paleotsunami evidence on kaua'i and numerical modeling of a

©2014 American Geophysical Union. All rights reserved.

Paleotsunami Evidence on Kaua‗i and Numerical Modeling

of a Great Aleutian Tsunami

Rhett Butler1, David Burney2, and David Walsh3

________________________

Additional supporting information may be found in the online version of this article.

1 Hawai‗i Institute of Geophysics and Planetology, University of Hawai‗i at Manoa, Honolulu, HI

2 National Tropical Botanical Garden, Kalaheo, HI

3 Pacific Tsunami Warning Center, Honolulu, HI

Corresponding author: R. Butler, Hawai‗i Institute of Geophysics and Planetology, University of

Hawai‗i at Manoa, Honolulu, HI

([email protected])

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/2014GL061232


[1] The Hawaiian Islands‘ location in the middle of the Pacific Ocean is

threatened by tsunamis from great earthquakes in nearly all directions. Historical

great earthquakes Mw>8.5 in the last 100 years have produced large inundations and

loss of life in the Islands, but cannot account for a substantial (≤600 m3) paleotsunami

deposit in the Makauwahi sinkhole (Figure 1) on the Island of Kaua‗i [Burney et al.,

2001]. Using high-resolution bathymetry and topography we model tsunami

inundation of the sinkhole caused by an earthquake with a moment-magnitude of Mw

~9.25 located in the eastern Aleutians. A preponderance of evidence indicates that a

giant earthquake in the eastern Aleutian Islands circa 1425-1665 AD—located

between the source regions of the 1946 and 1957 great tsunamigenic earthquakes—

created the paleotsunami deposit in Kaua‗i. A tsunami deposit in the Aleutians dated

circa 1530-1660 AD is consistent with this eastern Aleutian source region [Witter et

al., 2013].


1. Introduction

[2] Basing estimates of maximum tsunami amplitude upon recent history is

dangerous and ill-advised, as witnessed by the devastation in Japan from the tsunami

generated by the 2011 Mw 9.1 Tohoku earthquake, as well as the disastrous Indian

Ocean tsunami from the 2004 Mw 9.3 Sumatra-Andaman earthquake. In evaluating

tsunami threats it is necessary to consider the possibility of great, megathrust Mw 9+

earthquakes at most subduction zones [e.g., McCaffrey, 2008]. Butler [2012a]

reviewed the tsunamigenic potential of the Aleutian Islands threatening the Hawaiian

Islands, and concluded that a giant earthquake in the eastern Aleutian Islands located

between the 1946 and 1957 Mw 8.6 earthquakes, which generated the largest

tsunamis recorded in Hawaii, would focus substantial tsunami energy directed at

Hawaii.

[3] A systematic analysis of giant earthquake sources (Mw ≥ 9.25) along the

Aleutian-Alaska arc was conducted for Hawaii State Civil Defense (SCD) in order to

verify the adequacy of current tsunami evacuation maps [Butler, 2014]. This analysis

modeled earthquakes with the extremes of fault area, mean fault slip, and slip nearest

the trench that characterized the largest megathrust earthquakes of the last century:

2004 Mw 9.3 Sumatra-Andaman, 1960 Mw 9.5 Chile, and 2011 Mw 9.1 Tohoku,

respectively. The analysis concluded that a great Mw 9+ Aleutian earthquake could

generate a tsunami in Hawaii larger than historically observed, exceeding current

tsunami inundation maps. To augment this theoretical, model-based approach to

tsunami inundation along Hawaiian coasts, paleotsunami evidence was sought in the

Aleutians and Hawaii for events pre-dating the historical record. A substantial

tsunami deposit on the southeast coast of the Island of Kaua‗i provides one data point

corroborating the possibility of prior Mw 9+ events.

2. Paleotsunami Evidence

2.1 Hawaiian Islands

[4] Although there is evidence for local mega-tsunamis caused by giant submarine

landslides due to flank collapse of volcanic edifices making up the Hawaiian Islands

[e.g., Moore and Moore, 1984; Satake et al., 2002; McMurtry et al., 2004], the


youngest of these events is >10,000 yrs BP [McMurtry et al., 2004]. There is scant

evidence in the literature for more recent Holocene tsunamis, apart from depositional

evidence from recent large tsunamis during the past century (e.g., 1946, 1957, etc.).

There is an archaeological and legendary reference to a tsunami at Kualoa Beach in

Kaneohe Bay, Oahu, subsequent to its occupation by the Hawaiian people in circa

1040-1280 AD [see Supplementary Material; Carson and Athens, 2007; Handy and

Handy, 1972]. A chant attributed to Huluamana and composed in the 16th century

describes a tsunami-like event on the west coast of Molokai [Lander and Lockridge,

1989]. For the Limahuli Bog on northwestern Kaua‗i Burney [2002] reports evidence

suggesting a prior large tsunami event, ―The wedge of sand about 50 cm below the

surface along the northern edge of the bog is similar to the surficial material derived

from the 1946 tsunami, and perhaps represents a similar late prehistoric event such as

the one Burney et al. [2001] recorded about 400 yrs BP at Maha‗ulepu [Southeastern

Kaua‗i].‖

[5] The best paleotsunami evidence to date within the Hawaiian Islands is on

Kaua‗i in the Makauwahi Sinkhole (21.8883°N 159.4188°W) on the southeast coast

(Figure 1) about 10 km southwest of Nawiliwili Harbor, about 100 m from the shore

[Burney et al., 2001]. The sinkhole (see Supplementary Material, Figures S1 and S2)

is part of a limestone cave complex (within a Pleistocene eolianite—lithified

calcareous dune deposits) where the central roof collapsed about 7,000 BP. A few

large, partially re-dissolved speleothems (stalactites) to ~0.5 m diameter occur,

notably along the walls of the sinkhole, and indicate that the sinkhole is a collapsed

cave. The sinkhole is large, about 30 by 35 m, and the walls are 6 to 25 m high above

the flat floor of the sinkhole, filled mostly with terrestrial sediment deposits. At the

northern and southern end of the sinkhole, there are still caves opening into the

sinkhole. The northern cave has a small portal opening facing the Waiopili Stream.

This narrow portal serves as the only entrance to the complex.

[6] Excavation of the site revealed [Burney et al., 2001]:

"This gradual sedimentation was truncated by an extremely high-

energy sedimentation event. About four or five centuries ago (cal yr

AD 1430–1665), a severe marine overwash of the site, probably a

tsunami, deposited allochthonous [originating at a distance from their

present location] stones and fractured eolianite in a lens up to 1 m thick


at the lowest point of the sinkhole rim along the east wall, thinning out

in the far reaches of the caves as turbidite fans and gravel beds."

"The layer is composed of boulders, cobbles, gravel, and sand.

These rocks, being highly fractured, mostly angular, and lacking an in

situ patina, are consistent with an interpretation of the layer as the

result of a single high-energy event. Other components of the unit

include marine elements such as coral fragments, abraded mollusc

shells, and coarse beach sand."

"Likewise, classification of stones also shows a strong contrast with

all other units, with a significant component of allochthonous stones,

notably terra rossa (lithified red soil) and a dense black vesicular basalt

in this unit only. Both rock types are common on the beach and on the

slope seaward of the cave."

[7] This paleotsunami layer is about 80 cm thick and found in excavations on both

edges of the sinkhole and in cores in the middle. A core published by Burney et al.

[2001] is shown in Figure S2, with pictures from a recent excavation site at the

northern edge (Figure S3), showing the layer in situ and examples of the basalt rocks

and coral found in the deposit (many boulders were >100 kg). The lowest edge of the

sinkhole lies 7.2 m above mean sea level at the side adjoining the sea. Considering

the area and thickness of the layer, the volume of rocks and material in the layer is

estimated to be about 600 m3. This is a large volume, equivalent to about 9 standard

shipping containers.

[8] In the north cave "all cores record a thin band of angular gravel". The portal

entrance in the north cave is about 1.2 m tall, and has been excavated to its maximum

opening of about 2.5 m without evidence of the large basalt rocks of beach origin

typical of the tsunami layer. The deposits in the southern cave "trace a turbidite fan

thinning and fining southward into the rear of the cave". The southern cave's

connection to the ocean was severed at about the time of the main roof collapse (7,000

BP). Furthermore, excavation of the cave began a month before the 1992 Hurricane

Iniki—the largest hurricane in the historical record—directly struck this corner of

Kaua‗i with great force, leaving a very different type of deposit in the sinkhole,

consisting of plant debris and dune sands.

[9] This paleotsunami deposit is unique in that it is 100 m inland and 7.2 m uphill

from the sea, placing strong constraints on the causative tsunami. The largest


historical tsunamis recorded in Hawai‗i have run-ups measured in the vicinity of the

sinkhole. The 1960 Chilean (Mw 9.55) tsunami had 3 m run-up, the 2011 Japan (Mw

9.1) event had 1-2 m run-up, and the 1964 Alaska (Mw 9.2) event showed no

significant run-up. There is no run-up measurement from the 1952 Kamchatka (Mw

9.0) tsunami. Tsunami run-ups from the 1946 and 1957 Aleutian earthquakes (Mw

8.6) were 2.4 and 2.1 m, respectively. None of the tsunamis generated by the largest

historic earthquakes in the circum-Pacific and the Aleutians have come close to

inundating the Kaua‗i sinkhole.

[10] Only two possibilities present themselves for the means of the tsunami

deposition: the tsunami deposit could have entered via the portal through the north

cave, or else occurred as an overwash of the seaward eastern wall. In order to

examine these possibilities first-hand, a visit was made to the sinkhole in February

2013. The recently excavated northern edge of the sinkhole presented the same ~0.8

m tsunami layer as previously observed by Burney et al. [2001] at the southern

excavation site and cores in the middle of the sinkhole. Evidence was sought as to

whether the tsunami filled the sinkhole via the northern cave portal, which has a lower

elevation of ~1 m above mean sea level. To move this volume of material through a

small portal would imply substantial hydraulic forces that would direct rocks as

projectiles toward the cave ceiling (<3 m high) and walls. However, there is no

evidence of projectile impacts on the north cave walls and ceiling. Further, there are

abundant, fine speleothems undisturbed on the cave ceiling that may date back either

before sinkhole roof collapse 7,000 years ago, or prior to the tsunami event.

However, given uncertain conditions of evaporative exsolution of CaCO3 in the open

cave versus slow precipitation in the humid enclosed cave before roof collapse, this

evidence is indeterminate. Nonetheless, other than a "thin band of angular gravel" the

north cave lacks evidence of the tsunami deposit found within the sinkhole.

Therefore, although a tsunami flood may have entered via the portal, much of the

volume in the tsunami deposit must have overwashed the sinkhole wall at >7.2 m.

[11] Burney et al. [2001] have dated the tsunami deposit to 1430-1665 cal yr AD

years (calibrated range at 95% confidence interval). Although short-lived materials

were used in dating to minimize inherent age bias, some 14C dates could be biased

older, as some older, reworked material may be included in the tsunami deposit.

Hence the younger half of the distribution seems more likely. Better precision would

be obtained from Uranium-series dating of fresh, unaltered coral found in the layer.


2.2 Sedanka Island in the Aleutians

[12] The only known paleotsunami site explored in the Aleutians is on Sedanka

Island near Dutch Harbor, Alaska, at the edge of the eastern Aleutians adjoining the

zone of the 1946 earthquake [Witter et al., 2013]. This site shows evidence of 5 large

local tsunamis pre-dating the 1957 event. This tsunami deposit on Sedanka Island

reaches nearly a kilometer inland and 18 m above mean sea level. Pre-publication

results show that the deposits date back to about 1600 BP, with the most recent, 1957-

event horizon subsequent to a tsunami deposit dated circa 1530-1665 AD [Witter et

al., 2013].

2.3 Pacific Northwest

[13] Progress has been made in identifying and dating paleotsunami evidence for

the 1700 Cascadia earthquake that caused tsunamis in both the Pacific Northwest and

Japan. [e.g., Atwater et al., 2005]. Nonetheless, an examination of the paleotsunami

studies [e.g., Peters at al., 2007] shows evidence for a tsunami prior to the 1700

Cascadia event at about nine sites from British Columbia to Oregon within the range

of dates indicated by the Kaua‗i and Aleutian studies.

3 Tsunami Models

[14] We use NEOWAVE (Non-hydrostatic Evolution of Ocean Wave) of Yamazaki

et al. [2009, 2011] to model each tsunami from generation at the earthquake source to

inundation at the coastline of Kaua‗i. The hydrostatic version of NEOWAVE that does

not include the effect of dispersion was implemented for this study, due to the

computationally intensive nature of the fully non-hydrostatic simulations (>1 month

per simulation). The digital elevation model incorporates the National Geophysical

Data Center (NGDC) ETOPO1 Global Relief Model at 1 arcmin resolution [Amante

and Eakins, 2009], used for modeling Pacific basin-wide tsunami propagation, and

increasingly detailed special data sets from many sources (see Supplementary

Material: Methods), implemented in four levels of nested grids to model tsunami

propagation across the Pacific and inundation at Kaua‗i coastal area in the vicinity of

the Makauwahi sinkhole. The resolution at the sinkhole is ~9 m. The NEOWAVE

models for the sinkhole were supplemented with tsunami forecasts for the Japanese


and U.S. Pacific west coast using the NOAA SIFT/SIM code [e.g., Gica et al., 2008],

with a resolution in the harbors of about ~60 m. Earthquake sources with moment-

magnitude 9.0 > Mw ≤ 9.6 were distributed along the Aleutian-Alaska and

Kamchatka subduction zones to assess the tsunamigenic effects in Hawai‗i using the

extreme faulting parameters observed globally in the largest megathrust earthquakes

of the last 100 years [e.g., Butler, 2012; Supplementary Material and Tables S1 &

S2].

4. Inundation results at the Makauwahi Sinkhole

[15] We modeled tsunami inundation at the Makauwahi sinkhole for nine

earthquake scenarios Mw ≥ 9.25. Each of the giant earthquake scenarios (Table S1

and Figure S4) that included the eastern Aleutians inundated the sinkhole. In Figure

S5, the results are shown for the smallest event that inundated the sinkhole, a Mw

9.25 earthquake on a fault 600 x 100 km2 with uniform 35 m fault slip. The high-

resolution (~9 m/pixel) map clearly shows the tsunami overtopping the lower eastern

wall of the sinkhole at an elevation of about 8-9 m. Therefore, giant Mw 9+

earthquakes along the Aleutian-Alaska arc could plausibly have caused the Kaua‗i

paleotsunami deposit. The Mw 9.2 Alaska earthquake of 1964 did not produce

significant tsunami run-up at the site because the subduction zone geometry directed

the largest waves toward the southeast, away from the Hawaiian Islands.

[16] We next considered the sensitivity of run-up at the paleotsunami site to the

source region of the earthquake along the arc of the subduction zone. Since the

smallest Mw 9.25 event centered within the eastern Aleutians (fault 600 x 100 km2

with uniform 35 m fault slip) may have inundated the sinkhole, we forecast tsunami

inundations for two earthquakes with the same fault parameters, but in adjoining

sections of the subduction zone, shifted eastward and westward in the eastern

Aleutians (Figure 2 and Figure S6). The first is a comparable Mw 9.25 event situated

along the Alaska Peninsula section of the Aleutian-Alaska arc to the east between the

1946 and 1964 events in the region of the Shumagin Islands and 1938 earthquake.

The second is a comparable event to the west, across the 1957 earthquake zone.

Neither of these simulations generated a tsunami that would inundate the Kaua‗i

sinkhole (Figure 3).


[17] Although the Mw 9.0 earthquake of 1952 in Kamchatka did not produce a

significant tsunami at the Kaua‗i sinkhole, the geometry of the Kamchatka subduction

zone nonetheless focuses tsunami energy toward the Hawaiian Islands. Modeling the

1952 earthquake, Johnson and Satake [1999] concluded that much of the slip on the

fault occurred down-dip from the trench, which diminishes tsunami excitation. We

considered an Mw 9.25 Kamchatka earthquake (fault 600 x 100 km2 with uniform slip

of 35 m fault slip) where the faulting occurred within ~100 km of the trench (Figure

S6). The tsunami forecast (Figure 2) for this Kamchatka event did not inundate the

sinkhole in Kaua‗i (Figure 3). Similarly for the Marianas—which also focuses

tsunami energy toward Hawai‗i and where there has not been a great historic

earthquake and tsunami—forecast models (not shown) indicate that earthquakes

comparable in size to Aleutian events generate smaller tsunamis from the Marianas

Islands.

[18] We then examined characteristics of an eastern Aleutian earthquake required

to inundate the sinkhole. Keeping the average fault slip at 35 m, varying the slip from

20 to 50 m along the fault length did not yield significantly different results [Butler,

2014]. However, varying the fault slip with depth wherein the largest slip is nearest

the trench, as observed for the 2011 Tohoku earthquake, does increase the tsunami

inundation of the Kaua‗i sinkhole. Successive tsunami forecasts were generated with

earthquakes having decreasing uniform fault slip: 30 m, 25 m, 20 m, and 17.5 m (see

Supplementary Material and Table S2). The results indicate that about 35 m of slip

(equivalent to a Mw 9.25) is required to achieve run-ups inundating the sinkhole

(Figure S7)

[19] Finally, using the NOAA SIFT/SIM forecast model, we calculated the

inundation along the Pacific coasts of Japan, U.S., and Canada for the Mw 9.25 east

Aleutian event. In Japan, the median coastal amplitude is only 64 cm, with a

maximum of 103 cm. Unlike the Cascadia event, which directs energy toward Japan

[e.g., Atwater et al., 2005], an Aleutian event does not, and hence the coastal tsunami

amplitudes would be indistinguishable from the normal tidal variations without the

aid of tide gauge instruments [Kenji Satake, personal communication, 2014].

However, there is corroborating evidence consistent with the Aleutian event discussed

herein along the Pacific Coast of U.S. and Canada, where maximum forecast tsunami

amplitudes in harbors have a median of nearly 3 m and a maximum of nearly 9 m at

Port San Luis of San Luis Obispo, California. Further, the SIFT forecast offshore of


the Makauwehi sinkhole shows a 7 m tsunami amplitude—a detailed NOAA

inundation simulation is not available for the site—that would lead to greater run-up

at the sinkhole itself, corroborating the NEOWAVE results.

5. Discussion

[20] The paleotsunami deposit in the Makauwahi sinkhole on Kaua‗i appears to be

associated with an eastern Aleutian source region. None of the giant historical Mw

9+ earthquakes around the circum-Pacific have come close to inundating the sinkhole,

and these events have included azimuths to Japan, Kamchatka, Alaska, and Chile.

However, earthquakes situated in the eastern Aleutians—where the orientation of the

subduction zone is adverse to Hawai‗i—with faulting parameters comparable to these

extreme events have been shown to forecast tsunamis with sufficient energy and

amplitude to produce the observed inundation at the sinkhole. The unique geometry

of the east Aleutians with respect to the Hawaiian Islands focuses the tsunami energy.

Comparable giant earthquakes adjacent to the eastern Aleutians do not forecast

sinkhole inundation, even where the amount of average slip on the fault is as great as

35 m—the largest ever measured from earthquake source parameters. This does not

mean that other earthquake zones could not have caused the Kaua‗i paleotsunami

deposit, but rather that such events would necessarily have to exceed the fault

displacements seen historically in giant earthquakes.

[21] The scant paleotsunami evidence available in the Aleutians is fortunately

situated near the edge of the eastern Aleutians, west of the zone of the great 1946

earthquake and tsunami. Six paleotsunami sand deposits at the Sedanka Island site

were observed [Witter et al., 2013] including the recent 1957 deposit at the top of the

soil stratigraphy. The next deeper paleotsunami layer on Sedanka Is. has been dated

circa 1530-1660 AD, and fits within the range of dates, 1430-1665 AD, associated

with the age distribution for the Kaua‗i paleotsunami deposit. Finally, corroborating

evidence in paleotsunami dates on the Pacific West Coast of the U.S. and Canada are

consistent with the Kaua‗i data.

[22] The Sedanka tsunami dates indicate six events in the last 1600 years.

However, within the full range of the Kaua‗i stratigraphy [Burney et al., 2000], there

was only one deposit evident. Therefore it may be concluded that the second layer in

the Sedanka stratigraphy represents the largest tsunami event of the group, and further


conclude that the Kaua‗i event was among the largest earthquakes in the Pacific

during the past 7,000 years since the collapse of the Makauwahi cave roof into the

sinkhole.

[23] In summary, although there are alternate possible sources capable of causing

the Kaua‗i paleotsunami deposit [see Supplemental Material, Alternate Hypotheses],

their likelihoods are much less than the ongoing tectonic activity at subduction zones.

Furthermore, based upon forecast studies, the known tsunamigenic earthquake zones

in Hawaii do not appear to generate local tsunamis with sufficient amplitude on

Kaua‗i to cause the paleotsunami deposit. A preponderance of evidence indicates that

a giant earthquake in the eastern Aleutians generated a great tsunami between 350 and

575 yrs ago, leaving dated, paleotsunami evidence both on Kaua‗i and Sedanka Island

in the eastern Aleutians, and along the Pacific West Coast of the U.S. and Canada.

[24] To match the observed inundation at the Makauwahi sinkhole on Kaua‗i, an

earthquake with Mw ~9.25 and with average fault displacement ~35m is indicated by

these hydrostatic tsunami simulations. Including dispersive effects into a full non-

hydrostatic simulation will affect the phase relationships of the arriving energy, but

are unlikely to greatly influence the total tsunami energy arriving at the site. Given

the volume of material in the paleotsunami deposit, the tsunami must not merely

overtop the sinkhole, but rather overwash with sufficient flow-depth and velocity to

carry the debris into the sinkhole. Although no debris-flow dynamics have been

calculated, earthquakes with Mw ~9.25 overwash the eastern edge of the sinkhole

with over one meter clearance, even considering the maximum peak-to-trough tidal

variation of about 1m in the vicinity of the sinkhole.

6. Conclusions

[25] A preponderance of evidence indicates that a giant Mw ~9.25 earthquake

centered in the eastern Aleutians occurred ~350 to ~575 years ago. This earthquake

had an average fault displacement comparable to the largest earthquakes during the

past 100 years. The effect of geometric focusing of tsunami energy due to the

orientation of the subduction zone is fundamental. The model-forecast tsunami from

this event exceeds all historical tsunamis in the Hawaiian Islands in the last two

hundred years.


[26] Given the tectonic convergence rate of the eastern Aleutian subduction zone at

7 cm/yr or 7 m/century, there has been 24 to 40 m of convergence accumulated since

this prior event—sufficient for another giant earthquake of nearly the same

magnitude, if the contribution of fault creep is discounted (e.g., for the 2010 Chile

earthquake Lay [2011] notes that largest slip occurred where the fault was partially

creeping). There is no indication of when a similar Aleutian earthquake might

happen, but simply that there is the capacity to produce a comparable event. Indeed,

the tsunami deposit in the Makauwahi sinkhole is unique in the 7,000-year

stratigraphy. It is unknown whether the uniqueness of this event reflects its rarity, or

rather a recent change in the style of faulting in the Aleutian subduction zone.

Whereas six tsunami deposits are found on Sedanka Island going back nearly 1600

years [Witter et al., 2013], only one of these—the second most recent layer—

corresponds in time to an event with sufficient energy to inundate the Makauwahi

sinkhole. Further paleotsunami studies in both the Hawaiian and the Aleutian Islands

are needed to resolve the tsunami history of the Hawaiian Islands.

[27] The focus of tsunami energy from the Aleutians directed toward the State of

Hawaii, and the short 4.5 hours tsunami propagation time, underscores the importance

of tsunami readiness for Aleutian events. Hawaii State Civil Defense must make

evacuation decisions 3 hours prior to tsunami arrival. Other than the few NOAA

DART® (Deep-ocean Assessment and Reporting of Tsunamis) buoys stationed near

the Aleutian Islands, there are no sensors that can characterize a potentially great

tsunami from the Aleutians as it propagates toward Hawaii. Furthermore, key

Aleutian DARTs are often down for months at a time, awaiting repair following the

winter storm season. Deploying two additional next-generation tsunamimeters

between Hawaii and the Aleutians would substantially enhance coverage, corroborate

near-field data, and provide a level of redundancy, giving better warning system

resilience to the loss of critical sensor data. The integration of tsunami sensors into

the repeaters of undersea telecommunication cables traversing the North Pacific

would greatly benefit our ability to rapidly resolve the tsunami wavefield in real-time

and augment tsunami preparedness [Butler, 2012b].


Acknowledgements

[28] This work was supported in part by the Hawai'i State Civil Defense and by the

University of Hawai‗i (UH) School of Ocean and Earth Science and Technology. We

thank the Hawai'i Tsunami Mapping Project at UH, led by Kwok Fai Cheung, for

providing access to their NEOWAVE tsunami code for high-resolution tsunami

forecast simulations. RB thanks Yefei Bai for his excellent assistance in running the

NEOWAVE code, and for thoughtful discussions of the results. RB also thanks Gerard

Fryer of the NOAA Pacific Tsunami Warning Center, and Kwok Fai Cheung and

Yoshiki Yamazaki of UH for many tsunami discussions.

[29] Pre-publication results from the Sedanka paleotsunami survey from Rob

Witter of the US Geological Survey significantly refined the conclusions of this

paper. Paleotsunami data for this paper are found at the Makauwahi Cave.

Earthquake source parameters used in modeling Figures 2 and 3 are found in

Supplementary Table S1.

[30] Work on the paleotsunami deposit at Makauwahi Cave has been supported by

NSF grant NSF DEB-9707260 to DB and additional funding from the National

Geographic Society. Thanks to Lida Pigott Burney, staff and volunteers of the

Makauwahi Cave Reserve and the Kaua‗i Archaeological Field School for assistance

with collection and analysis of the sediments. Thanks also to Grove Farm Company

for permission to work on their property. SOEST contribution No. 9190. HIGP

contribution No. 2048.

References

Amante, C. and Eakins, B.W. (2009). ETOPO1 1 Arc-Minute Global Relief

Model: Procedures, Data Sources and Analysis. NOAA Technical

Memorandum, NESDIS NGDC-24.

Atwater, B. F., S. Musumi-Rokkaku, K. Satake, Y. Tsuji, K. Ueda, and D.

Yamaguchi (2005). The orphan tsunami of 1700: Japanese clues to a

parent earthquake in North America. US Geological Survey Professional

Paper, paper 1707, 133 pp.

Burney, D. A., H. F. James, L. P. Burney, S. L. Olson, W. Kikuchi, W. L.

Wagner, M. Burney, D. McCloskey, D. Kikuchi, F. V. Grady, R. Gage,


and R. Nishek (2001), Fossil evidence for a diverse biota from Kaua‗i and

its transformation since human arrival, Ecological Monographs, 71(4), pp.

615–641.

Burney, D. A., (2002). Late Quaternary chronology and stratigraphy of twelve

sites on Kaua‗i. Radiocarbon, 44, 13-44.

Butler, R. (2012a), Re-examination of the potential for great earthquakes

along the Aleutian island arc with implication for tsunamis in Hawaii,

Seismological Research Letters, 83(1), 30-39, doi: 10.1785/gssrl.83.1.

Butler, R. (2012b). Strategy and roadmap: Using submarine cables for climate

monitoring and disaster warning, International Telecommunication Union,

Geneva, 30 pp., http://www.itu.int/en/ITU-T/climatechange/task-force-

sc/Pages/default.aspx.

Butler, R. (2014). Great Aleutian Earthquakes, Hawai‗i Institute of

Geophysics and Planetology, Peer-Reviewed Report HIGP-2014-1, 170

pp., http://www.higp.hawaii.edu/reports/2014/

Carson, M. T., and J. S. Athens (2007), Integration of Coastal

Geomorphology, Mythology, and Archaeological Evidence at Kualoa

Beach, Windward O‗ahu, Hawaiian Islands, The Journal of Island and

Coastal Archaeology, 2:1, 24-43.

Chesley S. R. And S. N. Ward (2006). A quantitative assessment of the human

and economic hazard from impact-generated tsunami. Natural Hazards, 38:

355–374, DOI 10.1007/s11069-005-1921-y.

Ekstro m, G., and E. R. Engdahl (1989). Earthquake source parameters and

stress distribution in the Adak Island region of the central Aleutian Islands,

Alaska. Journal of Geophysical Research 94 (B11), 15,499–15,519.

Gica, E., M. C. Spillane, V. V. Titov, C. D. Chamberlin, and J. C. Newman

(2008), Development of the forecast propagation database for NOAA‘s

short-term inundation forecast for tsunamis (SIFT), NOAA Technical

Memorandum OAR PMEL-139, Pacific Marine Environmental Laboratory

Seattle, WA, 89pp.

Handy, E. S. C. and E. G. Handy (1972), Native Planters in Old Hawaii: Their

Life, Lore, and Environment. Bernice P. Bishop Museum Bulletin No.

233. Honolulu, HI: Bishop Museum Press, 447.

Hayes, G. P., D. J. Wald, and R. L. Johnson (2012). Slab1.0: A three-

http://www.itu.int/en/ITU-T/climatechange/task-force-sc/Pages/default.aspx

http://www.itu.int/en/ITU-T/climatechange/task-force-sc/Pages/default.aspx


dimensional model of global subduction zone geometries. Journal of

Geophysical Research, 117, B01302, doi:10.1029/2011JB008524.

Johnson, J., and K. Satake (1999). Asperity distribution of the 1952 great

Kamchatka earthquake and its relation to future earthquake potential in

Kamchatka. Pure and Applied Geophysics, 154 (1999) 541–553.

Keating, B.H., 1987. Summary of radiometric ages from the Pacific. IOC

Tech. Ser. 32, UNESCO, Paris.

Lander, J. F., and P. A. Lockridge (1989). United States Tsunamis (Including

United States Possessions) 1690-1988, National Oceanic and Atmospheric

Administration, National Geophysical Data Center, Boulder, Colorado,

USA, Publication 41-2, 265 pp., page 23.

Lay, T. (2011). A Chilean surprise, Nature, 471, 174–175, 10 March 2011.

Lay, T., Ammon, C.J., Kanamori, H., Yamazaki, Y., Cheung, K.F., and Hutko,

A.R. (2011). The 25 October 2010 Mentawai tsunami earthquake (Mw

7.8) and the tsunami hazard presented by shallow megathrust ruptures.

Geophysical Research Letters, 38(6), L06302, Doi: 10.1029/

2010GL046552.

Ma, K.-F., H. Kanamori and K. Satake (1999). Mechanism of the 1975

Kalapana, Hawaii, earthquake inferred from tsunami data , Journal of

Geophysical Research, 104, 13153-13167.

McCaffrey, R. (2008). Global frequency of magnitude 9 earthquakes.

Geology, March 2008; v. 36; no. 3; p. 263–266; doi: 10.1130/G24402A.1.

McMurtry, G. M., P. Watts, G. Fryer, J. R. Smith and F. Imamura (2004).

Giant landslides, mega-tsunamis, and paleo-sea level in the Hawaiian

islands, Marine Geology, 203 219-233.

Moore, J.G., and G. W. Moore (1984). Deposit from a giant wave on the

island of Lanai, Hawaii. Science 226, 1312-1315.

Moreno, M. S., Bolte, J., Klotz, J., Melnick, D. (2009). Impact of megathrust

geometry on inversion of coseismic slip from geodetic data: Application to

the 1960 Chile earthquake. Geophysical Research Letters, 36, L16310,

DOI: 10.1029/2009GL039276.

Pacheco, J. F., L. R. Sykes and C. H. Scholz (1993). Nature of seismic

coupling along simple plate boundaries of the subduction type. Journal of

Geophysical Research, 98, 14133–14159.


Peters, R., B. Jaffe, and G. Gelfenbaum (2007). Distribution and sedimentary

characteristics of tsunami deposits along the Cascadia margin of western

North America. Sedimentary Geology, 200, 372–386.

Satake, K., Smith, J.R., Shinozaki, K., 2002. Three-dimensional reconstruction

and tsunami model of the Nuuanu and Wailau giant landslides. In:

Takahashi, E., Lipman, P., Garcia, M., Naka, J., Aramaki, S. (Eds.),

Hawaiian Volcanoes: Deep Underwater Perspectives. AGU Monograph

128, 333-346.

Tichalaar, B. W., and L. J. Ruff (1993). Depth of seismic coupling along

subduction zones. Journal of Geophysical Research, 98(B2), 2017-2037.

Wessel, P., and Smith, W.H.F. (1991). Free software helps map and display

data, Eos Transactions American Geophysical Union, 72(41), 441-446.

Witter, R. C., G. A. Carver, A. M. Bender, R. W. Briggs, G. R. Gelfenbaum,

and R. D. Koehler (2013). Six large tsunamis in the past ~1700 years at

Stardust Bay, Sedanka Island, Alaska. EOS Transactions American

Geophysical Union, Abstract NH44A-08.

Yamazaki, Y., Kowalik, Z., and Cheung, K.F. (2009). Depth-integrated, non-

hydrostatic model for wave breaking and runup. International Journal for

Numerical Methods in Fluids, 61(5), 473-497.

Yamazaki, Y., Cheung, K.F., and Kowalik, Z. (2011). Depth-integrated, non-

hydrostatic model with grid nesting for tsunami generation, propagation,

and run-up. International Journal for Numerical Methods in Fluids, 67(12),

2081-2107.


Figure 1. The inset map shows the location (red dot) of the Makauwahi sinkhole on

the southeastern coast of Kaua‗i in the Hawaiian Islands. The scale for the inset map

is about 12.2 km on a side. The town of Līhu‗e and Nawiliwili harbor are to the

northeast.


Figure 2. Maximum tsunami amplitudes in meters are forecast for identical (size,

fault slip) Mw 9.25 earthquakes: (upper left) the east Aleutians; (upper right) the

Alaska Peninsula region extending eastward from the Shumagin Islands to the west of

Kodiak Island; (lower left) a quasi-1957 event; and (lower right); a quasi-Kamchatka

event. The red circles are centered on Kaua‗i and encircle the Big Island. Note that

only the east Aleutian tsunami energy is directed primarily towards Kaua‗i.


Figure 3. High-resolution tsunami inundation forecasts at the Makauwahi Sinkhole

on Kaua‗i are shown, respectively, for the Mw 9.25 events in Figure 1. The map scale

is about 321 m on a side. Only the east Aleutian earthquake (upper left) inundates the

sinkhole, reaching 8 to 9 m above mean sea level. The center of the sinkhole is

indicated with a small magenta dot.

1

Online supplementary material for

Paleotsunami Evidence on Kaua‘i and Numerical Modeling

of a Great Aleutian Tsunami

Rhett Butler1, David Burney2, and David Walsh3

[1] These supplementary materials provide additional information regarding (1)

legendary tsunamis in Hawai‘i; (2) the setting of the Kaua‘i paleotsunami deposit, (3)

detailed methods and models used in the tsunami forecasts; (4) tsunami sensitivity to the

sinkhole topography; and (5) alternate hypotheses for the Kaua‘i tsunami deposit. Two

tables of earthquake source characteristics are included with additional figures illustrating

the main text.

1. Legendary Hawaiian References to Tsunamis

[2] The date is 1500-1600. The earliest reference to a tsunami in Hawaii came from

the following chant attributed to Huluamana and composed in the 16th century: “The sun

shines brightly at Kalaeloa which sank into the sea. A huge wave came and killed its

inhabitants scattering them and leaving only Papala‘au; their cries are all about.” It

describes a tsunami like event on the west coast of Moloka‘i [Lander and Lockridge,

1989].

[3] There is a historical reference in native Hawaiian lore regarding a prior large

tsunami just north of Kaneohe. “The land now called Kualoa was formerly Paliku

[upright cliff], for its salient feature, the great cliff at its back. It was here that the

primordial goddess Haumea battled alone against the warriors of Kumuhonua in

1 Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Manoa, Honolulu, HI 2 National Tropical Botanical Garden, Kalaheo, HI 3 Pacific Tsunami Warning Center, Honolulu, HI

2

legendary times preceding the great tidal wave that inundated all the coast from Kualoa

south to He‘eia. Here was built the high shrine to Lono, the god of storm, who saved

Wakea and Haumea in the flood.” [Handy and Handy, 1972; Carson and Athens, 2007]

2. Setting of the Makauwahi Sinkhole on Kaua‘i

[4] The setting for the paleotsunami study in maps, diagrams, and photos of the site

and the deposit is presented in Figures S1, S2, and S3.

3. Methods and Models

3.1 Computational Method

[5] We use NEOWAVE (Non-hydrostatic Evolution of Ocean Wave) of Yamazaki et

al. [2009, 2011b] to model each tsunami from generation at the earthquake source to

inundation at the coastline of Kaua‘i. The staggered finite difference model builds on the

nonlinear shallow-water equations with a momentum conservation scheme to

approximate breaking waves as bores or hydraulic jumps as in a finite volume model

[e.g., Wei et al., 2006; and Wu and Cheung, 2008]. The code accommodates up to five

levels of two-way nested grids to describe processes of different time and spatial scales

from the open ocean to the coast.

[6] NEOWAVE has been validated against the benchmarks put forth by the National

Tsunami Hazard Mitigation Program and the National Science Foundation, and is

approved by the National Ocean and Atmospheric Agency (NOAA) for use in tsunami

inundation mapping [Yamazaki et al., 2012a]. NEOWAVE has been validated with near

and far-field measurements from the 2009 Samoa, 2010 Mentawai, 2010 Chile, 2011

Tohoku, 2012 Haida Gwaii, and the 2013 Santa Cruz Islands tsunamis [Lay et al., 2011a,

2011b, 2013a, 2013b; Roeber et al., 2010; Yamazaki and Cheung, 2011; Yamazaki et al.,

2011a, 2011c, 2012b, 2013].

[7] For calculation of tsunami forecasts for the Japanese and Pacific West Coasts, we

used the SIFT (Short-term Inundation Forecast for Tsunamis) computer code [Titov and

González, 1997; Titov and Synolakis, 1998; Titov et al., 2005; Gica et al., 2008; Tang et

3

al., 2009; references contain extensive method validations] of the National Oceanic and

Atmospheric Administration (NOAA). Complete inundation forecasts were computed

using the NOAA Stand-by Inundation Models (SIMs) for 20 harbors along the Pacific

Coast. SIMs were not available for Japanese harbors, and tsunami amplitudes at the

100 m bathymetry contour were extrapolated to the coast.

3.2 Digital Elevation Model

[8] The National Geophysical Data Center (NGDC) ETOPO1 Global Relief Model at

1 arcmin resolution [Amante and Eakins, 2009] is used for modeling Pacific basin-wide

tsunami propagation. ETOPO1 has approximately 1850 m resolution near the Hawaiian

Islands, where higher-resolution datasets are used. The majority of the offshore

bathymetry is the 1.5 arcsec (46-m) resolution University of Hawai'i SOEST multibeam

data and the gaps are filled by the 5 arcsec (154-m) U.S. Geological Survey (USGS) I-

2809 dataset. The near-shore bathymetry source is the SHOALS (Scanning Hydrographic

Operational Airborne LiDAR Survey) dataset, which was procured by the US Army

Corps of Engineers (USACE) between 1999 and 2004. The data extends from the

shoreline to approximately 40 m water depth at 4-m horizontal resolution. Data from

hydrographic surveys and nautical charts supplements the near-shore bathymetry, mostly

inside harbors and marinas.

[9] The topography is from the USGS 0.33 and 1 arcsec (10 and 30-m) Digital

Elevation Models, which include the SRTM (Shuttle Radar Topography Mission) data.

LiDAR (Light Detection and Ranging) topography data are used near the Kaua‘i coastline

with 1-m horizontal resolution extending from the shoreline to the 15 m elevation

contour—the data for the north and south facing shores procured by USACE and Federal

Emergency Management Agency, respectively. NB: the small portal opening to the

sinkhole within the north cave is not considered in the model. The Generic Mapping

Tools (GMT) of Wessel and Smith [1991] is utilized to merge these DEM data sources,

and extract the computational grids for tsunami modeling.

[10] This study implemented four levels of nested grids to model tsunami propagation

across Pacific and inundation at Kaua‘i coastal area a vicinity of the Makauwahi

sinkhole. The level-1 grid at 2 arcmin resolution (~3000 m) extends the North Pacific

4

Ocean to describe tsunami generation and propagation. The level-2 grid at 15 arcsec

(~463 m) and the level-3 grids at 3 arcsec (~90 m) resolve tsunami transformation around

Hawaiian Islands and the Kaua‘i Island, respectively. The level-4 grid at 0.3 arcsec (~9

m) is located southeast of Kaua‘i to model near shore wave transformation and

inundation around Makauwahi sinkhole. It will be noted that ~9 m is approaching the

limit of resolving the features of the sinkhole.

[11] For the SIFT/SIM tsunami forecasts along the Pacific West Coast, the initial

forecasts were pre-computed at 4-arcminute resolution in the open ocean, and stored at

16-arcmin resolution. Nested grids are used in the SIMs to achieve successively greater

detail [Tang et al., 2009]: a regional grid of 2-arcmin (∼3700 m), intermediate grids of

12-18 arcsec (∼370–555 m) at the Makauwehi coast and elsewhere, and a harbor region

grid of about 2-arcsec (∼60 m) resolution.

3.3 Earthquake Sources

[12] Nine earthquake sources with moment-magnitude 9.25 ≥ Mw ≤ 9.6 were

distributed along the Aleutian-Alaska and Kamchatka subduction zones to assess the

tsunamigenic effects in Hawai‘i using the extreme faulting parameters observed globally

in the largest megathrust earthquakes of the last 100 years (see Supplementary Material

Tables S1 & S2). The Mw 9.5 Chilean earthquake had about 35 m of fault slip averaged

over the fault surface, derived from the largest seismic studies [Kanamori and Cipar,

1974; Cifuentes, 1989; Butler, 2012]. Even for the smallest overall estimates for this

earthquake, about 35 m of slip was observed in a segment of the earthquake equivalent to

a Mw 9.0 event itself [Moreno et al., 2009]. The 2004 Mw 9.3 Sumatra-Andaman

earthquake demonstrated extreme length of faulting, extending about 1400 km long

[Ammon et al., 2005; Stein and Okal, 2007; Tsai et al., 2005]. The 2011 Mw 9.1 Tohoku,

Japan earthquake, though relatively short in length (<450 km), showed extreme slip of

greater than 50 m at the shallowest portion of the fault near the subduction zone trench,

which further enhanced the tsunami [Lay et al., 2011b; Yamazaki et al., 2011c].

[13] Each of the scenarios that included the eastern Aleutian segment (Figure S4) of

the subduction zone focused tsunami energy toward the Hawaiian Islands (Figure S5).

Faulting scenarios also considered ruptures extending ≥ 1,000 km both eastward and

5

westward from the eastern Aleutian section (Figure S4), to model effects resultant from

an event similar to the 2004 Sumatra-Andaman earthquake. Summarizing, tsunami

effects in Hawai‘i are compared and contrasted in Figure 3, for earthquakes of

comparable size and dimension located adjacent to the Eastern Aleutians and also in

Kamchatka.

4. Tsunami Sensitivity to Sinkhole Topography

[14] Tsunami forecasts for each of the earthquakes that ruptured across the eastern

Aleutians in Table S1 inundate the sinkhole to a sufficient depth to have overtopped a

7.2 m wall. Using the same 35 m fault slip, great earthquakes outside of this tectonic

region could not do so. Since the smallest earthquake capable of inundating the sinkhole

was a Mw 9.25 event within the eastern Aleutians, the effect of decreasing the uniform

slip from 35 to 17.5 m are reviewed in Figure S7.

[15] Care must be taken in interpreting Figures 3 and S7. Since the pixel resolution is

~9 m, features smaller that this are naturally averaged over. The eastern wall of the

sinkhole is less than 9 m in thickness, and hence when averaged across the sinkhole and

exterior slope, the height is effectively decreased to about ~4 m. In the panel of

inundation maps shown in Figure S7 for eastern Aleutian events in Table S2, only the 35

m uniform fault slip reaches the >7 m height of the actual sinkhole, and overtops it with

margin. For uniform fault slip a value of 30 m results in amplitudes ~6.5 m, with

concomitant decrease for smaller values of slip.

5. Alternate Hypotheses

[16] Although the link between the eastern Aleutians and the Kaua‘i paleotsunami

deposit is compelling, we also reviewed other possible sources. For other distant, giant

earthquake sources, the inundation necessary to form the Kaua‘i deposit could not be

achieved, even assuming fault parameters corresponding to the largest historic

observations. Local Hawaiian sources were considered. The Big Island has experienced

earthquakes generating tsunamis. The most recent and best studied is the 1975 Kalapana

earthquake (Mw 7.7) on the south flank of Kilauea [e.g., Ma et al., 1999]. This event

6

produced a tsunami at the tide gauge in Nawiliwili harbor of 0.1 m (NGDC). Even a

Mw 8 event, which is three times more energetic, along the southern coast of the Big

Island would not produce a large tsunami on Kaua‘i. Larger events approaching Mw 9

cannot reasonably be achieved for an island only about ~100 km x 100 km in size.

Further, the tsunamigenic zone for such an event is limited to the submarine portion of

the fault near the coast.

[17] An earthquake source on the south Kona coast would direct a tsunami at a 45°

angle to the azimuth to Kaua‘i. Tsunami modeling [Cheung, 2010] of a south Kona

event—using a Kalapana-style earthquake source—yielded tsunami amplitudes at Kaua‘i

only about 3 times greater than those from the Kalapana source region. Although it is

conceivable that a Kalapana-style earthquake on a 50-km fault along the north Kona

region of the Big Island could direct larger tsunami energy toward Kaua‘i, the

shallowness (<1500 m) of the coastal water will limit the tsunami height compared with

Kalapana and South Kona source regions. To accept this hypothesis, there should be

contemporaneous evidence of larger run-ups on the closer islands and the Big Island.

[18] There have been submarine landslides associated with Kaua‘i with estimated ages

at ~3.8 to 5 Ma [Keating, 1987; McMurtry et al., 2004]. Such an event is capable of

generating a local tsunami sufficiently large as to inundate the Kaua‘i sinkhole.

However, there is no compelling evidence for giant submarine landslides in the Hawaiian

Islands in the past 10,000 yrs [McMurtry et al., 2004]. Nonetheless, a smaller, local

submarine landslide at the Southeastern coast of Kaua‘i could possibly create a large

local tsunami deposit. To corroborate this hypothesis, additional data are required. First,

there should be evidence in the offshore bathymetry. Secondly, for a local Kaua‘i

submarine landslide, we may not expect large run-ups elsewhere in the Hawaiian Islands.

Therefore, a principal confirmation for an Aleutian source for the Kaua‘i deposit will be

paleotsunami evidence elsewhere in the State, such as the Kawainui marsh in Kailua on

Oahu, or in Waipio Valley of the Big Island. Lacking such confirmation, a closer review

of the Kaua‘i bathymetry may be required to confirm the local submarine landslide

source. In Hawai‘i we do not have a basic understanding of the rate of tsunamigenic,

local submarine landslides in the past thousands of years.

7

[19] Finally, asteroid impacts will generate tsunamis. Recent estimates [Chesley and

Ward, 2006] suggest that the chances are about 1 in 70 million/year that a given generic

coastal point in the ocean will experience an asteroid (>300 m diameter) tsunami with

>10 m near-shore heights. The most probable impact-generated tsunamis have near-

shore heights <10 m and derive from asteroids 100–400 m diameter. For example, a

bolide 400 m in diameter striking the ocean at 12 km/s at 1000 km off the California

coast will produce tsunami run-ups of only about 5 m in Hawaii [Chesley and Ward,

2006]. Therefore, whereas the Kaua‘i paleotsunami deposit could have been caused by a

bolide impact within about 2000 km from the Island, there also is no evidence supporting

the hypothesis.

References

Amante, C. and Eakins, B.W. (2009). ETOPO1 1 Arc-Minute Global Relief

Model: Procedures, Data Sources and Analysis. NOAA Technical

Memorandum, NESDIS NGDC-24.

Ammon, C. J., C. Ji, H.-K. Thio, D. Robinson, S. Ni, V. Hjorleifsdottir, H.

Kanamori, T. Lay, S. Das, D. V. Helmberger, G. Ichinose, J. Polet, and D.

Wald (2005). Rupture process of the great 2004 Sumatra-Andaman

earthquake. Science, 308, 1133–1139.

Burney, D. A., H. F. James, L. P. Burney, S. L. Olson, W. Kikuchi, W. L.

Wagner, M. Burney, D. McCloskey, D. Kikuchi, F. V. Grady, R. Gage, and R.

Nishek (2001), Fossil evidence for a diverse biota from Kaua‘i and its

transformation since human arrival, Ecological Monographs, 71(4), pp. 615–

641.

Butler, R. (2012), Re-examination of the potential for great earthquakes along the

Aleutian island arc with implication for tsunamis in Hawaii, Seismological

Research Letters, 83(1), 30-39, doi: 10.1785/gssrl.83.1.

Carson, M. T., and J. S. Athens (2007), Integration of Coastal Geomorphology,

Mythology, and Archaeological Evidence at Kualoa Beach, Windward O‘ahu,

Hawaiian Islands, The Journal of Island and Coastal Archaeology, 2:1, 24-43.

Chesley S. R., and S. N. Ward (2006). A quantitative assessment of the human

8

and economic hazard from impact-generated tsunami. Natural Hazards, 38:

355–374, DOI 10.1007/s11069-005-1921-y.

Cheung, K. F. (2010). Hawaiʻi Tsunami Mapping Project: Data Sources,

Procedures, and Products. Final Report for Oʻahu Inundation Maps,

University of Hawaiʻi at Manoa, Honolulu, Hawaiʻi, 91 pp.

Cifuentes, I. L. (1989). The 1960 Chilean earthquakes. J. Geophys. Res. 94, 665–680.

Gica, E., M. C. Spillane, V. V. Titov, C. D. Chamberlin, and J. C. Newman

(2008), Development of the forecast propagation database for NOAA’s short-

term inundation forecast for tsunamis (SIFT), NOAA Technical Memorandum

OAR PMEL-139, Pacific Marine Environmental Laboratory Seattle, WA,

89pp.

Handy, E. S. C. and E. G. Handy (1972), Native Planters in Old Hawaii: Their

Life, Lore, and Environment. Bernice P. Bishop Museum Bulletin No. 233.

Honolulu, HI: Bishop Museum Press, 447.

Kanamori, H. and J. J. Cipar (1974). Focal process of the great Chilean

earthquake, May 22, 1960. Phys. Earth Planet. Int., 9(20), 128-136.

Keating, B.H., 1987. Summary of radiometric ages from the Pacific. IOC Tech.

Ser. 32, UNESCO, Paris.

Lander, J. F., and P. A. Lockridge (1989). United States Tsunamis (Including

United States Possessions) 1690-1988, National Oceanic and Atmospheric

Administration, National Geophysical Data Center, Boulder, Colorado, USA,

Publication 41-2, 265 pp., page 23.

Lay, T., Ammon, C.J., Kanamori, H., Yamazaki, Y., Cheung, K.F., and Hutko,

A.R. (2011a). The 25 October 2010 Mentawai tsunami earthquake (Mw 7.8)

and the tsunami hazard presented by shallow megathrust ruptures.

Geophysical Research Letters, 38(6), L06302, Doi: 10.1029/ 2010GL046552.

Lay, T., Yamazaki, Y., Ammon, C.J., Cheung, K.F., and H. Kanamori (2011b).

The 2011 Mw 9.0 off the Pacific coast of Tohoku earthquake: Comparison of

deep-water tsunami signals with finite-fault rupture model predictions. Earth,

Planets and Space, 63(7), 797-801.

Lay, T., Ye, L., Kanamori, H., Yamazaki, Y., Cheung, K.F., and C. J. Ammon

9

(2013a). The February 6, 2013 Mw 8.0 Santa Cruz Islands earthquake and

tsunami. Tectonophysics, http://dx.doi.org/10.1016/j.tecto.2013.07.001 in

press.

Lay, T., Ye, L., Kanamori, H., Yamazaki, Y., Cheung, K.F., Kwong, K., and K.

D. Koper (2013b). The October 28, 2012 Mw 7.8 Haida Gwaii underthrusting

earthquake and tsunami: Slip portioning along the Queen Charlotte Fault

transpressional plate boundary. Earth and Planetary Science Letters,

http://dx.doi.org/10.1016/j.epsl.2013.05.005i in press.

Ma, K.-F., H. Kanamori and K. Satake (1999). Mechanism of the 1975 Kalapana,

Hawaii, earthquake inferred from tsunami data , Journal of Geophysical

Research, 104, 13153-13167.

McMurtry, G. M., P. Watts, G. Fryer, J. R. Smith and F. Imamura (2004). Giant

landslides, mega-tsunamis, and paleo-sea level in the Hawaiian islands,

Marine Geology, 203 219-233.

Moreno, M. S., Bolte, J., Klotz, J., Melnick, D. (2009). Impact of megathrust

geometry on inversion of coseismic slip from geodetic data: Application to the

1960 Chile earthquake. Geophysical Research Letters, 36, L16310, DOI:

10.1029/2009GL039276.

Roeber, V., Yamazaki, Y., and Cheung, K.F. (2010). Resonance and impact of the

2009 Samoa tsunami around Tutuila, American Samoa. Geophysical Research

Letters, 37(21), L21604, Doi: 10.1029/2010GL044419.

Stein, S. and Okal, E. A. (2007). Ultralong period seismic study of the December

2004 Indian Ocean earthquake and implications for regional tectonics and the

subduction process. Bulletin of the Seismological Society of America, 97(1A),

S279-S295, doi:10.1785/0120050617.

Tang, L., V. V. Titov, and C. D. Chamberlin (2009), Development, testing, and

applications of site-specific tsunami inundation models for real-time

forecasting, Journal of Geophyical. Research, 114, C12025,

doi:10.1029/2009JC005476.

Titov, V. V., and C. S. Synolakis (1998), Numerical modeling of tidal wave

runup, Journal of Waterway, Port, Coastal, and Ocean Engineering, 124(4),

10

157–171.

Titov, V. V., and F. I. González (1997), Implementation and testing of the Method

of Splitting Tsunami (MOST) model, NOAA Technical Memorandum ERL

PMEL-112, 11 pp, NOAA Pacific Marine Environmental Laboratory, Seattle,

WA.

Titov, V. V., F. I. González, E. N. Bernard, J. E. Ebel, H. O. Mofjeld, J. C.

Newman, and A. J. Venturato (2005), Real-time tsunami forecasting:

Challenges and solutions, Natural Hazards, 35, 40-58.

Tsai, V. C., G. P. Hayes and Z. Duputel (2011). Constraints on the long-period

moment-dip tradeoff for the Tohoku earthquake, Geophysical Research

Letters, 38, L00G17, doi:10.1029/2011GL049129.

Wei, Y., Mao, X.Z., and Cheung, K.F. (2006). Well-balanced finite volume model

for long-wave runup. Journal of Waterway, Port, Coastal, and Ocean

Engineering, 132(2), 114-124.

Wessel, P., and Smith, W.H.F. (1991). Free software helps map and display data,

Eos Transactions American Geophysical Union, 72(41), 441-446.

Wu, Y.Y. and Cheung, K.F. (2008). Explicit solution to the exact Riemann

problem and application in nonlinear shallow-water equations. International

Journal for Numerical Methods in Fluids, 57(11), 1649-1668.

Yamazaki, Y., Kowalik, Z., and Cheung, K.F. (2009). Depth-integrated, non-

hydrostatic model for wave breaking and runup. International Journal for

Numerical Methods in Fluids, 61(5), 473-497.

Yamazaki, Y. and Cheung, K.F. (2011a). Shelf resonance and impact of near-field

tsunami generated by the 2010 Chile earthquake. Geophysical Research

Letters, 38, L12605, Doi: 10.1029/2011GL047508.

Yamazaki, Y., Cheung, K.F., and Kowalik, Z. (2011b). Depth-integrated, non-

hydrostatic model with grid nesting for tsunami generation, propagation, and

run-up. International Journal for Numerical Methods in Fluids, 67(12), 2081-

2107.

Yamazaki, Y., Lay, T., Cheung, K.F., Yue, H., and Kanamori, H. (2011c).

Modeling near-field tsunami observations to improve finite-fault slip models

11

for the 11 March 2011 Tohoku earthquake, 38, L00G15, Doi:

10.1029/2011GL049130.

Yamazaki, Y., Cheung, K.F., Kowalik, Z., Lay, T., and Pawlak, G. (2012a).

NEOWAVE. In Proceedings and Results of the 2011 NTHMP Model

Benchmarking Workshop, Boulder: U.S. Department of

Commerce/NOAA/NTHMP (NOAA Special Report), pp. 239-302.

Yamazaki, Y., Cheung, K.F., Pawlak, G., and Lay, T. (2012b). Surges along the

Honolulu coast from the 2011 Tohoku tsunami. Geophysical Research Letters,

39, L09604, Doi: 10.1029/2011GL050386.

Yamazaki, Y., Cheung, K.F., and Lay, T. (2013). Modeling of the 2011 Tohoku

tsunami from finite-fault inversion of seismic waves. Bulletin of

Seismological Society of America, 103(28), 1444-1455.

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Tables

Table S1. Faulting parameters are shown for earthquakes modeled in tsunami forecasts at the Kaua‘i sinkhole.

Earthquake Mw Uniform Fault

Slip, m Region (Figure 2)

SIFT subfaults*, fault length and area

Mw 9.25 ‡ 35 m East Aleutians ac18-23ab 600 km, 60,000 km2

Mw 9.25

35 m Alaska Peninsula ac26-31ab 600 km, 60,000 km2

Mw 9.25 35 m Quasi-1957

ac12-17ab 600 km, 60,000 km2

Mw 9.25 35 m Quasi-Kamchatka ki2-7ab 600 km, 60,000 km2

Mw 9.25ab ‡ (50-20m)

50 m (b), 20 m (a) 35 m average

East Aleutians ac18-23ab 600 km, 60,000 km2

Mw 9.29ab ‡ (50-20m)

50 m (b), 20 m (a) 35 m average

East Aleutians ac18-24ab 700 km, 70,000 km2

Mw 9.43 ‡ 35 m 1957, East Aleutians, 1946, Shumagin,

ac16-26ab 1100 km, 110,000 km2

Mw 9.45 ‡

35 m 1957, East Aleutians, ac13-24ab 1200 km, 120,000 km2

Mw 9.6 ‡ 35 m East Aleutian, 1946, Shumagin, 1938

ac18-31ab, ac21-31z 1400 km, 195,000 km2

*Each subfault has a unique identification code and corresponding location, fault geometry, and depth—see Gica et al., [2008] and its appendices. For example, ac18-23b refers to "Aleutian-Cascadia" subfaults 18 through 23, tier b (along the trench), which is 600 km long and 50 km wide. Tiers a, z, and y are subfaults successively further from the trench, and deeper. The fault width varies with the number of 50-km-wide subfault tiers incorporated in the earthquake. Earthquake Mw corresponds with a rigidity of 44 GPa for PREM. All events are modeled as pure thrust mechanisms. ‡Tsunami forecasts from these events inundated the Kaua‘i sinkhole. Note that all events including the eastern Aleutian segment caused inundation.

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Table S2. Faulting parameters for earthquakes located in eastern Aleutians with decreasing average displacements and Mw for a fixed fault area.

Earthquake Mw Uniform Fault

Slip, m Region (Figure 2)

SIFT subfaults*, fault length and area

Mw 9.25 ‡ 35 m East Aleutians ac18-23ab 600 km, 60,000 km2

Mw 9.2 30 m East Aleutians ac18-23ab 600 km, 60,000 km2



Mw 9.05 17.5 m East Aleutians ac18-23ab 600 km, 60,000 km2

*same as Table S1. All events are modeled as pure thrust mechanisms. ‡Tsunami forecasts only from this event inundated the Kaua‘i sinkhole.

14

Figures.

Figure S1. The Makauwahi sinkhole, on the side of a lithified calcareous sand dune, is

viewed toward the southeast from an apparent altitude of 342 m. Inset photos show two

of the wall edges, indicating the edges of the sinkhole. Small white star in left inset

indicates location of north cave in Figure S3. The east wall (left) is 7.2 m above mean sea

level, and about 100 m from the ocean. Note for scale the people in the right image.

Photo credits: RB (left), Gerard Fryer (right), GoogleMaps (background).

15

Figure S2. The location and detail of the Makauwahi Sinkhole on the Island of Kaua‘i are

mapped in plan view within the Hawaiian Islands. To the right a stratigraphic core is

shown for Site 6 on the map in the middle of the sinkhole, noting the paleotsunami

deposit 2 m below the surface (layer VI, stones and gravel). Other cores and excavations

within the perimeter of the sinkhole show this paleotsunami layer. Since 2001, further

excavation at Site 15 also reveals the paleotsunami layer, as shown in Figure S3. Map

and core from Burney et al., [2001].

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Figure S3. Site view of paleotsunami deposit. (upper right) The star locates the edge of

the north cave in Figure 2. The arrow indicates the excavation at Site 15 in Figure S1.

(upper left) Dr. Burney points to the paleotsunami layer 2 m below the surface. Since the

site is below the local water table, the water was pumped out via the hoses shown.

Decimeter stick is noted for scale. Note layer change from mud to dark cobbles. (lower

left) Examples of basalt cobbles retrieved from the paleotsunami layer, water bottle for

scale. (lower right) Pristine coral obtained in tsunami layer, centimeter scale indicated.

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Figure S4. Earthquake source models that include the eastern Aleutians in Table S1 are

illustrated, indicating the individual subfaults and the Mw moment magnitude. The “ab”

faults have 50 m fault slip near the trench and 20 m down-dip, averaging to 35 m. The

other faults have uniform 35 m fault slip. The color scale indicates the initial tsunami

amplitude at the source, in meters. The upper left event is shown in Figure S5.

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Figure S5. The maximum tsunami amplitudes are shown for a Mw 9.25 east Aleutian

earthquake from the source to the sinkhole. (upper left) The red circle shows the location

of Kaua‘i, which lies directly in the focus. (upper right) The tsunami forecast for the

Hawaiian Islands grid is shown. Note the focusing upon Kaua‘i even at this scale with

near-coastal amplitudes of ~5 m. (lower right) Tsunami forecast for the southeastern

coast of Kaua‘i. The sinkhole is indicated by magenta circle southwest of Nawiliwili

harbor in Lihue. The map scale is about 12.2 km on a side. (lower left) The Makauwahi

sinkhole is inundated at about 8-9 m above mean sea level. The map scale is about 0.5

km on a side.

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Figure S6. Four Mw 9.25 earthquake source regions from Table S1 are shown

corresponding to the tsunami forecasts in Figure 2 of the main text. Individual subfaults

are colored with the initial tsunami amplitude at the source, in meters. The top event is

shown in Figure S5.

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Figure S7. Inundation forecasts are plotted at the Makauwahi sinkhole for smaller values

of fault slip and magnitude, Mw, for east Aleutian earthquakes in Table S2. The source

region is noted in Figure S5. The detailed topography derived from the LiDAR data are

higher resolution (~1 m) than the tsunami forecast resolution (~9 m), and hence narrower

features are averaged. The narrow east wall has an apparent, average height of about 4 m,

rather than 7.2 m, due to averaging across the depth of the sinkhole and outer slope.

Neither of the upper events (Mw 9.05 and 9.1) overtop the wall. The inundation levels for

the Mw 9.15 and 9.2 are about 4.5 and 6.5 m, respectively, and less than the actual height

21

of the east wall. Tidal variations near the sinkhole range ± 0.3 m to a maximum of 0.5 m

(spring tide) about mean sea level, introducing uncertainty at least this large into the

measurement. Note that the tsunami forecast for 30 m of slip, Mw 9.2, does not reach the

7.2 m limit.

paleotsunami evidence on kaua'i and numerical modeling of a

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