The search for geologic evidence of distant-source tsunamis using new field data in California

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dc.contributor.authorWilson, Ren_AU
dc.contributor.authorHemphill-Haley, Een_AU
dc.contributor.authorJaffe, BEen_AU
dc.contributor.authorRichmond, Ben_AU
dc.contributor.authorPeters, Ren_AU
dc.contributor.authorGraehl, Nen_AU
dc.contributor.authorKelsey, Hen_AU
dc.contributor.authorLeeper, Ren_AU
dc.contributor.authorWatt, Sen_AU
dc.contributor.authorMcGann, Men_AU
dc.contributor.authorHoirup, DFen_AU
dc.contributor.authorChagué-Goff, Cen_AU
dc.contributor.authorGoff, JRen_AU
dc.contributor.authorCaldwell, Den_AU
dc.contributor.authorLoofbourrow, Cen_AU
dc.date.accessioned2017-03-13T03:15:18Zen_AU
dc.date.available2017-03-13T03:15:18Zen_AU
dc.date.issued2014en_AU
dc.date.statistics2017en_AU
dc.description.abstractA statewide assessment for geological evidence of tsunamis, primarily from distant-source events, found tsunami deposits at several locations, though evidence was absent at most locations evaluated. Several historical distant-source tsunamis, including the 1946 Aleutian, 1960 Chile, and 1964 Alaska events, caused inundation along portions of the northern and central California coast. Recent numerical tsunami modeling results identify the eastern Aleutian Islands subduction zone as the “worstcase” distant-source region, with the potential for causing tsunami runups of 7–10 m in northern and central California and 3–4 m in southern California. These model results, along with a review of historical topographic maps and past geotechnical evaluations, guided site selection for tsunami deposit surveys. A reconnaissance of 20 coastal marshlands was performed through site visits and coring of shallow surface sediments to determine if evidence for past tsunamis existed. Although conclusive evidence of tsunami deposits was not found at most of the sites evaluated, geologic evidence consistent with tsunami inundation was found at two locations: Three marshes in the Crescent City area and Pillar Point marsh near Half Moon Bay. Potential tsunami deposits were also evaluated at the Carpinteria Salt Marsh Reserve in Santa Barbara County. In Crescent City, deposits were ascribed to tsunamis on the basis of stratigraphic architecture, particle size, and microfossil content, and they were further assigned to the 1964 Alaska and 1700 Cascadia tsunamis on the basis of dating by cesium-137 and radiocarbon methods, respectively. The 1946 tsunami sand deposit was clearly identified throughout Pillar Point marsh, and one to two other similar but highly discontinuous sand layers were present within 0.5 m of the surface. A tsunami-origin interpretation for sand layers at Carpinteria is merely consistent with graded bedding and unsupported by diatom or foraminiferal assemblages. Additional studies, including age dating, grain-size, and microfossil analyses are underway for the deposits at Crescent City, Pillar Point marsh, and Carpinteria, which may help further identify if other tsunami deposits exist at those sites. The absence of evidence for tsunamis at other sites examined should not preclude further work beyond the reconnaissance-level investigations at those locations.en_AU
dc.identifier.citationWilson, R., Hemphill-Haley, E., Jaffe, B., Richmond, B., Peters, R., Graehl, N., Kelsey, H., Leeper, R., Watt, S., McGann, M., Hoirup, D. F., Chagué-Goff, C., Goff, J., Caldwell, & D., Loofbourrow, C. (2014). The search for geologic evidence of distant-source tsunamis using new field data in California: Chapter C of Ross, S.L., and Jones, L.M., eds., The SAFRR (Science Application for Risk Reduction) tsunami scenario: U.S. Geological Survey Open-File Report 2013-1170-C, 122 p., doi:10.3133/ofr20131170c.en_AU
dc.identifier.govdoc8027en_AU
dc.identifier.issn2331-1258en_AU
dc.identifier.paginationvii, 122en_AU
dc.identifier.placeofpublicationReston, Virginiaen_AU
dc.identifier.urihttp://dx.doi.org/10.3133/ofr20131170cen_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/8482en_AU
dc.language.isoenen_AU
dc.publisherU.S. Geological Surveyen_AU
dc.subjectGeologyen_AU
dc.subjectTsunamisen_AU
dc.subjectSedimentsen_AU
dc.subjectGeologic surveysen_AU
dc.subjectGeologic depositsen_AU
dc.subjectCaliforniaen_AU
dc.subjectAleutian Islandsen_AU
dc.subjectAlaskaen_AU
dc.subjectChileen_AU
dc.titleThe search for geologic evidence of distant-source tsunamis using new field data in Californiaen_AU
dc.typeExternal Reporten_AU
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