1. Tsunamis and Tsunami Detection Systems
December 1, 2010
Physical Oceanography Presentation
Jeana Drake
Tsunamis and Tsunami Detection Systems

2. What is a tsunami? Shallow water wave Long wavelength
~200 km
Small amplitude in open ocean
~30 cm
Caused by earthquakes, landslides, volcanic eruptions, meteor impacts l h
Tsunami = japanese for harbor wave
= 200,000 m, hmax = 5000 m
h/l = 1/40
h/l < 1/20 = shallow water wave

3. Why are tsunamis a problem?
Shallower depths near coasts force a decrease in l
That water has to go somewhere
Increase amplitude
E = (1/2)rga2
r = density
g = gravity
a = amplitude
Except for very large tsunamis, waves do not break.
Bays may shape tsunami and force increased amplitude.

4. Tsunami warning: simple
c = √(gh)
g ~10 m/s
haverage ~ 4000 m
c ~ 200 m/s
Portugal to Cuba (1755)
~7000 km
~9.5 hrs

5. Tsunami warning: complicated
Regional
Seismic data from local earthquakes
Coastal tide gauges
DART buoys
International
DART
SOFAR channel
DART = deep ocean assessment and report of tsunamis, developed by NOAA
SOFAR = sound fixing and ranging channel – depth at which the speed of sound is minimal, traps earthquake energy

6. Tsunami warning: New
GPS-based detection of horizontal & vertical movement of the seafloor near an epicenter.
GREAT
GITEWS
Quicker calculations
Fewer false alarms

7. References DART. www.noaa.gov
Falk et al Near real-time GPS applications for tsunami early warning systems. Natural Hazards and Earth System Science 10:
Knauss, J.A Introduction to Physical Oceanography. Waveland Press, Inc.
Song, Y.T Detecting tsunami genesis and scales directly from coastal GPS stations. Geophysical Research Letters: 34.