LECTURE 10

SCIENTIFIC MILEST ONES

from HIST ORICAL TSUN AMIS

[ Pacific Ocean; 1700-2007 ]

© Northwestern University, 2007

Over the past 25 years...

→→ We hav e"discovered" new earthquakes

Example: Cascadia, 1700

THE CASCADIA EARTHQ UAKE of 26 JANUARY 1700

• Reconstructed from tsunami records in Japan.

• Confirmed by analysis of paleotsunami data(dead trees; terraces).

• Prior to Satake et al.’s work, Cascadia couldhave fit the model of a decoupling, perma-nently creeping, subduction zone.

→ We now understand that this subduc-tion zone is the site of relativley rare(400 yr ?) but gigantic interplate thrustearthquakes.

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1687

20011868

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Nazca

Rid

ge

PISCO

Lima (Callao)

Camana

AricaIlo

MollendoMejia

Islay

YaucaSan Juan

Lomas

Ica

Huacho

Barranca

Chimbote

2007

SOUTHERN PERU — 13 AUGUST 1868

Catastrophic Earthquake and Tsunami

Destroyed Arica, Peru [now Chile].

[Tsunami moved USS Wateree3 km inland at Arica.]

Tsunami destroyed cities along the Southern Shore of Peru,including Pisco, more than 1000 km from Arica.

Tsunami damage in Hawaii; Noticedin Japan.

May have carved large icebergs from Antarctic ice sheets (?)

USING TSUNAMI SIMULATIONSto EVALUATE HISTORICAL EVENTS

Example:1868 South Peru"Arica" Earthquake

Catastrophic destruction by tsunami atPisco, Peru

Modeling requires900 km fault rupture extending past NazcaRidge, and thus

M0 ≈ 1 × 1030 dyn-cm

(in the league of Sumatra 2004...)

PISCO"Short"

Fault

(600 km)

LONG

FA ULT

(900 km)

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1746

Nazca

Rid

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PISCO

Lima (Callao)

Camana

AricaIlo

MollendoMejia

Islay

YaucaSan Juan

Lomas

Ica

Huacho

Barranca

Chimbote

2007

IMPLICATIONS of 1868 ARICA EVENT

1. Earthquake is HUGE

2. Rupture "jumped" the Nazca Ridge

* What constitutes a "barrier"?

3. Note variability of rupture in Large [Peruvian] earthquakes

NOTE:The2007 event [partially]

andthe1687 event [probably]

also jumped[into]the Nazca Ridge...

SANRIKU, JAPAN — 15 JUNE 1896

First documented "tsunami earthquake"

• Run-up to 25 m on Sanriku coast;

• Yet, [tentative] instrumental magnitude onlyM = 7. 2

• Rupture must be very slow and may involve accretionary prism

[Tanioka and Satake,1996]

Estimated 27,000 killed

• Run-up of 2.5 m (9 m (??)) in Hawaii;Damage in Santa Cruz, California.

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UNIMAKUnimak Pass

Davidson Bank

Scotch Cap

Cold Bay

Shumagin Is.

ALASKA PENINSULA

UNALASKA

SANAK

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THE ALEUTIAN TSUN AMI of 01 APRIL 1946:A PERSISTING CHALLENGE

• A rather moderate earthquake (MPAS = 7. 4 )

• A devastating transpacific tsunami

• A catastrophic local tsunami

Scotch Cap lighthouse eradicated.

THE QUESTION REMAINS

How to model the source of the tsunami: A giganticearthquake source, or a large underwater landslide,triggered by the seismic event?

DESTRUCTION OF THE LIGHTHOUSEAT SCOTCH CAP, UNIMAK Is.

[Photog.H. Hartman; Courtesy G. Fryer]

Before(1945)

After (est. 03-04 (?) Apr. 1946)

01 APRIL 1946 TSUNAMI in HILO, Hawaii

•

FIRST DEVASTATING TSUNAMI IN U.S. HIST ORY

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Peninsula

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01 APR 1946

1946 ALEUTIAN EARTHQUAKE & TSUNAMI

• Recent study [Lopez and Okal,2006] shows very largeseismic moment (M0 = 8. 5× 1028 dyn-cm), but veryslow, bilateral rupture (VR = 1. 12km/s).

• This makes it the slowest earthquake ever studied, withΘ = −7. 03.

Isla Juan Fernandez, Chile,23 November 2000.

Diego Arcas (USC) interviews 82-yr. old resident Mr.Reynolds Green, a witness of the 1946 Aleutian tsunami,12500 km from its source.

ALEUTIAN TSUN AMI, 1946

First event for which field work was conducted on the basisof interviews of elderly residents.

[Okal,1999−2001].

CONCLUSION of 1946 SURVEYS

• The exceptional amplitudes in the near field(42 m)require generation by an underwater land-slide.

• The far-field dataset features both amplitude anddirectivity requiring generation by a large seis-mic dislocation.

→ Numerical simulations adequately predict mostobservables using acceptable parameters for bothsources.

KAMCHATKA — 04 NO V 1952

• This very large earthquake(M0 = 3. 5× 1029 dyn-cm) allowed thefirst ever observation of the Earth’s freeoscillations [Benioff, 1954].

• It generated a devastating tsunami inthe near field, killing upwards of 5000persons (which would make it the mostdevastating tsunami in the 20th cen-tury), and eradicating the Naval Base atSevero-Kuril’sk.

• This evidence, long kept a State secret,has slowly emerged in the past 15 years.

Severo-Kuril’sk : 9 m.Bay of Kitovaya : 18.4 m

• This very large earthquake(M0 = 3. 5× 1029 dyn-cm)allowed the first ever observationof the Earth’s free oscillations.

[Benioff, 1954]

Hilo was again devastated by the Chilean tsunami of 22 May1960. Sixty-oneresidents lost their lives.

Yet, in this case, a warning had been given, but residents failedto heed it.

CHILE — 22 MAY 1960

• Largest earthquake ever recorded and measured(M0 = (2 to 5)× 1030 dyn-cm)

• Last devastating Transoceanic tsunami in the Pacific.

Hilo, Hawaii, 23 May 1960

RATHER, "CURIOUS" RESIDENTS CONGREGATED ON THE WATER LINE !!!

The 1960 Chilean tsunami went on to hit the coast of Japan where it killed about 200 people.

Arrival of the tsunami at Onagaw a(Sendai Coast), 24.5 hours after origin time

04:40 JST (+24:29) 04:50 JST (+24:34)

04:45 JST (+24:39) 07:30 JST (+27:19)

ALASKA — 28 MARCH 1964

• Second largest earthquake ever recorded(M0 = 1. 0× 1030 dyn-cm) [Tsai et al.,2005].

• Last major tsunami to affect the U.S. (Seward, Alaskaand Crescent City, California).

Locomotive moved 1 km inland by 1964 tsunami at Seward,Alaska.

• Motivated creation of Alaska Tsunami Warning Center.

ALASKA — 28 MARCH 1964Singular geometry of subduction zone alongAlaska Peninsula results in directivity patternsparing Hawaii (for once), but focusedtowards California.

→ Explains exceptional level of destructionat Crescent City (12 deaths; 4 at NewportBeach, Oregon) and generally benigncharacter in Central Pacific (Hawaii,Tahiti).

Note also that many residents of Cres-cent City were drowned bysecond,larger wave, afer they had returned toclean up their damaged houses.

[Ben-Menahem and Rosenman,1972]

KURILES — 10 JUNE 1975

• "Tsunami Earthquake" following larger event in 1973.

→ [Local] tsunamis for the two events comparable, despitemuch smaller seismic moment in 1975 (see relevantsurface wav es).

• This type of event could correspondto the release of stress induced intothe sedimentary wedge (hence rup-turing slowly) by stress transferfrom the earlier main shock.

[Fukao,1979]

Regular Earthquake (1973)Tsunami Earthquake (1975)

Seismic waves

Tsunamis

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- NICARAGU A — 02 SEP 1992

• First major "Tsunami Earthquake" during modern instrumental era.

RED Events are SLOW (Θ ≤ − 5. 8)

NICARAGU A — 02 SEP 1992

• Motivated introduction of slowness parameterΘ[Newman and Okal,1998].

•1992Nicaragua

NICARAGU A — 02 SEP 1992

• The earthquake is found to be deficient inT waves, asexpressed by the parameter

γγ = log10TPEF

M0

[Okal et al.,2003].

CompareT waves at the same Polynesian station (TPT)from a regular earthquake (Costa Rica; 1990)and the1992 Nicaragua earthquakeof similar moment:

γ1992γ1992 − γ1990γ1990 = − 2. 06

1992 Deficient by TWO ORDERS of MAGNITUDE

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PAPUA NEW GUINEA — 17 JULY 1998

Then deadliest reported tsunami in 65 years

→→ RECALL

• Run-up too large for earthquake size

• Extreme lateral concentration of damage

• Tsunami minimal in far field

• Tsunami late with respect to earthquake source

First evidence ofseismicallyseismicallygenerated landslide tsunami

Validation of overland flow into lagoons

VANUATU — 26 NOV 1999

• Spontaneous night-time self-evacuation

following post-PNG Video

EDUCATION WORKS !!

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ALEUTIAN — 17 NOV 2003• First successful operational use of DART sensors to

call off an alert.

• The tsunami from this small earthquake was notrecorded at the distant Alaska and West Coast DARTsites.

However, a new station, only 900 km from the epicen-ter, clearly recorded the tsunami, at an amplitude of 3cm peak-to-peak.

→

This signal was interpreted by V.V. Titovin terms of source size and a real-timesimulation performed to predict the run-up in Hawaii. As a result, the pendingalert was called off by PTWC.

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01-May-1915

15-Nov-2006

S e a o f

O k h o t s k

Pacific Ocean

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Simushir

Matua

Shiashkotan

13-Jan-2007

01-May-1915

15-Nov-2006

SIMUSHIR (Central Kuril Is.) − 15 NOVEMBER 2006

M0 = 3. 5× 1028 dyn*cm

First large earthquake in the Central Kurils since 1915.

The event is not slow, but may bedelayed (as for Peru, 2001).

Local effects surveyed in Summer, 2007.

Run-up reaches 10 m inSimushir (Dushnaya Bay)and up to 15−20 m onMatua.

The latter figures arehigher than expected, andcould result from localtopography (bays, cliffs) orlocalized lanslides.

Fortunately, these islandsare presently unpopulated(even by bears...).

[courtesy J. Bourgeois andM. Nikula, U. Wash.]

Matua I.(12 km long)

Tsunami watermarkson Matua

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D = 6300 (+) km

15-Nov-2006 Crescent City

2006 KURIL TSUNAMI DID SIGNIFICANT DAMAGE

in CRESCENT CITY, California

• Harbor struck 8.5 hours after seismic O.T.

• Damage reached US$ 700,000.

• Wav e height reached 1.7 m (pk-to-pk) on local tide gauge

• Damage resulting from (i) beamingof some tsunami energy towardsNorthern California; (ii) non-linearamplification by bay and harbor.

Tidal gauge record

Damage to docks in harbor Direction of flow into harbor

Docks H, G, Fseverely damaged

[Uslu,2007]

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01-Apr-2007

SUBSEQUENT TSUNAMIS (ctd.)

5. Solomon Is., 01 April 2007 [ The Miracle ? ]

M0 = 1. 6× 1028 dyn*cmPreliminary Results:

[H. Fritz, pers. comm., April 2007]

Local Tsunami, resulting in significant damage on several islands

More than 500 houses destroyed; 35 dead or missing

The community apparently had the reflex of Self-Evacuation

(probably conditioned by the memory of strong waves during a volcano-seismic swarm in the 1950s ?)