Where the
ocean is over 6,000 m deep, unnoticed tsunami waves can travel
at the speed of a commercial jet plane, over 800 km per hour
(~500 mi per hour). They can move from one side of the Pacific
Ocean to the other in less than a day. This great speed makes it
important to be aware of the tsunami as soon as it is generated.
Scientists can predict when a tsunami will arrive at various
places by knowing the source characteristics of the earthquake
that generated the tsunami and the characteristics of the
seafloor along the paths to those places. Tsunamis travel much
slower in shallower coastal waters where their wave heights
begin to increase dramatically.
Calculated
tsunami travel times for an earthquake occurring off the coast of
Chile. Each concentric curve represents one hour of tsunami travel
time.
During
post-tsunami field surveys, inundation and runup measurements are
taken to describe the tsunami effects. Inundation is defined as
the maximum horizontal distance inland that a tsunami penetrates.
Runup is the maximum vertical height above mean sea level that the
sea surface attains during a tsunami. Actual tsunami wave heights
can be measured from the amplitude of the wave signals seen on sea
level or tide gauge instruments. |
