1. The devastating impact of seismic sea waves
Tsunami
The devastating impact of seismic sea waves

2. Tsunami (harbor wave) earthquake submarine volcanic eruption
Caused by processes that abruptly move large volumes of ocean water:
earthquake
submarine volcanic eruption
coastal/submarine landslide or rockfall
extraterrestrial impact

3. How do Earthquakes cause tsunami?

4. Tsunami causes
Unless there is an underwater landslide, strike-slip earthquakes WILL NOT cause tsunami
Most tsunami generated by subduction zones

5. Tsunami wave speed
Travel at high speeds : 400 to 500 mph (~200 yards/sec)
Alaska to CA 4 to 7 hrs
Alaska to Hawaii 4 to 6 hrs
Chile to Hawaii 14 to 15 hrs
Chile to Japan 22 to 33 hrs

6. Tsunami nears shore
As wave gets into shallow water bottom of wave drags along ocean floor
Top of wave still moving fast: can cause cresting of wave, and breaking onto shore

7. Tsunami run-up
Run-up = measurement of height of water onshore observed above a reference sea level
Generally don’t get big gigantic wave
Water comes as a fast moving rise in tide that rapidly moves inland
NOT JUST ONE WAVE…multiple waves coming in about ½ hour or so apart

8. Damage due to tsunami
Waves often full of debris (trees, cars, pieces of wood etc.)
As the wave recedes, the debris drags more stuff with it
Can recede as much as about ½ mile out to see, leaving shoreline empty with flopping fish, boats, etc. on the bottom

9. Detecting a tsunami Pressure recorder on bottom of ocean
Buoy to communicate readings via satellite
Tsunami Warning Centers issue warning

10. Tsunami Warning Centers
Hawaii and Alaska
When EQ considered capable of generating tsunami, send warning with estimated arrival time
Once tsunami hits somewhere, tsunami watch established to monitor tide gauges and ocean buoys

11. Tsunami Warning When warning is issued – low lying areas are evacuated
U.S. Coast guard issues warnings over marine frequencies
Some places have sirens