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Cascadia tsunami deposit database


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The Cascadia Tsunami Deposit Database contains data on the location and sedimentological properties of tsunami deposits found along the Cascadia margin. Data have been compiled from 52 studies, documenting 59 sites from northern California to Vancouver Island, British Columbia that contain known or potential tsunami deposits. Bibliographical references are provided for all sites included in the database. Cascadia tsunami deposits are usually seen as anomalous sand layers in coastal marsh or lake sediments. The studies cited in the database use numerous criteria based on sedimentary characteristics to distinguish tsunami deposits from sand layers deposited by other processes, such as river flooding and storm surges. Several studies [...]


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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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