Earth Sciences 240A - Lecture 17 - Tsunami
Terminology/Character
“Seismic sea wave”: common but wrong
Period – Wavelength:
Normal wave: 10 sec; 150 m; Tsunami: 1 hr; 200 km
Velocity: Varies with ocean depth;
Magnitude Estimate
Attempted scale like Richter: Imamura-Iida
Scale : Calculated as function of max. wave height in open ocean
Not very satisfactory!
Generation
Quick elevation/subsidence of ocean
floor blocks
Most effective in
subduction zones
Quick displacement of large water
volume
Submarine/supermarine landslide
Violent submarine volcanic eruption
Cosmic body impact
Approach to land
Bottom of wave on ocean bottom
Wave amplitude increases with shallowing sea floor (‘shoaling’)
Wave speed/energy remains high
Land-Fall
Commonly, first moderate wave
followed by water ‘draw-down’
Reduction of energy:
Bottom friction
Land erosion
Turbulence
Reflection/interference
‘Run-up’
Wave height on-shore
10, 20, 30 meters
measured
Examples:
1929
Earthquake→Landslide→Tsunami
Broken telephone submarine cables
29 deaths
Registered in
1952 research on area:
First documentation of turbidity currents
1964
Earthquake→Submarine landslide→Tsunami
122 deaths (106 in
5.4 hrs later:
1960:
Huge earthquake (M 9.5)→I-I scale:
8.6 tsunami
490-2290 deaths; >$0.5 B damage
Off-shore boats lost
Run-up est. 25 m
1755
Earthquake (8.5) Azores-Gibraltar→3 tsunami; waves 5-13 m high
60,000 deaths in
Many deaths around
Recent research: Contributing
submarine landslide
Tsunami Warning
System
Circum-Pacific; 26 participating countries
Headquarters: near
Two (NOAA) warning centers:
ATWC in Palmer,
PTWC in
Based on fault break type/magnitude
Warning steps
Earthquake data interpretation
NOAA Weather Radio System
Direct VHF broadcast of danger
US Coast Guard
Track/broadcast marine data to
ships, shore facilities
Local authorities/emergency
managers
Execute emergency plans
“All Clear”
Next: Volcanoes
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BEFORE NEXT LECTURE