NUREG/CR-6966 

PNNL-17397

Tsunami Hazard Assessment at 

Nuclear Power Plant Sites in the 

United States of America 

Draft Report for Comment

Office of New Reactors 
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NUREG/CR-6966 

PNNL-17397 

Tsunami Hazard Assessment at 

Nuclear Power Plant Sites in the 

United States of America 

Draft Report for Comment 

Manuscript Completed: August 2008 

Date Published: August 2008 

Prepared by 

R. Prasad 

Pacific Northwest National Laboratory 

P.O. Box 999 

Richland, WA 99352 

E. Cunningham, NRC Project Manager 

G. Bagchi, NRC Technical Monitor 

NRC Job Code J3301 

Office of New Reactors 
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E-mail: Richard.Raione@nrc.gov 
iii

ABSTRACT

We describe the tsunami phenomenon with the

focus on its relevance for hazard assessment at

nuclear power plant sites. Chapter 1 includes an

overview of tsunamis and mechanisms that generate tsunamis. Three tsunamigenic

mechanisms—earthquakes, landslides, and

volcanoes—are considered relevant for hazard

assessment at nuclear power plant sites. We

summarize historical tsunami occurrences,

including descriptions of source mechanisms and

damages caused by these events. Historical

landslides and potential landslide areas in earth’s

oceans are described. We describe the

hierarchical-review approach to tsunami-hazard

assessment at nuclear power plant sites in

Chapter 2. The hierarchical-review approach

consists of a series of stepwise, progressively

more-refined analyses to evaluate the hazard

resulting from a phenomena at a nuclear power

plant site. We recommend that the hierarchicalreview approach employ a screening analysis to

determine if a site is subject to tsunami hazard

based on the presence of a tsunamigenic source

and the location and elevation of the site. The

screening analysis is expected to ensure that

analysis and review resources are not wasted at

sites with little potential of exposure to tsunamis. 

Chapter 3 describes the effects tsunami waves may

have at a nuclear power plant site. These effects

result in hazards that may directly affect the safety

of a plant’s structures, systems, and components. 

Structures, systems, and components important to

the safety of a plant should be adequately designed

and, if required, protected from these hazards. 

Chapter 4 describes data required for a detailed

tsunami-hazard assessment and sources of these

data. We recommend using existing resources and

previously completed tsunami-hazard assessments,

if available and appropriate. Detailed tsunamihazard assessment at a nuclear power plant site

should be based on the probable maximum

tsunami. Chapter 5 defines the probable

maximum tsunami, its determination at a site, and

subsequent hazard assessment. We point out that

a tsunamigenic source that produces probable

maximum tsunami hazards at a site may not be

determined a priori. It may be necessary to

evaluate several candidate sources and the

tsunamis generated from them under the most

favorable tsunamigenic source and ambient

conditions. The set of hazards obtained from all

such scenario tsunamis should be considered to

determine design bases of the plant structures,

systems, and components. Chapter 6 describes

international practices by Japan and the

International Atomic Energy Agency, which are

reviewed for completeness. The appendix

provides a stepwise guide to site-independent

analyses for tsunami-hazard assessment.

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v

FOREWORD

The Indian Ocean tsunami of December 2004 led the NRC to take the initiative to examine its criteria for

nuclear plant siting evaluation against tsunami hazards. Site evaluation against tsunami hazards, as

incorporated into the Standard Review Pan, was determined to be comprehensive; however, it needed to

be updated to incorporate current understanding of tsunami sources, modeling near shore and on-shore

wave surge, draw-down, erosion and other associated effects. In 2005, the National Tsunami Hazard

Reduction Program was initiated by the President, and the current study was conducted by the Pacific

Northwest National Laboratory in collaboration with the Pacific Marine Environmental Laboratory

(PMEL) of the National Oceanic and Atmospheric Administration (NOAA) to ensure that NRC's

guidance on site evaluation against tsunami hazards are consistent with the National Program.

The focus of this study has been to examine tsunami hazards at nuclear power plant sites, to review

offshore and onshore modeling of tsunami waves, to describe the effects of tsunami waves on nuclear

power plant structures, systems, and components, to develop potential approaches for screening sites for

tsunami effects, to identify the repository of historic tsunami data, and to examine the ways to approach

site safety assessment for tsunami for an NRC reviewer.

NRC's Office of Nuclear Regulatory Research (RES) has initiated a comprehensive research program on

source characterization, modeling, tsunami effects and probabilistic hazard framework, as appropriate. 

The RES program is intended to fill in the information gaps that exist on tsunami sources for the Atlantic

and the Gulf coast areas of the continental United States, and limited characterization of submarine

deposits that can slide and cause landslide induced tsunami. Results from the RES program, combined

with technical tsunami modeling software from NOAA PMEL will enable comprehensive tsunami hazard

assessment at future nuclear power plant sites following the site safety assessment approach described

here.

 

vii

CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

1 Tsunami and Other Tsunami-Like Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Introduction ........................................................... 1

1.2 Definition ............................................................. 3

1.3 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3.1 Earthquakes ................................................... 3

1.3.2 Landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.3.3 Volcanoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.4 Some Historical Occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.4.1 1958 Lituya Bay Landslide and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.4.2 1980 Spirit Lake Debris Flow and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.4.3 1946 Aleutian Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.4.4 1929 Grand Banks Landslide and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.4.5 1964 Valdez Arm Landslide and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.4.6 1960 Chile Earthquake and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.4.7 The “Orphan” Tsunami of 1700 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.4.8 1963 Vaiont Reservoir Landslide and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . 18

1.4.9 2004 Sumatra Earthquake and Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1.5 Landslides in Earth’s Oceans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1.5.1 The Pacific Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

1.5.2 The Gulf of Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1.5.3 The Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2 Hierarchical Hazard Assessment Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.2 Regional Screening Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.3 Site Screening Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.4 Detailed Tsunami Hazard Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.5 Site Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
viii

2.5.1 Historical Tsunami Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.5.2 Paleotsunami Evidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.5.3 Regional Tsunami Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.5.4 Site-Specific Tsunami Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2.5.5 Site-Specific Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3 Effects of Tsunami at a Nuclear Power Plant Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.2 Flooding Due to Runup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.3 Dry Intakes During Drawdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.4 Scouring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.5 Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.6 Hydrostatic and Hydrodynamic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.7 Debris and Projectiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.8 Tidal Bores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4 Databases and Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.2 Topography and Bathymetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.2.1 Topography Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.2.2 Bathymetry Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4.3 Tides and Sea-Level Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.4 Tsunami Wave Heights, Runup, and Drawdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.5 Near-Shore Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.6 Seismic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.7 Geophysical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.8 Paleotsunami Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5 Probable Maximum Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.2 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.3 Determination of Probable Maximum Tsunami at a Nuclear Power Plant Site . . . . . . . . 50

5.3.1 Tsunamigenic Mechanisms and Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5.3.2 Source Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5.3.3 Initial Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

5.3.4 Wave Propagation Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

5.3.5 The NOAA Center for Tsunami Research Tsunami Propagation Database . . 53
ix

5.4 Hazard Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5.4.1 High Water Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5.4.2 Low Water Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5.4.3 Scouring Near Safety-Related Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.4.4 Deposition Near Safety-Related Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.4.5 Forces on Safety-Related Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.4.6 Debris Accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.4.7 Projectiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.5 Combined Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

6 International Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6.2 Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6.3 International Atomic Energy Agency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Appendix A - Tsunami Hazard Assessment at a Hypothetical Nuclear Power Plant Site . . . . . . . . . A.1

FIGURES

1-1 A far-field oceanic tsunami .................................................. 1

1-2 A near-field oceanic tsunami ................................................ 2

1-3 A tsunami in an inland water body ............................................ 3

1-4 Vertical component of displacement due to a shallow dipping thrust ................. 5

2-1 The DLZ screening rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6-1 Conceptual illustration of design tsunami (JSCE, 2002), adapted with permission . . . . . . . 60

6-2 Schematic representation of tsunami wave overflow of offshore structures (JSCE, 2002),

adapted with permission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

6-3 Schematic representation of tsunami overflow of coastal structures (JSCE, 2002),

adapted with permission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
x

TABLES

1-1 Runups recorded at various locations for the 1960 Chile tsunami . . . . . . . . . . . . . . . . . . . . 17

5-1 Drag coefficients for ratios of width to depth (w/ds) and width to height (w/h)

[adapted from FEMA (2005)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

5-2 Value of dynamic pressure coefficient, Cp, as a function of probability of exceedance

[adapted from FEMA (2005)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5-3 Impact durations for selected construction materials [adapted from FEMA (2005)] . . . . . . 58
xi

EXECUTIVE SUMMARY

The U.S. Nuclear Regulatory Commission (NRC)

Office of New Reactors (NRO) is responsible for

the licensing and regulatory oversight of civilian

nuclear power reactors and research reactors in the

United States. Commission Paper SECY-06-0019

(Reyes 2006) described how recent developments

within the United States and abroad have

contributed to increased interest in licensing and

construction of new reactors. Nuclear energy is

also encouraged by the 2005 Energy Act, which

contains a provision for U.S. Government standby

support for any delays due to NRC reviews. In the

Staff Requirements Memorandum, dated May 10,

2005, from the April 6, 2005, Commission

Briefing on Status of New Site and Reactor

Licensing, the Commission requested that the staff

update licensing-guidance documents, including

the Standard Review Plan (SRP), NUREG-0800

(NRC 1996) to support new reactor licensing. The

Pacific Northwest National Laboratory (PNNL)

assisted the NRC in updating the SRP. The

updated SRP was released by the NRC in March,

2007 (NRC 2007).

Licensing of nuclear power plants is regulated by

Title 10 of Code of Federal Regulation (CFR)

Parts 50, 52, and 100. Appendix A to 10 CFR Part

50, General Design Criteria for Nuclear Power

Plants, contains criterion 2 (GDC 2), which

requires that structures, systems, and components

important to safety be designed to withstand the

effects of natural phenomena, including tsunamis. 

A series of regulatory guides (RG) provide guidance to licensees and applicants on implementing

specific parts of the NRC’s regulations, techniques

used by the NRC staff in evaluating specific

problems or postulated accidents, and data needed

by the staff in its review of applications for

permits or licenses. An update to RG 1.59 (NRC

1977) was expected to include guidance for

assessment of tsunamis as a flooding hazard, but

was never completed. An update to RG 1.59 is

currently underway.

In the wake of the December 26, 2004, Sumatra

earthquake and its accompanying tsunami that

resulted in widespread loss of life and property in

the Indian Ocean region, hazards posed by

tsunamis have emerged as some of the most severe

caused by natural phenomena. One operating

nuclear power reactor was shut down during this

tsunami, and, therefore, international nuclear

power plant operators and reviewers felt the need

to review the approach towards tsunami-hazard

assessment for existing and proposed sites. The

President of the United States launched an

initiative to improve domestic tsunami-warning

systems, and its first installment was signed into

law on May 11, 2005 (STC 2005). In April, 2006,

the NRC requested technical assistance from

Pacific Northwest National Laboratory in the

development of new guidance documents for

tsunami-related hazards at nuclear power plant

sites, consistent with the President’s initiative.

Section 2.4.6 of the SRP (NRC 2007) describes

review procedures and acceptance criteria for

probable maximum tsunami (PMT) hazards. 

However, technical guidance related to methods

and data required for tsunami-hazard assessment is

not the focus of the SRP. The National Oceanic

and Atmospheric Administration (NOAA) has the

responsibility to develop standards of accuracy for

tsunami-simulation models and to conduct

research to support the National Tsunami Hazard

Mitigation Program. NOAA’s responsibilities

were reaffirmed on December 20, 2006, when the

President signed the Tsunami Warning and

Education Act. NOAA’s Pacific Marine Environmental Laboratory (PMEL) operates the NOAA

Center for Tsunami Research (NCTR). NCTR’s
xii

objectives include the development and implementation of improved models to increase the

speed and accuracy of operational forecasts and

warnings, and development of improved methods

to predict the impacts of tsunamis on coastal

communities and infrastructure. To leverage the

extensive technical expertise and regulatory

authority that NOAA has and PNNL’s experience

with reviewing the first three Early Site Permit

applications, PNNL and NRC agreed to develop

guidance for tsunami-hazard assessment using a

set of two documents—this report, prepared by

PNNL, that focuses on the review guidance

relevant for NRC staff and a PMEL-prepared

NOAA Technical Memorandum titled “Scientific

and Technical Issues in Tsunami Hazard

Assessment of Nuclear Power Plant Sites”

(González 2007) to serve as the technical basis. 

As tsunami-simulation models are developed,

standardized, and released by PMEL for use by the

tsunami community, the NOAA Technical

Memorandum will be updated to include the stateof-the-art in tsunami-hazard assessment.

A hierarchical approach is recommended for

review of tsunami hazards at nuclear power plant

sites. An initial screening should be performed to

establish if the site is free from tsunamis. A

general rule based on horizontal distance (D),

longitudinal distance along a stream from an

estuary (L), and elevation (Z) of structures,

systems, and components (SSC) important to

safety could be used to reasonably demonstrate

that a plant may be safe from any tsunami hazards. 

Because tsunami runup and drawdown, and the

associated hazards, are highly site-specific, a priori

numerical limits on D, L, and Z cannot be

established. Site-specific analysis of data

combined with sound engineering judgment may

be used to justify that detailed tsunami hazard

assessment at the site may not be required. It is

expected that the majority of the sites located far

from the shoreline may be screened out. If the

initial screening indicates that tsunami hazards are

of concern, a detailed assessment of probable

maximum tsunami (PMT) hazards should be

performed. Generally, it may not be possible to a

priori determine the tsunamigenic source and

associated parameters that will result in PMT

hazards at a site. Therefore, a set of candidate

tsunamis generated by all possible tsunamigenic

sources should be simulated to determine the

worst hazard at the site. Because tsunami-wave

characteristics are highly dependent on near-shore

bathymetry and geometry of inlets, bays, and

coves, the hazards are expected to be highly

spatially variable in the near-shore area. Maps of

worst-case PMT-wave characteristics and hazard

metrics should be compiled from the scenario

tsunami simulations and used to determine design

bases and any required protection for affected SSC

important to safety.

At this time, efforts at NOAA PMEL are

underway to develop a community tsunamimodeling system. The standards, criteria, and

procedures for evaluation of tsunami numerical

models have been published by NOAA in

Technical Memorandum OAR PMEL-135. The

community tsunami-modeling system would

greatly aid the estimation of PMT hazards.
xiii

ACKNOWLEDGMENTS

Early and enthusiastic support for the initiative for

this study was provided by Dr. Brian Sheron,

Director of RES, Mr. Michael Mayfield, Director,

Division of Engineering, NRO, Dr. Nilesh

Chokshi, Deputy Director, Division of Site and

Environmental Reviews, NRO and Dr. Eddie

Bernard, Director, PMEL, NOAA.

The author wishes to sincerely acknowledge

technical discussions, guidance, and suggestions

provided by Mr. Lance Vail, PNNL. Comments

provided by Mr. Goutam Bagchi, Dr. Hosung

Ahn, Dr. Christopher Cook, Dr. Ann Kammerer,

and Mr. Mark McBride, all of NRC, helped

improve this report. Dr. Frank González and 

Dr. Vasily Titov, both of NOAA PMEL,

graciously provided comments on technical

aspects of tsunamis.

Mr. Stuart Saslow, Ms. Janie Vickerman, 

Ms. Julie Hughes, Mr. Kevin Ghirardo, and Ms.

Liz Davis, all of PNNL, provided excellent project

support. Editorial review of this report was

performed by Ms. Sheila Bennett and Ms. Angie

Aguilar, PNNL.

Financial support from the Division of New

Reactor Licensing, Office of Nuclear Reactor

Regulation, and later, the Office of New Reactors,

NRO, of the NRC is gratefully acknowledged. 

Preparation of this report would have been

impossible without the continued guidance and

support of Mr. Goutam Bagchi, the NRC

Technical Monitor.

1

1 TSUNAMI AND OTHER TSUNAMI-LIKE WAVES

1.1 Introduction

The word tsunami is a Japanese word that literally

means “harbor (‘tsu’) wave (‘nami’).” A tsunami

is a series of water waves that propagate from the

point of generation (the location of the

tsunamigenic source) toward the shore. Typically,

the term tsunami refers to an oceanic tsunami

caused by the initiation of the tsunami waves due

to the vertical displacement of the water column

by some submarine tsunamigenic source. 

However, tsunami or tsunami-like waves can also

be generated in inland water bodies by sources that

have appropriate tsunamigenic characteristics.

Tsunamis can be severely destructive to

infrastructure, human life, and the economy

located near the coast. These waves can travel

great distances in the form of gravity waves with

little loss of energy. The waves increase in

amplitude as they reach shallow water near the

shore. The waves may inundate large areas

onshore depending on local bathymetry and

topography. The hydrostatic and hydrodynamic

forces associated with the waves can damage

structures. The structures on land may also be

impacted by water-borne debris and projectiles.

Tsunamis are of great interest to nuclear power

plants located near a shoreline that may be

affected by tsunamis. Tsunami hazards that may

affect safety should be considered in the siting of

the plant. The design of the SSC important to

safety should also consider tsunami hazards to

ensure that the threat posed to the plant and,

subsequently, to public health and safety are

adequately mitigated in the design bases.

There are three distinct “phases” of a tsunami, as

illustrated in Figure 1-1. A far-field tsunami is

one for which the source is located more than

625 mi (1000 km) from the area of interest.

Figure 1-1. A far-field oceanic tsunami.
2

Little energy is lost during propagation of the

tsunami waves, and the speed at which these

waves travel can be estimated based on the theory

of shallow-water waves. The propagation phase of

the tsunami waves can be approximated well with

linear theory. The final phase of the tsunami is the

inundation phase, where the waves enter shallower

waters near the shore, shorten in wavelength, and

increase in amplitude. Nonlinear effects become

significant during the inundation phase and cannot

be neglected. The amplification of the wave

depends on the local, near-shore bathymetry. The

geometry of the shoreline— combined with

bathymetry—can also lead to reflection,

refraction, trapping of waves, and other

interactions that may further modify the characteristics of the tsunami waves. The runup is

defined as the maximum ground elevation that the

tsunami waves reach above a datum.

Figure 1-2 shows a near-field oceanic tsunami. 

The source for a near-field tsunami is generally

less than 625 mi (1000 km) from the area of

interest. Due to the proximity of the source to the

shore, the waves arrive at the area of interest

quickly, which may limit the time available for

evacuation or protective actions.

Figure 1-2. A near-field oceanic tsunami.

Figure 1-3 shows a tsunami generated in an inland

water body, such as a lake or a man-made reservoir, initiated by a seismic source beneath the

water body. Other causes, like hillslope failures

and subaerial landslides, may also be appropriate

as a source mechanism for tsunami-like waves

generated in inland water bodies. Hillslope failure

is the term generally used to describe a slope

failure caused by increased pore-water pressure

that results in loss the of sheer strength in the soil

and may lead to sliding along weakened layers. 

Subaerial landslide is the term generally used to

describe a landslide that starts above the surface of

the water body and impacts the water body,

generating a tsunami-like wave.
3

Figure 1-3. A tsunami in an inland water body.

1.2 Definition

The National Oceanographic and Atmospheric

Administration defines tsunamis as “...a series of

very long waves generated by any rapid, largescale disturbance of the sea.”

The International Tsunami Information Center of

the Intergovernmental Oceanographic Commission—a part of the United Nations Educational,

Scientific, and Cultural Organization—defines

tsunamis as “...a series of traveling waves of

extremely long length and period, usually

generated by disturbances associated with

earthquakes occurring below on near the ocean

floor.”

For the purposes of this report, we adopted the

following definition:

A tsunami is a series of water waves generated

by a rapid, large-scale disturbance of a water

body due to seismic, landslide, or volcanic

tsunamigenic sources.

Note that this definition is not limited to oceanic

tsunamis. Landslide sources may include submarine and subaerial slides and ice falls. Volcanic

sources include the effects of pyroclastic flows

and caldera collapse. The effects of a caldera

collapse may be similar to a submarine or a

subaerial landslide, depending on the location and

the characteristics of the event.

1.3 Mechanisms

Tsunamis are generated by rapid, large-scale

disturbance of a body of water. Therefore, only

geophysical events that release a large amount of

energy in a very short time into a water body

generate tsunamis. The most frequent cause of

tsunamis is an earthquake. Less frequently,

tsunamis are generated by submarine and subaerial

landslides, by pyroclastic flows and caldera

collapses during volcanic eruptions, meteorite

impacts, and by ice falls.

1.3.1 Earthquakes

The most frequent source of tsunami generation is

a submarine earthquake. Earthquakes primarily

generate tsunamis through vertical displacement of

the floor of the water body that results in a

simultaneous (often assumed identical) displacement of the overlying water column. Because of

the tsunami-generation sequence associated with

earthquakes, dip-slip earthquakes are more

efficient at generating tsunamis than strike-slip
4

earthquakes. However, Tanioka and Satake

(1996) show that it is possible for a strike-slip

fault to generate major tsunamis under certain

conditions where horizontal displacement of a

steep slope leads to a significant vertical displacement of the water column.

To generate a major tsunami, a substantial amount

of slip and a large rupture area is required. 

Consequently, only large earthquakes with magnitudes greater than 6.5 generate observable

tsunamis. The controlling source parameter that

determines tsunami severity is the seismic

moment, M0, defined as

M DA 0 

where is the shear modulus or rigidity, is the D

average slip, and A is the rupture area. Moment

magnitude of the earthquake, Mw, is computed

through the empirical relationship

M log M 9.05 w     2  3 0

The generation of the tsunami from an earthquake

event is carried out in three steps:

1. fault rupture modeling

2. calculation of coseismic displacements

3. calculation of initial wave field.

Fault-rupture modeling

The most commonly used rupture model is based

on elastic dislocation. Elastic dislocations under

the assumption of uniform slip are called Volterra

dislocations. For a given earthquake magnitude

Mw, rupture area A, and shear modulus , it is

possible to estimate an equivalent uniform slip. 

However, Geist (2005) explains that literature

demonstrates that the assumption of uniform slip

implies that the deformation is concentrated at the

edges of the rupture. Relaxation of the

uniform-slip assumption to allow for variable slip

in the dip direction for a dip-slip fault results in

concentration of the deformation near the center of

the rupture zone and substantially higher vertical

displacements (Geist and Dmowska 1999), leading

to a greater initial tsunami wave height.

The less frequently used rupture model is based on

crack theory (Geist and Dmowska 1999), in which

a uniform static stress drop, rather than a uniform

slip, is specified. The seismic moment and the

uniform stress drop are related by (Lay and

Wallace 1995)

M WL 0

3

8

2 	 


where is the uniform static stress drop, W is 


the width of the rupture, and L is the length of the

rupture.

Analysis of seismic-waveform data and other

theoretical and numerical studies of rupture

dynamics have shown that slip distribution is

strongly heterogeneous, such that the slip distribution can rarely be considered uniform and

conforms to the crack theory only in certain cases

(Yomogida 1988). For far-field tsunamis, the

effects of slip distribution are attenuated by the

time the tsunami reaches the site. However, for

near-field tsunamis, care should be taken to use an

appropriate rupture model because slip

heterogeneity has a significant effect on tsunamiwave heights. For an arbitrary slip distribution,

discretized cells of uniform dip-slip and the point

source expressions of Okada (1985) can be used. 

Geist and Dmowska (1999) show the effects of

slip heterogeneity modeled using discretized cells

on the local tsunami wave field.

Calculation of coseismic displacements

Coseismic displacement of the floor of the water

body can be estimated using analytical expression

of Okada (1985) for homogeneous earth structure

and a rectangular planar fault for cases where the

rupture is represented by a Volterra elastic

dislocation. Analytic expressions for coseismic

displacements have been developed for crack

models of rupture using Chebyshev polynomials

(Dmowska and Kostrov 1973; Rudnicki and Wu
5

1995). In general, a heterogeneous slip field can

be discretized into cells of planar, uniform slip

using the point source expressions of Okada

(1985). These techniques apply to planar faults in

a homogeneous elastic medium only.

For non-planar faults, Jeyakumaran et al. (1992)

and Jeyakumaran and Keer (1994) developed

analytical expressions that use triangular dislocations and curved slip zones. For non-planar faults

in heterogeneous medium, numerical techniques,

like finite elements, or boundary elements may

also be used (Yoshioka et al. 1989; Zhao el al.

2004).

Calculation of initial wave field

The vertical component of the coseismic displacement of the floor of the water body dominates

tsunami generation. Therefore, dip-slip

earthquakes are more efficient in tsunami

generation. Tanioka and Satake (1996) also show,

however, that tsunamis can be generated under

certain conditions by earthquakes in which

horizontal displacement is large relative to the

vertical displacement. Figure 1-4 shows a

situation where the displacement occurs on a

shallow dipping thrust. The horizontal movement

of the upper plate to the left of its original position

results in a significant vertical component,

generating a tsunami wave. Tanioka and Satake

(1996) report this situation for the June 2, 1994,

Java, Indonesia, earthquake of Mw 7.8, which

generated a tsunami with a maximum runup of

37 ft (11.3 m).

If a strike slip fault results in horizontal displacement of a steep slope, a tsunami may also be

generated by the vertical component of the

displacement. Tanioka and Satake (1996)

proposed this mechanism for the November 14,

1994, Mindoro earthquake of Mw 7.1 that

generated a tsunami with a maximum runup of

24 ft (7.3 m) in the Phillipines.

Figure 1-4. Vertical component of displacement due to a shallow dipping thrust.

The vertical component of the displacement due

only to the horizontal movement of the slope is

expressed as (Tanioka and Satake 1996)

u u 

H

x

u 

H

y hx y 












6

where x and y denote horizontal dimensions, ux and

uy are the horizontal displacements, H is the water

depth measured positive downward, and uh is the

vertical component of the displacement measured

positive upward. The total vertical displacement of

the floor of the water body for a fault motion that

also has a vertical displacement, uz, is therefore 

 uz + uh. Depending on the characteristics of the

fault and slope displacement, uh may contribute

significantly to the total vertical displacement of the

floor of the water body. Tanioka and Satake (1996)

suggest that this phenomenon may explain some of

the tsunamis generated by the so-called tsunami

earthquakes that are relatively small in magnitude

yet generate major tsunamis.

The time during which the rupture takes place and

results in displacement of the bottom of the water

body can be considered instantaneous relative to the

propagation speed of tsunamis. Therefore, the

initial tsunami wavefield mimics the verticaldisplacement field of the bottom of the water body. 

Wavelength components of the verticaldisplacement field that are less than approximately

three times the water depth are attenuated through

the water column, but this phenomenon is mostly a

concern in shallow and surface faulting. The initial

displacement of the water surface can be assumed

identical to that of the bottom of the water body

under the assumption that water is an

incompressible fluid.

Source parameters

Earthquake source parameters for tsunami

generation are related to the characteristics of the

dislocation. These parameters fall into two general

categories: those that scale with the magnitude of

the earthquake and those that relate to material

properties of the rupture zone.

Magnitude distribution

The frequency distribution of the magnitude of

earthquakes is given by the Gutenberg-Richter

(G-R) power law (Kagan 2002):

log[N(M )] a b w w  M

where N(Mw) is the number of earthquakes with

magnitudes greater than Mw and a and b are

parameters of the power law function. The slope

of the distribution (b) has been fairly well established in literature, but there is considerable debate

on how to specify the tails of the distribution. The

distribution is truncated on the high end because

of the requirements of the preservation-of-energy

principle. Kagan (2002) described four common

forms of the size distribution for large-magnitude

earthquakes. There are essentially three

approaches to define the shape of the G-R

distribution for large magnitudes: (1) the

characteristic model, which assumes that the

largest earthquake occurs at approximately the

same location and at approximately the same

magnitude; the G-R distribution is specified up to

the magnitude of the largest aftershock of the

characteristic earthquake (Wesnousky 1994); (2) a

regionally modified G-R relationship; a

continuous distribution where the right tail of the

distribution falls off rapidly at a rate greater than

the G-R slope, b; and (3) a globally modified G-R

relationship that is based only on tectonic

boundary type (Bird and Kagan 2004). Some

studies (Kagan and Jackson 1991, 1995; Rong et

al. 2003; Okal et al. 2006) indicate that the

characteristic model may not be valid. There is

some concern that regionally modified G-R

relationships may suffer because of a lack of

sufficient earthquake data to reliably estimate their

parameters. Because of this, Bird and Kagan

(2004) proposed a global G-R relationship based

only on tectonic boundary type. Also, for

subduction zones, the corner magnitude(a) is very

high ( ). Thus, unless proven otherwise, 9.58 0.46

0.48





it should be assumed that earthquakes with

moment magnitude greater than 9 can occur. Bird

and Kagan (2004) provide the corner magnitude

for oceanic convergent boundaries as . 8.04 0.22

0.52





(a) The slope of the G-R relationship increases for

earthquakes of magnitudes greater than the corner

magnitude, resulting in a rapid falloff of the

distribution.
7

Fault dimensions

Fault dimensions consist of the rupture length, the

rupture width, and the slip amount (more accurately, the distribution of the slip amount). 

Although the dimensions of the rupture scale with

seismic moment, past a certain magnitude, the

width of the rupture saturates. The saturation width

depends on the frictional stability of the rupture

zone, which varies with depth (Scholz 1990). 

Rupture length and slip may continue to increase

after the saturation of the rupture width with a

corresponding increase in seismic moment. 

General scaling relationships for rupture dimension

are available (Geller 1976; Kanamori and Anderson

1975; Wyss 1979).

Dip

Dip is the angle between the fault plane and the

horizontal plane. It is generally determined from

geophysical studies or from analysis of past events.

Strike

Strike is the geographic orientation usually given as

a compass direction of the fault plane. It is also

determined from geophysical studies or from

analysis of past events.

Slip vector

Slip vector refers to the direction and amount of the

slip during the earthquake. Relative motion

between the plates at a convergent boundary almost

always has an oblique component that results in a

compression component as well as a shear or

transcurrent component of strain (Soofi and King

2002). The orientation of this relative motion can

attain any value between 0° and 90°, called the

angle of obliquity. Generally, oblique convergence

results in strike-slip and dip-slip components,

thereby partitioning the slip into these two

directions. The amount of slip partitioning controls

the orientation of the slip vector along the interplate

thrust. In cases of a fully slip-partitioned

subduction zone, the earthquake has a pure thrust

mechanism that has the maximum tsunamigenic

efficiency.

Slip distribution

As discussed above, the amount of slip along the

rupture can be highly variable. The slip heterogeneity can have a significant effect on near-field

tsunami amplitudes, but its effects are significantly

dampened in the far field. Slip-distribution

models that account for heterogeneity are

generally based on self-affine properties of rupture

dynamics (Andrews 1980; Mai and Beroza 2002). 

The average slip for these models is estimated

from the overall seismic moment, and the falloff

of the seismic wavenumber spectrum is estimated

from far-field displacement spectrum observed on

seismograms. Andrews (1980) showed that a slipdistribution spectrum that decays as k-2 in the wave

number (k) domain is consistent with the widely

observed -2 decay (Aki 1967) in the frequency

() domain. Herrero and Bernard (1994) proposed

the “k-square” model, in which the slipdistribution spectrum decays as k-2 beyond a

corner wavenumber, kc. The corner wavenumber

was related to fault length. These slip-distribution

models can be used to generate a suite of scenario

patterns of slip distribution, which has been used

in ground-motion studies (Berge et al. 1998;

Somerville et al. 1999) and may also be used in

tsunami source models.

Mai and Beroza (2002) point out that models of

slip distribution based on self-affinity are essentially fractal and, therefore, contain no characteristic length scale to describe the size of asperities. 

Somerville et al. (1999) found that the number of

asperities and their size increase with seismic

moment. They suggested that it may be possible

to constrain the simulated slip-distribution patterns

from a “k-square” model using the correlation of

the size and the number of asperities with the

seismic moment.

There is also an indication that slip may exhibit

larger fluctuations than that predicted by the

Andrews (1980) model. Lavallée et al. (2006)

suggests that random variables from the Lévy

distribution may be suitable for generating

scenarios under these circumstances.
8

Shear modulus

Shear modulus is the constant of proportionality in

Hooke’s Law that relates shear stress to shear

strain. It is also described as the initial linear slope

of the stress-strain curve for shear. There is a large

variation in the value of the shear modulus due to

the large variety of types of rocks that are present in

subduction zones. Shear modulus can be measured

(Saffer et al. 2001) or deduced from earthquake

source-time functions (Bilek and Lay 1999, 2000).

The variation of shear modulus with depth was

shown to have a large effect on tsunamigenic

potential of earthquakes: Okal (1988) showed,

using a theoretical study, that a one tenth seismic

moment located in low-rigidity sedimentary rocks

resulted in an order-of-magnitude increase in the

initial tsunami amplitude. This phenomenon may

also explain tsunami earthquakes that are relatively

small in magnitude yet generate large tsunamis. If

these earthquakes are located at a shallower depth

near the trench, and the subduction zone consists of

low-rigidity material, four conditions favorable to a

more efficient and greater tsunami generation are

possible:

1. release of seismic moment in low-rigidity rocks

increases slip compared to the same moment

release in a higher-rigidity material

2. shallow rupture initiation increases the

possibility of the rupture of the floor of the

water body, which also tends to increase the

slip

3. shallow focal depth increases the coseismic

displacement

4. greater water depth near oceanic trenches

results in greater amplification of the tsunami

waves during shoaling.

1.3.2 Landslides

There are two broad categories of landslides: 

(1) submarine or subaqueous landslides that are

initiated and progress beneath the surface of the

water body and (2) subaerial landslides that are

initiated above the water and impact the water body

during their progression or fall into the water body. 

The movement of a large mass of the slide or the

impact of the fall displaces the water in the

direction of the movement and can lead to generation of a tsunami wave on the surface of the water

body. Once the initial wavefield is generated, it

propagates outward from the source region. A

review of submarine landslides is given by

Hampton et al. (1996).

Source types

Landslides occur in several ways, depending on

the geologic composition of the slope, steepness of

the slope, triggering mechanism, and pore-water

pressure. There are five classes of slope movement (Varnes 1978): (1) falls, (2) topples,

(3) translational and rotational slides, (4) lateral

spreads, and (5) flows. Depending on the location,

material properties, and properties of the trigger, a

combination of these movements may occur. 

These combined movements are called complex

slope movements.

The initial tsunami-wave generation is affected by

the type and the time history of the slope movement. Therefore, it is important to identify these

parameters of the landslide in the area of interest. 

In a given area, several types of landslide events

may occur that are capable of generating tsunamis. 

For example, in Alaska, destructive local tsunamis

have occurred due to subaerial landslides (e.g.,

Lituya Bay in 1958) and as a result of submarine

landslides in Valdez Arm of the Prince William

Sound that were triggered by the 1964 Great

Alaska earthquake. In southern California,

tsunamis have been generated in the geologic past

by submarine mud flows in Santa Barbara Channel

and by debris avalanches in Palos Verdes.

Subaerial landslides have also occurred in inland

lakes (a tsunami-like wave in Spirit Lake caused

by debris flow after eruption and collapse of

Mount St. Helens dome in 1980) (Waitt and

Pierson 1994) and man-made water-storage

reservoirs (a tsunami-like wave in Vaiont

Reservoir in Italy caused by a massive hillslope

failure and resulting landslide into the reservoir)

(Kiersch 1964; Hendron and Patten 1985).
9

Submarine landslides

Several mechanisms can trigger a submarine

landslide. The most common of these is an

earthquake, such as the 1929 Grand Banks (Fine

et al. 2005), 1946 Aleutian (López and Okal 2006),

1964 Valdez (Lee et al. 2003), and the 1998 Papua,

New Guinea, (Satake and Tanioka 2003) tsuna mis. 

Often, landslides triggered by an earthquake, can

occur very shortly after the earthquake such that the

generated tsunami is affected by both source

mechanisms (Johnson and Satake 1997; Satake and

Tanioka 2003; López and Okal 2006). Many of the

events in the National Geophysical Data Center

tsunami catalog that are attributed to landslides may

have such a composite source. In other instances,

the slope failure may occur several hours after the

triggering earthquake (Seed et al. 1975).

Tsunami generation mechanism

Tsunami generation from landslides can, in

principle, be modeled similar to that from an

earthquake. The physics of the slide are used to

estimate the displacement of the overlying water

column to determine the initial tsunami wavefield. 

A series of papers by Jiang and LeBlond (1992,

1993, 1994) describe the physics of submarine

mudslide and the waves it generated. Heinrich

et al. (2001) used granular material to simulate slide

dynamics.

Onset of shear failure of a slope under normal stress

can be described by the Mohr-Coulomb failure

criterion:


    c' ( u) tan

where  is the shear stress, c’ is the cohesion of the

slope material,  is the normal stress, u is the pore

pressure, and  is the angle of friction (repose

angle). The analysis of mass movement after

failure can be analyzed using models proposed in

literature (e.g., Imran et al. 2001).

Landslide tsunamigenic sources have two

properties that are different from the earthquake

sources: (1) landslide-generated tsunamis have a

very strong directivity in the direction of mass

movement, and (2) the source cannot be

considered to generate an instantaneous

displacement of the still-water level due to the

time it takes for the slide to evolve, during which

the characteristics of the surface waves are

affected. Because of the time-dependent nature of

source evolution, a completely coupled model

(e.g., Jiang and LeBlond 1994) or a kinematic

model (Lynett and Liu 2002) is generally preferred

for modeling of landslide-generated tsunamis.

Initial wave characteristics

The outgoing wave from the landslide source

propagates in the direction of the slide with its

amplitude affected by the terminal velocity of the

movement (Trifunac et al. 2002, 2003). The

characteristics of the backgoing wave depends on

the acceleration of the slide and appears as a

depression wave approaching the shore. Two

parameters of the slide primarily affect tsunami

generation: the volume and time history of the

slide.

Volume distribution

The frequency distribution of submarine landslide

volume follows a power law similar to that for

terrestrial landslides (Issler et al. 2005; ten Brink

et al. 2006). The volume distribution is particularly important in estimating the large landslides;

however, care should be exercised in the estimation because a large slide may be a composite of

multiple smaller failures (Lee et al. 2004). It is

also important to evaluate how the slide was

displaced (Locat et al. 2004) and to be able to

distinguish submarine landslides from sediment

waves (Lee et al. 2002).

The tail of the landslide volume distribution also

follows the general upper-truncated power-law

form (Burroughs and Tebbens 2005), similar to the

modified Gutenberg-Richter distribution for

earthquake magnitudes. It is not clear whether the

truncation is a result of physical limitation on

maximum size of landslides or of insufficient

observations of large events. However, factors

(i.e., downslope length of the continental shelves)

may help limit the maximum size of submarine
10

landslides. Assumptions also need to be made

while converting observed submarine landslide

extent to volume.

Locat and Lee (2002) compiled a global database of

known submarine landslides that included volume

and run-out distance.

Slide speed and acceleration

Tsunami generation from submarine landslide is

greatly affected by the time history of the slide

movement: the near-field tsunami amplitude is

sensitive to the initial acceleration, and the far-field

tsunami is sensitive to the maximum velocity of the

slide (Trifunac et al. 2002, 2003). The initial wave

height may also be influenced by the depth of the

center of mass of the slide (Murty 1979). There is a

lack of direct observation of submarine-landslide

dynamics, particularly in its tsunamigenic stages.

Landslide speed may be determined from physical

modeling of landslide dynamics (Locat et al. 2004). 

In the absence of physical modeling, lack of direct

observation limits the landslide dynamics to be

modeled using a single parameter, such as its speed

or duration. Likely, bathymetric slope and base

friction are important parameters that affect

landslide speed. Most modeling studies use speeds

in the range of 66–246 ft/sec (20–75 m/sec). 

Maximum tsunami-wave amplitude results when

the terminal speed of the slide matches the phase

velocity ( ) of the tsunami waves. c gh 

Cohesiveness and fluidity

The tsunami generated by a submarine landslide is

also affected by the relative rigidity of the slide

mass during the failure. More rigid slides that

behave more like a single mass have greater

efficiency at generating a tsunami than slides that

quickly disintegrate into turbidity flows. 

Geomorphological analysis can help identify the

type of initial failure, and laboratory analysis of

core samples may assist in the determination of the

properties of the slide material.

Investigation of tsunamigenic landslides

Investigation of tsunamigenic landslides in the

area of interest may involve several steps:

1. identification of the area of interest

2. literature review of existing documentation in

the area of interest

3. compilation of existing seafloor and coastal

data (e.g., multibeam, seismic, cores, etc.);

actual Geologic Long-Range Inclined Asdic

(GLORIA, a side-scanning sonar system that

produces digital images of the seafloor)

images may be an excellent starting point in

the U.S. Exclusive Economic Zone (EEZ) area

(Schwab et al., 1993;

http://coastalmap.marine.usgs.gov/gloria/).

(See Section 2.4.)

4. preparation of an inventory of mass movements and corresponding slide properties

(volume, shape, material properties, type of

failure, etc.)

5. identification of source area

6. detailed investigation of characteristic slides,

including geotechnical testing to estimate

material properties

7. retrospective analysis of historical slides to

estimate their tsunamigenic potential

8. detailed tsunami analysis from landslides:

slope failure analysis, post-failure slide

dynamics, and tsunami generation.

Subaerial landslides

The geographical areas where subaerial landslides

occur are more restricted than those where

submarine landslides occur. Subaerial landslides,

by definition, start on land and then impact a water

body. Therefore, their occurrence is generally

limited to areas of steep coastal or shoreline

topography. One exception to this limitation is

debris flow that originates away from the shores

but reaches and impacts the water body (e.g., the

debris flow from 1980 collapse of the Mount St.

Helens dome into Spirit Lake).
11

The impact velocity of subaerial landslides can be

significantly greater than those for submarine

landslides. However, typically, subaerial landslides

displace less water than submarine slides; thus, the

geographical extent of their damage is more

limited.

Many of the largest subaerial landslides are

triggered by earthquakes (e.g., the 1958 Lituya Bay

landslide) and some by classic hillslope failure

mechanisms under wet conditions (e.g., the 1963

Vaiont Reservoir landslide) (Kiersch 1964;

Hendron and Patten 1985).

Tsunami generation mechanism

Subaerial landslides can be classified into two

categories (Walder et al. 2003): (1) those that start

near the shore and have substantial run-out under

water (release-at-shore type) and (2) those that start

higher up, such that a substantial portion of their

run-out is over the land (initial-velocity type). The

physical parameter that distinguishes these two

types of subaerial landslides is the slide impact

Froude number (the ratio of slide velocity at entry

to the long-wave phase velocity of the tsunami

waves).

The tsunami-generation mechanism for the releaseon-shore subaerial landslide is very similar to that

of submarine landslides. The tsunami waves are

generated primarily due to the displacement of the

water. On the other hand, tsunami waves from

initial-velocity-type subaerial landslides are

generated primarily due to the impact of the slide

with the water (Heinrich 1992). 

Initial wave characteristics

Due to similarities of the tsunami-generation

mechanism in release-on-shore subaerial landslides

and submarine landslides, these landslides can be

treated similarly in terms of initial wave

characteristics.

The hydrodynamics of the impact of a fast-moving

mass on water is very complex. Fritz et al. (2003a,

2003b, 2004) carried out laboratory studies, and

Mader and Gittings (2002) performed full, threedimensional Navier-Stokes hydrodynamics

modeling of impacts on the water body. These

studies suggest that near the site of the impact,

complex flow separation and crater formation

occurs. Near-field wave characteristics of these

strongly non-linear waves is described by Fritz et

al. (2004). Lynett et al. (2006) suggested

modifications to standard hydrodynamics theory

for full, three-dimensional modeling of release-onshore subaerial landslide-generated waves where

the slide is not completely submerged in water. 

Walder et al. (2003) derived scaling relationships

to estimate the near-field hydrodynamic response

while treating the “splash zone” as a black box

because of the complexity and turbulent nature of

the flow.

Source parameters

The source parameters associated with subaerial

landslides are the impact Froude number and the

density and the dimensions of the slide. Heinrich

et al. (1998) also suggested that the frontal shape

of the slide also has an effect on wave generation. 

It is also likely that cohesiveness of the slide

material has a significant effect on wave

generation.

Ice falls

An overview of the glacial processes that may

result in large masses entering water is described

by Richardson and Reynolds (2000). These

processes include snow and ice avalanches. Ice

avalanches are categorized into frontal-block

failure (calving when the front of the glacier is in

water), ice-slab detachment, and ice-bedrock

failure (in which part of the bedrock is included in

the failure). Tinti et al. (1999) described a

historical example of approximately 6 ft (2 m)

waves generated in a lake by a frontal-block

failure 247,000-565,000 ft3

 (7000-16,000 m3) in

volume in the western Italian Alps. 

Ice avalanches moving downslope will behave

similar to initial-velocity subaerial landslides, and

likely primary source parameters are volume and

impact Froude number. Calving will behave as a

topple entering the water. Maximum volume of
12

ice avalanches in the European Alps is given in

Huggel et al. (2004).

1.3.3 Volcanoes

Tsunamis can occur due to a variety of mechanisms

associated with active and Holocene-age volcanoes

that are located in or near the oceans or other

bodies of water. The 1883 Krakatau and mid-17th

century BC Santorini tsunami events are ascribed to

volcanic activity.

Source types

Begét (2000) lists the following source types

associated with volcanic activity:

1. pyroclastic flow into the water

2. submarine caldera collapse

3. submarine explosion

4. debris avalanches and flank failures.

Less-common mechanisms include rapid seafloor

inflation (Satake and Kanamori 1991; Kanamori

et al. 1993) and coupling of the ocean with atmospheric shock waves (Begét 2000). A combination

of several source types may also be a factor in the

tsunami generation due to volcanic activity (e.g.,

1883 Krakatau and mid-17th century BC Santorini

events). No submarine volcano is continuously

monitored by a volcano observatory (Begét 2000).

Pyroclastic flows

Pyroclastic flows consist of debris flows and

avalanches of hot, gas-rich material that quickly

flows downslope. Pyroclastic flows are produced

by explosive volcanic eruptions. When the

pyroclastic flow reaches the water, the hot material

separates into a dust cloud of hot ash and gas and a

denser material. This dense material can generate a

tsunami (Legros and Druitt 2000; Watts and

Waythomas 2003), and is thought to be the most

efficient tsunami generator of several mechanisms

investigated (Watts and Waythomas 2003).

This mechanism is similar to the subaerial

landslides and avalanches. The tsunami events that

have been generated by pyroclastic flow include the

1997 Montserrat (Lesser Antilles) event (Heinrich

et al. 1998) and the 3500-years-before-present

Aniakchak events (Waythomas and Neal 1998;

Watts and Waythomas 2003). The primary source

parameters, similar to the subaerial landslide

source mechanism, are the impact Froude number,

density, and dimensions of the tsunamigenic

portion of the flow.

Submarine caldera collapse

Caldera collapses that occur under water result in a

sudden depression of the water surface that

hydrodynamically evolves into tsunami waves

(Latter 1981; Gray and Monaghan 2003). 

Examples of tsunamis generated by caldera

collapses are Santorini (Gray and Monaghan 2003)

and the 1883 Krakatau (Nomanbhoy and Satake

1995) events, although both are thought to have

generated tsunamis by a combination of volcanic

mechanisms, one of which is caldera collapse. 

Gray and Monaghan (2003) performed laboratory

experiments and numerical modeling to

investigate the mechanism of wave generation and

propagation caused by a caldera collapse. Their

study found that the primary source parameters

were caldera dimensions, fixed wall height, and

the cavity depth after the collapse.

Submarine explosions

Although large submarine hydromagmatic explosions are possibly limited by large hydrostatic

pressures on volcanoes (Begét 2000), regionally

destructive waves caused by explosive eruptions

have occurred in the past (the 1883 Krakatau

event, Nomanbhoy and Satake 1995). Belousov

et al. (2000) describe tsunamis generated in

Karymskoye Lake in Kamchatka, Russia, by a

1996 subaquatic explosive eruption. Newhall and

Self (1982) proposed the volcanic explosivity

index (VEI), which is a relative measure of the

size or magnitude of explosive volcanic eruptions. 

VEI can be linked to the potency of an explosion

and, consequently, its tsunamigenic potential.

Debris avalanches and flank failures

Volcanoes have produced some of the largest

debris avalanches (Locat and Lee 2002) and,
13

consequently, have the potential to generate severe

tsunamis. Some historical examples of tsunami

events generated by debris avalanches and flank

failures are the 1741 Oshima, Japan (Satake and

Kato 2001), the 1782 Unzen, Japan, the 1883

Augustine, the 1888 Ritter Island (Ward and Day

2003), the prehistoric Nuuanu and Wailau

landslides off the Hawaiian islands (Satake et al.

2002) and off Stromboli (Tinti et al. 2000), and the

1981 Spirit Lake from Mount St. Helens dome

collapse and debris avalanche (Waitt and Pierson

1994).

Avalanches can be triggered by volcanic activity or

may occur during the erosional phase, but they

occur most commonly from sector or flank

collapses (Ui et al. 2000). Volcanic rocks

commonly have greater cohesion than material that

is primarily clastic, such as mud slides. This

property may also increase the tsunamigenic

potential of debris avalanches.

The tsunami generation from flank failures occurs

through a combination of mechanisms. Volcanic

spreading results in over-thrusting along a

décollement on the edge of the volcanic flank

(Lipman et al. 2002, 2003; Morgan et al. 2003),

which results in a very shallow thrust fault similar

to subduction thrusts due to earthquakes. A large

earthquake on the base décollement may result in

large-scale slumping on the hanging wall, such as

on the south flank of Hawaii (Cannon et al. 2001). 

Klein et al. (2001) indicated that the volcanic flank

regions of Hawaii are the most seismically active

regions. Most of the far-field energy of the tsunami

from the 1975 Kalapana flank earthquake was due

to the earthquake; however, regionally, the

concomitant landslide also added to the tsunami

amplitude (Ma et al. 1999). The 1868 Kau

earthquake along the southern flank of Hawaii also

generated a far-field tsunami (Klein et al. 2001). 

Combining the tsunami displacement fields from

individual mechanisms for such events may be

required.

1.4 Some Historical Occurrences

This section describes some of the historical

occurrences of tsunamis caused by various

geophysical and seismic mechanisms. These

events were selected to demonstrate several

aspects of tsunami generation and analysis: (1) to

illustrate the diversity of locations, including

inland water bodies; (2) to illustrate the source

mechanisms, including earthquakes, earthquakeinduced submarine and subaerial landslides,

hillslope failure, and volcanic activity; (3) to

illustrate the difficulties associated with determination of the source mechanism, especially

when observed data are limited; and (4) to

illustrate the use of paleotsunami records in

identification of the source.

1.4.1 1958 Lituya Bay Landslide and

Tsunami

Lituya Bay is located in southeastern Alaska

(Miller 1960). This bay is narrow at 9 mi (14 km)

long and 2 mi (3.2 km) wide at its widest point. 

Lituya and Crillon glaciers flow into the Gilbert

and Crillon inlets, the two arms at the head of the

bay, respectively. These two arms of the bay are

part of a great trench along the Fairweather fault. 

Outer parts of the bay have gentle slopes. However, the inner parts of the bay are fjord-like with

steep slopes rising 2200 ft (670 m) to 6000 ft

(1828 m).

An earthquake with Mw=8.3 occurred on the

Fairweather fault on July 7, 1958. The earthquake

caused a large landslide on the northeast slope of

the Gilbert Inlet. The landslide started at an

altitude of approximately 3000 ft (914 m). The

estimated volume of the landslide was more than

1 billion ft3

 (30 million m3). The landslide caused

the water in the Gilbert Inlet to surge onto the

opposite slope with the runup reaching a height of

1720 ft (524 m). Miller (1960) also reported that

several such large waves have occurred in Lituya

Bay; the 1958 wave was the highest in terms of

runup. The other four waves that occurred in

1854, 1974, 1899, and 1936 were all less than
14

490 ft (149 m) in terms of runup. The 1958 Lituya

Bay tsunami runup is the largest documented in the

NGDC tsunami runup catalog.

1.4.2 1980 Spirit Lake Debris Flow and

Tsunami

On May 18, 1980, Mount St. Helens erupted after a

few-months-long activity that resulted in a bulge

(or cryptodome) on the north part of the mountain. 

A moderate earthquake caused the entire north

flank of the dome to collapse (Waitt and Pierson

1994), although some argue that the earthquake was

caused by the debris avalanche (Kanamori et al.

1984). The initial landslide consisted of two

separate slide-blocks that removed about 0.6 mi (1

km) of the dome. Sudden depressurization because

of removal of the overburden resulted in an

explosive expansion of the cryptodome, followed

by a pyroclastic density current with front speed

exceeding 313 mph (500 km/hr) (Waitt and Pierson

1994). Within 5 minutes of the earthquake and

collapse of the flank, the density currents had

spread 16 to 28 km (10 to 17.5 mi) from the source.

The toe of the pyroclastic density flow reached

Spirit Lake and entered it at approximately

156 mph (250 km/hr), filling the lake with sediment

and generating a tsunami by displacing the water in

the lake (Waitt and Pierson 1994). The water

surface of Spirit Lake was raised from 3199 ft 

(975 m) to 3406 ft (1038 m). The tsunami runups

on the west and east arms of the lake were 820 ft

(250 m) and 738 ft (225 m) above the original

water surface elevation.

According to the NGDC tsunami runup catalog, the

runups reported in the Spirit Lake are the second

and the third largest ever observed, smaller only

than the 1958 Lituya Bay event.

1.4.3 1946 Aleutian Tsunami

On April 1, 1946, near the Aleutian trench off the

Unimak Island in the eastern Aleutian Islands, an

earthquake of moderate surface magnitude, Ms=7.4,

generated a destructive Pacific-wide tsunami. 

Researchers agree that this earthquake is one

example of a tsunami earthquake, one that

generates a tsunami disproportionately large

compared to its surface magnitude. The tsunami

generated a runup of 115 ft (35 m) on Unimak

Island, Alaska, and a runup of 55 ft (16.8 m) in

Hawaii. The Scotch Cap lighthouse on Unimak

Island was completely destroyed and five people

were killed. The tsunami resulted in 159 deaths in

Hawaii, five in Alaska, two in Marquesas Islands,

and one in California.

The precise tsunami-generation mechanism of this

event has been a subject of much debate in the

research literature. A landslide component in the

generation of the tsunami was suggested by Sykes

(1971) and described in detail by Kanamori

(1985). The landslide component was later

de-emphasized (Johnson and Satake 1997), but not

conclusively ruled out. Tanioka and Seno (2001)

suggested that an uplift caused by displacement of

an accretionary deposit near the trench, in addition

to the uplift caused by the underthrusting fault,

could explain observed tsunami waveforms both in

the near-field (Unimak Island) and in the far-field

(Hawaii and the U.S. Pacific coastline). Fryer et

al. (2004) argued that a single landslide source

was responsible for this tsunami event based on

the highly directive nature of the tsunami waves in

the far field, rapid decay of the tsunami wave in

the lateral direction, and period of the waves. 

Using United States Geological Survey (USGS)

Geological Long Range Inclined Association

imagery, they also identified a candidate landslide

on the Aleutian shelf that is 15.6 mi (25 km) wide,

40.6 mi (65 km) long, and has a volume of

48.8–73.2 mi3

 (200–300 km3). López and Okal

(2006) used more recently available seismic data

and concluded that a very slow rupture accounts

for the large far-field tsunami amplitudes, and a

concomitant landslide is necessary to explain the

large near-field runup at Scotch Cap.
15

1.4.4 1929 Grand Banks Landslide and

Tsunami

On November 18, 1929, an earthquake of Mw=7.4

occurred on the southern edge of the Grand Banks,

about 175 mi (280 km) south of Newfoundland. 

The Grand Banks are a group of underwater

plateaus off the coast of Newfoundland on the

North American continental shelf. The earthquake

caused a large landslide that turned into a turbidity

current, flowing more than 625 mi (1000 km) to the

east (Fine et al. 2005). The turbidity current

severely damaged trans-Atlantic telegraph cables. 

Although all of the cables along the continental

slopes were broken, none on the continental shelf

was damaged.

The area of the submarine landslide coincided with

the epicenter of the earthquake. Later, ocean-floor

mappings and timings of the cable breaks were

used to estimate the area of the landslide at

approximately 7813 mi2

 (20,000 km2). The

estimated volume of this landslide was 48.8 mi3

(200 km3). The landslide generated a trans-Atlantic

tsunami that was observed as far as the Azores

Islands and Portugal. The tsunami was also

recorded on tide gauges at Atlantic City, New

Jersey, and Charleston, South Carolina. The

tsunami resulted in 27 deaths in Newfoundland and

one in Nova Scotia.

The runups reported in the NGDC tsunami runup

database for the 1929 Grand Banks tsunami were

23 ft (7 m) in Taylor’s Bay, 15.4 ft (4.7 m) in

Placentia Bay, and 15 ft (4.57 m) at Burin and Port

Au Bras, all in Newfoundland. On the U.S.

Atlantic coast, recorded runups were a foot (0.3 m)

at Ocean City, Maryland, and 2.2 ft (0.68 m) at

Atlantic City, New Jersey. The 1929 Grand Banks

tsunami is notable for a couple of reasons: it was

one of the very few catastrophic tsunamis to occur

in the Atlantic, and it was one of the very few

transoceanic tsunamis generated by a landslide.

1.4.5 1964 Valdez Arm Landslide and

Tsunami

On March 27, 1964, the second-largest earthquake

on record, with Mw=9.2, occurred in Prince

William Sound in Alaska at the boundary of the

Pacific plate, subducting beneath the North

American plate. The epicenter was approximately

6.25 mi (10 km) east of the mouth of College

Fjord, and approximately 56 mi (90 km) west of

the town of Valdez (old Valdez). The depth of the

earthquake was about 15.6 mi (25 km). The area

affected by the vertical deformation due to the

earthquake was estimated to be approximately

100,000 mi2

 (250,000 km2). The average slip was

estimated to be 14.4 ft (9 m).

The great earthquake resulted in several subaerial

and submarine landslides on and near the Alaskan

coast. The town of Valdez was built on unconsolidated deltaic deposits. During the earthquake,

the sediments under the waterfront area near the

town liquefied under seismic vibrations, and a

large section of the delta, approximately 4000 ft

(1219 m) long by 600 ft (183 m) wide, collapsed

into the bay and generated a local tsunami. The

combined effects of the earthquake and the local

tsunami destroyed the waterfront, including the

facilities of the Valdez port. The earthquake also

generated a tsunami that reached Valdez several

hours later. The runups from the local tsunami

were 170 ft (51.8 m) at the Valdez Inlet, 113 ft

(34.4 m) at Kings Bay, 100 ft (30.5 m) at Aialik,

and 79 ft (24.2 m) at Blackstone Bay, all in

Alaska. The maximum runups due to the transPacific tsunami generated by the earthquake in

Washington State was 15 ft (4.5 m) at Wreck

Creek; that in Oregon was 11.5 ft (3.5 m) at

Bandon; at Depoe Bay, Nehalem River, and at

Yaquina Bay, that in California was 28.9 ft (8.8 m)

at Van Damme State Park, and that in Hawaii was

16 ft (4.9 m) in Waimea Bay, Oahu, Hawaii. The

damage at the old Valdez town was so great that

the town was moved from its old location to a new

area. The new town is located at a higher

elevation and on more-stable ground.
16

The earthquake also caused major damage in

Seward, Alaska, at the head of Resurrection Bay,

along the east side of the Kenai Peninsula. An

approximately 0.6-mi- (1-km-) long section of the

waterfront began sliding toward the sea, caused by

large-scale offshore landslides, within one minute

of the strong ground shaking. This area contained

three large docks, many oil tanks, and a railroad

yard. Pipes from the oil tanks ruptured and the oil

tanks overturned causing a fire. The offshore

landslides generated a tsunami 32.8 ft (10 m) in

height that struck south of Seward, causing

extensive damage. Seismically generated tsunami

waves, also 32.8 ft (10 m) high arrived

approximately 30 minutes later, and caused

additional damage. In all, 13 deaths in were

reported in Seward. The NGDC tsunami runup

database lists a runup of 27.2 ft (8.3 m) for Seward

from the earthquake and landslide-generated

tsunami.

This event is one example in which the earthquake

ground motion occurred coincident with the local

tsunami generated from the subaerial landslide into

the bay. The damage, therefore, was a combined

effect of both earthquake ground motion and the

flood wave.

1.4.6 1960 Chile Earthquake and Tsunami

On May 22, 1960, the largest recorded earthquake,

of Mw=9.5, occurred off the coast of south-central

Chile, in the Nazca subduction zone, where the

Nazca plate is subsiding below the South Americal

plate. The total rupture length, over a period of

days, was approximately 625 mi (1000 km), one of

the longest ever reported. The earthquake

generated a trans-Pacific tsunami. The tsunami

caused 61 deaths and $75 million in damages in

Hawaii. In Japan, the tsunami resulted in 

138 deaths and $50 million in damages. Thirty-two

deaths were reported in the Philippines from the

tsunami. The U.S. Pacific Coast sustained $500

million damage. The near-field tsunami devastated

the Chilean coast. More than 2000 deaths, 

3000 injuries, 2 million homeless, and $550 million

in damages were reported in southern Chile. 

The earthquake caused widespread land deformation along much of the fault. A subsidence of

approximately 6.6 ft (2 m) occurred in the coastal

mountains; uplifts of 1.6 ft (0.5 m) were observed

along the foothills of the Andes, and offshore

islands were raised up to 19.7 ft (6 m). The

Puyehue volcano erupted two days after the

earthquake. Several landslides near Tralcan

mountains blocked San Pedro River that drains

Riñihue Lake, the lowest of the seven lakes that

receive inflow from Enco River. Due to the

blockage, water in Riñihue Lake started to rise

rapidly and would have resulted in a catastrophic

flood downstream if it had overtopped the 78.7-ft-

(24-m-) high dam, affecting several towns and the

city of Valdivia. An effort was undertaken by the

military, an electric utility company, and an

economic-development organization of the

government to control the waters in Riñihue Lake. 

Several drainages to the other lakes were dammed

to reduce inflow into the lake chain. The main

dam was lowered from 78.7 ft (24 m) to 49.2 ft

(15 m) to allow approximately 106 billion ft3

(3 billion m3) of water to drain from the lake

gradually. The work took two months to

complete. For this event, the NGDC database

reported the following tsunami runups shown in

Table 1-1.

1.4.7 The “Orphan” Tsunami of 1700

Accounts of flooding from a tsunami in January,

1700, exist in Japanese documents written at that

time (Atwater et al. 2005). The described effects

of the tsunami include villagers fleeing to higher

ground, damage to salt kilns and fishing shacks,

drowned crops, water flooding a castle moat and

entering a government storehouse, houses and

buildings that were washed away, and a fire. 

There was no advance warning of an earthquake

preceding the tsunami. In fact, no account

mentioned associated shaking, and two accounts

noted the lack of an earthquake warning. By the

1990s, this tsunami had become Japan’s bestdocumented tsunami of unknown origin. The

runups from the 1700 tsunami in Japan were

estimated to range from about 6.6 ft (2 m) to more 
17

Table 1-1. Runups recorded at various locations

for the 1960 Chile tsunami.

Location Maximum Runup

Australia 5.6 ft (1.7 m)

Chile 82 ft (25 m)

Japan 21 ft (6.4 m)

Mexico 8.2 ft (2.5 m)

New Zealand 13.1 ft (4 m)

Papua New Guinea 5.9 ft (1.8 m)

Peru 5.6 ft (1.7 m)

Pitcairn Islands 40 ft (12.2 m)

Russia 15.4 ft (4.7 m)

Samoa 16 ft (4.9 m)

United States Up to 35 ft (10.7 m)

 Montague Island, Alaska 7.5 ft (2.29 m)

 Cresent City, California 5.5 ft (1.68 m)

 Princeton, California 7.25 ft (2.21 m)

 Stinson Beach, California 5 ft (1.52 m)

 Ahihi Bay, Maui, Hawaii 8.9 ft (2.7 m)

 Anakua Point, Kauai, Hawaii 9.8 ft (3 m)

 Aweoweonui, Hawaii 10.8 ft (3.3 m)

 Coconut Island, Hilo, Hawaii 15 ft (4.6 m)

 Haena, Kauai, Hawaii 13.5 ft (4.1 m)

 Hana Bay, Maui, Hawaii 15 ft (4.6 m)

 Hilo, Hawaii 35 ft (10.7 m)

 Honolulu Landing, Oahu, Hawaii 14.1 ft (4.3 m)

 Honuapo, Hawaii 17 ft (5.2 m)

 Kaalualu Bay, Hawaii 17 ft (5.2 m)

 Southeastern coast of Hawaii 17 ft (5.2 m)

 Depoe Bay, Oregon 5.9 ft (1.8 m)

 Seaside, Oregon 4.9 ft (1.5 m)

 Willapa Bay, Washington 2 ft (0.61 m)

than 16.4 ft (5 m) (Satake et al. 2003; Tsuji et al.

1998) on the eastern Japanese coast.

Because there was no mention of a nearby earthquake in the Japanese documents for the 1700

tsunami, researchers in the 1990s attempted to find

its source far away from Japan. Potential sources

around the Pacific Rim, other than Cascadia,

conflicted either with the year of occurrence of the

tsunami or with the wave heights and runups

estimated for the tsunami. South American

catalogs were used to identify sources of tsunamis

observed in Japan in 1687 (Callao earthquake),

1730 (Valparaiso earthquake), and 1751

(Concepción earthquake). The 1952 Kamchatka

earthquake, which was the third largest of the 20th

century, produced wave heights comparable to the

1700 tsunami only in the north of Japan. The

second largest earthquake of the 20th century, the

1964 Alaska earthquake that produced the

devastating tsunami in Valdez Arm of Prince

William Sound, had a strong directivity away from

Japan and produced wave heights of less than 3 ft

(1 m) in Japan. The Cascadia source for the 1700

tsunami was proposed by Satake et al. (1996), who

not only were able to find evidence to support the

date of occurrence of this great source earthquake,

but also, remarkably, the hour. Satake et al.

(1996) also estimated that the moment magnitude

of this Cascadia earthquake was most likely

approximately 9. They presented arguments in

favor of this opinion based on the estimated wave

heights on the coast of Japan for the 1700 tsunami,

and based on numerical simulations of a transPacific tsunami with the source in Cascadia. Also,

an earthquake of Mw=8.2 that occurred on October

4, 1994, off the Kuril Islands near Japan produced

tsunami heights less than 1 ft (0.3 m) on the

Pacific Coast of the United States. Satake et al.

(1996) suggested that, reciprocally, a source in

Cascadia that produced wave heights greater than

6.6 ft (2 m) on the east coast of Japan would have

to be significantly larger than Mw=8.2.

As the study of plate tectonics and giant earthquakes (those of Mw>9) advanced during the

1960s through the 1980s, much debate took place

regarding the nature of seismicity in the Cascadia. 

Efforts were undertaken in the late 1980s to

identify geological evidence of past giant earthquakes in the area (Atwater 1987).

Subduction zones are characterized by downwarping of the subducting place and bulging of the

overriding plate as stress builds up at the interplate

boundary. During earthquakes, the leading edge

of the overriding plate breaks free, releasing the

stress; the seaward portion of the overriding plate

springs up and the continental side subsides. The

effect of the seaward, upward springing creates the

leading tsunami wave by upward displacement of
18

the water column. The leading positive wave

travels away from the continental side of the

subduction zone. On the continental side,

subsidence results in an initial depression of the

water column that is frequently observed as the

initial withdrawal of the sea before the arrival of the

first (positive) tsunami wave. The subsidence on

the coast results in previously dry coastal land

becoming submerged by sea water in a very short

period of time. The effects of a tsunami that follow

the earthquake may also lead to deposition of sand

or mud layers. In the late 1980s, geologists

investigated bays and river mouths along the

Pacific Coast. At nearly every site, they found

evidence that land had dropped. The evidence

included groves of dead tree trunks of western red

cedar that stand in tidal marshes, termed ghost

forests. Also, thousands of tree stumps buried in

the marshes were seen exposed by flowing water in

the banks of tidal streams. The investigation also

found buried remains of tidal marshes. In sediment

cores, investigators found muddy tidal deposits on

peaty marsh soils, which supports evidence of past

earthquakes in Cascadia.

Geologists in the 1980s and 1990s also found

evidence of tsunamis that consisted of sand sheets

near bays and mouths of rivers. The sand sheets

taper inland and contain microscopic siliceous

shells of marine diatoms. In alternating layers of

sand and mud, the researchers found that, at most

sites, sand arrived just before tidal mud began

covering freshly subsided soil. This evidence led

them to conclude that the sand was brought in by a

tsunami of nearby origin. The sequence of events

put forth was that an earthquake on the interplate

boundary abruptly generated a local tsunami and, at

the same time, lowered the adjoining coast; the

subsequent near-field tsunami created sand

deposits. Using radiocarbon dating and tree-ring

interpretation, researchers estimated that nearly all

sites from southern British Columbia to northern

California along the Pacific Coast had most

recently subsided within the past 400 or 500 years,

and that the southern Washington coast had

subsided after 1680 (Atwater et al. 2005).

Researchers also attempted to detect differences in

timing of the earthquake-induced subsidence

among the sites. Differences in timing would

indicate different source earthquakes and would

also limit the size of the ruptures. Radiocarbon

dating of dead plants and tree-ring pattern

matching did not narrow the timing to more than a

few decades. The evidence did not conclusively

prove either hypothesis of Cascadia rupture; a

single giant rupture and earthquake that would

require all dates to coincide or a series of smaller

earthquakes during a few decades. However, the

time window of either of these two Cascadia

events was indeed reduced to the period of

1695–1720. The research of Satake et al. (1996)

finally brought the evidence from Cascadia

together with the written records from Japan to

conclude that the parent earthquake of the 

1700 orphan tsunami was a giant earthquake in

Cascadia.

The evolution of our understanding with respect to

the 1700 tsunami is an excellent example of

paleotsunami research complemented by old

records and anecdotal evidence.

1.4.8 1963 Vaiont Reservoir Landslide

and Tsunami

On October 9, 1963, a massive landslide occurred

on the southern hillslope of the reservoir behind

Vaiont Dam, located about 100 mi from Venice,

Italy (Kiersch 1964). The landslide was caused by

shear failure of the overlying limestone along thin

clay layers under increased pore pressure. The

landslide area was 1.25 mi (2 km) long and 1 mi

(1.6 km) wide. The total estimated volume of the

slide was 8.4 billion ft3

 (238 million m3).

The landslide filled the reservoir 1.25 mi (2 km)

upstream from the dam completely to a height of

574 ft (175 m) above the original water level. The

landslide speed was reported as reaching

50–100 ft/sec (15-30 m/s). The tsunami wave

generated by the slide ran up more than 850 ft 

(260 m) above the original reservoir water level. 

The tsunami wave also overtopped the dam by an
19

estimated 328 ft (100 m) and flowed downstream. 

The height of the flood wave approximately 1 mi

(1.6 km) downstream from the dam was estimated

to be 230 ft (70 m).

1.4.9 2004 Sumatra Earthquake and

Tsunami

On December 26, 2004, the fourth largest recorded

earthquake of Mw=9.1 occurred off the western

coast of northern Sumatra in the Indian Ocean. 

Stein and Okal (2007) presented an analysis that

may revise the moment magnitude of this

earthquake to Mw=9.3 , making it the second largest

on record, after the great 1960 earthquake in Chile. 

The earthquake occurred due to the subduction of

the Indian plate below the Burma microplate, which

is a sliver plate between the Indian and the Sunda

plates. This earthquake was the first giant (Mw>9)

earthquake since the 1964 Alaska earthquake.

The USGS reported the epicenter at 3.3N,

approximately 155 mi (255 km) south-southeast of

Band Aceh, Sumatra, Indonesia. The rupture

progressed north to about 7N, with a total rupture

length of approximately 750 mi (1200 km), and the

rupture zone was reported to be approximately 

125 mi (200 km) wide with an average slip of 36 ft 

(11 m) (Stein and Okal 2007).

This earthquake generated a devastating

transoceanic tsunami that traveled across the globe. 

The runup measured in Crescent City, California,

was 2 ft (0.61 m); that at Atlantic City, New Jersey,

was 0.75 ft (0.23 m); and that at Trident Pier,

Florida, was 1.1 ft (0.34 m). The near-field tsunami

in Sumatra devastated the coastline, with a

maximum runup of 167 ft (50.9 m) at Labuhan on

the northwest coast of Sumatra. The tsunami

traveled across the Indian Ocean and affected

several countries, including India [maximum runup

of 31.4 ft (9.56 m)], Malaysia [maximum runup of

13.1 ft (4 m)], the Maldives [maximum runup of

14.5 ft (4.43 m)], Myanmar [maximum runup of 9.5

ft (2.9 m)], Somalia [maximum runup of 31.2 ft(9.5

m)], Sri Lanka [maximum runup of 37 ft (11.3 m)],

and Thailand [maximum runup of 64.2 ft (19.57

m)]. The tsunami caused approximately 300,000

deaths and unprecedented damage in countries

around the Indian Ocean, with Indonesia

accounting for more than 

228,000 fatalities.

The Madras Atomic Power Station, a commercial

nuclear power plant owned and operated by the

Nuclear Power Corporation of India Limited

(NPCIL), and located near Chennai, India, was

affected by the tsunami generated by the 2004

Sumatra earthquake (NPCIL 2007). At approximately 9:15 pm local time on December 26, 2004,

the condenser cooling pumps of Unit 2 of the

installation were affected due to flooding of the

pump house and subsequent submergence of the

seawater pumps by tsunami waves. The turbine

was tripped and the reactor shut down. The unit

was brought to a cold-shutdown state, and the

shutdown-cooling systems were reported as

operating safely. Unit 1 of the installation was

shut down for refurbishment at the time of this

event. After detailed inspection of the plant by the

NPCIL and the Atomic Energy Regulatory Board

of India, the plant resumed normal operations on

January 2, 2005. Adjacent to the Madras Atomic

Power Station, a prototype fast-breeder reactor

was under construction at the time of the 2004

tsunami. Work on the concrete raft at the bottom

of the excavated pit was in progress when the

tsunami waves flooded the pit. Most of the

workers were safely evacuated due to the alertness

of supervisors; however, there was one fatality. 

The tsunami waves deposited debris and sediment

in the pit over the partially poured concrete. The

pit was subsequently dewatered, and the debris

was removed before construction resumed.

1.5 Landslides in Earth’s Oceans

The understanding of submarine landslides is a

recent development spurred by availability of

high-quality seafloor mapping data [e.g., the

USGS GLORIA mapping effort of the USGS

started in 1984]. GLORIA is a side-scanning

sonar system that produces digital images of the

seafloor. The intensity of backscattered sound is a
20

function of the gradient, the surface roughness, and

the texture of the seafloor. Raw GLORIA data

were processed to correct for geometric and

radiometric distortions and mosiacked to produce

2by 2images of the survey area. Sixteen images

were produced for the Gulf of Mexico, 21 for the

Atlantic coast, and 36 for the Pacific Coast.

Another tool for mapping the bathymetry of the

seafloor is the use of multibeam sonar system

(Hughes-Clarke et al. 1996). Multibeam sonars

first became available in 1971, but hardware to deal

with the large volumes of data produced by these

systems and the limitations of positioning systems

available at the time precluded their general use. 

Since then, many such systems have become

available and rapid processing of the data

advanced. Initially, these systems were used for

industrial applications, such as surveys of offshore

platform sites and pipeline route corridors. The

values of this tool for bathymetric surveys was

recognized with time.

GLORIA imagery has been used to identify

submarine landslides near the Hawaiian islands

(Lipman et al. 1988; Moore et al. 1989, 1994a, b),

mapping of features of the continental slope in the

Gulf of Mexico (Rothwell et al. 1991) and

landslides (Twichell et al. 1993), and investigation

of landslide zones in the Atlantic (Booth et al.

1993; McGregor et al. 1993; O’Leary et al. 1987;

O’Leary 1993; Popenoe et al. 1993; Schwab et al.

1991, 1993).

1.5.1 The Pacific Ocean

McAdoo et al. (2000) present results of a

morphometric analysis of submarine landslides off

the coasts of Oregon, California, Texas, and New

Jersey. They used multibeam bathymetry data, in

addition to GLORIA images, to identify scars left

by submarine landslides. Widespread evidence of

slope failure and submarine landslides was found in

each of the four margins investigated. Properties of

these landslides were measured or estimated using

multibeam bathymetry and GLORIA images. The

parameters of the landslides measured by the

authors included latitude, longitude, area, depth of

the headscarp of the landslide, and runout length

of the landslide. The volumes of the landslides

were estimated using the thickness of the slides

and assuming a wedge geometry for the slides. 

The authors presented a table of parameters for the

investigated submarine landslides (see Table 1 of

McAdoo et al. 2000).

This table included 20 submarine landslides in the

Oregon margin with slide areas ranging from

0.4 mi2

 (1 km2) to 93.4 mi2 (239 km2). Depth to

the headscarp for these slides ranged from 1800 ft

(549 m) to nearly 9600 ft (2924 m). The estimated

volumes for the Oregon margin landslides ranged

from less than 0.02 mi3

, or 3.6 billion ft3 (0.1 km3),

to 10.4 mi3

, or 1527.3 billion ft3 (42.5 km3). The

runout lengths varied from less than 0.6 mi (1 km)

to 13.8 mi (22 km).

In the California margin, 25 submarine landslides

were identified by McAdoo et al. (2000) that

ranged in area from 2.7 mi2

 (6.8 km2) to 205 mi2

(525 km2). Depth to the headscarp of these slides

ranged from 2707 ft (825 m) to 8914 ft (2717 m). 

The estimated volumes of the landslides ranged

from 0.05 mi3

, or 7.2 billion ft3 (0.2 km3), to

6.7 mi3

, or 991.9 billion ft3 (27.6 km3). The runout

lengths varied from 1.7 mi (2.7 km) to 31.9 mi 

(51 km).

Mass movement features in the Monterey Bay

region of the central California coast are described

by Greene and Ward (2003). Multibeam bathymetric data collected by the Monterey Bay

Aquarium Research Institute show mass wasting

occurring along the northern slope of the Santa

Barbara basin. Similar data collected by the

USGS offshore from Long Beach, California,

show a large debris avalanche. A small landslide

was reported that occurred at the head of the

Monterey Canyon during the 1989 Loma Prieta

earthquake. A small tsunami, approximately 1.6 ft

(0.5 m) high, was generated from this event. 

Extensive mass wasting, including larger landslides, covering an area of 
21

184 mi2 (470 km2), are identified on the continental

slope of the Monterey Bay region. Individual

landslides range in size from small 0.4 mi2

 (1 km2)

to very large—comparable to the size of the

Monterey Bay—and exceed 8.5 mi3

 or 

1258 billion ft3

 (35 km3) in volume.

Greene and Ward (2003) reported simulated

tsunamis from three identified landslides. The

Ascension Canyon landslide is located at a depth of

approximately 1969 ft (600 m), is 0.94 mi (1.5 km)

long, 1214 ft (370 m) wide, and about 164 ft (50 m)

thick. According to Greene and Ward (2003)

modeling, the initially generated tsunami wave was

nearly 6.6 ft (2 m) high. The runup was calculated

to be 9.8 ft (2.98 m) on the coast near Davenport,

well below the 32.8 ft (10 m) high coastal cliffs. 

The runup on the Monterey Peninsula was

estimated to be 1.7 ft (0.52 m), and those at Santa

Cruz and Moss Landing were estimated to be 4.4 ft

(1.34 m) and 1.2 ft (0.36 m).

The second landslide used by Green and Ward

(2003) to simulate a tsunami was the Tubeworm

Slump in the Monterey Canyon. The slide area was

6.3 mi2

 (16 km2) with a runout of 984 ft (300 m)

and a volume of 0.6 mi3

 or 86 billion ft3 (2.4 km3). 

The first arrival of the tsunami waves at the

Monterey Peninsula was a 3.3-ft (1-m) high

positive wave, and that at Santa Cruz was a 6.6-ft

(2-m) deep trough.

The third tsunamigenic landslide used by Greene

and Ward (2003) was a large mass-movement field

exceeding 35 mi2

 (90 km2) in area in the Monterey

Meander. The mass movement is composed of

several retrogressive slumps and debris flows. In

the event of a hypothetical large failure in this area,

the authors estimated that tsunami waves could

reach heights of 36.1 ft (11 m) in the Monterey

area, 26.2 ft (8 m) at Moss Landing, and 6.6 ft (2

m) at Santa Cruz.

Lee et al. (2003) describe case studies of three

submarine landslide environments: Resurrection

Bay, Alaska; Commencement Bay, Washington;

and the Los Angeles margin near Palos Verdes,

California. These submarine landslides and massmovement sites were identified on recently

available multibeam-sonar data.

The Resurrection Bay landslide, which occurred

during the great 1964 Alaska earthquake, generated local tsunamis that devastated the waterfront

at Seward, Alaska (see Section 1.4.5).

Commencement Bay is located near Tacoma,

Washington. The Puyallup River flows into the

bay, carrying meltwater from the glaciers of

Mount Rainier, including large quantities of

glacial silt leading to the growth of a delta at an

average rate of 1.6 mi (2.5 km) per 1000 years

(Dragovich et al. 1994). The high sedimentaccumulation rate leads to high excess pore-water

pressure, creating favorable conditions for slope

failure. Two failures have been recorded in the

past (Gardner et al. 2001), one in 1894, without a

precursor earthquake, and another in 1992 during

the Nisqually earthquake. The 1894 failure

resulted in a tsunami reported to be 10 to 20 ft

(3 to 6 m) high. The 1992 event did not cause any

tsunami. Lee et al. (2003) identified a number of

features on the multibeam bathymetry map of

Commencement Bay, including large sediment

lobes off the mouth of the Puyallup River. They

also mapped a 1.25-mi (2-km) long submarine

channel and identified it as the 1894 landslide. 

The channel is 1476 ft (450 m) wide at its head.

The submarine-landslide field located to the south

of the Palos Verdes Peninsula has been known for

a long time, but the details of the morphology

became available recently using multibeam

bathymetric surveys (Gardner and Mayer 1998;

Gardner et al. 1999). Two landslides were

identified on the multibeam imagery. One of the

landslides was dated using radiocarbon techniques

and found to be approximately 7500 years old. 

The age of the other landslide is unknown. 

Landslide debris was identified as far as 6.3 mi (10

km) from the base of the slope, indicating the

landslides had considerable momentum. Lee et al.

(2003) concluded that both landslides were

probably tsunamigenic. Locat et al. (2004)
22

developed a simplified model of the landslide and

simulated a tsunami based on this event. The

amplitude of the tsunami was not estimated

precisely because of uncertainty in landslide source

parameters.

1.5.2 The Gulf of Mexico

In the Gulf of Mexico, 25 submarine landslides

were identified by McAdoo et al. (2000) with areas

ranging from 3.8 mi2

 (9.6 km2) to 2152 mi2

(5509 km2

). Depth to the headscarp of these

landslides varied from 397 ft (121 m) to 7871 ft

(2399 m). The estimated volume of these landslides ranged from 0.2 mi3

, or 28.7 billion ft3

(0.8 km3), to 37.2 mi3, or 5470 billion ft3

(152.2 km3). The runout lengths varied from 1.9 mi

(3 km) to 104 mi (167 km). Tripsanas el al. (2003)

described the slope instabilities in the Bryant

Canyon area in the northwest Gulf of Mexico. 

Bryant Canyon acts as a conduit for the transport of

sediment from the Mississippi River to the abyssal

plain of the Gulf of Mexico.

Ten Brink et al. (2008) conducted a recent literature

survey to identify landslide sources in the Gulf of

Mexico. They described three distinct geologic

provinces in the Gulf of Mexico Basin: a carbonate

province, a salt province, and a canyon-to-deepsea-fan province. Salt that originally underlay

Louisiana, southern Texas, and offshore of the Bay

of Campeche in Mexico was eroded and

subsequently deposited during the early

development of the basin. Subsequently, sediment

eroded off the North American continent was

deposited over the salt and the overburden caused

the salt to migrate seaward. At present, the salt

underlies large parts of the northern Gulf of Mexico

and the southwest corner of the Gulf of Mexico in

the Bay of Campeche. The Sigsbee Escarpment is

a cliff located south of Louisiana and Texas that

marks the seaward limit of the salt. The deposition

of the salt was followed by formation of carbonate

reefs along much of the margin of the Gulf of

Mexico Basin. At present, the reef system is

exposed along the Florida Escarpment and the

Campeche Escarpment. The escarpments stand

approximately 4900 ft (1500 m) above the abyssal

plain with gradients locally as steep as 20. 

Sediment from erosion by North American rivers

delivered sediment into the basin that resulted in

the creation of a series of deep-sea fans. Three of

these fans are the Bryant Fan, Mississippi Fan, and

Eastern Mississippi Fan. The Mississippi Fan is

the largest and covers most of the eastern part of

the gulf.

Landslides have occurred in each of the three

provinces of the Gulf of Mexico Basin (ten Brink

et al. 2008). Landslides in the carbonate province

have occurred both on the steep Florida and

Campeche Escarpments as well as on gentler

slopes above the escarpments. A large talus

deposit(a) was identified at the base of the

Campeche Escarpment, but its full extent and the

amount of material of an individual failure is

unknown. Talus blocks are also observed along

the base of the southern Florida Escarpment. 

Talus deposits at heads of some box canyons are

less than 6 mi2

 (15 km2) in area. Large collapse

scars along the central part of the West Florida

Slope are present. The entire slide scar is approximately 75 mi (120 km) long and 19 mi (30 km)

wide and may have a total volume of 244 mi3

(1000 km3

). The slide, located at approximately

the same latitude as Tampa, Florida, may have had

at least three generations of failure. Another

extensive area of collapse was mapped in the

southern portion of the West Florida slope that

may be 6–11 mi (10–17 km) long.

Ten Brink et al. (2008) did not find any published

reference to landslides in the salt province in the

Bay of Campeche. Detailed bathymetric mapping

of the northern Gulf of Mexico revealed a unique

morphology consisting of relatively small circular

basin features 2.5–20 mi (4–33 km) wide with

areas of 2–122 mi2

 (5–312 km2). The GLORIA

imagery has identified 37 landslides in the salt

province and along the base of the Sigsbee

Escarpment. The largest of these landslides is

(a) Sloping mass of rock debris deposited at the base

of a cliff.
23

located in the northwest part of the Gulf of Mexico

and is approximately 71 mi (114 km) long, 33 mi

(53 km) wide, and 879 mi2

 (2250 km2) in area.

A large landslide complex, approximately 9000 mi2

(23,000 km2) in area, was identified in the upper

portions of the Mississippi Fan (ten Brink et al.

2008). The total volume of the deposits have not

been estimated accurately. The Eastern Mississippi

Fan also has a relatively large landslide that

partially buries the canyon at the head of the fan

and is approximately 96 mi (154 km) long, 14 mi

(22 km) wide, and 941 mi2

 (2410 km2) in area.

The characteristics of submarine landslides in the

Gulf of Mexico are not well understood due to a

lack of data in certain regions. The age, style, and

distribution of landslides is still incomplete. Ten

Brink et al. (2008) recommended that age dating,

compilation of multibeam bathymetry data, and

mapping of the Campeche Bay area are required to

refine understanding of submarine landslides in the

Gulf of Mexico. Until further research is

undertaken and completed, tsunami-hazard

assessment for landslide sources in the Gulf of

Mexico should be carried out on a case-by-case

basis.

1.5.3 The Atlantic Ocean

In the Atlantic Ocean, a giant submarine landslide

complex known as the Storegga landslide complex,

(Bryn et al. 2003), is located off the coast of

Norway. The slide is gigantic, 854 mi3

 or

126 trillion ft3

 (3500 km3) in volume, 35,156 mi2

(90,000 km2) in area, 10,547 mi2 (27,000 km2) in

slide-scar area, with 281 mi (450 km) long runout. 

The slide is characterized by several strata of buried

mass movements that occur on parallel slip surfaces

in marine clay layers (Bryn et al. 2003). These

slides have occurred on a semi-regular basis during

the past 500,000 years, in good agreement with the

cycles of main continental-shelf glaciation. The

trigger mechanism is believed to be seismic activity

associated with glacioisostatic rebound.(a) The most

recent of the Storegga slides, believed to have

occurred around 8200 years ago, also generated a

tsunami that reached surrounding coasts

(Bondevik et al. 1997).

In the Faroe Shetland Channel, located between

the Faroe Islands and Shetland Islands in the

Atlantic, a slide known as the Afen slide was first

recognized on Towed Ocean Bottom Instrument

(TOBI) side-scanning sonar data. The data was

acquired for the Atlantic Frontiers Environmental

Network (AFEN). The maximum width of this

slide is 1.9 mi (3 km), and the length of the scour

and debris lobe is 7.5 mi (12 km) (Bulat 2003). 

Wilson et al. (2003) used the TOBI image

compiled by Bulat (2003), the British Geological

Survey regional seismic survey data, and

geotechnical data obtained from sediment cores

within the slide area to assess phases, modes, and

characteristics of the Afen slide.

In the continental margin off the coast of New

Jersey, McAdoo et al. (2000) identified 

13 submarine landslides that ranged in area from

2 mi2

 (5 km2) to 24.2 mi2 (62 km2). Depth to the

headscarp of these landslides varied from 4675 ft

(1425 m) to 7051 ft (2149 m). The estimated

volume of these landslides ranged from 0.07 mi3

,

or 10.8 billion ft3

 (0.3 km3), to 1.3 mi3, or

187 billion ft3

 (5.2 km3). The runout lengths

varied from 1.6 mi (2.5 km) to 13.1 mi (21 km).

Ward and Day (2001) described the potential

collapse of the Cumbre Vieja volcano on the

island of La Palma which is in the Canary Islands,

off the west coast of Morocco. The Cumbre Vieja

volcano has been the most active volcano in the

Canary Islands during the last 125,000 years. It

occupies the southern one-third of the La Palma

Island, with slopes of 15 to 20 degrees. The flankfailure scenario described by Ward and Day

(2001) involves a single N-S rift under the west

(a) The uplifting of land once depressed under the

weight of glacial ice (Ranalli, 2001).
24

flank of the volcano. The detachment fault(a)

surfaced as a west-dipping normal fault along the

crest of the volcano during its 1949 eruption. The

scrap extends 2.5 mi (4 km) and has a maximum

offset of 13.1 ft (4 m). The fault has been inactive

since 1949. Ward and Day (2001) postulated that a

future eruption near the top of the Cumbre Vieja

will trigger a flank failure. Based on geological

evidence from existing lateral-collapse scars,

bathymetric and imaging sonar surveys of La Palma

and other locations, and comparisons with other

flank failures of volcanoes (Mount St. Helens), the

authors estimated the future dimensions of the slide

block could be 9.4–12.5 mi (15–20 km) in width

and 9.4–15.6 mi (15–25 km) in length. The authors

suggested that the mean thickness of the slide block

could range from 0.6 mi (1 km) to 1.2 mi (2 km). 

Based on these dimensions, Ward and Day (2001)

estimated that the volume of a future flank failure

could range from 36.6 mi3

, or 5391 billion ft3

(150 km3

), to 122.1 mi3, or 17,969 billion ft3

(500 km3

).

Ward and Day (2001) considered the worst-case

slide block of 122.1 mi3

 or 17,969 billion ft3

(500 km3

) in volume that break away and falls into

the ocean and slide for 37.5 mi (60 km) until it

reaches flat ocean bottom at a depth of 13,123 ft

(4000 m). The authors proposed a maximum

runout velocity of 328 ft/s (100 m/s). The authors

noted that the chosen runout velocity was

substantially less than the tsunami celerity, a

minimum of approximately 459 ft/s (140 m/s),

corresponding to the ocean depth near the La Palma

slide in excess of 6562 ft (2000 m). The tsunami

simulations carried out by Ward and Day (2001)

resulted in a 2953-ft (900-m) high dome of water

representing the initial waveform, slightly less than

the mean thickness of the sliding block. The

simulation resulted in 32.8-ft (10-m) high waves in

Newfoundland and those of 65.6–82 ft (20–25 m)

height on the Florida coast.

Mader (2001) described another attempt to model

the tsunami generated from a worst-case flank

failure of the Cumbre Vieja volcano. Physical

modeling of the slide moving as a single block by

Herman Fritz, using the experimental setup

described by Fritz et al. (2001), indicated an initial

waveform with a 2133 ft (650 m) waveheight, a

18.8–25 mi (30–40 km) wavelength, and a

3–4 minute period. The wave was described as an

intermediate wave and not a shallow-water

tsunami wave. The wave would disperse significantly as it propagated away from the source in the

Atlantic. Mader (2001) simulated the tsunami

across the Atlantic using the nonlinear shallowwater model SWAN (Mader 2004) that includes

Coriolis and frictional effects. The author noted

that using a shallow-water wave model to describe

the propagation of intermediate waves would only

provide an estimate of the upper limit of the

amplitude and the period of the waves. A

10-minute Atlantic bathymetry generated from the

2-minute Mercator Global Marine Gravity

topography of the earth was used in the tsunami

simulation. The initial waveform was a 2133 ft

(650 m) high, with a 12.5 mi (20 km) radius. The

maximum simulated tsunami wave heights at

deep-water locations off the eastern coast of the

United States was 9.8 ft (3.0 m) at a water depth of

9587 ft (2922 m) east of Washington, D.C.

Mader (2001) also estimated the effect of

dispersion on the propagation of the tsunami

caused by the Cumbre Vieja flank failure using the

ZUNI model (Mader 2004) that solves twodimensional time-dependent Navier-Stokes

equations for incompressible flow. The author

concluded, based on the results of the ZUNI

simulations, that the tsunami wave heights off the

coast of the United States would be less than 1 m

and, even after amplification of the tsunami waves

due to shoaling, the waves would not present a

major hazard.

Pararas-Carayannis (2002) critically evaluated the

Cumbre Vieja flank-failure tsunami-simulation

studies regarding three aspects: (1) if the massive

volcanic collapses could occur as postulated, (2) if (a) Parallel zones of weakness inside a volcano along

which subsidence often occurs.
25

the source dimensions and initial modeling

parameters were correctly evaluated from proper

coupling mechanisms, and (3) if the modeling

studies were properly validated. The last of the

three was impossible to ascertain because historical

records of a tsunami generated by massive flank

failures of island stratovolcanoes is documented.

A review of present volcanic flank instabilities and

flank collapses in the past (Pararas-Carayannis

2002) revealed massive slides that occurred in the

Canary Islands (Day et al. 1999), Cape Verde (Day

et al. 1999; Elsworth and Day 1999), the Hawaiian

Islands (Moore et al. 1989, 1994a; Moore and

Clague 1992; Lipman 1995), and other places. 

These events are documented in literature. 

However, the mechanisms of these prehistoric

failures are not completely understood. Island

stratovolcanoes appear to slide along their bases

more frequently, and occasional locking of these

slides may trigger large slope failures or

earthquakes. Cumbre Vieja is composed of layers

of pillow lavas interspersed with pyroclastic

material (Pararas-Carayannis 2002).

The island of La Palma was formed by three

statovolcanoes that rise several thousand feet 

above the sea floor. The volcano Taburiente lies to

the north, and the central and southern parts of the

island were formed by the volcanoes Cumbre

Nueva and Cumbre Vieja. More than half of the

subaerial volume of the island was removed by

landslides and erosion during the past 

1 million years (Pararas-Carayannis 2002). The

Cumbre Nueva giant landslide, 48.8 mi3

, 

7187 billion ft3

 (200 km3), in volume, occurred

approximately 560,000 years ago (Carracedo et al.

1999) that removed material in the west-central part

of the island. The island is composed of two main

rock layers separated at an elevation of

approximately 1400 ft (427 m) above mean sea

level (Pararas-Carayannis 2002). The thickness of

pillow lavas ranges from 32.8 to 1148 ft (10 to 

350 m). The upper layer consists of basaltic lavas

and pyroclastic materials. Extensive erosion has

taken place on the north part of the island, and to a

lesser extent on Cumbre Vieja’s flanks. PararasCarayannis (2002) concluded that the existic

basaltic flows and dikes would significantly limit

the volume of any future slope failure, and any

such failure would either occur in steps or

contained by ring dikes. The author did not find

any evidence of a massive failure of the western

flank of Cumbre Vieja along a deeper detachment

surface. There is no extensive fault system along

Cumbre Vieja’s rift zone. The 13.1 ft (4 m) offset

near the summit was suggested to be along a

detachment fault by Ward and Day (2001). 

However, Pararas-Carayannis (2002) found no

seismic or geologic data to support this suggestion; the offset could also have resulted from

superficial gravitational settling or from collapse

of a magmatic chamber.

Pararas-Carayannis (2002) evaluated the

monolithic block movement of the Cumbre Vieja

flank failure suggested by Ward and Day (2001). 

Flank collapses of island stratovolcanoes can be

triggered by isostatic load adjustments, erosion,

build-up of gaseous, hydrothermal, or magmatic

pressure, violent eruptions, or collapse of

magmatic chambers. An evaluation of the forces

needed to cause the massive failure along a

detachment surface suggested by Ward and Day

(2001) was carried out by Pararas-Carayannis

(2002). A force close to the base of the mass, or at

least near the center of the mass, is needed to

trigger a monolithic collapse due to exceedance of

the shear strength along a slide plane. PararasCarayannis (2002) found that a force needed to

move a 122.1 mi3

, or 17,969 billion ft3 (500 km3),

monolithic block is unrealistic. There is also no

evidence of significant magmatic-chamber

collapse along the crest of Cumbre Vieja (PararasCarayannis 2002). The erosion on volcanic

islands results in deposition of unconsolidated

sediments. Large accumulations of these unconsolidated deposits can slide under gravity due to

ground motion during earthquakes. On the La

Palma Island, large amounts of sedimentary

material, primarily gravel mixed with basaltic lava

has accumulated on the western slope due to

erosion of the Taburiente caldera, where a large

surface landslide can occur due to a large
26

earthquake, with the existing volcanic dikes

providing some stabilization to these sediments

(Pararas-Carayannis 2002). The author concluded

that a large monolithic-slope failure of the

dimensions suggested by Ward and Day (2001) is

unlikely. A review of some other mechanisms also

resulted in the same conclusion (PararasCarayannis 2002).

Pararas-Carayannis (2002) also evaluated the slide

kinematics proposed and used by Ward and Day

(2001) for their mega-tsunami simulation. The

author found that the slide was assumed to be a

monolithic rotation along a detachment fault rather

than a turbulent flow of pyroclastic and pillow-lava

material of large sizes. The monolithic-slide model

also ignored the effect of cohesion among the

particles within the mass that would resist

movement and the effects of water turbulence

behind the mass that would slow down the slide

velocity. Rotational movement along a detachment

fault should also be characterized by a reduction in

slope with depth, which was not accounted for in

the slide model of Ward and Day (2001). The

maximum speed of the Grand Banks slide was

estimated (Fine et al. 2005) at about 

37.5–62.5 mi/hr (60–100 km/hr). It consisted of

unconsolidated deposits rapidly moving downslope

as a turbidity current. Ward and Day (2001) used a

maximum slide speed of 328 ft/s (100 m/s), or 

225 mi/hr (360 km/hr), far in excess of the

maximum speed of the Grand Banks slide. PararasCarayannis (2002) argued that the mostly largesized particles composed of pyroclastics and pillow

lava of Cumbre Vieja cannot move as fast as

turbidity currents.

Pararas-Carayannis (2002) stated that the tsunami

generation and propagation model used by Ward

and Day (2001) used several assumptions that

resulted in overestimation of the tsunami wave

heights. The initial waveform was estimated by

Ward and Day (2001) based on a monolithic

122.1 mi3

, or 17,969 billion ft3 (500 km3), block

moving rapidly with a maximum velocity of

328 ft/s (100 m/s) for 37.5 mi (60 km) until it

reached flat ocean bottom at a depth of 13,123 ft

(4000 m). Pararas-Carayannis (2002) argued that

incorrect assumptions leading to exaggerated

source dimensions, slope instabilities, and slide

speeds resulted in overestimation of initial

tsunami-source parameters. The tsunamipropagation model used by Ward and Day (2001)

treated the wave as a shallow-water wave,

ignoring the amplitude attenuation away from the

source (Pararas-Carayannis 2002). Also, as stated

by Mader (2001), even the slide following the

massive flank collapse proposed by Ward and Day

(2001), with its overstated source dimensions, will

only generate a short-period wave with a

maximum period of approximately 3 to 4 minutes,

which will behave as an intermediate wave rather

than a shallow water wave. Shallow-water waves

undergo a geometric spreading, but not the

significant wavelength-dependent dispersion

(Pararas-Carayannis 2002) that characteristically

affects shorter-period waves.

Wynn and Masson (2003) pointed out that the

understanding of the initial stages of a landslide,

which influence its tsunamigenic characteristics, is

limited. Therefore, models of landslide-generated

tsunamis remain highly dependent on poorly

defined landslide parameters. The authors suggest

that this understanding may be improved by

studying the turbidite(a) deposits that are directly

linked to known volcanic-island landslides.

Wynn and Masson (2003) obtained piston cores

from two sites in the Agadir Basin, located about

187.5 mi (300 km) north of the Canary Islands, at

a water depth of approximately 14,764 ft

(4500 m). In the core sequences, the two youngest

turbidites rich in volcanic material are correlated

with the two most recent landslides on the Canary

Islands. The correlations were made using dating

of the turbidites, mineralogy of the turbidites,

geochemical data, and analysis of seafloor

morphology to define pathways of the turbidity

(a) Sedimentary deposits formed by turbidity currents

in deep water at the base of the continental slope

and on the abyssal plain, first described by Bouma

(1962).
27

currents. Both sequences showed layered deposits

with layers of fine particles located higher in the

sequences. The layer near the bottom, which

contained the coarsest material, was the thickest. 

The two turbidites were separated from other

turbidites by well-defined layers of pelagic or

hemipelagic(a) sediment layers indicating separation

of the deposition time of the turbidites of 

1000 years or greater. Within each turbidite, no

pelagic or hemipelagic sediment layers occur. 

Bioturbation(b) occurs in both turbidites, and the

extent of bioturbation decreases downward within

the turbidite. Based on these observed features of

the turbidites, Wynn and Masson (2003) concluded

that the layers within the turbidites were not

separated by substantially large time intervals, and,

therefore, are all linked to the same turbidity-flow

event. Wynn and Masson (2003) tentatively

suggested that the layers within the turbidites

linked to Canary Island landslides represent

multiple stages of failure of a single landslide

event. The turbidite correlated to the El Golfo

landslide on the northwest flank of the El Hierro

island exhibited three layers; the turbidite

correlated to the Icod landslide on the north flank

of the Tenerife island showed nine layers. The

authors interpreted the three layers of the first

turbidite as indicative of a three-stage failure of the

El Golfo landslide, and the nine layers of the

second turbidite as indicative of a nine-stage failure

of the Icod landslide. The authors also examined

and discounted other possible explanations for

layering of the turbidites, including flow reflection

from basin margins or seamounts, flow surging or

eddy formation, and transport through multiple

channels. The authors also estimated that each

layer would take at least two days to deposit based 

on an analysis of the grain sizes, the thickness of

the layers, and the settling velocity of fine-grained

sediment.

Wynn and Masson (2003) also attempted to assess

the mechanism that created the individual turbidity

currents that resulted in the layering of the

(Masson et al. 2002), an argument could be made

that the sediment was deposited by a single event. 

As demonstrated by the summary of current

research literature, the study of tsunamigenic

landslides, although advancing rapidly, is not

sufficiently mature to provide readily applicable

engineering solutions. Each phase of a tsunami

generated by a landslide should be studied with the

help of experts in this area on a case-by-case basis,

as required at a proposed nuclear power plant site.

(a) Pelagic sediments are of marine origin that

accumulation in deep abyssal plains far from

terrestrial sources of sediments; hemipelagic

sediments consist of both terrestrial and marine

sediments and occur closer to the continents.

(b) Bioturbation refers to the mixing of benthic flora

and fauna with sediment particles.
28
29

2 HIERARCHICAL HAZARD ASSESSMENT APPROACH

2.1 Introduction

A hierarchical-assessment approach consists of a

series of stepwise, progressively more refined

analyses to evaluate the hazard resulting from a

phenomena at a given nuclear power plant site. If

the safety of a nuclear power plant can be demonstrated by a simple and bounding analysis, the

resources and time required by more-refined

assessment methods can be saved. However, the

simpler analysis should meet the requirements of

GDC 2 and all other applicable Nuclear

Regulatory Commission regulations.

With respect to tsunamis, the hierarchical-hazardassessment approach could be considered as a

series of three steps:

1. Is the site region subject to tsunamis?

2. Is the plant site affected by tsunamis?

3. What are the hazards posed to safety of the

plant by tsunamis?

The first step above can also be regarded as a

regional screening test. If the site region is not

subject to tsunamis, no further analysis for tsunami

hazards is required. Absence of credible

tsunamigenic sources in the site region may result

in a determination that the site region is not

subject to tsunamis. However, this finding should

be supported by region-specific evidence. If the

answer to the first question is affirmative or

undetermined—based on available information—

an analysis of the tsunami hazard is required (i.e.,

the second step of the hierarchical-assessment

approach should be performed).

The second step can be regarded as a sitescreening test. This step determines whether

safety system control important to safety of the

plant are exposed to hazards from tsunamis. It

may be possible to determine that, even though the

general site region is subject to tsunamis, the plant

itself is sited and designed in such a way that its

safety is not affected. For example, if all SSC

important to safety of the plant are located at an

elevation above the maximum wave runup due to

the PMT, more specific tsunami-flooding

assessment may not be needed for the site.

The third step is the most refined assessment, in

which site-specific analyses are carried out to

determine hazards posed by the PMT to the SSC

important to safety of the plant and to determine

whether any protection is required. This step

involves postulation of PMT source mechanisms,

estimation of PMT source characteristics,

initiation of the PMT wave, propagation of the

PMT wave from the source toward the site, and

estimation of tsunami hazards at the site.

The term tsunami typically relates to an oceanic

tsunami generated by submarine seismic,

landslide, or volcanic sources. However, tsunamilike waves can also be generated in inland water

bodies by subaerial landslides and seismic causes

[e.g., the 1811–1812 tsunami-like waves caused

by the New Madrid earthquakes on the Mississippi

River (Lockridge et al. 2002); the potential of a

tsunami caused by earthquakes in Lake Tahoe

(Ichinose et al. 2000); the tsunami in Spirit Lake

during the May 18, 1980, eruption of Mount St.

Helens (USGS 2007)]. The regional screening test

should consider the likelihood of occurrence of a

tsunami or a tsunami-like wave in a water body

near the nuclear power plant site.

2.2 Regional Screening Test

A regional survey and assessment of tsunamigenic

sources should be performed to determine the

potential that a tsunami may pose a hazard to the

site. Significant hazards to the site may arise both

from near-field and far-field tsunamis. The
30

regional survey and assessment should include all

potential far-field sources and mechanisms that

generate tsunamis.

Nuclear power plant sites in the United States can

generally be classified into two categories: coastal

sites (located on or near a coastline) and inland

sites (located at significant distance from the

coastline). Coastal sites should consider hazards

from oceanic tsunamis; inland sites should

consider the possibility of a tsunami-like wave in

water bodies in the region.

The regional screening test involves the following

steps:

1. a comprehensive search for historical and

paleotsunami records in the region

2. in the absence of historical tsunami records, a

comprehensive search for potential

tsunamigenic sources and the potential for

tsunami generation in nearby water bodies.

Sources of historical and paleotsunami data are

described in Chapter 4, Databases and Data

Collection, of this report. A comprehensive search

of these national and international (where needed)

data repositories should be carried out to list all

historical tsunamis that occurred in the region. 

When available, wave height, inundation extent,

runup, and drawdown associated with these events

should be described. Paleotsunami data and inferences drawn by experts from these data should

also be included in the report because these datasets extend the historical record and may include

events more severe than those actually recorded.

The fact that no historical tsunami records can be

found for a region does not necessarily result in a

conclusion that the region is free of tsunami

hazards. A comprehensive search for potential

tsunamigenic sources that may create a tsunami in

regional water bodies should be carried out. An

example of such a study is described by González

et al. (2003).

2.3 Site Screening Test

One possible way to answer the question in the

second step of the hierarchical-assessment

approach described above is to use a site-screening

test to compare the location of the plant site with

the area affected by tsunamis in the region. 

Figure 2-1 shows three possible locations of a

plant located near a coast. Location 1 could be

safe if the horizontal extent of inundation caused

by the probable maximum tsunami was less than

the horizontal distance (D). The horizontal extent

of inundation varies depending on the

characteristics of the tsunami waves, shoreline,

and beach geometry and topography, and the

effective obstruction to the inland flow of tsunami

waves on the shore. According to the NGDC

historical tsunami database (NGDC 2007), the

maximum horizontal extent of inundation is listed

as 3.4 mi (5.5 km) for the December 26, 2004,

Indian Ocean tsunami on the island of Sumatra,

Indonesia. Anecdotal evidence indicates that the

maximum extent of horizontal inundation on the

island may have reached 5.0 mi (8.0 km).
31

Figure 2-1. The DLZ screening rule.

Location 2, located on a river near an estuary,

could be safe if the backwater effects or bores

induced by the PMT affected areas in extent less

than the longitudinal distance (L) measured along

the river. Bores can be induced by a tsunami

(Koch and Chanson 2005) and were observed in

Hawaii in 1946, in Japan in 1983 and 2003, and in

Thailand, Malaysia, and Sri Lanka in 2004. Bores

propagating upstream from the mouth of a river

may be caused by tsunamis under favorable

hydraulic conditions and can travel upstream

several tens of miles (km) from the estuary
32

(Chanson 2005). Bores are similar to traveling

hydraulic jumps that move upstream. The

downstream part of the bore is characterized by

subcritical flow with greater depth of flow and the

upstream part is supercritical. The river should be

able to support supercritical flow to form the bore.

Location 3, a site located on the coast, could be

safe if the runup caused by the PMT did not reach

its grade elevation (Z) and all SSC important to

safety of the plant are located at or above this

grade elevation. In the NGDC historical tsunami

database, the runup is defined as the maximum

ground elevation that the tsunami waves reach

inland from the shore. The maximum runup

reported in the NGDC historical tsunami runup

database, 1720 ft (524 m), is associated with the

massive 1958 Lituya Bay subaerial landslide

[more than 1 billion cubic ft (30 million cubic m)

in volume] and tsunami (Miller 1960). The

database contains runup heights of 820 ft (250 m)

and 738 ft (225 m) above the surface of the Spirit

Lake on the west and east arms of the lake caused

by the collapse of the upper 1500 ft (460 m) of the

dome of Mount St. Helens and subsequent gigantic

debris fall into the lake (Waitt and Pierson 1994). 

The Lituya Bay slide occurred on one slope of a

narrow bay, causing the unusually high runup on

the opposite slope. The enormous debris fall from

collapse of the Mount St. Helens dome was the

cause of the unusually high runups in Spirit Lake. 

Oceanic tsunamis have caused runups as high as

328 ft (100 m) in Indonesia (Banda Sea earthquake

and tsunami of 1674). The maximum runup

caused by the 2004 Sumatra tsunami was 167 ft

(50.9 m), observed on the Sumatra island.

The preceding discussion clarifies that the severity

of tsunami hazards is strongly affected by local

characteristics. Therefore, accurate estimation of

hazards posed by tsunamis to a nuclear power

plant site requires site-specific analyses. 

However, it is also clear that unusually high

tsunami runups have only been recorded for

unusually rare events (e.g., Lituya Bay and Spirit

Lake tsunamis). If these extremely rare events are

excluded, even the largest historical tsunamis do

not exceed runup of approximately 328 ft (100 m)

and do not inundate areas more than a few miles

(km) inland from the shore. Also, tsunamiinduced bores do not travel more than a few tens

of miles (km) upstream from the mouth of a river. 

Therefore, it may be possible to screen sites based

on a combination of historical record, site-specific

geophysical and topographical data, and sound

engineering judgment. Detailed site-specific

tsunami hazards assessments should be completed

for sites that would be affected by tsunamis and

for sites for which a conclusive determination

cannot be made that they are free of tsunami

hazards.

A situation similar to that shown in Figure 2-1

may also exist for inland sites located near a body

of water in which a tsunami may be caused by

seismic, landslide, or volcanic sources. The DLZ

rule may still be applied to the inland sites to

determine if the site is safe from the hazards posed

by tsunamis.

2.4 Detailed Tsunami Hazard

Assessment

If the site-screening test does not establish the

safety of the nuclear power plant site from hazards

posed by tsunamis, a detailed assessment of these

hazards should be undertaken to ensure that the

plant design bases adequately account for these

hazards.

A companion to this report is the National Oceanic

and Atmospheric Administration Pacific Marine

Environmental Laboratory (PMEL) Technical

Memorandum OAR PMEL-136, titled “Scientific

and Technical Issues in Tsunami Hazard

Assessment of Nuclear Power Plant Sites”

(González et al. 2007), which describes the stateof-the-art in tsunami-hazard assessment, including

data sources, paleotsunami identification

approaches, and tsunami propagation and

inundation simulation. González et al. (2007)

should be used as a reference for technical bases

for a detailed tsunami-hazard assessment.
33

2.5 Site Investigation

For a detailed tsunami-hazard assessment at a site

of interest, a thorough investigation is needed to

establish the history of tsunamis at a given nuclear

power plant site and to collect site-specific data

required for estimation of the hazard metrics. 

These investigations should lead to the determination of historically recorded tsunamis and compilation of known pre-historical records. An

analysis of all tsunami data should be carried out

to determine the potential mechanisms that may

generate a tsunami capable of affecting the site. 

The analysis should also specify tsunami characteristics and the corresponding damage at the

site. The frequency and severity of tsunamis at the

site from historical and prehistorical data should

be estimated.

Because both near- and far-field tsunamis require

investigation, the compilation of historical

observations and prehistorical data may need to

access international databases as well as those

archived and maintained in the United States.

2.5.1 Historical Tsunami Records

The first step in site investigation is establishing

the history of tsunamis at and near the proposed

site. All available historical data related to

tsunamis should be collected. Where available,

these data should include information regarding

1. date and time of occurrence

2. source mechanism

3. source location

4. source parameters

5. wave height on bottom pressure gauge and

tide records

6. tidal records or ambient water levels at the

time of tsunami arrival

7. tsunami runup

8. tsunami inundation (horizontal distance the

waves reached from the shore)

9. damages caused.

The NGDC historical tsunami database is the most

comprehensive compilation of tsunami events. 

The database should be searched for historical

events in the vicinity of the site. The NGDC

tsunami database also provides metadata regarding

the tsunami events and references to where these

events were first reported or analyzed. The metadata often hold much additional information about

the nature of tsunami observation, the source

mechanism, and damages caused by the event. A

careful review of the metadata and references cited

should also be compiled for the site of interest.

Some of the tsunami-like events are also listed as

seiches in the NGDC database. These events can

be selected using the “type of measurement”

search criteria set to “seiche.” Tsunami events

caused by volcanic activity are cross-linked to the

NGDC volcanoes database, which can provide

additional information regarding the tsunamigenic

volcanic activity.

Seismic activity can trigger landslides, and

tsunamis can be generated by both these source

mechanisms and may arrive at a site within a short

period of time. The NGDC database should be

queried for such events, and all references listed in

the metadata should be searched to determine the

sequence of events. These records, even if

anecdotal, can provide significant information

regarding concurrence of source mechanisms and

consequent enhancement of tsunami impacts at the

site.

Based on the collected historical data, tsunami

activity at and near the site should be thoroughly

described. This description should list all

observed source mechanisms, the ranges of source

parameters and characteristics, the ranges of

tsunami runup and inundation, and the extent of

damage suffered.
34

2.5.2 Paleotsunami Evidence

Because the recorded history of tsunamis in the

United States is relatively short, there are

insufficient data related to, indeed even complete

absence of, tsunami activity, depending on the

location of the site. The problem is exacerbated

because large and destructive tsunamis are

relatively infrequent events. One way to supplement the relatively short observed record is the

evidence provided by paleotsunami data (see

Chapter 3 of González et al. 2007).

At this time, no central database of paleotsunami

information for use in the United States exists. 

One such effort is described by Peters et al. (2003)

that focuses on the Pacific Northwest coast and the

tsunamis originating in the Cascadia subduction

zone.

It may be necessary to carry out a site-specific data

collection to seek geologic evidence of tsunamis

near the proposed nuclear power plant site. In

general, sites within approximately 62.5 mi 

(100 km) of the coast should be searched for

tsunami and boulder deposits in locations likely to

preserve tsunami deposits, such as coastal marshes

and shallow lakes. However, expert assistance

may be needed for this search and subsequent

interpretation of the candidate deposits (González

et al. 2007).

2.5.3 Regional Tsunami Assessments

A regional tsunami-hazard assessment, previously

carried out by other responsible agencies, may be

available for areas that are frequently subject to

tsunamis. A thorough search should be carried out

to identify and evaluate the applicability of such

assessments to the proposed nuclear power plant

site. Most tsunami-hazard-assessment studies are

carried out from the point of view of flooding

hazard from inundation and potential for loss of

life and damage to property and infrastructure. 

The tsunami hazards assessment for a nuclear

power plant site needs to address several aspects

of the hazard from tsunamis (see Chapters 3 and 5

of this report). The existing regional tsunamihazard assessment may be used as a starting point

for a more focused site-specific assessment.

González et al. (2006) describe a pilot study of

tsunami hazards to update Federal Emergency

Management Agency flood hazards maps for

Seaside, Oregon (see Appendix D of González

et al. 2007).

The González et al. (2006) study was carried out

for the area near the towns of Seaside and Gearhart

on the Oregon coastline. This area was chosen for

the study because it is similar to many coastal

communities and because there was a strong local

interest in such a study. The study developed two

inundation maps, one for the 100-year-returnperiod tsunami and the other for the 500-yearreturn-period tsunami. The components of the

study were:

1. source specification: based on literature

review and consultation with tsunami experts,

a database of quantitative probabilistic models

of local and far-field earthquake tsunami

sources in the Cascadia, Alaska-Aleutian, and

Peru-Chile subduction zones was developed

2. data acquisition: a paleotsunami deposit

mapping and interpretation study was carried

out, along with acquisition of historical

records and eyewitness accounts

3. model development: a new, high-resolution

digital elevation model (DEM) based on the

latest available topography, bathymetry, and

tidal information was developed. A sitespecific tsunami inundation model was

developed and tested with available tsunami

observations, including paleotsunami data,

historical records, and eyewitness reports

4. probabilistic tsunami hazard estimation

5. study-specific database development

6. analysis and interpretation of tsunami impacts.

In the context of tsunami-hazard assessment at

proposed nuclear power plants for determination

of safety, a similar procedure may need to be

adopted, with the notable exception of the use of a
35

PMT in the place of a chosen return period to

specify the design tsunami and the corresponding

probabilistic hazard estimation. Also, the

González et al. (2006) study only used earthquake

sources for tsunami generation. The tsunamihazard assessment at a proposed nuclear power

plant site will also need to include landslide and

volcanic sources.

As illustrated above, regional tsunami-hazard

assessment studies should be carefully evaluated

to ascertain their applicability to tsunami-hazard

assessment at a proposed nuclear power plant site. 

These studies can serve as a starting point, and

may provide valuable sources of data focused on

the needs of the safety determination at the site.

2.5.4 Site-Specific Tsunami Mechanisms

For a proposed nuclear power plant site, a

thorough search should be undertaken to catalog

sources of all known (observed historical tsunami

event or thoroughly analyzed and agreed-on

paleotsunami record) and proposed (based on

paleotsunami evidence) tsunami events at and near

the site. These sources should include both nearand far-field sources. All three tsunamigenic

source mechanisms should be investigated.

For each source mechanism, a list of candidate

tsunamigenic sources should be created. 

Information on source parameters should be

collected using literature surveys and contacting

agencies and organizations with relevant expertise. 

Experts in the relevant fields may need to be

consulted for estimation of parameters when no

published values exist. Sources known to have

generated tsunamis in the past should already be

available from the compilation of historical

tsunami records recommended by Section 1.4.1. 

The observed tsunami data and known or

estimated parameters of these known sources

should be used to validate tsunami-simulation

models.

In addition to compiling the parameters (known or

estimated), particular attention should be given to

the orientation of the source with respect to the

proposed nuclear power plant site. The orientation

of the source, particularly landslides, can strongly

affect the directivity of the tsunami waves. 

Therefore, even a relatively moderately strong

tsunamigenic source may result in a greater hazard

to the site than a stronger source that is not

optimally oriented to the site of interest. 

Similarly, particular attention should be paid to

sources near the site because any generated

tsunami waves from these sources would have

little attenuation compared to waves that travel to

the site from a great distance. Source parameters

that are important for tsunami generation and

subsequent hazard estimation are described in

Chapter 5 of this report.

2.5.5 Site-Specific Data

Site-specific geospatial and geophysical data are

required for accurate simulation of the near-shore

dynamics of tsunami waves and the estimation of

tsunami-hazard metrics. A selection of these

hazard metrics are described in Section 5.4 of this

report. Site-specific geospatial data that are

required for accurate simulation of the tsunamiwave dynamics primarily consist of fine-scale

maps of near-shore topography and bathymetry. 

Data sources for topography and bathymetry are

described in Section 4.2 of this report. Sitespecific geophysical data are related to

specification of tsunamigenic source characteristics and to estimation of tsunami-hazard

metrics. Tsunamigenic source characteristics are

described in Section 5.3 of this report.

37

3 EFFECTS OF TSUNAMI AT A NUCLEAR

POWER PLANT SITE

3.1 Introduction

Tsunamis can result in a severe hazard to safetyrelated cooling-water systems as well as other SSC

important to safety of a nuclear power plant. The

primary effect of the tsunami waves on a plant site

is flooding (directly from tsunami waves, or from

backwater effects or tidal bores caused upstream

from the mouth of a river, depending on the

location of the site) and loss of cooling water (due

to dry intakes during drawdown caused be

receding tsunami waves). However, there are also

several other effects, mainly from hydrodynamic

forces that can cause severe damage to structures

and the foundations of these structures. If any of

these structures are safety-related, they should be

designed to withstand these effects or be protected

adequately from these effects to ensure the safety of

the nuclear power plant.

3.2 Flooding Due to Runup

The most obvious hazard from a tsunami is

flooding. As the tsunami waves approach the

shoreline, they increase in amplitude and reduce in

wavelength. The waves, depending on local

bathymetry and topography, can inundate significantly large areas inland from the shoreline. The

maximum ground elevation that the inundating

waves reach is called the runup.

The protection from flooding effects of tsunami

waves can be provided in a manner similar to

other flooding mechanisms: either the SSC

important to safety can be located above the

maximum runup due to the PMT or adequate

flooding protection for the SSC important to safety

can be provided to ensure that function is not

compromised. Belts of trees and mangroves

provide barriers to tsunami by effectively

increasing frictional resistance to wave runup. 

The feasibility and effectiveness of such measures

should be investigated.

3.3 Dry Intakes During Drawdown

During recession of the tsunami waves (alternatively, approach of the depression wave), water

level at the shoreline is lowered. The amount of

lowering depends on local bathymetry. The areal

extent of recession can be significantly large. 

Nuclear power plants that depend on an intake or

intakes that are located offshore for their safetyrelated cooling water needs should ensure that the

maximum extent of recession and the accompanying lowering of the water level near the intake

location do not result in dry intakes.

Protection from receding tsunami waves can be

provided in a manner similar to other low-water

mechanisms: either the safety-related intakes can

be located sufficiently away from the shoreline

and in deeper waters that the recession and the

accompanying lowering of the water level does

not result in dry intakes, or alternative sources of

safety-related water supply can be made available

that are independent of the water body that is

affected by the receding tsunami waves.

3.4 Scouring

The behavior of the tsunami waves in shallow

waters near the shore is very complex. Tonkin

et al. (2003) carried out experiments to investigate

the scouring effects of tsunamis around cylindrical

structures. They found that the scouring at the

front (facing the oncoming waves) of the cylinder

could be explained by a standard shear-stress

model. However, they also observed rapid

scouring in the sand substrate at the back of the

cylinder at the end of the tsunami drawdown,

when flow velocity was decreasing rapidly. This
38

rapid scour created the largest and deepest scour

holes. The investigators proposed that the

observed scour at the back of the cylinder may be

explained by considering the effects of pore

pressures in the substrate during the tsunami. The

rapidly decreasing water level at the end of the

tsunami drawdown may create large-pore pressure

gradients, resulting in a buoyant force on the

substrate. When these buoyant forces are large

enough to decrease the effective normal load

substantially and result in loss of shear strength,

even low-flow velocities of the tsunami currents

may result in rapid scouring. In extreme cases, a

complete loss of shear strength may occur, leading

to liquefaction of the substrate.

A nuclear power plant that locates any safetyrelated structures, particularly a safety-related

intake structure, where tsunami currents may

potentially result in scouring and the resulting

damage to the foundations of such structures,

should ensure that the structures are adequately

designed to resist the scouring forces of tsunamis. 

An obvious alternative is to provide a source of

safety-related cooling water that is independent of

the water body experiencing the tsunami and,

therefore, is not exposed to the scouring effects of

tsunamis.

3.5 Deposition

Tsunami currents near the shoreline are highly

turbulent, capable of carrying debris and sediment. 

As the waves recede, the sediment and debris can

be deposited at and near the shoreline. For a

nuclear power plant, all SSC important to safety

should be located and designed such that they are

not affected by the deposition of debris and

sediment from tsunami waves and currents.

3.6 Hydrostatic and

Hydrodynamic Forces

Hydrostatic force acts laterally on structures. It

can result from standing water resulting from

tsunami inundation or from interaction of tsunami

water moving slowly and encountering the

structures.

Hydrostatic forces will also be experienced by

intake structures that are located offshore. The

intake structure may experience a cyclic hydrostatic loading as tsunami waves pass over it. The

hydrostatic pressure during the passage of a crest

will be higher and lower during passage of a

trough due to normal still-water level (Yeh et al.

2005).

Hydrodynamic forces result from rapidly moving

water and its interaction with structures. On-shore

structures may experience impacts on the sides

facing the oncoming wave, drag forces on the

sides, and suction on the downstream end of the

structure (Yeh et al. 2005).

Yeh et al. (2005) provide a set of generalized

expressions for wave and flood loads on structures. These include expressions for hydrostatic

force, buoyant force, hydrodynamic force, surge

force, impact force, and breaking-wave forces. 

Loading combinations are also described. 

Evaluation of tsunami loadings on a reinforced

concrete building is also provided (see the

appendix in Yeh et al. 2005).

3.7 Debris and Projectiles

Tsunamis are capable of dislodging and transporting a wide range of debris from sediment to

large boulders (Mastronuzzi and Sanso 2000) to

other water-borne projectiles (automobiles, trees,

boats, etc.). Debris and projectiles can compound

the impacts on structures. Yeh et al. (2005)

describe the behavior of water-borne projectiles. 

Projectiles are considered to impact the structures

at the same elevation as the water-surface level. 

The uncertainty in the estimation of the duration of

the impact is thought to be the most likely cause of

errors in the estimation of the impact forces. The

duration of impact forces, however, are affected

primarily by the natural frequency of the structures

(Chopra 1995).
39

Adequate design criteria should be employed for

SSC important to safety exposed to impacts from

water-borne debris and projectiles. An alternative

is to locate SSCs so that they will not be exposed

to water-borne debris and projectiles.

3.8 Tidal Bores

Tidal bores are similar to traveling hydraulic

jumps that move upstream from the mouth of the

river. They are generally caused by a rapid and

large change in the downstream water-surface

elevation (Chanson 2005; Koch and Chanson

2005).

Tidal bores can be induced by a tsunami (Koch

and Chanson 2005), and were observed in Hawaii

in 1946, in Japan in 1983 and 2003, and in

Thailand, Malaysia, and Sri Lanka in 2004. Tidal

bores propagating upstream from the mouth of a

river may be caused by tsunamis under favorable

hydraulic conditions and can travel upstream

several tens of miles (km) from the estuary

(Chanson 2005). The downstream part of the bore

is characterized by subcritical flow with greater

depth of flow, and the upstream part is supercritical. The river should be able to support

supercritical flow to form the bore.

The effect of a tidal bore propagating upstream to

a nuclear power plant site is similar to a flood

wave propagating downstream. This may result in

flooding of the site depending on the height of the

bore. Bores dissipate as they travel upstream. If

the site is sufficiently far away from the estuary,

the bore may not flood the site. Siting and

protection criteria for tidal bore are similar to

those for other flooding mechanisms.

41

4 DATABASES AND DATA COLLECTION

4.1 Introduction

In the United States, tsunami records are archived

by the NGDC, which is one of the three environmental data centers within the National Environmental Satellite, Data, and Information Service. 

The NGDC also operated World Data Centers for

Marine Geology and Geophysics and Solid Earth

Geophysics. Together, WDC and NGDC acquire,

process, and distribute global marine and terrestrial data. They also have a role in post-event data

collection of tsunami sources and effects that

supports modeling, engineering, planning, and

educational goals.

The primary access to the NGDC data archive is

via the internet at http://www.ngdc.noaa.gov. This

website archives data on natural hazards

(earthquakes, tsunamis, and volcanoes), marine

geology and geophysics (including ocean drilling

data, well logs, grain size data, and sediment

thickness), and bathymetry and topography data

[including combined bathymetry and topography

datasets, multibeam data, National Ocean Service

(NOS) hydrographic surveys, and global relief

data (ETOPO2, ETOPO5, etc.)].

4.2 Topography and Bathymetry

One of the most important datasets for use in

tsunami modeling is bathymetry and topography. 

Tsunami waves travel at different speeds in waters

of different depths, and, therefore, the wave front

is modified as the waves propagate in a water

body with varying depth. In deep waters where

the tsunami waves have long wavelengths, the grid

points needed to resolve the wavelength in

numerical models can be spaced far apart; therefore, a relatively low resolution relief data may be

used (e.g., the 2 and 5 arc-second digital global

relief datasets ETOPO2 and ETOPO5) without

compromising the accuracy of model predictions. 

However, in shallower waters, the wavelength of

the tsunami waves shorten. Thus, accurate and

high-resolution relief data are needed (e.g., highresolution NOS surveys) to resolve the wave and

to ensure accuracy of model predictions. 

Topography data may be even more important

because inundation models typically have the most

uncertainty in their predictions.

4.2.1 Topography Data

Digital topography data have traditionally been

created, verified, and distributed by the USGS

(http://edc.usgs.gov/geodata/). The USGS topography data are available at 1:24,000 scale for

7.5-min quadrangles. The digital data are also

available at 32.8-ft (10-m) horizontal resolution

with a nominal vertical accuracy of 3.3 ft (1 m). 

Traditionally, USGS digital topographic data do

not extend below the surface of the water into

water bodies. Areas covered by the water bodies

are typically shown at some nominal constant

elevation above the mean sea level.

Currently, the best quality digital topographic data

can be created using airborne light detection and

ranging (LiDAR) technology. LiDAR is an active

imaging system similar to a radar. It transmits

laser pulses to a target and measures the time for

the signal to be reflected back to the sensor. The

LiDAR-mapping flights are usually flown at

altitudes of 1000–6500 ft (300–2000 m) and use

near-infrared light (1.045–1.065 μm). Areas

approximately 70 percent of the altitude in width

can be covered. Horizontal resolutions as small as

2.5 ft (0.75 m) with a horizontal accuracy of

approximately 3.3 ft (1 m) can be obtained. The

vertical accuracy can be approximately 0.5 ft

(0.15 m). However, in many cases, dedicated

LiDAR mapping may be required to obtain such

data, and costs can be significant.

The NOAA Coastal Services Center (CSC)

acquires high-resolution topographic data using

remote sensing under the topographic-change
42

mapping project since 2001 (see the website at 

http://www.csc.noaa.gov/crs/tcm/). The topographic-change mapping project followed the

Airborne LiDAR Assessment of Coastal Erosion

(ALACE) project, a partnership between the

NOAA CSC, the National Aeronautics and Space

Administration Observational Sciences Branch,

and the USGS Center for Coastal Geology, that

collected LiDAR data along the U.S. coastline

from 1996 until 2000 using the NASA Airborne

Topographic Mapper sensor. The NOAA CSC

distributes digital elevation data derived from two

sensing technologies: LiDAR and IfSAR or

InSAR, the Interferometric Synthetic Aperture

Radar, which uses radar pulses. The data can be

found at the CSC website

(http://maps.csc.noaa.gov/TCM/).

4.2.2 Bathymetry Data

Digital global relief data are available from the

NGDC at two resolutions: 2 arc-seconds

(ETOPO2v2 dataset published in June 2006) and 

5 arc-seconds (ETOPO5). The dataset covers the

whole globe from -90to +90in latitude and -

180to +180in longitude. Both the cellcentered version (where the cell boundaries are

lines of even minutes of latitude and longitude,

centered on intersections of lines of odd minutes

of latitude and longitude; a grid of 5400 rows and

10,800 columns) and the grid-centered version

(where the cell boundaries are lines of odd minutes

of latitude and longitude centered on intersections

of lines of even minutes of latitude and longitude;

a grid of 5401 rows and 10,801 columns) are

available. Subsets of these datasets may be used

for tsunami propagation modeling for far-field

tsunamis.

The NOS hydrographic database (NOSHDB) is

maintained by the NGDC and is located at the its

website

(http://www.ngdc.noaa.gov/mgg/bathymetry/hydr

o.html). The NOSHDB provides extensive

coverage of coastal waters and exclusive economic

zones of the United States and its territories. 

Initially, the database was created by digitizing the

sheets of hydrographic surveys completed between

1851 and 1965. Since 1965, NOS survey vessels

have acquired data digitally. The database is

available for interactive search and download on

the internet at

http://map.ngdc.noaa.gov/website/mgg/nos_hydro/

viewer.htm. The database may also be obtained as

a stand-alone set of DVD-ROMs or CD-ROMs

with included search software. Data for the nearshore inundation modeling domain may be

downloaded for creation of a computational grid

for a particular site. Depending on the capabilities

of the tsunami-simulation software, NOSHDB

data may be used to create nested grids within the

ETOPO2v2 grid for propagation and inundation

simulations.

The NGDC is also developing high-resolution

combined bathymetry and topography DEM for

applications of the Method of Splitting Tsunamis

(MOST) model

(http://www.ngdc.noaa.gov/mgg/inundation/tsuna

mi/general.html). These DEMs are being

developed using the best digital available data

from federal and state agencies, academic

institutions, and private companies.

Various sources of data are merged and supplemented when required by additional handdigitized data. A set of quality-control checks is

carried out for consistency of the final DEM to

remove artifacts. Several DEM grids on the East

Coast (Virginia Beach, Virginia; Savannah,

Georgia; Myrtle Beach, South Carolina; Cape

Hatteras, North Carolina; San Juan and Mayaguez,

Puerto Rico), the coast of Alaska (Dutch Harbor

and Sand Point), the Gulf Coast (Panama City,

Florida), and the West Coast (Port San Luis,

California) are already completed. The cell size of

these DEMs is 1/3 arc-second [approximately 

32.8 ft (10 m)].

Multibeam bathymetry data are available from the

NGDC, which is the national archive in the United

States

(http://www.ngdc.noaa.gov/mgg/bathymetry/multi

beam.html). The NGDC database contains over
43

1.6 million nautical miles (3 million km) of ship

trackline data and hydrographic multibeam survey

data. Bathymetric grids, three-dimensional

images, and data can be downloaded from the

NGDC. Several other sources of multibeam data

also exist: the Canadian marine multibeam

bathymetric data

(http://gdr.nrcan.gc.ca/multibath/index_e.php), the

Woods Hole Oceanographic Institution multibeam

bathymetry data

(http://mbdata.whoi.edu/mbdata.html), and the

Marine Geoscience Data System

(http://www.marine-geo.org/).

Bathymetry data collected using LiDAR and

IfSAR by the NOAA CSC are available from the

CSC (http://maps.csc.noaa.gov/TCM/) archived

from the ALACE project and the continuing

topographic-change mapping project. An

evaluation of various publicly available global

bathymetry datasets is presented by Marks and

Smith (2006).

4.3 Tides and Sea-Level Anomalies

The Center for Operational Oceanographic

Products and Services (CO-OPS) located within

NOAA’s NOS collects, archives, analyzes, and

distributed a variety of oceanic and coastal data,

including historical water-level data via the

National Water Level Program (NWLP). The

NWLP consists of a network of long- and shortterm water-level stations. There are 175 long-term

stations, 261 coastal stations, and 55 Great Lakes

stations for which tide data are available at

http://tidesandcurrents.noaa.gov/station_retrieve.s

html?type=Tide+Data. The database also contains

historical tide data from stations located all over

the world. Data can be retrieved for more than

2700 historical stations.

4.4 Tsunami Wave Heights,

Runup, and Drawdown

The NGDC tsunami-source-event database is

located on the Internet at the website 

http://www.ngdc.noaa.gov/hazard/tsu.shtml. The

tsunami-source-event database is global in extent

and contains information on tsunamis, including

source description and location, date and time of

occurrence, event magnitude, water height, and

corresponding damages. The database can be

searched online for source type, source location,

time periods of interest, runup location, and effects

of the tsunami. More than 2300 events are listed

in the tsunami-source-event database.

The NGDC tsunami-runup database is located on

the Internet at the website

http://www.ngdc.noaa.gov/hazard/tsu_db.shtml. 

Similar to the tsunami-source-event database, the

tsunami-runup database is global in extent. It

contains each runup reported for all tsunamis in

the tsunami-source database as a separate entry. 

For each runup, date and time, country, location,

maximum water height, inundation distance,

tsunami source parameters, and effects of tsunami

runup are stored. More than 9200 runup events

are listed in the database.

The databases allow several search parameters that

can be effectively used to search for historical

tsunami information for a location of interest. 

Metadata stored along with each record also

includes a short description and lists references for

each event and runup. Drawdown is not reported

in the database. Typically, drawdown

observations are difficult to obtain from post-event

surveys and are generally inferred from eyewitness

accounts or, in rare circumstances, from remotesensing images.

4.5 Near-Shore Currents

Near-shore currents can be classified as tidal and

non-tidal currents. Tidal currents are periodic and

follow the tide cycle. Non-tidal currents or ocean

currents include permanent currents in oceanic

circulatory systems. Tidal current data are

measured at several locations on the U.S. coastlines by NOS using Physical Oceanographic

Real-Time System (PORTS), available from

NOAA 
44

(http://tidesandcurrents.noaa.gov/station_retrieve.s

html?type=Current+Data).

Ocean currents are organized flows that persist

over a time period in a geographical location in the

ocean. These currents transport water, heat,

chemicals, and organisms from one part of the

ocean to another. Wind is one of the primary

forces that drive these currents. Wind creates a

surface stress, causing water particles to move. 

Over large distances, the flow is affected by the

Coriolis force. Another cause of oceanic currents

is difference in water density, which depends on

temperature, salinity, and the pressure of

surrounding water. The density differences cause

what is known as thermohaline flow in the oceans. 

Some data related to open ocean currents are

archived at the University of Miami Rosenstiel

School of Marine and Atmospheric Science

(http://oceancurrents.rsmas.miami.edu/).

4.6 Seismic Data

The NGDC earthquake database is located on the

Internet at the website

http://www.ngdc.noaa.gov/hazard/earthqk.shtml. 

It contains data on more than 5000 destructive

earthquakes since 2150 B.C. in a catalog of

significant earthquakes. A significant earthquake

is defined as an earthquake that resulted in

moderate damage ($1 million or more), a

magnitude of 7.5 or more, 10 deaths, a modified

Mercalli intensity(a) of X, or a tsunami. 

The NGDC earthquake-intensity database contains

information on more than 23,000 U.S.

earthquakes, including their locations, magnitudes,

focal depths, and reported damages. The

earthquakes listed in this database span the period

1638 to 1995.

The NGDC also distributes a global CD-ROM

database of over 4 million earthquakes from

2100 B.C. to 1995 A.D. Online databases can be

interactively searched as required for a particular

application.

(a) The modified Mercalli intensity is given in Roman

numerals ranging from I to XII. The values on the

intensity scale are based on a subjective description

of the effects of the earthquake:

I. Not felt except by a very few under especially

favorable circumstances.

II. Felt only by a few persons at rest, especially on upper

floors of buildings. Delicately suspended objects may

swing.

III. Felt quite noticeably indoors, especially on upper

floors of buildings, but many people do not recognize

it as an earthquake. Standing motor cars may rock

slightly. Vibration like passing truck. Duration

estimated.

IV. During the day felt indoors by many, outdoors by

few. At night some awakened. Dishes, windows, and

doors disturbed; walls make creaking sound. 

Sensation like heavy truck striking building. 

Standing motorcars rock noticeably.

V. Felt by nearly everyone; many awakened. Some

dishes, windows, etc., broken; a few instances of

cracked plaster; unstable objects overturned. 

Disturbance of trees, poles, and other tall objects

sometimes noticed. Pendulum clocks may stop.

VI. Felt by all; many frightened and run outdoors. Some

heavy furniture moved; a few instances of fallen

plaster or damaged chimneys. Damage slight.

VII. Everybody runs outdoors. Damage negligible in

buildings of good design and construction slight to

moderate in well built ordinary structures;

considerable in poorly built or badly designed

structures. Some chimneys broken. Noticed by

persons driving motor cars.

VIII. Damage slight in specially designed structures;

considerable in ordinary substantial buildings, with

partial collapse; great in poorly built structures. Panel

walls thrown out of frame structures. Fall of

chimneys, factory stacks, columns, monuments,

walls. Heavy furniture overturned. Sand and mud

ejected in small amounts. Changes in well water. 

Persons driving motor cars disturbed.

IX. Damage considerable in specially designed structures;

well-designed frame structures thrown out of plumb;

great in substantial buildings, with partial collapse. 

Buildings shifted off foundations. Ground cracked

conspicuously. Underground pipes broken.

X. Some well-built wooden structures destroyed; most

masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides

considerable from river banks and steep slopes. 

Shifted sand and mud. Water splashed over banks.

XI. Few, if any (masonry), structures remain standing. 

Bridges destroyed. Broad fissures in ground. 

Underground pipelines completely out of service. 

Earth slumps and land slips in soft ground. Rails bent

greatly.

XII. Damage total. Waves seen on ground surfaces. Lines

of sight and level distorted. Objects thrown upward

into the air.
45

Global earthquake data are also archived at the

USGS National Earthquake Information Center

(http://earthquake.usgs.gov/regional/neic/index.ph

p). The database contains information on

earthquakes from 2000 B.C. through the current

week because it is updated dynamically. The

database can be searched interactively on the

website as required for a given site or region.

4.7 Geophysical Data

In addition to tsunami and earthquake databases,

the NGDC also archives a volcano database

(http://www.ngdc.noaa.gov/hazard/volcano.shtml). 

The significant-volcanic-eruptions database

contains information on more than 400 eruptions

dating from 1750 B.C. The volcano-location

database contains information on more than 

1500 volcanoes. The tsunami database is crosslinked with the volcano database, indicating which

observed tsunamis have a volcanic-source mechanism. The volcano database contains the volcanicexplosivity index, which is one of the source

parameters for a tsunamigenic volcanic event.

Offshore tsunami waves are measured primarily

by bottom pressure gauges that record data in realtime. In the 1980s, NOAA PMEL developed

deep-ocean tsunameters for early detection and

measurement of tsunami waves and application of

this information to a warning system. This project

was called Deep-ocean Assessment and Reporting

of Tsunamis (DART; see

http://nctr.pmel.noaa.gov/Dart/index.html). A

DART system consists of a bottom pressure

recording (BPR) system connected to a surface

buoy for real-time reporting of recorded data. The

system can detect tsunami waves as small as

0.4 in. (1 cm). In December 2006, there were

25 fully functioning DART locations, 20 in the

Pacific Ocean (including five along the U.S. West

Coast and seven along the southern Alaska coast

and Aleutian Islands), four in the Atlantic, and one

in the Gulf of Mexico. There are an additional 14

locations planned for future DART deployment.

The edited BPR data from the DART system and

historical BPRs are available from the NGDC for

the period 1986 to 2004. Real-time DART data

are available from the NOAA National Data Buoy

Center (http://www.ndbc.noaa.gov/dart.shtml).

Currently, no databases (global or regional) are

available that catalog submarine landslides and

their characteristics. As described in Section 2.4

of this report, extensive site-specific geological,

seismic, and geotechnical data, some using

advanced imaging techniques, may be needed to

completely characterize submarine landslides. 

The interpretation of these datasets is also an

advancing area of research. As more accurate and

higher-resolution bathymetry and submarine

geophysical data are compiled, offshore historical

landslides and zones of potential landslides can be

more readily identified (see Mayer 2006; Marks

and Smith 2006). The NGDC tsunami-runup

database can be searched using the cause of the

tsunami parameter set to the mechanism of

interest. Tsunami runups that are attributed to

landslides sometimes contain data regarding the

landslide properties, including extent and volume.

The NGDC also archives a grain-size database of

sea-floor sediments. The database contains over

17,000 sea-floor samples from the Outer Continental Shelf Environmental Assessment Program

(OCSEAP), academic institutions, and the U.S.

Navy. The metadata include the name of the

collecting institution, the ship, the cruise, the

sample identifier, the location, the date of collection, the water depth, the sampling device, the

method of analysis, the weight of the sample, the

sampling interval, and the raw-weight percentages. 

Some of the samples also have texture information

(percentage of sand, silt, and clay) and statistical

measures of grain size, such as mean, median,

standard deviation, skewness, and kurtosis of the

grain-size distribution. The NGDC grain-size

database can be interactively searched at the

website

http://www.ngdc.noaa.gov/mgg_grainsize/index.js

p . For example, a search off the West Coast of

the United States, bounded by a rectangle with
46

latitudes ranging from 32N to 44N and

longitudes ranging from 122W to 130W,

returned four matching cruises and 22 samples.

4.8 Paleotsunami Data

Tsunamis deposit sediment in the runup zone. 

These deposits can be overlain by sediments

brought to the site by other mechanisms and, over

a long period of time, may get buried in the soil

profile. The NGDC is compiling a database of

paleotsunami data (see Appendix A of González

et al. 2007). However, no central repository of

paleotsunami data exists at this time.

Prehistoric tsunamis have been identified based on

the deposits in the Pacific Northwest (Atwater and

Moore 1992; Benson et al. 1997; Peters et al.

2003), in Kamchatka (Pinegina and Bourgeois,

2001; Pinegina et al. 2003), in Japan (Nanayama et

al. 2003), in the North Sea (Dawson et al. 1988),

and in Hawaii (Moore 2000; Moore et al. 1994a,

1994b). Peters et al. (2003) compiled a database

of deposits related to tsunamis in the Cascadia. 

This database contains the location and

sedimentological properties from 59 sites located

in the Pacific Northwest, starting in northern

California and extending to Vancouver Island,

British Columbia. The database references 

52 published studies until the year 2002 that

describe these tsunami deposit sites. The

individual studies cited in the report use several

different criteria to distinguish tsunami deposits,

which usually manifest as anomalous sand layers

in coastal mashes and lacustrine sediments, from

sand layers deposited by other processes, such as

river flooding or storm surges.

Preliminary identification of tsunami deposits is

carried out by searching for layers of sand or

coarse-grained material in outcrops and sediment

cores from environments where deposition of sand

layers is unusual, such as in coastal marshes and in

lakes (Peters et al. 2003). Tsunamis can transport

a variety of sizes of sediment, ranging from sand

particles to large cobbles and boulders. Sand

layers can also be deposited by other processes,

such as storm surges or river flooding, in these

environments. Usually, a combination of key

factors related to the deposited layer are used to

distinguish it as a tsunami deposit. These key

characteristics include biological markers, spatial

distribution of the deposits, sediment characteristics, and geochemistry. The presence of marine

macro and microfossils is used to infer a marine

source for the sediment layer. Progressively

inland thinning and finning of the deposited layer

is often used to suggest a marine surge rather than

river flooding as the mechanism responsible for

these deposits. Composition and texture of sand

grains can be compared with upriver deposits to

distinguish the mechanisms responsible for these

deposits. Geochemical indicators, such as

bromine enrichment, have also been used to

indicate marine source of the deposits.

Usually, it is more difficult to distinguish stormsurge deposits from those due to tsunamis because

both contain marine macro- or microfossils, have

saltwater chemistry, and progressively thin and

fine inland from the shore. The distance from the

shore of the deposits, the presence of several

relatively thick normally graded(a) layers that may

indicate several high-energy tsunami waves, and

the presence of rip-up clasts that also indicate high

energy of the tsunami waves are used to distinguish deposits of tsunami origin.

Association of the sand layer with paleoseismicity

is also used to link a sand layer to a tsunami

source. Coseismic coastal subsidence may

accompany great earthquakes on subduction zones

(Atwater 1996). A buried tsunami sand layer may

be deposited over a layer of marsh peat, which is

then overlain by tidal mud after subsidence.

The database compiled by Peters et al. (2003)

contains data on the age, number of deposits,

sedimentary characteristics, and identifying

features of the Cascadia tsunami deposits. 

(a) Normal grading of a sediment layer refers to

upwards fining in contrast to inverse grading that

refers to an upwards coarsening of sediments
47

Although the focus of the database is on tsunamis

originating in the Cascadia subduction zone, data

related to transoceanic tsunamis have also been

included. However, the authors stated that

tsunami deposits located in the Puget Sound area

that are not believed to be of Cascadia origin were

excluded.

The database is presented as a spreadsheet and a

geographic information system coverage. The

database includes the following information

related to each reported deposit:

1. location: the name of the place where the

tsunami deposit is located, including the name

of the state

2. catalog number: an arbitrary serial number

3. site number: a number assigned to the

deposits, in ascending order with latitude

4. core/section/secondary location: individual

cores from a site that are listed separately are

identified using a core number, or the section

or secondary location number used by the

referenced study

5. latitude and longitude

6. depositional setting: such as a lake, coastal

marsh, freshwater marsh, etc.

7. physiographic setting: such as head of inlet,

coastal lake or marsh, etc.

8. inundation distance: inland from the shore

9. inundation reference: such as open coast,

upriver, etc.

10. elevation above mean sea level

11. barrier elevation: elevation of a barrier that the

tsunami must have crossed to lay the deposit

12. observation/sampling method: method used to

collect the data, such as observation from and

outcrop, the type of coring device used, etc.

13. number of cores/sampling localities at a site

14. number of subsidence events associated with

great earthquakes on the Cascadia subduction

zone, irrespective of their association with

tsunamis

15. number of tsunami events documented at the

site

16. whether coseismic subsidence was present

17. number of tsunami deposits at a site that are

associated with coseismic subsidence

18. number of tsunami deposits at a site that are

not associated with coseismic subsidence

19. event number referring to the tsunami or

subsidence, from youngest to oldest

20. tsunami event number, from youngest to

oldest

21. subsidence event number, from youngest to

oldest

22. amount of subsidence

23. age of deposition in radiocarbon years before

present (usually reported relative to 1950

A.D.)

24. age range: the range of possible ages in

calendar years before present (present taken as

1950 A.D.)

25. correlated date: the date of the event the

deposit is correlated to by the author, or

otherwise accepted

26. method used to determine the age of deposits

27. thickness of the tsunami deposit

28. maximum thickness

29. geometry: gradient, landward thinning, and

continuity of the deposit

30. number of tsunami deposit layers

31. layer thickness

32. layer characteristics, such as texture, grading,

etc.

33. underlying and overlying material

34. lower and upper contacts that bound the

deposit

35. grain size range, distribution, and description

36. textural gradient in the horizontal direction,

such as landward fining or fining away from

the channel

37. textural gradient in the vertical direction

38. sorting, which is a measure of the variability

of grain sizes in the deposit

39. other sedimentary properties described by

authors of the original report

40. minerological composition of sediment grains,

such as presence of quartz, feldspar, or lithics

41. inclusions, such as plant material, shells,

microfossils, artifacts, etc.

42. flow direction as indicated by the deposit

43. microfossils, such as forams and diatoms

44. chemical evidence
48

45. additional description pertaining to the

deposits, the site, or publications that do not fit

other categories

46. reference, including type and date of

publication

47. a reference map of the location.

At this time, no similar sources of paleo-tsunami

data are known that describe other regions of the

United States. It may be necessary to collect sitespecific data using the same methods and

approaches described above. The list of characteristics given above may be used as a starting

point of the inventory of site-specific paleotsunami

characterization.
49

5 PROBABLE MAXIMUM TSUNAMI

5.1 Introduction

Consideration of tsunamis in determination of

safety of a nuclear power plant is required by

Title 10 of the Code of Federal Regulations,

Part 50, Appendix A, General Design Criterion 2,

Design bases for protection against natural

phenomena, which states:

Structures, systems, and components important to safety shall be designed to withstand

the effects of natural phenomena such as

earthquakes, tornadoes, hurricanes, floods,

tsunami, and seiches without loss of capability to perform their safety functions. The

design bases for these structures, systems, and

components shall reflect: (1) Appropriate

consideration of the most severe of the natural

phenomena that have been historically

reported for the site and surrounding area,

with sufficient margin for the limited

accuracy, quantity, and period of time in

which the historical data have been accumulated, (2) appropriate combinations of the

effects of normal and accident conditions with

the effects of the natural phenomena and

(3) the importance of the safety functions to be

performed. (Emphasis added.)

The PMT is not estimated using a probabilistic

approach. It is, on the contrary, a deterministic

approach that incorporates ideas of transposition

and maximization, similar to the methods adopted

by the National Oceanic and Atmospheric Administration National Weather Service Hydrometeorological Reports for estimation of Probable

Maximum Precipitation (Schreiner and Riedel

1978). At this time, sufficient observed data

regarding tsunamis, particularly large tsunamis,

and their effects are not available to support a

comprehensive probabilistic tsunami-hazard

analysis or PTHA (e.g., see Geist and Parsons

2006) at all probable nuclear power plant sites in

the United States to arrive at a set of design bases. 

In the future, as more data are collected and

scientific methods advance, PTHA may become a

viable tool to assess tsunami hazards and to

specify these design bases.

A complete PMT assessment is only required if

the hierarchical-hazard-assessment approach

described in Chapter 2 of this report results in a

determination that the site region and the site are

subject to tsunami hazards, or that the result of the

hierarchical assessment is inconclusive that the

site is not subject to hazards from a tsunami.

5.2 Definition

For the purposes of this report, we have adopted

the following definition of the PMT:

PMT is that tsunami for which the impact at

the site is derived from the use of best

available scientific information to arrive at a

set of scenarios reasonably expected to affect

the nuclear power plant site, taking into

account (1) appropriate consideration of the

most severe of the natural phenomena that

have been historically reported for the site and 

surrounding area, with sufficient margin for

the limited accuracy, quantity, and period of

time in which the historical data have been

accumulated; (2) appropriate combinations of

the effects of normal and accident conditions

with the effects of the natural phenomena; and

(3) the importance of the safety functions to be

performed.

The salient points of this definition of a PMT are

(1) it allows use of the best available scientific

methods and data, (2) it accounts for the limited

period of time in which tsunami data have been

collected in the United States, (3) it allows for

sufficient margin in design bases to account for the

limited accuracy and quantity of observed data,
50

and (4) it allows for accounting of the importance

of the safety functions to be performed by the

affected SSC.

5.3 Determination of Probable

Maximum Tsunami at a

Nuclear Power Plant Site

The Standard Review Plan (USNRC 2007)

describes PMT hazards and the approach for

determination of safety of a nuclear power plant. 

The areas of review for a nuclear power plant

siting include historical tsunami data, the PMT

including relevant source mechanisms, tsunami

propagation and inundation models, wave runup,

inundation, and drawdown, hydrostatic and

hydrodynamic forces, debris and projectiles, and

effects of sediment erosion and deposition. The

following subsections describe the approaches and

methods for determination of the PMT and

hazards posed by it at the nuclear power plant site.

5.3.1 Tsunamigenic Mechanisms and

Sources

For determination of the PMT, three mechanisms

should be considered: earthquakes, landslides, and

volcanoes. Regardless of a site being coastal or

inland, if it is located near a water body that can

support generation of a tsunami or a tsunami-like

wave triggered by any of the three mechanisms, a

PMT assessment should be carried out.

Because both near- and far-field sources should be

considered for determination of the PMT, the

search area for tsunamigenic mechanisms can be

quite large, especially for sites located on the

coasts. This search should review all available

sources of historical and prehistorical data and

create a list of tsunamigenic sources for all

mechanisms that may be relevant for the nuclear

power plant site.

It may not be possible to a priori determine which

tsunamigenic source may generate the PMT. 

Several candidate sources and the tsunamis

generated from them may require evaluation under

the most favorable tsunamigenic source and

ambient conditions. Deterministic tsunami

propagation and inundation modeling can be

carried out with appropriately conservative sets of

source parameters to evaluate the final PMT for a

given nuclear power plant site.

5.3.2 Source Parameters

For determination of the PMT, conservative values

and ranges of source parameters should be

specified. This ensures that the design bases of the

nuclear power plant will not be exceeded. A

comprehensive search of historical and prehistorical records should be undertaken to identify

potential tsunamigenic sources relevant to the

nuclear power plant site. It is possible that for

some tsunamigenic mechanisms and sources, a

corresponding historical or prehistorical tsunami

may not be identified, in part due to the relatively

short period of record. However, for such mechanisms and sources, their maximum tsunamigenic

parameters may be estimated and a deterministic

hydrodynamic modeling used to assess their

potential impact at the nuclear power plant site.

Determination of source parameter values associated with the three mechanisms may require

expert opinion supplemented with historical case

studies and available historical data. An example

of such a study is given by González et al. (2003).

The following source parameters for each of the

source mechanisms should be determined.

Earthquakes

The source parameters for a tsunamigenic

earthquakes are

1. location (latitude, longitude, and depth)

2. moment magnitude, Mw

3. fault dimensions (rupture length and

width)

4. dip

5. strike
51

6. slip distribution

7. shear modulus.

Landslides

The source parameters for a submarine landslide

are

1. slide location (latitude and longitude)

2. slide orientation (directivity)

3. slide volume

4. slide speed and acceleration

5. cohesiveness of the slide material.

The source parameters for a subaerial landslide,

including ice falls, in addition to those listed above

for submarine landslide are

1. density of slide material

2. impact Froude number.

Volcanoes

The source parameters for a tsunamigenic

pyroclastic flow are

1. location

2. orientation

3. density of the flow material

4. dimensions of the flow

5. impact Froude number.

The source parameters for a caldera collapse are

1. location

2. orientation

3. caldera dimensions

4. fixed wall height

5. cavity depth after the collapse.

The source parameters for a submarine volcanic

explosion are

1. location

2. volcanic Explosivity Index.

The source parameters for tsunamigenic-debris

avalanches and flank failures are similar to those

for submarine and subaerial landslides.

5.3.3 Initial Waveform

The tsunamigenic mechanism results in the

displacement of the water surface, which is the

initial tsunami waveform. This initial waveform

evolves hydrodynamically into the train of waves

that propagates from the source toward the site. 

For short-duration mechanisms (i.e., when the

duration of source dynamics is much smaller than

the period of the tsunami waves), the coupling

between the source and the initial waveform can

be neglected without significantly affecting the

properties of the tsunami waves. This approach is

suitable for earthquake-generated tsunamis. The

formulation of Mansinha and Smylie (1971), later

modified by Okada (1985), based on an elastic

earth crust may be used to specify the initial

waveform. The Okada formulation is a closedform analytical expression and applies to point and

finite rectangular sources, suitable for computing

an average slip for the entire fault plane. For more

complex ruptures, a slip-distribution model may

be needed. One way to construct a complex

rupture pattern is to divide the fault plane in a

series of smaller faults, each of these individually

described by an Okada formulation. Usually, the

displacement pattern of the bottom is assumed to

also apply to the water surface and, therefore, also

specifies the initial waveform of the tsunami.

The velocity of landslides can often be comparable

to the phase velocity of the tsunami waves

generated by it. Explicit landslide models should

be employed in such cases (e.g., Titov and

González 2001). Some examples of landslide

models applied for tsunami generation are

described by Jiang and LeBlond (1992), Watts

(1998), and Fine et al. (1999).

Because the volcanic mechanisms that generate

tsunamis are often similar to submarine and

subaerial landslides, explicit models of initial

waveform generation from volcanic source

mechanisms may be needed.
52

5.3.4 Wave Propagation Simulation

Oceanic tsunamis

Tsunamis generated by large earthquakes have

long wavelengths due to the large spatial scale of

the seismic source. The tsunami wavelengths can

range from tens to hundreds of miles. The tsunami

wavelength is large compared to the depth of the

water [the deepest point in Earth’s oceans is the

Mariana Trench in the Pacific at 6.8 mi

(10.9 km)], and, therefore, tsunami waves are

called long waves or shallow water waves, the

latter term referring to the shallowness of the

water compared to the wavelength.

Although closed-form expressions are available

that describe some properties of the tsunami (e.g.,

the propagation speed of the tsunami in deep

ocean, which can be used to approximately

determine the time of arrival of a far-field tsunami

at a given site), detailed behavior of tsunami-wave

dynamics can only be determined using numerical

simulations.

Two community numerical models are available:

(1) the Method of Splitting Tsunami (MOST)

developed originally at University of Southern

California (Titov 1997; Titov and Synolakis 1997)

and since implemented, maintained, and improved

at NOAA’s Pacific Marine Environmental

Laboratory (Titov and González 1997); and (2) the

set of models (TSUNAMI-N1, TSUNAMI-N2,

and TSUNAMI-N3 for simulation of near-field

tsunamis and TSUNAMI-F1 and TSUNAMI-F2

for simulation of far-field tsunamis) developed by

Imamura and colleagues (Imamura et al. 2006). 

These models have the advantage of widespread

use in the tsunami-modeling community and have

benefitted from comparisons with observed

tsunami data and subsequent updates to the model

formulations.

Summary of the MOST model

The MOST model is a suite of numerical programs

that simulate all three phases of the tsunami:

generation by an earthquake, propagation across

the ocean, and runup.

Tsunami generation is simulated using the fault

plane model of Okada (1985). This model

assumes an incompressible water layer overlies an

elastic half space that represents the crust of the

earth.

The MOST model uses non-linear shallow-water

wave equations, including Coriolis terms,

expressed in a spherical coordinate system. 

Dispersion of the tsunami waves, which is an

effects of the dependence of wave celerity on the

frequency of component waves, is handled by

taking advantage of the numerical dispersion

inherent in a finite difference scheme as suggested

by Shuto (1991). This dispersion scheme allows

MOST to use non-dispersive governing equations. 

The governing equation are (Titov and González

1997)

h (uh) (vh cos )

R cos

0

u

uu

R cos

vu

R

gh

R cos

gd

R cos

fv

v

uv

R cos

vv

R

gh

R

gd

R fu

t

t

t

+

+ =

+ ++ = +

+ ++= −

λ φ

λ φ λ λ

λ φφ φ

φ

φ

φ φφ

φ

where denotes the direction along the longitude,

 denotes the direction along the latitude, t denotes

time, h(, , t) is the amplitude of the wave, d(, ,

t) is the depth of undisturbed water, u(, , t) is the

depth-averaged velocity in the direction of the

longitude, v(, , t) is the depth-averaged velocity

in the direction of the latitude, R is the radius of

the earth, g is the acceleration due to gravity,

f=2sin is the Coriolis parameter, is the

angular velocity of the earth, and subscripts , ,

and t denote partial derivatives with respect to

those space and time dimensions. A more detailed

description of the model can be found in González

et al. (2007).

Summary of the Immamura models

Two general classes of tsunami models, one for

near-field tsunamis (TSUNAMI-N1, TSUNAMI-
53

N2, and TSUNAMI-N3) and the other for far-field

tsunamis (TSUNAMI-F1 and TSUNAMI-F2)

were described by UNESCO (1997) and Imamura

et al. (2006).

The near-field tsunami models use a cartesian

coordinate system, and the far-field tsunami

models use a spherical coordinate system. Both

sets of models are based on the non-dispersive,

nonlinear, shallow-water wave-governing

equations similar to that used by the MOST

model; the far-field models also incorporate the

Coriolis terms in their governing equations. Both

sets of models use a finite-difference discretization

scheme to solve the governing equations over a

computational grid.

TSUNAMI-N1 uses linear approximation of the

nonlinear shallow-water wave equations with a

constant computational grid. TSUNAMI-N2 uses

linear approximation in deep waters and the

shallow-water wave equations in shallow waters

and for computing runup, both over a constant

computational grid. TSUNAMI-N3 uses linear

approximation of the nonlinear shallow-water

wave equations with a varying computational grid.

TSUNAMI-F1 model uses linear approximation of

the nonlinear, shallow-water wave equations to

simulate propagation of the tsunami in deep ocean

using a spherical coordinate system. TSUNAMIF2 model uses linear equations, but also includes

coastal runup simulations.

Tsunamis in other water bodies

Except for the very last stages of runup on the

shore, when the tsunami wave steepens to such an

extent that breaking may occur, the tsunami can be

considered a long wave (Titov and Synolakis

1997). Therefore, tsunami-like waves in other

bodies of water may also be simulated using the

models described above. The main difference

between oceanic tsunamis and tsunami-like waves

in other water bodies may be the source mechanism. Landslides and hillslope failures may be

more likely to generate tsunami-like waves in

water bodies other than oceans. Under these

circumstances, a source model may be needed to

describe the initial tsunami generation from

landslides, hillslope failures, and debris avalanches (i.e., subaerial landslides). The initial

waveform predicted by these source models may

be used to specify the initial conditions for the

tsunami propagation and inundation models, such

as those described above.

5.3.5 The NOAA Center for Tsunami

Research Tsunami Propagation

Database

Characteristics of far-field tsunamis generated by

an earthquake source depend mainly on a few

source parameters, like the location and

magnitude—assuming some typical displacement

mechanism (Titov et al. 1999; Gica et al. 2006). 

Also, linear approximation of the shallow-water

wave equations has been found to be applicable in

deep ocean. Therefore, a set of unit sources—

located along the tsunamigenic subduction zones

can be used to construct a tsunami-propagation

scenario from an earthquake of given magnitude

and a given location by linearly combining the

numerical solution from all unit sources—is

needed to describe an earthquake of interest.

This approach was used to construct a forecast

database of precomputed propagation solutions for

unit sources around the Pacific and a preliminary

database in the Atlantic. Details of the definition

of these unit sources is described by Titov et al.

(1999; 2005) and Gica et al. (2006). The source

parameters for the unit sources in the Pacific are

specified using the latest estimates of these

parameters in the corresponding subduction zones

(Kirby et al. 2006). A similar effort is also

underway to define unit sources in the Atlantic

that are of relevance to the U.S. coastline.

One potential use of the NOAA Center for

Tsunami Research (NCTR) tsunami-forecast

database is to provide boundary conditions to

near-shore inundation models. This approach of

separating the inundation modeling (which is site

dependent) and the modeling of generation and
54

propagation is an attractive approach. The NCTR

tsunami database can provide robust and verified

estimates of tsunami propagation. Near-shore data

collection for parameterization of a tsunami

inundation model and estimation of hazard

matrices can be carried out on case-by-case, sitespecific requirements. However, this approach is

available only for earthquake sources in the

Pacific and is being developed for Atlantic

sources. Submarine landslide and volcanic

sources are not treated similarly. Also, this

approach may not work for inland water bodies.

5.4 Hazard Assessment

The effects of a tsunami at a nuclear power plant

site are described in Chapter 3 of this report. In

this section, hazards, and specifically metrics that

describe these hazards and can be used in the

specification of design bases of the nuclear power

plant, are described.

The effects of tsunamis on the shoreline can be

highly variable depending on the characteristics of

the tsunami, including its directivity and wavelength, the interaction of the tsunami waves with

offshore and near-shore bathymetry, and the

geotechnical characteristics of the near-shore

substrate. Due to these geospatial variations and

the highly nonlinear behavior of the tsunami

waves near the shoreline, the severity of various

hazards from different tsunamis may be different. 

Consequently, the most severe occurrence of a

particular tsunami hazard at a site may result from

a set of tsunamis, not from a particular tsunami. 

Because the goal of the tsunami-hazards assessment is to determine the most severe hazard at a

site, hazard assessment from a set of PMTs may be

required. Therefore, tsunami-hazard assessment

should consider a set of candidate PMTs for which

hazards at the site should be determined. The

hazard that is the most severe among this set of

candidate PMTs should be used.

5.4.1 High Water Level

Flooding is the most obvious of the hazards from a

tsunami. The runup, which is defined as the

maximum ground elevation that the tsunami waves

reach above a standard datum, is the metric used to

define the high-water level. Ambient water

conditions, such as high tide, can affect the highwater level.

The runup is obtained as an output from the

inundation model. Significant progress has been

made in the recent past to improve the inundation

models, especially with regard to validation of

model predictions with observed runup data (Titov

and Synolakis 1997). Model predictions of runups

can be in disagreement with observations, often by

a large margin and especially with regard to the

maximum observed runup along the coastline

(Titov and Synolakis 1997). Some of the errors

may be attributed to insufficient resolution of local

bathymetric and topographic data.

Along with the maximum runup, the areal extent

of the tsunami runup should also be considered. 

The uncertainties in model prediction of runup

also extend to the prediction of areal extent of

flooding during tsunami inundation.

Due to significant uncertainty that still exists in

predictions from inundation models, care should

be taken in application of these models and use of

their predictions to specify design bases with

respect to the locations of SSC important to safety

as well as their grade elevations. Where possible,

inundation models should be verified with locally

available runup data. Sufficient margins should be

provided for these uncertainties in all design bases

that may be derived from such simulations.

5.4.2 Low Water Level

Low-water level can lead to a dry intake, compromising the safety of a nuclear power plant if the

intake is used to provide safety-related cooling

water. The drawdown, which is defined as the

minimum water-surface elevation caused by the

tsunami waves at the shoreline, is the metric used

to describe low-water level. Ambient conditions,

such as low tide, can affect the low-water level.
55

The drawdown, similarly to the runup, is predicted

by the inundation model. Because of uncertainty

inherent in the predictions from the inundation

models, arguments similar to those for runup also

apply to the drawdown. In addition, it is more

difficult to obtain accurate measurements of

drawdown caused by a tsunami because these

locations are under water during normal conditions. Usual techniques, like high-water marks or

elevation of debris lines used to infer runups

during post-tsunami surveys, are not applicable. 

Accurate measurements of drawdown mainly

relies on eyewitness accounts, photographs, or

satellite imagery. Therefore, validation of

drawdown predictions from inundation models is

more difficult than that for runups.

Due to the reasons described above, care should be

taken in interpretation of drawdown predictions

from inundation models, and sufficient margins

should be provided in all design bases that may be

affected by these predictions.

5.4.3 Scouring Near Safety-Related

Structures

Tonkin et al. (2003) proposed a scour enhancement parameter , defined as the fraction of the

buoyant weight of the sediment grains that is

supported by the pore-water pressure gradient. 

They provided an expression for  as a function of

the depth of the substrate given

 as 



 (d ) P

d

1 4 i erfc d

2c T s

b s

2 s

v

 





























 

where is the buoyant specific weight of the  b

saturated soil, ds is the movable soil depth, cv is the

coefficient of consolidation, P is the peak surface

pressure that decreases linearly to zero over the

time period T, and i2

erfc[] is the second integral

of the complementary error function. Tonkin et al.

(2003) found that the scouring occurred to a depth

such that the estimated value of  was 0.5.

The condition that any enhanced scour may take

place is obtained by letting ds0, which yields the

following expression (Tonkin et al. 2003):





 ( ) 0 2 P

	  b v c T

The expressions above may be used to estimate if

any enhanced scouring near safety-related

structures is expected to occur during tsunami

inundation and drawdown. The foundations of

safety-related structures should be designed to

protect against scouring. An alternative option

may be to site all safety-related structures in areas

that are not exposed to enhanced scouring caused

by tsunami waves.

5.4.4 Deposition Near Safety-Related

Structures

No models of sediment transport during tsunamis

have been established. On a case-by-case basis,

site-specific determination of sediment transport

and accumulation, and their effects on SSC

important to safety, should be undertaken. All

SSC important to safety should be sited such that

sediment accumulation would not result in loss of

their functionality.

5.4.5 Forces on Safety-Related Structures

Hydrostatic force

The hydrostatic force, fh, per unit width on a wall

that is not overtopped by the tsunami waves is

given by Yeh et al. (2005):

f 1

2

 g h

u

2g h

p

2 2

















 

where  is the density of water, g is the acceleration due to gravity, h is the water depth, and up is

the component of water velocity normal to the

wall. The force acts horizontally at a distance hR

above the base of the wall, with hR given by the

follow expression (Yeh et al. 2005):
56

h 1

3

h

u

2 g R

p

2



















Notice that the hydrostatic force also includes a

velocity head component, in contrast with

traditional definition of hydrostatic forces. The

velocity head is included because inundating water

during tsunami runup will typically have a

significant velocity component.

Hydrodynamic force

The parameters of tsunami flow that are important

to assess dynamic effects (González et al. 2007)

are total flow depth,

h d   ,

where d is the still water depth and  is the local

amplitude of the tsunami; the tsunami current

speed,

V uv , 2 2 

where u and v are velocity components in the two

horizontal directions in a reference coordinate

system; the acceleration of tsunami current in the

direction of the flow,

, dV

dt

where t refers to the time dimension; the inertial

component,

h , dV

dt

and the momentum flux,

hV . 2

Kanoglu and Synolakis (2006) investigated the

evolution of two simple waveforms on a simple

sloping beach and found that even for wave runup

over simple geometries, the points of maximum

depth of inundation and maximum flow velocity

are not the same. They also found that the

location of the point of maximum velocity

depends on the incoming waveform. Therefore,

care should be exercised in interpreting a few

dynamic parameters estimated from inundation

models.

The hydrodynamic force, or the drag force, Fd, on

a structure in the tsunami flow field is given by

Yeh et al. (2005):

F 1

2 d dp C A u 2 

where Cd is the coefficient of drag and A is the

projected area of the structure on a plane normal to

the flow direction. Appropriate values of the

coefficient of drag are provided by FEMA (2005)

and reproduced here in Table 5-1.

Table 5-1. Drag coefficients for ratios of width

to depth (w/ds) and width to height (w/h)

[adapted from FEMA (2005)].

Ratio (w/ds or w/h) Cd

1—12 1.25

13—20 1.3

21—32 1.4

33—40 1.5

41—80 1.75

81—120 1.8

>120 2.0
57

Wave forces

Breaking wave forces on vertical piles and

columns is given by FEMA (2005):

F 1

2 bkrp db b g C D H 2 

where D is the diameter of the pile or column, Hb

is the breaking-wave height, and Cdb is the

breaking wave drag coefficient. FEMA (2005)

recommends Hb = 0.78 ds, where ds is the design

stillwater-flood depth. The recommended value of

Cdb is 2.25 for square or rectangular piles and

columns and 1.75 for round piles and columns

(FEMA 2005).

Breaking-wave forces on vertical walls is given by

FEMA (2005) based on two cases: (1) where the

wave breaks against a wall that encloses dry space

behind it, and (2) where the stillwater level is same

on both sides of the wall. The estimation equation

for fbrkw, the total breaking wave force per unit

width of the wall, is

 

 

f 1.1 C 2.41 g d for case 1

1.1 C 1.91 g d for case 2

brkw

p s

2

p s

2 



 

!

"

#

"





where Cp is the dynamic pressure coefficient

(Table 5-2 below).

Table 5-2. Value of dynamic pressure coefficient, Cp, as a function of probability of exceedance

[adapted from FEMA (2005)].

Cp Building Type Probability of Exceedance

1.6 Accessory structure, low hazard 0.5

2.8 Coastal residence 0.01

3.2 High-occupancy building or critical facility 0.001

5.4.6 Debris Accumulation

No models have been established for debris

accumulation during tsunamis. On a case-by-case

basis, site-specific determination of debris

transport and accumulation, and their effects on

SSC important to safety, should be undertaken. 

All SSC important to safety should be sited such

that debris accumulation would not result in loss

of their functionality.

5.4.7 Projectiles

The impact force, FI

, on the structures at the water

level is given by Yeh et al. (2005):

F m a m du

dt 

m 

u

t I b

b I

I



where m is the mass of the impacting projectile, ab

is the acceleration of the impacting projectile, ub is

the velocity of the impacting projectile, uI

 is the

approach velocity assumed equal to flow velocity,

and tI

 is the duration of impact. FEMA (2005)

provides durations of impact for different construction materials (Table 5-3).
58

Table 5-3. Impact durations for selected construction materials [adapted from FEMA (2005)].

Type of Construction

Material

Impact Duration (sec)

Wall Pile

Wood 0.7—1.1 0.5—1.0

Steel Not applicable 0.2—0.4

Reinforced concrete 0.2—0.4 0.3—0.6

Concrete masonry 0.3—0.6 0.3—0.6

Large objects transported by the tsunami waves,

such as boats, may turn into projectiles impacting

a structure at a height above the surface of the

water level. These potential impacts should be

studied carefully to specify the impact location on

the structure and appropriately modify the design

bases. The assumption that debris velocity is

equal to flow velocity may be accurate for small

objects, but may overestimate the debris velocity

of large objects (FEMA 2005).

5.5 Combined Effects

At the time a tsunami arrives at the nuclear power

plant site, ambient conditions may affect its

properties. For example, at a coastal site, tides can

affect the ambient highest and lowest water levels. 

From a design perspective, a low-tide level (e.g.,

the 90% exceedance low tide) should be combined

with the drawdown from the tsunami to arrive at

the low-water level. Similarly, a high-tide level

(e.g., the 10% exceedance high tide) should be

combined with the runup to arrive at the highwater level.

In the presence of offshore submerged currents,

the effects of these currents on the propagation and

inundation of tsunami waves should be

considered. It may be desirable to include the

effects of such currents in the tsunami propagation

and inundation models themselves to account for

any dynamic interaction between the current-flow

field and the tsunami-wave field.

For near-field earthquake-generated tsunamis, the

effects of the earthquake may need to be considered in combination with those of the tsunami. 

For example, ground motion due to the earthquake

may be an additional precursor to a potential

liquefaction of the soil near the foundation of

safety-related structures that are subsequently

inundated and scoured by tsunami waves. Under

such circumstances, the stresses from the earthquake ground motion should be considered in

addition to the buoyant forces due to the tsunamiwave action to arrive at the design-basis liquefaction potential.

The effects of a tsunamigenic event to trigger

another tsunamigenic event should also be

considered. For example, a severe earthquake may

generate a tsunami by vertical displacement of the

water column in a water body and may also trigger

a subaqueous landslide that may generate a

separate tsunami. The two tsunamis may combine

constructively to produce far larger tsunami

events. Some researchers suggest that these

concomitant tsunamigenic events may explain

some of the so-called tsunami earthquakes where

the generated tsunami is abnormally large

compared with the size of the tsunami expected

based on the earthquake magnitude alone.
59

6 INTERNATIONAL PRACTICES

6.1 Introduction

This section presents a review of accepted international practices for tsunami hazard assessment at

nuclear power plant sites.

6.2 Japan

Tsunami-hazard assessment is a necessity for

nuclear power plant sites in Japan. Consequently,

Japanese tsunami-hazard-assessment approaches

are some of the most advanced in the world. The

assessment method for the tsunami hazard at

Japanese nuclear power plants is described by the

Japanese Society of Civil Engineers (JSCE) (2002).

The Japanese assessment approach only describes

earthquake-induced tsunamis. Volcano- and

meteorite-induced tsunamis are considered

infrequent events in comparison with earthquakes

and are excluded from consideration. The hazard

caused at the nuclear power plant site is also

limited to estimation of high- and low-water levels

caused by the design tsunami.

The design tsunami is defined as one that causes

the maximum water rise or fall at the nuclear

power plant site. The design water level is defined

as the sum of water level caused by the design

tsunami in combination with an appropriate tidal

condition.

Even though Japan has the most extensive

historical database of tsunamigenic earthquakes,

significant uncertainty in source parameters exist. 

To account for this uncertainty, JSCE requires a

parametric study, varying the source parameters

within a reasonable range to numerically simulate

a number of scenario tsunamis. The tsunami or

tsunamis that cause the maximum water rise or fall

at the site are selected as design tsunamis.

Design tsunamis are verified by comparing the

water level it produces with the water levels

corresponding to all recorded and numerically

simulated historical tsunamis at the site. 

Additionally, the envelope of scenario tsunamiwater levels in the vicinity of the site should

exceed all recorded or simulated historical

tsunami-water levels. An illustration of the design

tsunami-concept is shown in Figure 6-1. The

numerical models used for simulation of scenario

tsunamis to estimate water levels at the site are

verified using historical tsunami observation.

Scenario tsunamis (thin black curves in

Figure 6-1) may produce maximum or minimum

water levels at points different from where the site

is located along the coastline in response to

directivity of the earthquake source and

bathymetry along the wave-propagation path from

the source to the coastline that modifies the

waveform. The scenario tsunami that results in

the maximum of minimum water level at the site

(thick black line in Figure 6-1) is the design

tsunami. Verification of the design tsunami is

based on two criteria: (1) the design tsunami

should produce a more severe water level than all

historically recorded tsunami water levels and all

numerically inferred water levels from historical

known tsunamis at the site (thick black curve

enveloping vertical bars at the site in Figure 6-1),

and (2) the envelope of scenario tsunamis (thick

red line enveloping all high water levels produced

by scenario tsunamis in Figure 6-1) should

produce more-severe water levels than all

historically recorded tsunami water levels and all

numerically inferred water levels from historically

known tsunamis in the vicinity of the site. Both

near- and far-field sources are considered for

determining design tsunamis.
60

Figure 6-1. Conceptual illustration of design tsunami (JSCE, 2002), adapted with permission.

Standard fault model and scenario earthquakes

A standard fault model is defined as an appropriate

earthquake model for a site that is used in

numerical tsunami simulations. The standard fault

model is chosen based on careful examination of

historical tsunamigenic earthquakes and other

information regarding seismic activity that are

relevant for a given site.

The fault motion is modeled using a rectangular,

uniform slip fault plane that is described using

nine parameters:

1. latitude of the reference point

2. longitude of the reference point

3. Depth of upper edge of the fault plane

4. fault length

5. fault width

6. slip amount

7. strike direction

8. dip angle

9. slip angle.

Scenario earthquakes are specified by varying

their respective fault motion parameters within a

reasonable range of the baseline parameter set, that

of the standard fault model. Fault motion

parameters whose variations can be probabilistically quantified are varied one standard deviation

from their baseline, standard fault model value.

Numerical tsunami simulation

The governing equations used in numerical

tsunami simulations are depth-averaged hydrodynamic equations that describe the tsunami wave

propagation in two dimensions. The linear version

of the governing equations may be used when the

ratio of wave height to water depth is sufficiently

small. Nonlinear equations should be used when

the ratio of wave height to water depth is not small

and nonlinearity of the governing equations cannot

be ignored. The equation of motion in this case

includes an unsteady term, a pressure term, a

bottom-friction term, and an advection term that

facilitate modeling of the steepening of the wave

front as it propagates in shallower waters. A

dispersion term may also be needed if the

curvature of the tsunami waves increases during

propagation.

Generally, for simulation of nearshore-tsunami

propagation, when the water depth is less than

656 ft (200 m), nonlinear governing equations are

employed. The recommendation is to use an
61

explicit finite difference scheme with a staggered

leapfrog method for discretization of the governing equations. Two methods are specifically

recommended: the Goto and Tanaka methods. 

Both methods use the staggered leapfrog scheme. 

The Goto method uses a conservation-type

advection term, whereas the Tanaka method uses a

nonconservation-type advection scheme. Friction

term in Goto method is based on a Manning

approach, whereas the Tanaka method uses a

general friction term. Horizontal eddy viscosity

term is used in the Tanaka method, but is

introduced in the Goto method if thought

necessary. The Goto method uses a first-order

upstream-difference scheme with associated

accuracy of first order for the advection term,

whereas the Tanaka scheme uses the LaxWendroff scheme with second-order accuracy.

The depth-averaged two-dimensional hydrodynamic equations may not be appropriate for use

in runup simulation if the local topography near

the maximum runup location possesses steep

slopes of a small valley. These conditions were

encountered near the village Monai on Okushiri

Island during the Hokkaido Nansei-Oki tsunami. 

In such cases, a model based on nonlinear threedimensional governing equations may become

necessary.

Far-field propagation of a tsunami can be

conducted using the linear version of the

governing equations because the wave height is

small compared to water depth during transoceanic

propagation of the waves. If the initial tsunami

profile has a wide range of frequency components,

wave velocity varies slightly for these frequencies

in deep water, causing shorter waves to arrive after

a longer delay. The use of the dispersion term

becomes essential to reproduce this effect. For

far-field tsunamis that travel transoceanic

distances, the Coriolis force due to earth’s rotation

should also be considered in the governing

equations.

Initial conditions for tsunami simulations

For modeling of tsunami waves propagation, the

initial disturbance of the water surface due to the

amount of vertical slip is needed. JSCE usually

determines the distribution of the vertical slip

using the Mansinha and Smylie (1971) method,

which assumes that elastic properties of the earth’s

crust near the fault are isotropic and homogeneous

(i.e., Poisson Ratio  is 0.25 and Lame’s constants

and 	 are equal). If the conditions of isotropy

and homogeneity cannot be assumed, JSCE

recommends using the Okada (1985) method,

which is more general.

Fault motions that generate large tsunamis are

assumed to last from several tens to approximately

120 seconds. Fault durations of this order are not

significantly different than an instantaneous

displacement of the seafloor in terms of the

numerical simulation of the tsunami waves. 

Dynamics of the slip should be considered if 

C.Tv /L is greater than 0.04, where C is the tsunami

wave velocity, Tv is the duration of the fault

motion, and L is the wavelength of the tsunami

wave in the direction of the width of the fault

plane.

The initial water-surface elevation is set equal to

the vertical slip amount if fault motion is considered essentially instantaneous. The initial

water-surface elevation is the still-water elevation

if a dynamic vertical slip amount is used to

characterize the tsunamigenic effect of a longduration fault motion. In both cases, the depthintegrated initial flux is set to zero.

Boundary conditions for tsunami simulations

Three general boundary conditions are needed in

tsunami wave-propagation simulations: (1) the 
62

offshore boundary condition, (2) the onshore

boundary condition, and (3) the overflow

boundary condition.

Offshore boundary conditions are specified at

boundaries through which the tsunami waves pass

unaltered. It is rather difficult to prescribe

boundary conditions that eliminate all reflection of

outgoing waves back into the computational

domain (see Chapter 5 in Vreugdenhil 1994). The

conventional method is to use discharge flux for a

progressive wave at the boundary based on the

method of characteristics (Aida 1969, 1970, 1974;

Iwasaki and Yo 1974). The free-transmissionboundary condition can also be specified using a

virtual complete reflecting wall at the open

boundary (Hino and Nakaza 1988; Imamura 2001)

with careful placement of the wall to achieve

accuracy. The latter method for specification of

an open-boundary condition is applicable only

when the incidence angle of the waves on the

boundary is nearly normal. Both boundary

conditions are applicable for tsunami waves

coming into the computational domain, a

condition that is required for near-field computation of a tsunami generated in the far field.

Onshore boundary conditions are specified at the

coastline. The nature of the boundary condition

depends on whether runup on the land is

considered. If tsunami runup is not considered, a

complete reflection-boundary condition is

specified by setting the discharge flux at the

coastline to zero. This condition is applied only

when water depth near the coastline is sufficient so

that the tsunami rundown does not expose the

bottom. If tsunami runup is considered, or if the

water depth near the coastline is shallow,

boundary conditions related to the runup front are

used. The shore topography is approximated

using a series of steps normal to the shoreline. At

every time step of the numerical solution, the

location of the tsunami front is determined based

on computed water depth in computational grid

cells. The method of Iwasaki and Mano (1979) is

used in which (1) the tsunami front is assumed to

be located at the boundary of the cell in which the

computed sum of wave height and still-water

depth is positive and the cell in which the

computed sum is zero or negative, (2) the total

water depth at the cell boundary for calculation of

the discharge flux is taken as the sum of the stillwater depth at the boundary and the higher wave

height of the two neighboring cells, (3) the

discharge flux is estimated assuming that the slope

of the water surface can be approximated to the

first order by the slope from the water level at the

wave front to the bottom depth of the neighboring

cell, and (4) when the total water depth approaches

zero, the advection term is neglected.

Overflow boundary conditions are specified when

the tsunami waves overtop a structure such as

breakwaters, dikes, or revetments (Figure 6-2). If

the structure is modeled as part of the ground

topography, the onshore boundary conditions for

runup computations are used. If the structure is

located offshore, usually placed at the boundary of

a grid cell in the discretization, two formulae are

used depending on whether the structure is

offshore or at the coastline.
63

Figure 6-2. Schematic representation of tsunami wave overflow of offshore structures (JSCE,

2002), adapted with permission.

For offshore structures, the formula by Honma

(1940) is used to compute the discharge over the

structure for complete and incomplete overflows:

 

q h 2 g h when h 2

3

 h

q 2.6 h 2 g h h when h 2

3

 h

1 1 21

2 12 2 1

$

 %





where h1 and h2 are the water depths measured

from the top of the structure in the front and the

back of the structure, μ=0.35, and g is the

acceleration due to gravity. When the waves do

not flow over the structure, a no-flow boundary

condition is imposed at the structure allowing

complete reflection of the tsunami waves.

For structures that are located at the coastline, the

discharge on the top of the structure is estimated

using the broad-crested weir formula (Aida 1977):

q 0.6 h g h 

where h is the depth of water measured from the

top of the structure and h is the drop in water

level on the top of the structure from its original

position (Figure 6-3).
64

h q

h

Figure 6-3. Schematic representation of tsunami overflow of coastal structures (JSCE, 2002),

adapted with permission.

Spatial grid considerations

JSCE (2002) described several considerations for

choosing the size of the spatial grid for use in the

numerical simulation of tsunamis, which are

described as adequate to obtain sufficient accuracy

when used with a staggered leapfrog scheme for

discretization of governing differential equations:

1. In the tsunami source region, the grid size

is determined based on dimensions of the

source region and the spatial scale of the

tsunami; as a rule of thumb, grid size

equal to 1/20th of one wavelength of the

tsunami is used.

2. In the tsunami propagation region, the grid

size is determined based on refraction of

tsunami waves caused by seafloor

bathymetric features and the spatial scale

of the tsunami; in regions of simple

bathymetry, grid size 1/20th of one

wavelength of the tsunami may suffice;

however, in regions where refraction

dominates, grid size as small as 1/100th of

the tsunami wavelength may be required.

3. In shallow waters near the coast, the

spatial grid size is determined based on

spatial scale of the tsunami, slope of the

seafloor, bathymetry and coastal topography, and size and shape of coastal

structures. Coastal areas with simple

bathymetry and topography and where

effects of coastal structures are insignificant, grid sizes varying from approximately 328 ft (100 m) at a water depth of

164 ft (50 m) or less to approximately

82 ft (25 m) approaching the coastline

may be sufficient. In the presence of ports

and harbors, grid size less than 1/5th of

the port entrance width may be necessary. 

Grid size less than 1/100th of the tsunami

wavelength may be necessary in V-shaped

bays where the ratio of the tsunami

wavelength to the length of the bay is less

than 6.

4. In the tsunami runup zone with simple

beach topography, the following criterion

is used:

 x

 g T2 7 10 4

&

$ ' 

when Manning’s coefficient of roughness,

n=0.03, is used, or

 x

 g T2 4 10 4

&

$ ' 
65

if the friction term is not considered in the

governing equations, where x is the grid

cell size, 
 is the slope of the beach, and T

is the period of the tsunami waves.

Computational time step

The computational time step in the numerical

scheme is determined from considerations of

stability. Usually, the time steps are set to satisfy

the Courant-Friedrichs-Lewy (CFL) condition,

which requires that the time step, t, should not be

larger than the travel time of the wave over one

grid cell:

  t x

2 g hmax

$

where hmax is the maximum water depth. In a

general case, where different grid-cell sizes are

used in different regions of the computational

domain, the time step is chosen such that the limit

set by the CFL condition for the largest grid-cell

size is not exceeded. In practice, however, the

chosen time step for the tsunami simulation is

smaller than the limit set by the CFL condition

because of two reasons: to ensure that numerical

errors are controlled, and to ensure that the time

step is appropriate during high-speed current

during the tsunami run-down when flow velocity

may become greater than the wave celerity.

Bathymetric and topographic data

The latest available, high-resolution bathymetry

data is recommended for use in the tsunami

simulations. Generally, recent advances in echosounding techniques and their application to

extensive areas provide high-quality bathymetry

data. For far-field tsunami simulations, globalscale bathymetry datasets are required. The

5-minute and 2-minute gridded global-relief

datasets are used.

Topographic data in the inundation area is

prepared according to the latest available

topographical maps. Numerical maps of the

Geological Survey Institute and Japan Map Center

are utilized. Changes are topography is also

considered. Careful consideration of disparate

georefrencing of global and Japanese datasets is

also carried out to maintain consistency between

datasets.

Application of the Japan approach to other

locations

Preliminary results from the application of the

Japan approach for estimation of tsunami-wave

heights were described at the workshop,

“Workshop on the Physics of Tsunami, Hazard

Assessment Methods and Disaster Risk Management (Theories and Practices for Implementing

Proactive Countermeasures),” held May 14–18,

2007 in Trieste, Italy. The workshop was jointly

sponsored by the International Atomic Energy

Agency (IAEA) and the Abdus Salam International Center for Theoretical Physics. Several

IAEA member countries had expressed interest in

2006 to begin applying the JSCE approach to

tsunami-hazard assessment at coastal nuclear

power plant sites. The availability of the JSCE

(2002) document has facilitated the implementation of the method in locations other than Japan.

Preliminary results from the application of the

method to a coastal nuclear power plant site in

India were presented. Two other locations, in

Pakistan and in Egypt, were in early data-collection phase at the time of this writing. The

conclusion drawn thus far from these early

attempts to adopt the JSCE approach point to the

reliance of the JSCE approach on the availability

of a substantially large historical database of

tsunami observations. These observations should

contain tsunami-source characteristics (the JSCE

approach only deals with earthquake sources) as

well as tsunami runup information at or near the

site of interest. At this time, few places outside

Japan meet the data requirements needed to

rigorously apply the JSCE approach. The IAEA

member countries will continue to collect more

data and attempt to adapt the JSCE approach to

their locations of interest.
66

6.3 International Atomic Energy

Agency

The International Atomic Energy Agency

publishes a set of standards for safety evaluations

of nuclear power plant sites. These standards are

divided into Safety Fundamentals, Safety Requirements, and Safety Guides, supplemented by

technical reports and preliminary technical

documents, called TECDOCs, that contain

illustrative examples.

The Safety of Nuclear Installations, Safety Series

No. 110 (IAEA 1993), in the Safety Fundamentals

series, presents basic concepts and principles

underlying the regulation and safe management

and operation of nuclear power installations. 

Chapter 5 of this document focuses on technical

aspects of safety of nuclear installations, including

those related to siting, design and construction,

and operation and maintenance of the installation.

Site Evaluation for Nuclear Installations (IAEA

2003a), in the Safety Requirements series, presents

the requirements that are based on the concepts

and principles documented in the fundamentals

series and must be met to ensure safety of a

nuclear installation. Chapter 3 of this document

lists tsunamis as one cause of flooding, the

evaluation of which is a requirement under the

IAEA guidelines. Flood Hazard for Nuclear

Power Plants on Coastal and River Sites (IAEA

2003b), in the Safety Guide series, provides

recommendations to meet the requirements

established in the Safety Requirements series

(IAEA 2003a) with respect to flood hazards,

including those caused by tsunamis, in the site

evaluation for nuclear power plants that may be

located on coastal and river sites.

IAEA (2003a) requirements state that the region in

which a candidate site is located should be

evaluated for potential for tsunamis. If such a

potential exists, prehistorical and historical data

should be collected. The frequency of occurrence,

magnitude, and height of regional tsunamis should

be estimated based on analysis of the collected

prehistorical and historical data and comparison of

the site region with similar regions that may have

been studied in greater detail with regard to

tsunamis. The hazards at the site should be

determined based on physical and analytical

modeling, where applicable. Coastal effects, such

as the amplification of the waves due to shoaling

and other coastal effects, should be considered.

IAEA (2003b) defines coastal sites as those that

are located in open coastal regions and on

enclosed or semi-enclosed bodies of water and

whose hydrological responses cannot be compared

to those of a small lake. Open coastal regions are

defined as those areas of land that are directly

exposed to a major body of water. Enclosed

bodies of water includes lakes and reservoirs. 

Semi-enclosed bodies of water include lagoons,

estuaries, gulfs, fjords, and rias.

IAEA (2003b) recommends that flooding resulting

from a PMT be considered for a coastal site. It

defines the PMT as “... the hypothetical tsunami

having that combination of characteristics which

will make it the most severe, in terms of flooding,

that can reasonably be expected to occur at the

site.” Tsunamigenic sources that should be

considered in site evaluation include earthquakes,

landslides (including submarine landslides),

submarine volcanoes, and falling ice. At a river

site, floods resulting from large waves induced by

volcanoes, landslides, and avalanches in water

basins should be considered.
67

Preliminary investigation

Preliminary investigation related to flooding

should be carried out at the site selection stage to

establish the potential of flooding at the candidate

site based on examination of available historical

data and application of empirical and approximate

methods to estimate the extreme flood (IAEA

2003b).

Catalogs of historical tsunamis should be searched

to determine whether the site is subject to

tsunamis. The potential for both near- and farfield sources to generate a tsunami that may affect

the candidate site should be investigated. Nearby

tide-gauge records may be used to estimate the

maximum recorded tsunami wave heights. Based

on coastal configuration, the correlation of

tsunami effects at the site and that at the tidegauge location may be established.

Preliminary estimates of the height and extent of

the extreme wave should be made from analysis of

collected historical data, bathymetry characteristics, and consideration of a conservative reference

water level. Maps prepared for land-use planning

and flood emergencies, aerial photographs and

satellite imagery, and any available PMT studies

in coastal areas may also be used for preliminary

screening of the site.

If the preliminary investigation results in the

conclusion that the site is potentially affected by

tsunamis, a detailed study should be carried out to

establish design bases for the proposed plant

(IAEA 2003b). 

Data collection

For a detailed tsunami-hazard assessment, a

diverse set of data is needed. This data set

includes hydrological, oceanographic and

hydrographic, seismic, and geophysical data:

1. locations and hydrological characteristics

of all nearby bodies of water, including

streams, rivers, lakes, reservoirs, estuaries,

gulfs and fjords, and oceans

2. hydrological and topographical characteristics of the site showing natural and

artificial drainage features and any

proposed changes

3. tides, sea-level anomalies, and water

levels of nearby bodies of water

4. bathymetry of water bodies, particularly

the near-shore region

5. locations and details of offshore

structures, such as seawalls or breakwaters

6. near-shore currents induced by tide and

wind

7. littoral drift

8. historical tsunami data, particularly

tsunamis recorded at the site

9. seismic and geological data to determine

source parameters

10. historical and potential future sites of

subaerial and submarine landslides

11. volcanoes, including submarine-volcanic

activity

12. sediment characteristics of the seafloor

near proposed plant structures.

Detailed topographic and bathymetric maps are

needed for tsunami-hazard assessment. If such

data do not exist for the area near the plant site,

surveys should be performed to prepare such maps

or collect data from available survey methods. 

Detailed topographic data are needed in the

tsunami-inundation zone. Detailed bathymetry

data is needed from the shoreline out to a water

depth of approximately 98–164 ft (30–50 m). 

Topographic and bathymetric maps or other

sources of these data, such as digital elevation or

depth data, should be combined at the shoreline to

create a seamless map or dataset.

Simulation of tsunami waves

IAEA (2003b) recommends that the PMT

generated from the worst-case tsunamigenicsource parameters should be determined. Both

near- and far-field sources should be considered. 

Historical records of tsunamis, if available, should

be used to validate the predictions of the numerical

models used for simulation of the tsunami waves.
68

For submarine earthquake-generated tsunamis, the

displacement of the sea floor should be estimated

based on the assumption that the fault movement

occurs in a semi-infinite elastic homogeneous

medium. The fault movement is characterized by

its location, depth, and length, and the width and

dislocation of the fault plane. The initial tsunami

waveform should be assumed to be the same as the

static vertical displacement of the sea floor. 

Application of more sophisticated techniques that

consider heterogeneity of fault movement should

be carefully validated.

For landslide-generated tsunamis, dynamics of the

mass movement should be determined to estimate

the initial tsunami waveform. The parameters that

describe the landslide dynamics include the

velocity, the duration, and the discharge of the

mass movement. For tsunamis generated by

volcanic activity, IAEA (2003b) recommends that

three generation mechanisms should be considered: the impact of rocks falling into the water

after ejection, an underwater explosion that may

result in a rapid rise of the water surface, and a

caldera collapse. Characteristics of the volcanic

mechanisms should be used to estimate the initial

tsunami waveform. The simulation of the tsunami

can be carried out in a manner similar to that for

the earthquake-generated tsunami.

Far-field tsunamis may be treated as long linear

waves while accounting for the Coriolis force

during the propagation phase. The initial tsunami

wavefield consists of many component frequencies that propagate at different celerities. For a

tsunami that travels long distances, the difference

in speed of component frequencies results in

dispersion of the waves. IAEA (2003b) recommends a parameter Pa, which may be used to

determine if dispersion effects should be considered in simulation of waves for a far-field

tsunami:

P 6 h

R

a

h a

1 3





 





where h is water depth, a is the horizontal

dimension of the tsunamigenic source, and R is the

distance from the tsunamigenic source to the site. 

If the value of Pa is larger than 4, frequencydependent dispersion effects may be neglected and

linear governing equations with accounting of the

Coriolis force may be used. Otherwise, linearized

Boussinesq equations that include the first-order

effects of frequency-dependent dispersion and the

effects of the Coriolis force should be used.

The long-wave approximation for near-field

tsunamis may not be applicable since short-period

components may also be significant near the

tsunamigenic source. IAEA (2003b) recommends

that simplifying assumptions for near-field

tsunami should be carefully and critically

examined and should be used only if they can be

demonstrated to provide conservative results. 

IAEA (2003b) recommends that for a water depth

exceeding 656 ft (200 m), linear long eave

equations are applicable. For shallower regions,

the shallow-water-wave theory with a term for

bottom friction included in the governing

equations should be used.

IAEA (2003b) recommends that near-shore

modification of tsunami waves should be

simulated using shallow-water equations,

including the effects of bottom friction. Large

oscillations of the water surface due to resonance

of the tsunami waves with natural frequencies of

the water body in the near-shore region should

also be investigated. IAEA (2003b) recommends

that tsunami runup be estimated from available

approximate theories of the phenomena or from

empirical relationships with careful consideration

of the ranges of validity of the assumptions

inherent in these approaches.

Tsunami impacts

Bottom shear caused by strong tsunami currents

may be significant in shallow waters. The safety

of plant structures may be affected by erosion and

deposition of sediments by the tsunami currents,

such as failure of a breakwater due to erosion or

deposition of sediment at a safety-related cooling-
69

water intake. IAEA (2003b) recommends that a

dedicated analysis of these effects should be

conducted. Measurement of sediment characteristics near the proposed locations of SSC

important to safety may be required to make an

assessment.

IAEA (2003b) recommends that three forms of

tsunami waves should be considered in estimation

of wave forces on structures:

1. non-breaking waves, which result in the

tsunami acting as a rapidly rising tide

2. tsunami waves breaking far from the

shoreline, which result in the tsunami

waves developing into fully formed bores

before reaching the shore

3. tsunami waves breaking near the shoreline, when the tsunami waves act as

partially formed bores.

Both static and dynamic forces due to the three

forms of the tsunami waves should be estimated

on the structures of the nuclear power plant.

Combined events criteria

IAEA (2003b) recommends that appropriate

combinations of extreme events with reference

water levels (tides) and wind waves should be

taken into consideration. Although precise

estimation of the numerical probability that a

given level of severity is exceeded by each

separate event or by some combination of these

events, conservative values of the probability that

the given level of severity will be exceeded by

each separate event and the likelihood that

separate events may occur together in a

combination should be estimated (IAEA 2003b). 

Further, reasonable values of the probability that a

given level of severity may be exceeded by a

combination of events should be estimated. 

Careful consideration of the duration of separate

events in the combination is also required. In

general, the greater the number of independent or

partially dependent events in the combination, the

lower the combined exceedance probability. 

IAEA (2003b) also notes that consideration of an

excessive number of events in combination may

result in overly conservative design bases and that

considerable engineering judgement may be

necessary in selecting appropriate combinations.

IAEA (2003b) recommends that tsunamis be

considered in combination with waves caused by

winds with a shorter recurrence interval. For

determination of the runup, an ambient high-tide

level should also be considered. IAEA (2003b)

does not mention combining effects of seismic

ground motion with the hazards from a

concomitant tsunami.

71

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A.1

Appendix A

Tsunami Hazard Assessment at

a Hypothetical Nuclear Power Plant Site

This appendix provides a set of guidelines that will be applicable to most nuclear power plant sites in the

United States. It presents the primary steps required to carry out tsunami hazard assessment at a

hypothetical nuclear power plant site. These steps are not all-encompassing because many of the

activities and analyses that need to be carried out are site-dependent and site-specific. 

A.1 Preliminary Data Collection and Site Screening

The tsunami hazard assessment at a nuclear power plant is carried out using a hierarchical approach (see

Chapter 1 of this report). The first step of this approach is to establish whether the region is subject to

tsunamis. If it is found that the general region is subject to tsunamis, a further search for the site itself is

conducted to determine the effect of the tsunamis on the site itself.

A.1.1 Is the Site Region Subject to Tsunamis?

A search of the National Geophysical Data Center (NGDC) tsunami database is carried out to determine

whether any historical tsunami events were reported at or near the site. The NGDC database can be

searched using the following parameters

• Runup Country: USA

• Runup State: the state where the proposed nuclear power plant is to be located

at http://www.ngdc.noaa.gov/nndc/struts/form?t=101650&s=167&d=166. The NGDC database also can

be searched for tsunami sources that may affect the site using the NGDC search at

http://www.ngdc.noaa.gov/nndc/struts/form?t=101650&s=70&d=7 using similar search parameters.

At the time this report was written, a search of the NGDC database for runups in California returned

503 records. A similar search for Florida, New Jersey, and Texas returned 9, 20, and 3 records,

respectively. The NGDC search of the tsunami sources for California returned 130 records. The

corresponding tsunami record search for Florida, New Jersey, and Texas returned 5, 11, and 3 records. 

The runup locations are plotted in Figure A-1. Erroneous and doubtful tsunami runup reports are

included in the NGDC database and may show up in the searches. For example, of the 503 tsunami runup

records returned for California, 24 are labeled as being erroneous, 28 are labeled as being very

questionable, and 14 are labeled as being questionable. Similarly, of the 130 records for tsunami runups

in California, 18 are labeled as being erroneous, 20 are labeled as being very questionable, and 14 are

labeled as being questionable. The tsunami source locations are plotted in Figure A-2.
A.2

Figure A-1. Tsunami runup locations in selected states (from the NGDC tsunami database).
A.3

Figure A-2. Tsunami source locations for reported runups in selected states.
A.4

The NGDC tsunami database also contains records and sources of inland tsunami-like waves that have

occurred in lakes and rivers. A search for tsunami runups in Washington State returned 88 records,

including two waves in Spirit Lake caused by the debris flow from the collapse of Mount St. Helen’s

dome during its 1980 eruption. A search for tsunami runups in Missouri returned two events, both related

to the 1811-1812 New Madrid earthquakes that caused waves in the Mississippi River.

The NGDC database also reports seiches induced by tsunamis and meteorological forcing. For example,

a tsunami runup search for Michigan returned four events; the source for one, a ground swell or wave in

the Detroit River, is listed as unknown, and the other three events are attributed to meteorologically

induced seiches in Lake Huron or to an offshore landslide.

Based on results from searches of the NGDC tsunami database, it can be determined if the general region

has been subjected to tsunamis or to tsunami-like waves.

A.1.2 Is the Plant Site Affected by Tsunamis?

Based on data from the NGDC tsunami database, an assessment is made regarding the degree to which

the proposed site itself is affected by tsunamis. It is possible that even though the region is subject to

tsunamis, the site itself may be safe. This is essentially a site screening step.

Historical tsunami data and other geophysical, topographical, and hydrological data are necessary to carry

out site-screening. These data include the following:

1. List of historical tsunamis and associated runups

2. Map of the proposed site and its vicinity

3. Map of potential tsunamigenic sources

4. Topographic and bathymetric maps

5. Geologic and geotechnical maps

6. Hydrological setting of the site

7. Onshore and offshore soil and substrate characteristics.

The list of historical tsunamis, the associated wave characteristics, and information regarding their

sources should already be available from the search conducted to identify tsunamis in the general region

of the proposed nuclear power plant. The location of the proposed nuclear power plant site and its

relation with the physiographic characteristics of the region should be evaluated from a map that has

sufficient resolution. The topographic and bathymetric maps provide baseline data for interpretation of

runup characteristics of the tsunami waves. The hydrological setting of the site allows the interpretation

of the interaction of tsunami waves with nearby water bodies such as an estuary, a natural or man-made

embayment, or other coastal structures.

The above data should be critically evaluated to answer the following questions:

1. Can a tsunami wave run up to the proposed grade elevation of the nuclear power plant?

2. Can tsunami waves inundate a sufficient distance from the shoreline to affect proposed facilities

of the nuclear power plant?

3. Can tsunami waves interact with near-shore geometry to result in resonance?
A.5

4. Can tsunami waves be expected to lead to severe erosion near the proposed nuclear power plant

facilities?

5. Can tsunami waves severely affect local communities and infrastructure?

It may be necessary to assemble an interdisciplinary team of experts to evaluate the data and to answer the

above questions. At this site-screening stage, it may not be necessary to precisely estimate the impacts

from tsunamis quantitatively. However, a thorough qualitative description can result in a very good

estimate of the amount of effort required to carry out a complete tsunami hazard analysis. This evaluation

can also indicate if the site is exposed to severe tsunami hazards and if the considerable effort to carry out

a subsequent complete tsunami hazard assessment is worthwhile.

Based on the evaluation of the degree of impact from tsunamis at the proposed site, a decision can be

made to proceed with a detailed tsunami hazard assessment to provide the bases for the design and the

protection of the SSC of the plant.

A.2 Site Investigation and Data Collection

To proceed with a detailed tsunami hazard assessment at the proposed nuclear power plant site, the

preliminary data collected for site screening needs to be supplemented by additional site investigation and

data collection. These data collection efforts may include paleo-tsunami investigations, compilation of

bathymetry and topography, collection of high-resolution nearshore bathymetry, characterization of

geophysical properties of the nearshore substrate, and tide or other water level records.

A.2.1 The Tsunami Record

If the historical tsunami record at the proposed site is relatively short, a paleo-tsunami investigation to

determine the existence and severity of prehistorical tsunamis should be considered. As a first step,

paleo-tsunami databases such as the one developed by Peters et al. (2003) should be searched to locate

data that may already be available from previous efforts. Paleo-tsunami experts should be contacted to

determine whether more recent data collection efforts are underway.

If paleotsunami data are not readily available for the proposed nuclear power plant site, a site-specific

paleo-tsunami investigation should be considered. Chapter 5 of this report lists the pieces of information

measured or interpreted from the paleo-tsunami deposits. It may be necessary to obtain expert help to

carry out paleotsunami surveys, data collection, and interpretation.

A.2.2 Bathymetry and Topography

For simulation of the propagation of the PMT waves and the inundation caused by the waves, goodquality bathymetry and topography data are needed. A search should be conducted to determine whether

a combined bathymetry and topography data set is available for the proposed nuclear power plant site or

its vicinity. This search may save much of the effort needed to create this data set from raw bathymetry

and topography data sources (see Chapter 5 of this report).

The extent of spatial coverage needed for tsunami simulation depends on several factors: (1) whether the

tsunami source is near-field or far-field, (2) whether pre-computed tsunami wave heights from far-field

sources are available (e.g., from the National Oceanic and Atmospheric Administration Center for
A.6

Tsunami Research [NOAA NCTR] database), and (3) the geometry of the shoreline. Global bathymetry

datasets may be used for tsunami propagation modeling from far-field sources if precomputed tsunami

wave heights from these sources are not available. The use of a global bathymetry data set may also be

necessary in near-shore inundation modeling that uses the NOAA NCTR pre-computed offshore tsunami

wave heights depending on the offshore distance at which these wave heights are provided.

The resolution of the near-shore bathymetry and topography data may be critical for accurate simulation

of the propagation and inundation of the tsunami waves. Available data sources described in Chapter 5 of

this report should be used to collect the best available bathymetry and topography data from the NGDC,

the National Ocean Service (NOS), and the U.S. Geological Survey (USGS). Airborne remote-sensing

technologies, like LiDAR and IfSAR, provide the best quality topographic data. Topographic and

bathymetric data derived from Light Detection And Ranging (LiDAR) and Interferometric Synthetic

Aperture Radar (IfSAR) systems can be obtained from the NOAA Coastal Services Center (CSC) (see

Chapter 5 of this report). In absence of NOAA CSC coverage, it may be necessary to carry out dedicated

data collection and processing.

A high-quality combined bathymetry and topography data set should be created by merging the available

onshore and offshore elevation information. Several spatial interpolation techniques are available in

geographic information system (GIS) software and can be used to create grids from irregularly spaced

point data or from elevation contour lines. The final grid for tsunami modeling should be created with all

cells set to non-zero elevation values because an elevation value of zero could cause anomalies in some

tsunami inundation models (González et al. 2006). A solution suggested by González et al. (2006) is to

use a small positive value for land grid cells (e.g., 0.01 m) and a correspondingly small negative value for

water grid cells (e.g., -0.01 m). The final Digital Elevation Model (DEM) grid should be checked for

consistency using known features on land and offshore.

A.2.3 Geophysical Data

Bottom pressure gauge data from available locations within the tsunami propagation and inundation

regions should be obtained from the NGDC. Water column height data obtained for the month of January

2007 at a DART station off the coast of San Francisco are shown in Figure A-3.

Tides or water surface elevation data are needed to specify antecedent conditions before the arrival of the

tsunami. Historical tide data available from the NOAA Center for Operational Oceanographic Products

and Services (CO-OPS) Tides and Currents website should be obtained. For example, Figure A-4 shows

the tide data for the month of January 2007 at the San Francisco station.
A.7

Figure A-3. DART water column height data for January 2007 at Station 46411.

Figure A-4. Tide-level data at San Francisco station 9414290.
A.8

A statistical analysis of historical tide data should be carried out to determine the appropriate tide levels at

specified exceedance probabilities. For example, the low tide level at the 90-percent exceedance

probability level could be used for the antecedent water level to determine the minimum tsunami water

surface elevation during rundown, and the high tide level at the 10-percent exceedance probability level

could be used as the antecedent water level to determine the maximum tsunami water surface elevation

during runup.

Tide-level data are also useful during validation of tsunami models. The data can be used to verify

whether the model predictions of tsunami wave heights compare well with observed water levels at these

locations. If possible, data from several tide gauges at different locations along the propagation path of a

few historical tsunamis should be used to assess the accuracy of the simulations.

Information regarding soil grain size distribution should be obtained from the NGDC. A search of the

NGDC grain-size database for the bounding rectangle ranging in latitudes from 32N to 44N and

ranging in longitudes from 122W to 130W returned four cruises and 22 samples. Table A-1 lists the

results of this search.

Table A-1. Search results from the NGDC grain size database.

Dataset Contributor Scientist Ship Cruise

01995001 LDEO† Horn Robert Conrad RC10

09005007 NAVOCEANO‡ Rehoboth D-5

09005039 NAVOCEANO Loomis Unknown L.I. 446

09005043 NAVOCEANO Loomis Unknown L.I. 450

†

Lamont-Doherty Earth Observatory

‡

U.S. Naval Civil Engineering Laboratory

Three tab-delimited files can be exported from the database search that contain cruise and sample data,

interval data, and weighted percentage data for each data set. The first few records of the cruise and

sample export file from a data set are shown in Table A-2.

The locations of these samples should be plotted on a map to determine whether they are appropriate for

use in tsunami hazard analysis at the proposed nuclear power plant site. If the number of samples is

found to be insufficient or the locations of the samples are found to be inappropriate to derive any

conclusions about the grain-size distributions near the proposed nuclear power plant site, a site-specific

data collection effort may be needed to determine these properties.

Soil properties like buoyant specific weight, coefficient of consolidation, and others may be required to

determine the hazard from tsunamis. Because such data usually is not expected to be available from

repositories, it would need to be obtained using site-specific surveys. The properties that need to be

determined from site-specific investigation will depend on the hazard indices being estimated or hazard

models being used.
A.9

Table A-2. Exported cruise and sample file from the NGDC grain-size database search for

dataset ID 01995001.

#******************************************************

#USDOC/NOAA/NESDIS/National Geophysical Data Center (NGDC)

#World Data Center for Marine Geology and Geophysics, Boulder

#Seafloor Sediment Grain Size Database

#Data Set WDCMGG00127

#URL http://www.ngdc.noaa.gov/mgg/geology/size.html

#file created: 12-MAR-07 as a sample level export

#questions to: Carla.J.Moore@noaa.gov

#phone: 303-497-6339 fax: 303-497-6513

#address: NOAA/National Geophysical Data Center

# 325 Broadway Code E/GC3

# Boulder, Colorado USA 80305-3328

#******************************************************

#------------------------------------------------------------

# MGG01995001

#------------------------------------------------------------

# Institution: Lamont-Doherty Earth Observatory (LDEO)

# Title: Acoustic Provinces of the North Pacific Based on Deep Sea Cores

# Report: Technical Report No. 3, CU-3-67 NAVSHIPS N00024-67-C-1186

# Set id: FE00502

# Authors: D.R. Horn

# Ships: Vema, Robert Conrad

# Cruises: 20,21,10

# Areas: North Pacific

# Funding: Navy-misc.

# Project: 

# # of samples: 248

# Cruise dates: April 1,1964- August 31,1966

# Devices: 248 cores

# Analyses: 248 texture, 245 engineering properties.

# Formats: Available in .pdf form. Grain size data in digital form

# # microfiche: 2

# # pages paper: 49

#-------------------------------------------------------------

mggid ship cruise sample device date_collected lat lon water_depth core_length sample_comments

01995001 Robert Conrad RC10 RC10156 core, piston 19660516 22.3333 157.8167 5402 

01995001 Robert Conrad RC10 RC10157 core, piston 19660517 24.7667 159.1333 5682 

01995001 Robert Conrad RC10 RC10158 core, piston 19660518 28.1167 160.6 5892 

01995001 Robert Conrad RC10 RC10159 core, piston 19660519 31.2167 162.3 5894 

01995001 Robert Conrad RC10 RC10160 core, piston 19660520 32.4667 159.8333 4621 

01995001 Robert Conrad RC10 RC10161 core, piston 19660521 33.0833 158 3587 

01995001 Robert Conrad RC10 RC10162 core, piston 19660522 31.4167 158.8 3913 

01995001 Robert Conrad RC10 RC10163 core, piston 19660522 32.7167 157.5 3550 

01995001 Robert Conrad RC10 RC10164 core, piston 19660523 31.7333 157.5 3766 

01995001 Robert Conrad RC10 RC10166 core, piston 19660523 31.8333 157.3333 3792 

....

....
A.10

The NGDC also archives data obtained during the Ocean Drilling Program and the Deep Sea Drilling

Project. These data sets contain information about grain-size distribution, particle density, porosity, and

other geophysical and geochemical parameters. These data sets should also be investigated to determine

their applicability to the proposed site.

A.2.4 Tsunami Sources

Three distinct categories of tsunami sources should be considered for the proposed nuclear power plant

site:

1. Known sources of historical tsunamis

2. Potential sources determined by a paleotsunami study

3. Sources that may generate a tsunami-like wave in a nearby inland water body.

A search of the NGDC tsunami source database should be conducted to determine the sources of

historical tsunami events at and near the proposed nuclear power plant site. As an example, Figure A-2

shows the tsunami source locations for the runup events for the states of California, Texas, Florida, and

New Jersey. The data from the NGDC database should be processed to exclude erroneous entries, and

tsunami experts should be consulted to determine whether any of the questionable tsunami sources are

credible for the proposed nuclear power plant site.

If a paleotsunami study was carried out, either a review of an existing effort or a site-specific one,

conclusions regarding potential tsunami sources that may affect the proposed site and its vicinity should

be considered.

The hydrological and topographical setting of the site should be thoroughly evaluated to determine

whether a tsunami-like wave in a nearby water body may result in a hazard at the proposed site. The

mechanisms that may generate a tsunami-like wave in nearby inland water bodies include hillslope

failures (similar to subaerial landslide), subaqueous landslides, and earthquakes. These sources should be

comprehensively documented with regard to their tsunamigenic potential.

A.3 Specification of the PMT

The PMT is the most severe tsunami that can reasonably occur at a site. Because the severity of tsunamis

that reach a site of interest is controlled not only by the severity of the source mechanism but also by the

behavior of the tsunami waves during propagation and inundation, it is generally not possible to a priori

determine the PMT source (González et al. 2007) for a specified site. However, parameters of similar

sources can be used to determine several candidate PMTs. These candidate PMTs should be further

evaluated to determine the most severe impact at the site.

Three source mechanisms of tsunami generation need to be considered: earthquakes, landslides (subaerial

and submarine), and volcanoes. Table A-3 lists the source parameters for the three source mechanisms

that can be used to determine the most severe source for the respective mechanisms.
A.11

Table A-3. Source parameters that control the severity of generated tsunamis.

Source Mechanism Source Parameters

Earthquakes Magnitude, depth, vertical displacement,

proximity to the site, orientation

Landslides Proximity to the site, volume, slope stability,

material properties, speed and acceleration

Volcanoes Proximity to the site, VEI, pyroclastic flow

properties, caldera size and depth

The most severe tsunamigenic earthquake should be determined by evaluating both near and far-field

earthquake zones. For example, for the West Coast of the United States, earthquake zones including the

Cascadia subduction zone (where the Juan de Fuca Plate is subducting below the North American Plate;

see Figure A-5), and subduction zones marked by the Aleutian trench (where the Pacific Plate is

subducting below the North American Plate), the Kurile trench (where the Pacific Plate is subducting

below the Okhotsk Plate), the Japan trench (where the Pacific Plate is subducting below the Eurasian

plate), the Philippine trench (a complex tectonic activity zone where the Eurasian and the Philippine

plates are converging), the Bougainville trench (northeast of Bougainville, the largest of the Solomon

Islands and a province of Papua New Guinea, where several micro-plates are interacting with the Pacific

Plates), and the Peru-Chile trench (where the Nazca Plate is subducting below the South American Plate)

should be investigated. The maximum moment magnitude that can reasonably be expected to occur at the

relevant earthquake zones should be determined. For each earthquake zone, a list of candidate PMT

earthquakes should be compiled with conservatively estimated source parameters that maximize the

tsunamigenic potential of the earthquakes. For example, an earthquake that results in a greater vertical

displacement will have a greater tsunamigenic potential than one with a smaller vertical displacement,

even if both had the same magnitude. Similarly, an earthquake closer to the site may result in a larger

tsunami because dispersion of the generated waves could be minimal. The relative orientation of the

rupture zone to the site can significantly affect the directivity of the tsunami waves; therefore, a smaller

earthquake that is optimally oriented to the proposed site can cause a more severe tsunami at the site.

Landslides often cause tsunamis that are locally severe but may be significantly weaker in the far-field. 

Therefore, the proximity of a tsunamigenic landslide to the site is very important. The stability of a slope

should be considered to determine possible landslide locations that may pose a tsunami hazard to the

proposed site. The tsunamigenic parameters for a landslide source are the volume, the speed and

acceleration of the slide, and the cohesiveness of the slide material. Conservative estimates of source

parameters should be made. Historical or known landslides as well as potential landslides should be

evaluated based on their respective tsunamigenic source characteristics. The landslides that have the

greatest potential to cause a severe tsunami should be selected in the candidate PMT landslides.

Tsunamis generated by volcanic activity in the vicinity of the proposed site should be evaluated, and their

tsunamigenic source parameters (listed in Table A-3) should be conservatively estimated. Tsunamis from

far-field sources may be of concern to the proposed site if the activity involves possible caldera collapse

or large flank failures. These far-field volcanoes should be evaluated with respect to 
A.12

Figure A-5. Tectonic plate boundaries of the world.
A.13

their tsunamigenic potential and the possibility of the generated tsunamis to reach the site. Based on an

evaluation of their tsunamigenic potential, candidate PMT volcanic sources should be selected.

All candidate PMT sources listed using the procedure described above should be used in tsunami

generation, propagation, and inundation simulations. Hazards from all of these tsunami simulations

should be evaluated to arrive at the hazards posed to the proposed site, as described below.

A.3.1 Scenario Tsunamis

Scenario tsunamis are those obtained from a set of different source parameters for each postulated

candidate PMT source. For example, for earthquake sources, the source parameters for each candidate

PMT should be varied within a reasonable range that is realistically possible to obtain scenario tsunamis. 

The NCTR database, when available for the postulated earthquake-induced PMT, should be consulted to

construct the scenario tsunamis by varying the location and number of unit sources. For each postulated

earthquake-induced PMT, a set of tsunamis should be obtained using the NCTR tsunami-forecasting

database approach. Each of these scenario tsunamis should be propagated to the site using site-specific

tsunami-propagation models, and inundation effects should be modeled using site-specific inundation

models. Tsunami hazards should be estimated for each scenario tsunami. The most severe hazard among

the scenario tsunamis for all candidate PMTs for all tsunamigenic mechanisms should be specified as the

site characteristic related to tsunamis.

A.4 Simulation of Tsunami Waves

For all scenario tsunamis, generation, propagation, and inundation modeling should be carried out. It

may be possible to use the precomputed offshore tsunami wave heights from the NCTR tsunami forecasts

database to set boundary conditions for inundation models for earthquake sources. However, if the

NCTR forecast database does not contain precomputed scenarios applicable to the proposed site, a

complete tsunami generation, propagation, and inundation modeling study may be required. Precomputed

offshore tsunami wave heights for sources other than earthquakes may not be feasible. Tsunamis from

these sources would need to be simulated on a case-by-case basis.

A tsunami modeling system, capable of modeling the three phases, generation, propagation, and

inundation, should be used to simulate the scenario tsunamis from each candidate PMT source selected

above. The tsunami modeling system should reflect the state-of-the-art in tsunami science. The tsunami

modeling system may be composed of different models that may be appropriate for the three phases of the

tsunami. The modeling system may also include different models that are appropriate for different source

mechanisms. However, all of the separate components of the modeling system should be properly

validated and verified using appropriate data, or shown to be accurate using site-specific data. Standards

for evaluating tsunami models are described by González et al. (2007, Appendix C). For tsunami hazard

assessment at proposed nuclear power plant sites, criteria for evaluating tsunami models that specifically

deal with verifying model predictions against historical tsunami observations are especially important. 

To reduce the effort involved with several separate validation and verification studies, use of a

community-accepted modeling system is recommended.
A.14

A.4.1 Generation

For each scenario of the postulated candidate PMT earthquakes, the initial tsunami waveform should be

estimated conservatively. For earthquake sources, the Okada (1985) formulation could be used to specify

the initial waveform. If the postulated rupture is highly heterogeneous, the Okada (1985) formulation

may be used with the rupture subdivided into several cells within which the slip distribution could be

assumed to be uniform.

Landslide and volcanic sources may need source-specific models of mass movement and tsunami

generation. Experts should be consulted to properly define and constrain tsunami generation models of

these sources with help from source surveys and model validation. For both of these sources, the

coupling of the generated tsunami wave with the dynamics of the mass movement should be carefully

investigated. If the coupling does not result in matching the speed of the mass movement with the speed

of the tsunami waves, the reasons for this mismatch should be documented.

It is also possible that concurrent tsunamigenic sources need to be considered during a tsunamigenic

event. For example, a tsunamigenic earthquake may generate a tsunami by vertical displacement of the

water column and also may cause a subaqueous landslide that subsequently generates another tsunami. 

These concurrent events also should be evaluated as a potential PMT event, especially if it is possible that

the separate effects of the concomitant events may combine to produce a more severe tsunami. It is also

possible that the initial waveforms from the concomitant tsunamigenic sources may be located at

significant distances from each other in space as well as in time. The potentially different locations and

directivity of concomitant tsunamis may result in significantly altered wavefields with potential impact on

the required extent of the modeling domain.

A.4.2 Propagation

The propagation of the generated tsunami waves from the source location toward the site should also be

modeled. The spatial extent of the modeling domain should be sufficient to account for the effects of the

bathymetry, the underwater mounts and ridges, and the presence of islands. The boundary conditions

should be carefully specified (see Chapter 6 of this report). For cases where concomitant tsunamis are

postulated (such as when a tsunamigenic earthquake triggers a landslide that also generates a tsunami),

the model simulations should be set up to account for the separate tsunami sources.

The precomputed offshore tsunami wave heights from the NCTR tsunami forecast database may be used

to reduce the effort of setting up and simulating an extensive area from the source to the proposed site. 

The precomputed offshore tsunami wave heights may be used to specify boundary conditions for a

significantly smaller modeling domain. Currently, only earthquake sources can be modeled using the unit

source approach, as demonstrated by the NCTR tsunami forecast database.

The propagation model should be chosen based on its acceptance in the tsunami modeling community. If

a model other than a widely accepted and validated one is used, the reason for this selection should be

documented, and the performance of the model should be clearly demonstrated using observed tsunami

wave heights and travel times.

The waves from the candidate PMT sources should be simulated for a sufficiently long duration to ensure

that all potentially large waves in the train of the tsunami waves have been simulated.
A.15

A.4.3 Inundation

During the inundation phase, the nonlinearity of the governing equations cannot be ignored. A model that

uses nonlinear governing equations should be used. Near-shore geometry, bottom friction, and

interaction of the tsunami waves with offshore and onshore structures can significantly affect the behavior

of the tsunami waves in the inundation phase and therefore have a significant impact on the estimation of

the metrics describing the hazards from the tsunami waves. Therefore, the model used to simulate the

inundation phase should be validated and verified against site-specific observations. If site-specific

observations are not available at the proposed site, model verification at similar sites may be used.

The simulations of the inundation phase of the scenario tsunamis for each candidate PMT should be

carried out to obtain the maximum runup elevation, the spatial extent of runup, the minimum drawdown

elevation, the spatial extent of drawdown, and the velocity and momentum fields.

A.5 Estimation of Hazards from the PMT

Based on the results from the inundation model for each scenario tsunami for all postulated candidate

PMTs, the most severe hazard metrics should be determined, including the following:

1. high-water level: a map of the highest water surface elevation

2. low-water level: a map of the lowest water surface elevation

3. potential for scouring: a map of the scour-enhancement parameter described in Chapter 5

4. deposition: a map of areas susceptible to deposition from tsunami wave action

5. forces: a map of the velocity field that may be used to estimate forces described in Chapter 5

6. debris accumulation: a map of areas susceptible to debris accumulation

7. projectiles: a map of the impact forces expected from a postulated worst-case projectile .

The maps obtained above should be specified as site characteristics related to tsunamis at the selected site. 

These site characteristics should be used to specify design bases for all SSC that are important to safety

and that may be exposed to tsunami hazards.

References

González F.I, E. Geist, C. Synolakis, D. Arcas, D. Bellomo, D. Carlton, T. Horning, B. Jaffe, J. Johnson,

U. Kanoglu, H. Mofjeld, J. Newman, T. Parsons, R. Peters, C. Peterson, G. Priest, V. Titov, A. Venturato,

J. Weber, F. Wong, and A. Yalciner. 2006. Seaside, Oregon Tsunami Pilot Study–Modernization of

FEMA Flood Hazard Maps, NOAA OAR Special Report, NOAA/OAR/PMEL, Seattle, Washington.

González F.I., E. Bernard, P. Dunbar, E. Geist, B. Jaffe, U. Kanoglu, J. Locat, H. Mofjeld, A. Moore,

C. Synolakis, and V. Titov. 2007. Scientific and Technical Issues in Tsunami Hazard Assessment of

Nuclear Power Plant Sites. NOAA Technical Memorandum OAR PMEL-136, Pacific Marine

Environmental Laboratory, Seattle, Washington.

Okada U. 1985. “Surface Deformation due to Shear and Tensile Faults in a Half-Space,.” Bulletin of the

Seismological Society of America 75(4):1135-1154.
A.16

Peters B., B. Jaffe, G. Gelfenbaum, and C. Peterson. 2003. Cascadia tsunami Deposit Database. U.S.

Geological Survey Open-File Report 03-13, and electronic database and GIS coverage [URL:

http://geopubs.wr.usgs.gov/open-file/of03-13/]. Accessed March 12, 2008.
BIBLIOGRAPHIC DATA SHEET

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NRC FORM 335

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NUREG/CR-6966

Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America

(Draft for Comment) 9 2008

J3301

Rajiv Prasad, Pacific Northwest National Laboratory Technical

Not Applicable

Pacific Northwest National Laboratory

P.O. Box 999

Richland, WA 99352

Division of New Reactor Licensing

Office of New Reactors

U.S. Nuclear Regulatory Commission

Washington, DC 20555

Elinor Cunningham, NRC Project Manager; Goutam Bagchi, NRC Technical Monitor

We describe the tsunami phenomenon with the focus on its relevance for hazard assessment at nuclear power plant sites.

Three tsunamigenic mechanisms—earthquakes, landslides, and volcanoes—are considered relevant. We summarize historical

tsunami occurrences, source mechanisms and damages caused by these events. Historical landslides and potential landslide

areas in earth’s oceans are described. The hierarchical-review approach to tsunami-hazard assessment consists of a series of

stepwise, progressively more-refined analyses to evaluate the hazard at a site. The hierarchical-review approach employs a

screening analysis to determine if a site is subject to tsunami hazard based on presence of a tsunamigenic source and the

location and elevation of the site. The screening analysis ensures that resources are not wasted at sites with little potential of

exposure to tsunamis. Tsunami hazards that may directly affect structures, systems, and components important to the safety of

a plant. Therefore, these structures, systems, and components should be adequately designed and, if required, protected. We

recommend using existing resources and previously completed tsunami-hazard assessments, if available and appropriate.

Detailed tsunami-hazard assessment at a nuclear power plant site should be based on the probable maximum tsunami. We

define the probable maximum tsunami, its determination at a site, and subsequent hazard assessment. A tsunamigenic source

that produces probable maximum tsunami hazards at a site may not be determined a priori. Therefore, several candidate

sources and the tsunamis generated from them under the most favorable tsunamigenic source and ambient conditions should

be evaluated. The set of hazards obtained from all such scenario tsunamis should be considered to determine design bases of

the plant structures, systems, and components. We describe international practices by Japan and the International Atomic

Energy Agency. The appendix provides a stepwise guide to site-independent analyses for tsunami-hazard assessment.

Tsunami

Tsunami-like waves

paleotsunami

source mechanism

runup

drawdown

scouring

hierarchical hazard assessment approach

Probable Maximum Tsunami

combined effects

PNNL-17397