UNITED STATES

DEPARTMENT OF COMMERCE

Carlos M. Gutierrez

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

VADM Conrad C. Lautenbacher, Jr.

Under Secretary for Oceans

and Atmosphere/Administrator

Office of Oceanic and 

Atmospheric Research

Richard W. Spinrad

Assistant Administrator

NOAA Technical Memorandum OAR PMEL-132

TACOMA, WASHINGTON, TSUNAMI HAZARD MAPPING PROJECT:

MODELING TSUNAMI INUNDATION FROM TACOMA AND 

Angie J. Venturato1

Chris C. Chamberlin1

Diego Arcas

Joint Institute for the Study of the Atmosphere and Ocean (JISAO)

University of Washington, Seattle, WA

Pacific Marine Environmental Laboratory

Seattle, WA

Pacific Marine Environmental Laboratory

Seattle, WA

January 2007

1

2

Vasily V. Titov

Harold O. Mofjeld2

Frank I. González

1

1

2

SEATTLE FAULT EARTHQUAKES
NOTICE

Mention of a commercial company or product does not constitute an endorsement by

NOAA/OAR. Use of information from this publication concerning proprietary products

or the tests of such products for publicity or advertising purposes is not authorized.

Contribution No. 2981 from NOAA/Pacific Marine Environmental Laboratory

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)

ii
Contents iii

Contents

1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2. Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3. Tsunami Sources . . . . . . . . . . . . . . . . . . . . . . . . . 2

3.1 Seattle Fault Scenario . . . . . . . . . . . . . . . . . . . . . . 3

3.2 Tacoma Fault Scenarios . . . . . . . . . . . . . . . . . . . . . 4

4. Tsunami Model . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.1 Digital Elevation Model Development . . . . . . . . . . . . . 7

4.2 Model Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5. Discussion of Modeling Results . . . . . . . . . . . . . . . . . 9

5.1 Seattle Fault Scenario . . . . . . . . . . . . . . . . . . . . . . 10

Offshore Dynamics . . . . . . . . . . . . . . . . . . . . . . . . 10

Inundation Details . . . . . . . . . . . . . . . . . . . . . . . . 10

5.2 Tacoma Fault Scenario . . . . . . . . . . . . . . . . . . . . . . 13

Offshore Dynamics . . . . . . . . . . . . . . . . . . . . . . . . 13

Inundation Details . . . . . . . . . . . . . . . . . . . . . . . . 15

5.3 Rosedale-Dominant Tacoma Fault Scenario . . . . . . . . . . 15

Offshore Dynamics . . . . . . . . . . . . . . . . . . . . . . . . 15

Inundation Details . . . . . . . . . . . . . . . . . . . . . . . . 16

6. Summary and Conclusions . . . . . . . . . . . . . . . . . . . . 17

7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19

8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix A: Modeling Products . . . . . . . . . . . . . . . . . . . 22

Appendix B: Data Credit . . . . . . . . . . . . . . . . . . . . . . . 23

Tacoma, Washington, Tsunami Hazard Mapping Project:

Modeling tsunami inundation from Tacoma and Seattle Fault

earthquakes

Angie J. Venturato1, Diego Arcas1, Vasily V. Titov1, Harold O. Mofjeld2, Chris D.

Chamberlin1, Frank I. Gonz ́alez2

Abstract. As part of a tsunami hazard mapping project funded by the National Tsunami

Hazard Mitigation Program, the NOAA Center for Tsunami Research (formerly known as the NOAA

Center for Tsunami Inundation Mapping Efforts) modeled tsunami inundation for the at-risk coastal

community of Tacoma, Washington. Three tsunamigenic moment magnitude 7.3 earthquake source

scenarios within the lower Puget Sound region were investigated: one along the Seattle Fault, and

two along the Tacoma fault based on the most recent geophysical evidence. A high-resolution

tsunami model was applied to estimate tsunami propagation in the southern Puget Sound region

and inundation along the greater Tacoma area. These model results (Appendix A) were provided to

the State of Washington for use in tsunami hazard maps to assist in the design of evacuation plans

for the at-risk study area.

1. Background

Puget Sound has a rich history of natural hazards, including large earthquakes, landslides, and delta failures. Geologic and historic evidence have

shown that some of these past events have generated tsunamis (Johnson et

al., 1999; Brocher et al., 2004; Sherrod et al., 2004). A 2002 workshop reviewed these historic events and recommended potential sources for tsunami

inundation modeling to further assess the coastal hazard (Gonz ́alez et al.,

2003). These recommendations included sources for the Tacoma region.

Though historic tsunamis within the region suggest a higher recurrence

rate for a landslide source (Table 1, Fig. 1), workshop participants suggested

that the “worst-case” scenario would likely have a seismic trigger (Gonz ́alez

et al., 2003). Therefore, this study focuses on tsunamigenic earthquakes

from Seattle and Tacoma fault sources based on the parameters established

by workshop participants and further refined by Tom Brocher and Tom Pratt

from the U.S. Geological Survey.

2. Study Area

The study area (Fig. 2) covers the coastal communities of Tacoma, Ruston,

Gig Harbor, northern University Place, and the Puyallup Nation reservation

in Pierce County and Federal Way, southern Vashon and Maury Islands of

King County, Washington. Dash Point State Park and several regional parks

(including Point Defiance, Titlow Beach, Sunrise Beach, and Ruston Way)

lie along the shores of the study area. The region also supports several

1Joint Institute for the Study of the Atmosphere and Ocean (JISAO), University of

Washington, Box 357941, Seattle, WA 98195-4235, USA 2NOAA, Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle,

WA 98115
2 Venturato et al.

recreational marinas, a major commercial port, two state ferry terminals,

and the Tacoma Narrows Bridge.

Maritime activity in Commencement Bay includes eight privately owned

marine terminals and the publicly owned Port of Tacoma. The Port of

Tacoma, the sixth largest commercial port in North America and the major

economic engine for Pierce County (Port of Tacoma, 2005), lies at the edge

of the Puyallup River delta. Eight waterways along the delta (Fig. 2b) are

maintained by the U.S. Army Corps of Engineers. A public esplanade lines

the western side of Thea Foss Waterway where several local outdoor events

take place.

The Puyallup River delta has a history of damaging submarine landslides

(Table 1). A landslide in 1894 generated a 10-foot wave that led to three

deaths, destroyed freight docks, and caused significant damage in historic

downtown Tacoma (Pierce County, 2004). In 1943, another submarine landslide produced a tsunami that destroyed jetties at the mouth of the Puyallup

River (Gonz ́alez et al., 2003). Several smaller, non-tsunamigenic landslides

have occurred on the delta since these events (Gardner et al., 2001).

The Narrows is a major recreational and commercial transit waterway

nested between Tacoma and the Kitsap Peninsula (Fig. 2a). High current

velocities occur in this channel with a range of 2–5 knots at ebb and flood

tides (National Ocean Service, 2006). The Tacoma Narrows Bridge, a primary thoroughfare, spans the midsection of The Narrows and is currently

under construction. The new bridge will consist of two suspension spans

and is scheduled for completion in 2008 (Washington State Department of

Transportation, 2005).

A tsunamigenic subaerial landslide at Salmon Beach occurred in 1949

three days after a surface-wave magnitude (Ms) 7.1 Olympia earthquake.

Estimated 6- to 8-foot tsunami waves were generated in The Narrows, damaging piers and boats in Gig Harbor and Salmon Beach (Lander, 1993; Chleborad, 1994).

3. Tsunami Sources

Three source scenarios were investigated for this study. One is based on a

moment magnitude (Mw) 7.3 earthquake along the Seattle Fault as described

in Titov et al., 2003. The other source scenarios are based on Mw 7.3

Table 1: Known historic tsunami events in the study area.

Event numbers are associated with estimated locations displayed in Fig. 1 (Chleborad, 1994; Gardner et al., 2001;

Gonz ́alez et al., 2003).

Event Number Date Type

1 1894 Deltaic submarine landslide

2 1943 Deltaic submarine landslide

3 16 April 1949 Subaerial landslide
Tacoma, Washington, Tsunami Hazard Mapping Project 3

Figure 1: Seattle and Tacoma fault segments used for the study (Brocher et al., 2004). Published fault

traces, co-seismic deformation, and known historic tsunami events are also displayed (Sherrod et al., 2004;

Johnson et al., 1999, 2004; Gonz ́alez et al., 2003; Gardner et al., 2001).

earthquakes along the Tacoma Fault provided by Brocher and Pratt based

on recent fault scarps detected through LIDAR mapping (Sherrod et al.,

2004). The detailed structure of both the Seattle and Tacoma faults are

under much debate; however, tsunamigenesis depends primarily on surface

displacement, which is fairly well determined by recent work in the field to

provide reasonable assessments of these fault structures (Pratt et al., 1997;

Johnson et al., 1999; Sherrod et al., 2004).

Brocher et al. (2004) suggest that the Seattle and Tacoma faults are

linked, such that a seismic event on one fault may trigger movement on

the other. Recent field evidence suggests displacements occurred along both

faults approximately 1100 years ago (Sherrod et al., 2004). Though the scenarios are constrained by these measured vertical displacements, this duality

was not considered in this study. Each fault model is described in detail in

the following subsections.

3.1 Seattle Fault Scenario

The Seattle Fault scenario is based on six segments of varying length, strike,

and slip (Table 2). The length and strike parameters are well within the
4 Venturato et al.

Figure 2: Study area of the tsunami hazard mapping project for Tacoma, Washington (a). Details of the

(b) Puyallup Delta region and (c) Gig Harbor. Seven sites were selected to delineate time series of tsunami

wave heights and current speeds (Fig. 6).

range of possibilities described in Gonz ́alez et al., 2003. The slip distribution was constrained to match vertical displacement estimates at Restoration

Point, Alki Point, and West Point (Fig. 1) from a Seattle Fault earthquake

in A.D. 900–930 (Bucknam et al., 1992; Atwater, 1999). Table 3 provides

a comparison of the computed model displacement (Fig. 3) with field estimates.

3.2 Tacoma Fault Scenarios

The Tacoma Fault scenarios were prepared by Tom Pratt and Tom Brocher.

Two scenarios of equal probability are considered due to geophysical evidence (Brocher et al., 2004; Sherrod et al., 2004). The west end (fault

segment T1) of both scenarios is based on a prominent geophysical lineament that extends through Case Inlet as evidenced by seismic tomography

and trenching (Sherrod et al., 2004). The eastern end from Case Inlet to

Dumas Bay is less defined, with at least three fault lines found north and
Tacoma, Washington, Tsunami Hazard Mapping Project 5

Figure 3: Modeled source scenarios for the (a)

Seattle Fault, (b) Tacoma Fault, and (c) Rosedaledominant Tacoma Fault. Vertical ground displacements are shown in meters.

south of Commencement Bay (Fig. 1). Given the uncertainty, two fault scenarios are considered: (1) the Tacoma Fault scenario based on published

fault traces from Johnson et al. (1999, 2004) and (2) the Rosedale-dominant

Tacoma Fault scenario based on an inferred wedge tip along the Rosedale

monocline (Brocher et al., 2004). The Tacoma Fault scenario is based on

fault segments T1 through T5 and the Rosedale-dominant Tacoma Fault

scenario is based on fault segments T1 and T6 (Table 4). The modeled slip

distribution (Fig. 3) for each scenario matches fairly well with preliminary

vertical displacement estimates at six field stations (Table 5) described by

Sherrod et al. (2004).
6 Venturato et al.

Table 2: Seattle Fault segment seismic parameters as described in Titov

et al. (2003) and displayed in Fig. 1.

Length Width Strike Dip Displacement

Fault Segment (km) (km) (deg.) (deg.) (m)

F1 15.2 35.0 87.9 60.0 1.0

F2 6.3 35.0 86.6 60.0 1.0

F3 8.9 35.0 96.0 60.0 12.0

F4 3.3 35.0 128.8 60.0 11.0

F5 11.5 35.0 99.3 60.0 4.0

F6 14.9 35.0 81.0 60.0 1.0

Table 3: Vertical deformation comparison

based on field estimates and the Mw 7.3 Seattle Fault model. Vertical deformation sites are

displayed in Fig. 1.

Site Field (m) Model (m)

Alki Point 4–6.5 3.6

Restoration Point 7 7.2

West Point −1 ± 0.5 −1.1

Table 4: Tacoma fault segment seismic parameters based on Sherrod et

al. (2004) and displayed in Fig. 1. The Tacoma Fault scenario is based

on segments T1–T5; the Rosedale-dominant Tacoma Fault is based on

segments T1 and T6 only.

Length Width Strike Dip Displacement

Fault Segment (km) (km) (deg.) (deg.) (m)

T1 10.0 14.1 268.9 45.0 5.6

T2 10.0 14.1 260.8 45.0 4.2

T3 10.0 14.1 274.0 45.0 2.8

T4 8.0 14.1 276.3 45.0 1.4

T5 8.0 14.1 279.5 45.0 1.4

T6 33.0 14.1 129.2 45.0 3.0

Table 5: Vertical deformation comparison based on preliminary field

estimates (Sherrod et al., 2004 and Sherrod, personal communication)

and the Mw 7.3 Tacoma and Rosedale-dominant Tacoma Fault models.

Vertical deformation sites are displayed in Fig. 1.

Tacoma Fault Rosedale-dominant

Site Field (m) Model (m) Model (m)

Lynch Cove 3 1.1 1.0

North Bay 4 2.3 2.2

Catfish Lake 4 3.2 3.4

Burley 1 1.3 −0.1

Wollochet Bay −1 −0.1 1.3

Dumas Bay 0 −0.1 −0.1
Tacoma, Washington, Tsunami Hazard Mapping Project 7

Figure 4: Extent and resolution of each digital elevation model (DEM) used in the study. The lowresolution DEM consists of only bathymetric depth values; the medium- and high-resolution DEMs consist

of both bathymetric depth and topographic elevation values relative to Mean High Water.

4. Tsunami Model

Tsunami propagation and inundation for the study region is computed using the Method of Splitting Tsunami (MOST) model (Titov and Gonz ́alez,

1997; Titov and Synolakis, 1995). MOST is a finite-difference long wave approximation model that has been extensively tested against laboratory experiments (Titov and Synolakis, 1998) and field data from historic tsunamis

(Titov et al., 2004). Titov et al. (2003) describes the application of the

MOST model for a tsunami in Puget Sound. The following sections briefly

describe the computational grids and specific modeling parameters used for

this inundation study.

4.1 Digital Elevation Model Development

The MOST model requires nested computational grids to calculate the complicated wave dynamics of tsunami generation, propagation, and inundation.

Three digital elevation models (DEMs) were developed for this study (Fig. 4).

Bathymetric and topographic data were collected from government agencies

and analyzed to select sources of the best quality (Appendix B). The spatial

density of the selected data ranged from 0.6 to 30 m.

The selected data were converted to geographic decimal degrees (North

American Datum of 1983) with vertical units of meters with respect to Mean

High Water. Bathymetric data were converted to Mean High Water using
8 Venturato et al.

Table 6: Vertical control. Values are with

respect to Mean Lower Low Water based on

the Tacoma National Ocean Service secondary

water-level control station 944-6484.

Datum Meters

TIDE22 (Local datum) 5.901

Mean High Water 3.336

Mean Sea Level 2.094

North American Vertical Datum 1988 0.758

Port datum (Local datum) 0.137

Mean Lower Low Water 0.000

Table 7: Quantitative root mean square (RMS) error estimate of the DEMs. Estimated RMS

error was calculated based on source references (Hess and Smith, 2004; Snyder, 1987) and methods

described in Venturato (2005). The total error is the sum of the quantitative values. Subjective

interpretation due to combining multiple data sources adds unknown error to the DEMs.

Horizontal Error Range Vertical Error Range

Error Type (m) (m)

Projection/datum conversion 0.15–0.25 0.03–0.20

Comparison with vertical control benchmarks N/A 0.27–1.81

Comparison with original data sources 0.67–10 0.35–0.98

Total known quantitative error 0.82–10.25 0.65–2.99

local datum conversions from the U.S. Army Corps of Engineers, the Port

of Tacoma, and the vertical datum conversion tool known as VDatum (Hess

and White, 2004). Topographic data were converted to Mean High Water

using tidal and geodetic benchmark information from the National Ocean

Service. Table 6 provides more information about vertical datum conversion

values.

A shoreline file representing the Mean High Water line was generated

based on data from the Washington State Department of Ecology and the

Port of Tacoma. Piers with open pile foundations were removed from the

shoreline data since tsunami waves can propagate under them.

DEMs of 1/3-, 1-, and 3-arc-second resolution for tsunami inundation,

propagation, and generation regions, respectively, were developed using Delauney triangulation and natural neighbor interpolation. Though assessing

the quality of a DEM based on multiple data sources is difficult, an attempt to quantify some factors of error (Table 7) were made using methods

described in Venturato (2005).

4.2 Model Setup

The 1/3-, 1-, and 3-arc-second DEMs were converted to ASCII raster grids

and then sub-sampled to 1-, 3-, and 9-arc-second grids to ease the computational load on the MOST model. Since the grids are based on a “bald-earth”

(Venturato et al., 2005), a bottom friction coefficient is used in the model.

The Manning parameter for this study was set to 0.055.
Tacoma, Washington, Tsunami Hazard Mapping Project 9

Figure 5: Maximum inundation (a, c, e) and maximum wave speeds (b, d, f) for each source scenario.

The Seattle Fault scenario has the most inundation and highest currents. The Tacoma Fault scenario has

significant inundation in the Port of Tacoma region, but with smaller amplitudes. The Rosedale-dominant

Tacoma Fault scenario depicts the least inundation and lowest current speeds.

5. Discussion of Modeling Results

All three scenarios create significant vertical displacements along their respective fault surfaces. The Seattle Fault scenario creates the most intense

currents and inundation (Figs. 5, 6) within the study area due to the large

displacement of water in the deepest and widest region of Puget Sound. The

Tacoma Fault scenario causes less inundation overall since much less water is displaced in the narrower and shallower regions of Carr Inlet, Colvos

Passage, and East Passage. The Rosedale-dominant Tacoma Fault scenario

causes the least amount of inundation in the study region due to relatively

small displacements in the regional channels.

Most inundation occurs within low-lying, relatively flat regions of the

study area such as the Port of Tacoma harbor in Commencement Bay. Minimal inundation occurs along steep topographical slopes. Consequently, the

inundation is determined primarily by local topography rather than offshore

wave dynamics. This correlates well with previous observations of long period tsunami waves, which lose their energy via bottom friction over long
10 Venturato et al.

penetration distances (Titov et al., 2003). The following sections provide

more details on the offshore wave dynamics and inundation of each tsunamigenic scenario.

Due to constraints of the inundation grid, the model does not cover the

full extent of wave propagation in the upper Puyallup River; subsequently,

the wave reflects off the edge of the grid boundary leading to potentially

nonphysical inundation within the City of Fife and Puyallup Nation territory.

5.1 Seattle Fault Scenario

Offshore Dynamics

The Seattle Fault source creates a sharp dislocation along the fault plane

extending across northern Kitsap Peninsula and eastward through south

Seattle. Minor subsidence occurs on the north side of the fault. South of the

fault, a large uplift occurs with a maximum 8 m in the southern Bainbridge

Island region and diminishing in intensity throughout the southern Puget

Sound region (Fig. 3). This rupture forms the initial tsunami wave between

Alki Point and Restoration Point, which is one of the deepest regions of

central Puget Sound. Two wave fronts are formed: one traveling north

impacting Elliott Bay and northern Puget Sound, and the other traveling

south toward Tacoma and southern Puget Sound. The southern wave front

splits into two upon striking the northern tip of Vashon Island 4 min after

initial deformation. The eastern and more intense front travels down East

Passage striking northern Maury Island and Dumas Bay and then reflecting

off the Ruston Way waterfront and southern Vashon Island 12 min after

generation (Fig. 7). The weaker west front travels down Colvos Passage

striking Point Defiance before joining with the stronger reflected wave in

Dalco Pass. Maximum wave crests of approximately 3.5 m amplitudes reach

Commencement Bay and Gig Harbor approximately 19 min after generation

(Fig. 6). Part of the primary front’s reflected wave energy travels north

into Quartermaster Harbor and back up East Passage toward Elliott Bay

and northern Puget Sound. The remaining wave energy travels into The

Narrows and then dissipates in southern Puget Sound. Smaller though still

significant waves continue to reflect back and forth within the study region

for 3 hr.

High (>1.5 m/s) wave velocities occur within Commencement Bay, Gig

Harbor, East Passage, Quartermaster Harbor, The Narrows, and Wollochet

Bay. Since the model does not dynamically include tidal currents, the current

speeds may be more substantial if these events occurred during a flood tide.

Inundation Details

Dumas Bay Park is the first area to be inundated in the study region approximately 10 min after tsunami generation (Fig. 8). Tsunami vertical runup

reaches 3.2 m with inundation extending 250 m inland.

Inundation along the Ruston Way waterfront starts approximately 12 min

after earthquake generation. This popular recreational area would be struck
Tacoma, Washington, Tsunami Hazard Mapping Project 11

Figure 6: Time series of tsunami wave heights and current speeds at select sites of the study region.

Figure 1 displays the associated site locations.
12 Venturato et al.

Figure 7: Modeled tsunami propagation in Puget Sound from the Seattle Fault scenario. Snapshots are in

15-min intervals with wave amplitudes in meters.

with an initial maximum 3.2-m wave overtopping several piers and inundating the sole roadway along the waterfront.

Approximately 14 min after generation, the tsunami starts to inundate

the Port of Tacoma and the Thea Foss Waterway, building to a 3.5-m wave

that overtops port facilities, the public esplanade, and adjacent low-lying

neighborhoods as harbor channels and the Puyallap River flood. The total

inundation area extends over 5 km inland along the Puyallup River delta.

Inundation occurs at both State ferry terminals approximately 18 min

after tsunami generation. The Tahlequah terminal at the southern point of

Vashon Island is hit with an initial 3.3-m wave with speeds ranging from

5–7 m/s and overtopping the dock and staging area. A 3.9-m wave strikes

the Point Defiance terminal and marina at speeds of approximately 3 m/s.

Inundation extends 80 m inland on a slag fill peninsula, an Environmental

Protection Agency Superfund site (Washington State Department of Transportation, 2006), flooding the main marina access road northeast of the

terminal.

The tsunami wave arrives at Gig Harbor approximately 19 min after
Tacoma, Washington, Tsunami Hazard Mapping Project 13

Figure 8: Modeled tsunami inundation in the study region from the Seattle Fault scenario. Snapshots are

in 10-min intervals starting near the time of initial inundation at the Port of Tacoma. Wave heights are in

meters with respect to Mean High Water.

generation. Tsunami vertical runups above 2 m occur along the northernmost tip of the harbor, inundating a local park. Current speeds are 1–2 m/s

within the harbor, and reach above 5 m/s at the harbor entrance.

High current speeds ranging from 2–3 m/s also occur in the Narrows

(Fig. 6). The initial wave reaches Titlow Park approximately 20 min after

tsunami generation. The southern half of Titlow Park and a rail line are

completely inundated with maximum wave runups reaching 3 m.

5.2 Tacoma Fault Scenario

Offshore Dynamics

The Tacoma Fault scenario creates a moderate uplift north of the fault plane

with minimal subsidence (<0.5 m) south of the fault. The sharpest dislocation (3.4 m) occurs along the western edge of the fault, with diminishing

intensity eastward. Much of the dislocation occurs on land and the shallow

regions of Lynch Cove, North Bay, and Burley Lagoon. Smaller ruptures

(0.7–2 m) along the eastern edge of the fault form the primary tsunami

wave energy within Colvos Passage, Quartermaster Harbor, and East Passage (Fig. 3).

The initial displacement splits the wave energy into northbound and
14 Venturato et al.

Figure 9: Modeled tsunami propagation in Puget Sound from the Tacoma Fault scenario. Snapshots are

in 15-min intervals with wave heights in meters.

southbound fronts. The southbound front in Colvos Passage strikes Point

Defiance 5 min after tsunami generation and subsequently splits further into

a 0.5-m wave traveling into Dalco Pass, a 0.7-m wave into Gig Harbor, and

a 0.8-m wave down The Narrows (Fig. 6).

The southbound front in East Passage creates a 1-m wave crest that

strikes Dumas Bay 3 min after generation before joining the wave in Dalco

Pass and a smaller wave from Quartermaster Harbor before reaching Commencement Bay. Part of the combined wave energy is reflected off the Ruston

wave waterfront and travels back into East Passage. The remaining wave

energy strikes the Port of Tacoma with a wave crest of 0.6 m approximately

10 min after generation.

The wave traveling down The Narrows reaches Fox Island 15 min after

generation and then splits into a wave front traveling up Hale Passage and

another toward Nisqually Reach dissipating in south Puget Sound (Fig. 9).

Wave crests of 0.8 m amplitudes reach Wollochet Bay 20 min after generation. Smaller wave activity is witnessed throughout the study region for

approximately 1.5 hr.
Tacoma, Washington, Tsunami Hazard Mapping Project 15

High current speeds (>1.5 m/s) occur at the entrance to Gig Harbor,

both ferry terminals, Port of Tacoma waterways, and the recreational area

of Dumas Bay.

Inundation Details

Dumas Bay Park is inundated approximately 3 min after tsunami generation

with vertical runups reaching 3.5 m (Fig. 5). The waterfront promenade

along the north side of Point Defiance Park is struck 5 min after generation

with maximum vertical runups reaching 2 m.

Inundation along both ferry terminals occur approximately 7 min after

generation with runups reaching 1.5 m and current speeds ranging from 2–

3 m/s. Gig Harbor is struck next at 8 min with maximum vertical runups

reaching 2 m and inundating the local boat marina. Inundation along the

Ruston Way waterfront starts approximately 8 min after generation with

the highest runup values of 2.4 m inundating the promenade and roadway.

The tsunami hits the Thea Foss Waterway and Port of Tacoma with an

initial 0.6-m wave 10 min after generation. The initial wave front does not

overtop port facilities; instead, the wave crest builds up in the waterways

and begins overflowing port banks at 15 min. Resonance in the waterways

and Puyallup River continue to overflow the channels, and the port and

public esplanade are slowly inundated over a period of 3 hr (Fig. 10). The

majority of the port has runup values around 1 m, though maximum vertical

runups reach 3 m at the termini of Blair and Thea Foss waterways and along

Puyallup River banks. The total inundation area extends over 3 km inland.

Current speeds are relatively low in The Narrows, ranging from 0.2–

0.4 m/s (Fig. 6). The initial wave crest inundates Titlow Park approximately

12 min after generation with maximum runups reaching 2.5 m and washing

over the rail line.

5.3 Rosedale-Dominant Tacoma Fault Scenario

Offshore Dynamics

The Rosedale-dominant Tacoma Fault scenario creates moderate uplift

(3.6 m) north of the fault plane. Like the Tacoma Fault scenario, the sharpest

dislocation occurs primarily on land and shallow waters along the western

edge of the fault. A smaller rupture (1.3 m) on the 33-km fault segment along

the Rosedale monocline initiates the primary water displacement within Carr

Inlet, Wollochet Bay, Hale Passage, and The Narrows (Fig. 3).

Within the primary rupture zone, high currents (>1.5 m/s) occur within

Wollochet Bay and along the shores of Titlow Park. Moderate current speeds

(0.5–1.2 m/s) occur within Hale Passage and The Narrows. Most of the

initial tsunami energy is directed toward Nisqually Reach traveling into Case

Inlet and Dana Passage (Fig. 2) where it dissipates in the shallow waters of

southwestern Puget Sound. A strong wave also strikes Burley lagoon at the

terminus of Carr Inlet within 10 min of generation (Fig. 11).

Remaining wave energy travels north up The Narrows with the initial

wave front diminishing from 0.8 to 0.4 m before reaching the entrance to
16 Venturato et al.

Figure 10: Modeled tsunami inundation in the study region from the Tacoma Fault scenario. Snapshots

are in 10-min intervals starting near the time of initial inundation at the Port of Tacoma. Wave heights are

in meters.

Gig Harbor 9 min after generation. Part of the wave continues up Colvos

Passage and dissipates in central Puget Sound. A 0.2-m wave front reaches

Commencement Bay 19 min after generation. This tsunami energy does not

dissipate quickly, but sloshes back and forth between the shores of the study

region (Fig. 6), starting inundation along the Port of Tacoma 30 min after

generation.

A second smaller wave front (0.4 m) travels up The Narrows due to

reflected energy from Carr Inlet, Wollochet Bay, and Nisqually Reach approximately 30 min after generation (Fig. 11). This wave combines with the

complicated wave activity within Dalco Pass, leading to a second minor wave

(0.2 m) striking the Port of Tacoma 40 min after generation. The tsunami

continues to dissipate within the region for 4 hr.

Inundation Details

The shores along Wollochet Bay and southern Titlow Park are inundated

within 5 min of tsunami generation with maximum runups of 1 m (Fig. 5).

Gig Harbor marina is inundated with 1.3 m vertical runups 12 min after

generation. The promenade along the north side of Point Defiance Park and

Point Defiance ferry terminal are inundated with a 1-m wave at the same
Tacoma, Washington, Tsunami Hazard Mapping Project 17

Figure 11: Modeled tsunami propagation in Puget Sound from the Rosedale-dominant Tacoma Fault

scenario. Snapshots are in 15-min intervals with wave heights in meters.

time. The Tahlequah ferry terminal receives minor inundation and current

speeds at both terminals are small (<0.3 m/s).

Inundation at the Port of Tacoma begins 30 min after generation as

tsunami energy builds up in the Puyallup River overtopping its banks. The

region around the river is slowly flooded with average vertical runups of

0.5 m (Fig. 12). This flooding starts to spill into Thea Foss Waterway 2 hr

after the earthquake, just as another round of minor tsunami waves reaches

the waterway. This causes resonant activity within the waterway that builds

up, eventually overflowing the channel and causing minor inundation (0.3 m)

along the Thea Foss esplanade 3 hr after the earthquake. The remaining

waterways do not contribute to the inundation.

6. Summary and Conclusions

This project studied local tsunami inundation and regional propagation effects in the greater Tacoma and Gig Harbor region based on three modeling scenarios simulating tsunamigenic earthquakes along the Seattle and
18 Venturato et al.

Figure 12: Modeled tsunami inundation in the study region from the Rosedale-dominant Tacoma Fault

scenario. Snapshots are in 10-min intervals starting near the time of initial inundation at the Port of Tacoma.

Wave heights are in meters.

Tacoma faults. The results of this study (Appendix A) are being used to

develop tsunami hazard maps for the area.

The results show that a Mw 7.3 earthquake along the Seattle Fault would

generate the most inundation at Tacoma and Gig Harbor. This conclusion

is credible given that the Seattle Fault displaces a significantly greater volume of water than either Tacoma Fault model. Additionally, the deep East

Passage acts like a one-dimensional channel allowing significant wave energy

to reach the lower Puget Sound region. Both Tacoma Fault scenarios displace less water and the wave series must travel through several shallower

channels, causing significant energy dissipation before reaching the shores of

Tacoma or Gig Harbor.

All three scenarios cause inundation along the Port of Tacoma and Puyallup River. However, the wave action causing the inundation is significantly

different for the Seattle Fault scenario in that the initial wave overtops the

port due to a high amplitude. The Tacoma scenarios cause inundation by

overflowing the harbor waterways over time.

Model results also show significantly high currents in the major marine

transit channels and ports for all three scenarios. Tidal currents were not included in the tsunami simulations but may add to the tsunami hazard. Mean
Tacoma, Washington, Tsunami Hazard Mapping Project 19

High Water is used as a background level for the inundation model, with the

assumption that tides interact linearly with the propagating tsunami wave.

This study provides a good first step toward analyzing the impact of

tsunamigenic earthquakes within Puget Sound on Tacoma and Gig Harbor.

However, this study does not consider tsunamigenic landslides that occur

due to earthquakes or other mechanisms. Lower Puget Sound has a history

of tsunamigenic subaerial and submarine landslides along the Puyallup delta

and The Narrows (Fig. 1, Table 1). Slope stability maps also suggest a high

probability of subaerial or submarine landslides within the study region.

Gonz ́alez et al. (2003) suggest that a deltaic submarine landslide associated

with a major earthquake would produce a credible “worst-case” scenario for

the study region.

The results of this study led to recommendations for future research in

tsunamigenic hazards within lower Puget Sound:

• Research the inclusion of dynamic tidal interaction with the model.

• Characterize the geometry of potential deltaic and non-deltaic landslides within the study region.

• Review the tsunamigenic sources for the hazard every few years as

new research adds to the understanding of the Seattle-Tacoma fault

structures and their possible relationship.

7. Acknowledgments

This research was funded by the National Tsunami Hazard Mitigation Program via a grant from the Washington State Emergency Management Division. This publication is partially funded by the Joint Institute for the

Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative

Agreement No. NA17RJ1232, Contribution #1338.

The authors thank George Crawford (Washington State Emergency Management Division), Tim Walsh (Washington State Department of Natural

Resources), Tom Brocher (U.S. Geological Survey), Brian Sherrod (U.S. Geological Survey), Tom Pratt (U.S. Geological Survey), and Craig Weaver

(U.S. Geological Survey) for assistance with the tsunamigenic sources for

this study.

We also thank Rene Rodriguez (University of Washington), Jon Kulju

(Port of Tacoma), and Lonnie Reid-Pell (U.S. Army Corps of Engineers) for

assistance with data sources and processing.

8. References

Atwater, B.F. (1999): Radiocarbon dating of a Seattle earthquake to A.D. 900–930.

Seis. Res. Lett., 70, 232.

Brocher, T.M., R.J. Blakely, and R.E. Wells (2004): Interpretation of the Seattle

Uplift, Washington, as a Passive-Roof Duplex. Bull. Seis. Soc. Am., 94(4),

1379–1401.
20 Venturato et al.

Bucknam, R.C., E. Hemphill-Haley, and E.B. Leopold (1992): Abrupt uplift within

the past 1700 years at southern Puget Sound, Washington. Science, 258, 1611–

1614.

Chleborad, A.F. (1994): Modeling and analysis of the 1949 Narrows landslide,

Tacoma, Washington. Bull. Assoc. Eng. Geol., 31, 305–327.

Gardner, J.V., E.J. van den Ameele, G. Gelfenbaum, W. Barnhardt, H. Lee, and S.

Palmer (2001): Mapping southern Puget Sound delta fronts after 2001 earthquake. Eos Trans., Am. Geophys. Union, 82(42), 485, 488–489.

Gonz ́alez, F.I., B.L. Sherrod, B.F. Atwater, A.P. Frankel, S.P. Palmer, M.L. Holmes,

R.E. Karlin, B.E. Jaffe, V.V. Titov, H.O. Mofjeld, and A.J. Venturato (2003):

Puget Sound Tsunami Sources—2002 Workshop Report. NOAA OAR Special

Report, 34 pp.

Hess, K.W., and S.A. White (2004): VDatum for Puget Sound: Generation of the

grid and population with tidal datums and sea surface topography. NOAA

Tech. Memo. NOS CS 4, 27 pp.

Johnson, S.Y., R.J. Blakely, W.J. Stephenson, S.V. Dadisman, and M.A. Fiser

(2004): Active shortening of the Cascadia forearc and implications for seismic

hazards of the Puget Lowland. Tectonics, 23, TC1011.

Johnson, S.Y., S.V. Dadisman, J.R. Childs, and W.D. Stanley (1999): Active tectonics of the Seattle fault and central Puget Sound, Washington—Implications

for earthquake hazards. Geol. Soc. Am. Bull., 111, 1042–1053.

Lander, J.F., P.A. Lockridge, and M.J. Kozuch (1993): Tsunamis affecting the

west coast of the United States 1806–1992. NGDC Key to Geophysical Record

Documentation 29, NOAA, 242 pp.

National Ocean Service (2006): Predicted Tidal Currents for The Narrows. http:

//tidesandcurrents.noaa.gov/

Pierce County (2004): Pierce County Hazard Mitigation Plan. Pierce County Department of Emergency Management, Section 4.

Port of Tacoma (2005): Economic Impact of the Port of Tacoma. Port of Tacoma

Commission, 42 pp.

Pratt, T.L., S. Johnson, C. Potter, W. Stephenson, and C. Finn (1997): Seismic

reflection images beneath Puget Sound, western Washington State: The Puget

Lowland thrust sheet hypothesis. J. Geophys. Res., 102(B12), 27,469–27,489.

Sherrod, B.L., T.M. Brocher, C.S. Weaver, R.C. Bucknam, R.J. Blakely, H.M.

Kelsey, A.R. Nelson, R. Haugerud (2004): Holocene fault scarps near Tacoma,

Washington. Geology, 32(1), 9–12.

Snyder, J.P. (1987): Map Projections—A working manual. USGS Professional

Paper 1395, 383 pp.

Titov, V.V., F.I. Gonz ́alez, E.N. Bernard, M.C. Eble, H.O. Mofjeld, J.C. Newman,

and A.J. Venturato (2004): Real-time tsunami forecasting: Challenges and

solutions. Nat. Haz., 35(1), 41–58.

Titov, V.V., F.I. Gonz ́alez, H.O. Mofjeld, and A.J. Venturato (2003): NOAA TIME

Seattle Tsunami Mapping Project: Procedures, Data Sources, and Products.

NOAA Tech. Memo. OAR PMEL-124, 21 pp.

Titov, V.V. and F.I. Gonz ́alez (1997): Implementation and testing of the Method

of Splitting Tsunami (MOST) model. NOAA Tech. Memo. ERL PMEL-112,

11 pp.

Titov, V.V., and C.E. Synolakis (1998): Numerical modeling of tidal wave runup.

J. Waterw. Port Coast. Ocean Eng., 124(4), 157–171.

Titov, V.V., and C.E. Synolakis (1995): Modeling of breaking and non-breaking

long wave evolution and runup using VTCS-2. J. Waterw. Port Coast. Ocean.

Eng., 121(6), 306–316.

Venturato, A.J. (2005): A digital elevation model for Seaside, Oregon: Procedures,

data sources, and analyses. NOAA Tech. Memo. OAR PMEL-129, 17 pp.
Tacoma, Washington, Tsunami Hazard Mapping Project 21

Washington State Department of Transportation (2006): Point Defiance and Tahlequah Ferry Terminal Feasibility Study. http://www.wsdot.wa.gov/Projects/

Washington State Department of Transportation (2005): The Tacoma Narrows

Bridge Project Folio. http://www.tacomanarrowsbridge.com/
22 Venturato et al.

Appendix A: Modeling Products

Model results, metadata, and documentation were provided to the Washington State Division of Geology and Earth Resources and the Washington

State Military Department Emergency Management Division, which are responsible for redistribution of these products. A list of the data series is

provided in Table A1. All geospatial data are in ESRI ArcGIS© format

with the following parameters:

• Projection: State Plane Coordinate System Zone 5626 (Washington

South)

• XY Units: feet

• Z Units: meters or meters/second

• Horizontal Datum: North American Datum of 1983

• Vertical Datum: Mean High Water

Table A1: Product summary.

Item Name Type

0 Presentations, Product Report, Grid Report Documentation

1 sea animation, tac animation,

tacrd animation

Animations of tsunami propagation and

inundation

2 DEMs, Legends, Shoreline, Timeseries sites,

Model Grids, Source Scenarios

Geospatial data in ESRI ArcGIS© shapefile

or ASCII Raster format

3 hi res images, low res images Images for use in maps or general

distribution

4 wa tacoma FGDC-compliant metadata

5 tac timeseries Tsunami time series at selected points of

interest
Tacoma, Washington, Tsunami Hazard Mapping Project 23

Appendix B: Data Credit

NOAA National Geodetic Survey (2004): Vertical Geodetic Control Data.

Silver Spring, Maryland. http://www.ngs.noaa.gov/

NOAA National Geophysical Data Center (2002): NOS Hydrographic Database, GEODAS Version 4.1.18. Boulder, Colorado. http://ngdc.

noaa.gov/

NOAA National Ocean Service (2004): Regional Water-Level Station Benchmarks. Silver Spring, Maryland. http://tidesandcurrents.noaa.

gov/benchmarks/

NOAA National Ocean Service Coastal Survey Development Laboratory

(2004): VDatum Transformation Tool Version 1.06. Silver Spring,

Maryland. http://nauticalcharts.noaa.gov/csdl/vdatum.htm

Port of Tacoma: 2002 Topographic contours. http://www.portoftacoma.

com/

U.S. Army Corps of Engineers (2001): Tacoma Harbor, Blair Waterway,

and Hylebos Waterway Condition Surveys. Seattle, Washington. http:

//www.nws.usace.army.mil/

U.S. Geological Survey EROS Data Center (1999): Seamless Data Distribution System National Elevation Dataset. Boulder, Colorado. http:

//seamless.usgs.gov/

U.S. Geological Survey (2001): Multibeam Mapping of the Major Deltas

of Southern Puget Sound, Washington, Open-File Report OF01-266.

Menlo Park, California. http://geopubs.wr.usgs.gov/open-file/

of01-266/

Washington State Department of Ecology (2001): Washington State Marine

Shorelines. Olympia, Washington. http://www.ecy.wa.gov/services/

gis/