The 1964 Great Alaska earthquake and tsunami: lessons learned in the 50 years since the dawn of plate tectonics

Talk by:

Peter J. Haeusslerpheuslr@usgs.gov 907-786-7447 U.S. Department of the InteriorU.S. Geological Survey, Anchorage, Alaska

1964 earthquake damage in Anchorage, Alaska

Earthquakes define the plate margins ‘magmatic arcs’ are related to subduction zones

Active faults and significant earthquakes of Alaska

Alaska subduction zone cross sectionNW SE

Plates of the world

99% in Alaska

EQ energy release in the US 1960-2010

Mike West, Alaska Earthquake Center

The 1964 Great Alaska Earthquake March 27th, 1964,

5:36 PM. Good Friday

Magnitude 9.2 2nd largest ever

recorded shaking lasted 4.5

minutes Huge rupture area

(~250x800 km)

Anchorage

Uplift and Subsidenceup

lift

subs

iden

ce

Uplifted tidal flat Uplifted dock at high tide

Village of Portage had to be abandoned ‘ghost forest’

Uplift and subsidence pattern is only consistent with a “megathrust”

Uplift

Subsidence

Max subsidence over large area of 2 m

Max uplift over large area of 4 m

USGS Geologist Dr. George Plafker

Tsunami Generation

This mechanism of tsunami generation first recognized from USGS studies of the 1964 earthquake

Tsunami Generation - landslide

Locally generated tsunamis

Alaskan deaths 106 of 122 from

tsunamis (87%) 85 of the 106 from

submarine landslide generated tsunamis (80%)

Alaskan fjords are an ideal environment for producing submarine landslides

The scientific legacy of the 1964 event: the fingerprint of the worlds’ largest earthquakes

Occurred at a pivotal time earth science Helped lead to acceptance of plate tectonics Showed the worlds largest earthquakes are

caused at convergent margins Provided a mechanism for launching trans-

oceanic tsunamis All giant megathrust earthquakes are understood

in the shadow of what was learned from 1964 (e.g. 2011 Japan, 2004 Indonesia, 1960 Great Chile, etc.)

1964 earthquake gave birth to modern earthquake detectives

Repeated pattern of uplift and subsidence with each megathrust earthquake allows us to determine the history of ancient earthquakes

Cascadia megathrust earthquake hazard

1964 Alaska perspective allowed identification of coastal OR and WA earthquake hazard

Copalis River ghost forest at extreme high tide, December 1997 (Atwater and others, 2005).

Geodesy: pre1964, today, and the future

conventionalsurveying

continuousGPS

‘campaign’GPS surveys

Pre-1964today

today andthe future

New tools reveal earth deformation between and during earthquakes

2011 M9.0 Tohoku, Japan, earthquake

From Grapenthin and Freymueller (2012)

Motion during earthquake

verticalhorizontal

2011 M9.0 Tohoku, Japan, earthquake

Japan invested in seafloor geodesy Data revealed huge offshore slip (~50+ m),

which made a particularly big tsunami We don’t know how unusual this was Japan success: relative little shaking related

building damage

TAPS Denali fault crossing

Success: Trans Alaska Pipeline withstood 5.4m (18ft) of fault offset during M7.9 quake

Before After

In the 50 years since 1964…

We’ve made big gains in understanding earthquakes

We have success in reducing losses We need to be vigilant

The most recent disaster fades from memoryJust before the next one strikes

- Ancient Japanese proverb