Geography and Oceanography - Chapter 6 docx

Earthquakes, Tsunamis, and the Oregon Coast When will the next Megaquake occur?. Tsunami  Sudden shifting of the ocean floor due to earthquakes, volcanic eruptions, and submarine slu

Earthquakes, Tsunamis,

and the Oregon Coast

When will the next Megaquake occur?

Why are tsunamis so destructive?

How much of the coast is affected?

Tsunami

 Sudden shifting of the ocean floor due to

earthquakes, volcanic eruptions, and

submarine slumping.

 open ocean: short heights, long wavelengths

(>100 km), and long periods 400-500 mph!!!

 shallow water: their length shortens and their

height increases dramatically.

 These are NOT tidal waves

Tsunami Animation

http://nctr.pmel.noaa.gov/animate.html

Sumatra 2004, >275,000 Dead!

Before

After

Courtesy of Mate 3 rd Class Tyler

J Clements/U.S Navy

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Japanese 8.9 Earthquake and Tsunami (March 11, 2011) ~18,000 dead

video: http://www.youtube.com/watch?v=TRDpTEjumdo

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Tsunami Sea floor thrust fault

2004 Sumatra M9.3, 1200km fault, 15m slip

Mega-Slumps can trigger tsunami

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Geologic record in Coastal

Estuaries

Multiple events

recorded in

coastal

sediments

Detective Story

Tracking down details

of the last big event

Records of a tsunami in

Japan for which there was no earthquake

Recurrence interval

Tsunami risk, PNW

Paleoseismology can address these questions

through development of long temporal and spatial

histories of past earthquakes

This works better in the submarine environment

than on land because of continuous sedimentation

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Cascadia: The

Movie This sequence shows the

Cascadia Holocene event sequence

The slides are timed at 1 sec = 400 years

Event pulses that correlate at all sites are shown by

flashes of the

“locked zone” in red Event “size” shown by intensity

of red shading

T18

T17a

T17

T16a

T16

T15

T14b

T14

T13

T12a

T12

T11

T10R2

T10d

T10c

T10R1

T10b

T10a

T10

T9a

T9

T8

T7

T6

T5a

T5

T4

T3

T2

T1 (AD 1700)

(Quasi) Time predictable model?

R 2 = 0.9851

0 10 20 30 40 50 60

0 1000

2000 3000

4000 5000

6000 7000

8000 9000

10000

Tim e (ca l yr BP)

Cumulative proxy for event "size"

A time predictable model, over 10,000 years of record, fits the actual

recurrence data quite well

If this is correct, we can predict the time, but not the size of the next Cascadia great earthquake, about 200 years from now for a full

margin rupture, and overdue for a southern margin rupture.

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Know this sign and where to go!