Acehtsunami

A tsunami cannot be prevented or precisely predicted—even if the right magnitude of an earthquake occurs in the right location. Geologists, oceanographers, and seismologists analyse each earthquake and based upon many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunami. One of the most important systems that is used and constantly monitored are bottom pressure sensors. These are anchored and attached to buoys. Sensors on the equipment constantly monitor the pressure of the overlying water column. This is deduced through the calculation:

P = \rho gh

where
P = the overlying pressure in Newtons per metre square,
ρ = the density of the seawater= 1.1 x 103 kg/m3,
g = the acceleration due to gravity= 9.8 m/s2 and
h = the height of the water column in metres.

Hence for a water column of 5,000 m depth the overlying pressure is equal to
\! P = \rho gh=(1.1 * 10^3 \frac{kg}{m^3})(9.8 \frac{m}{s^2})(5.0 * 10^3 m)=5.4*10^7 \frac{N}{m^2}=54MPa
or about 5.7 Million tonnes per metre square.[citation needed]

In instances where the leading edge of the tsunami wave is the trough, the sea will recede from the coast half of the wave’s period before the wave’s arrival