United States Geological Survey, Coastal and Marine Geology (CMG), Robert Peters, USGS, CMG, Pacific Science Center, Bruce Jaffe, USGS, CMG, Pacific Science Center, Guy Gelfenbaum, USGS, CMG, Western Region Service Cen, and Curt Peterson, Department of Geology, Portland State Univ, 2003, Cascadia Tsunami Deposit Database .
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Introduction - The Cascadia Tsunami Deposit Database is a compilation of published data on the location and sedimentary characteristics of tsunami deposits found along the Cascadia margin. It consolidates data from the earliest published reports on Cascadia tsunami deposits (e.g. Atwater, 1987, Reinhart and Bourgeois, 1987) to studies published or in press by the year 2002. This database and associated report is intended as a guide to the sedimentary features that characterize Cascadia tsunami deposits and to the locations where tsunami deposits have been found along the Cascadia margin. It also provides references for all of the tsunami deposits cited. The Cascadia Subduction Zone (CSZ) is situated off of the Pacific Northwest coast of North America, from Northern California to Vancouver Island, British Columbia (Figure 1). Great earthquakes (m > 8.0) on subduction zones have the potential to trigger large tsunamis. While not all subduction zones generate great earthquakes, it is believed that the CSZ has the potential to generate great earthquakes. The CSZ shares many features with other subduction zones that experience great earthquakes (Heaton and Kanamori, 1984). Geologic evidence for great earthquakes along the CSZ include turbidites off the Cascadia margin (Adams, 1990) and stratigraphic evidence of sudden coastal subsidence (e.g. Atwater et al., 1995, Nelson and Peronius, 1996). Although no great earthquakes have occurred on the CSZ since European colonization of the Pacific Northwest in the mid 1800s, an Indian oral tradition from the Pacific Northwest predating written records alludes to great shaking of the earth and coastal flooding (Heaton and Snavely, 1985, Clague, 1995). Geologic evidence for large tsunamis along the Cascadia margin has only recently been recognized. Atwater (1987) published a report attributing anomalous sand layers in marsh sediments from southern coastal Washington to tsunamis generated by great earthquakes on the CSZ. Since this time, more than 50 studies have been published, documenting numerous sites containing confirmed or potential tsunami deposits and detailing deposit characteristics along the Pacific Northwest coast from Northern California to Vancouver Island, British Columbia (Figure 2). This rapid increase in our knowledge of Cascadia tsunami deposits has led to a greater public awareness of tsunami hazards, and improved our ability to assess the risk from future tsunamis. Data from tsunami deposits have been included on tsunami inundation maps (e.g. Walsh et al., 2000). Tsunami deposits are a key component to the recognition and mitigation of tsunami hazards in the Pacific Northwest.
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Scope of the database - It is the goal of the authors that the database be comprehensive. The database currently cites 53 papers documenting 60 sites where known or potential tsunami deposits have been reported along the Cascadia margin (Figure 2). All known journal articles pertaining to specific sites along the Cascadia margin and published in English by the time of submission have been included. While every attempt has been made to include all theses and conference or symposium abstracts and proceedings that pertain to Cascadia tsunami deposits, the limited availability and inadequate referencing of some of these publications has made some omissions likely. Also, some conference abstracts that were superceded by journal publications were omitted if they did not contain any additional information. Similarly, if a USGS open file report was superceded by a USGS professional paper, only the professional paper was included. The Cascadia Tsunami Deposit Database documents the variety found in tsunami deposits along the Pacific Northwest coast. It contains data on the age, number of deposits, sedimentary characteristics and identifying features of Cascadia tsunami deposits. It includes data from Northern California, north of the Mendocino triple junction through Vancouver Island, British Columbia, Canada. While the focus of the database are deposits from tsunamis that originate from earthquakes on the CSZ, data from historical tsunami deposits originating from trans-oceanic tsunamis are included for comparison. Tsunami deposits located in the Puget Sound area that are not believed to be of a Cascadia origin are not included in the database.
Limitations of database - Care should be exercised in using this data. No attempt has been made to verify the data presented in this report. The data derive from a wide variety of studies with differences in focus, scope, and intent. Details concerning techniques, errors, difficulties, inconsistencies, variability, and potential alternate interpretations of the data are beyond the scope of this report. These are usually site-specific and the original citation should be consulted. This report contains data from both peer-reviewed journals and from publications not typically subjected to extensive peer review. Techniques varied widely among the various studies and the accuracy and precision between separate entries may not be comparable. No attempt has been made in this report to quantify errors. The exception is in dating the deposits, where the errors reported in the publications are included. Even these may not be comparable due to differences in material dated, sampling techniques, or in the case of ages reported in calendar years, the calibration curve used and the error estimation method (Stuvier and Becker, 1986, 1993). It is recommended that the original reference, supplied for each entry, be consulted before using data compiled in this report.
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