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U.S. Geological Survey Open-File Report 2010-1239

Identification of Tsunami Deposits in the Geologic Record: Developing Criteria Using Recent Tsunami Deposits

By Robert Peters and Bruce Jaffe

ABSTRACT

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There is a need for a clear procedure to identify tsunami deposits in the geologic record. Data from published studies documenting recent tsunami deposits provide a means of developing identification criteria based on the sedimentary characteristics of unequivocal tsunami deposits. Recent tsunami deposits have many sedimentary characteristics in common. All had sharp or erosional basal contacts. Sand was typically deposited in sheets that blanketed pre-existing topography and generally thinned landward. Deposit thickness was dependent on local topography; deposits were thicker in swales or local depressions and thinner on ridges or topographic highs. Deposits typically had 1–4 layers. Normal grading was common and often confined to individual layers. In muddy environments, sediments contained mud and soil rip-up clasts and mud often capped the deposits or layers. Boulders were often present, either isolated or scattered in groups. Sedimentary structures were rare, and included cross-bedding, laminations, scour and fill structures, and truncated flame structures. The composition, grain size, and surface texture of the grains reflected the coastal and nearshore source for the sediments. These sedimentary characteristics are the basis for developing site-specific tsunami deposit identification criteria that can be used in paleotsunami deposits investigations.

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Contact Information, Pacific Coastal and Marine Science Center
U.S. Geological Survey
Pacific Science Center
400 Natural Bridges Drive
Santa Cruz, California 95060
http://walrus.wr.usgs.gov/

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Suggested citation:

Peters, Robert, and Jaffe, Bruce E., 2010, Identification of tsunami deposits in the geologic record; developing criteria using recent tsunami deposits: U.S. Geological Survey Open-File Report 2010-1239, 39 p.



Contents

Abstract

Introduction

Sedimentary Characteristics of Recent Tsunami Deposits

Depositional Environments

Preservation

Developing Tsunami Deposit Identification Criteria

Conclusions

Acknowledgements

References Cited

one appendix


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