the U.S. Atlantic margin: Marine Geology, v. 353, pp. 31–54, doi: 10.1016/j.margeo.2014.02.011.
Watt, J.T., Johnson, S.Y., Hartwell, S.R., and Roberts, M., 2015, Offshore geology and geomorphology from Point Piedras Blancas to Pismo Beach, San Luis Obispo County, California: U.S. Geological Survey Scientific Investigations Map 3327, doi:10.3133/sim3327.