Introduction to Earthquakes and Tsunamis

Eldridge Moores

Distinguished Professor Emeritus of Geology, UC Davis

California Senate Energy Committee

Senator Alex Padilla, Chair,

April 14, 2011

Transform margin

LA basin, Cascade “megathrust”, C. RangesConvergent/subduction margins

Plate tectonics of the Earth

Folds

Faults and plate margins

(After Google Images)

Moores & Twiss, 1995

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Divergent margin

Tahoe V., Death Valley. San Andreas F.

Coast RangesLA region

San Andreas

California examples

Faults: •Shaking depends on size of e.q., distance, and nature of ground--greatest in loose sediments, less on bedrock

Tsunamis: •Result from change in ocean bottom shape and depth. •Involve entire water column, not just near-surface. •Velocities about 500 mph in deep ocean,

30-60 mph near shore, where water bunches up. •Near shore: may be focused or dispersed depending

on the shape of the sea floor.

•Principal Causes: •Earthquakes•Landslides•Explosive volcanic eruptions in shallow ocean

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After Atwater et al. (2005) USGS Prof. Pap. 1707

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Fig. 3-1 Fig. 3-2 Fig. 3-3

M9, 1700M92011

M7.9 1906

M7.9 1857

M71989

DCDC

SO

HB

(After Moores & Twiss,1995)

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Cas

cade

“Meg

athr

ust”

Vancouver I.

DC

SO

1906

1857

San G

regorio-Hosgri

1700

HB

(Moores & Twiss, ibid)

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(Atwater et al, 2005)

Atwater et al, 2005

After NRC Can.

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Fig. 7-1

Fig. 7-2

HB

Cascade tsunami model

Possible landslide locations thatmay cause tsunamis:•Hawaii•Basins off southern CA

ACTIVE: 10 cm/yr

SO

HawaiianIslands

Cliffs on ridges=landslides?

LA

World’s largestLandslide

After Moore et al., (1989)

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Fig. 8-1

Fig. 8-2Tsunami in Australia?

faults

Santa Barbara 1812 eq & “waves”

CONCLUSIONS:

•California is on an tectonic plate margin that has been active for millions of years, and will likely continue for millions of years.

•Active plate margins involve infrequent unpredictable events with large consequences.

•As Californians, we can expect a future earthquake/tsunami event as large as the recent Japan, event, possibly in our lifetime.

•We need to prepare present and future structuresand emergency procedures accordingly.

•We still have much to learn about Earth processes, and there may well be geologic surprises in our future.

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“Civilization exists by geologic consent--subject to change without notice.”

-Attributed to Will Durant

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