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The following background information on tsunami observations on coastal sea level stations was provided by the ITIC to participants during training courses in 2006 and 2007. It provides a practical illustration of the tsunami science principles.
a. Tsunami are a series of waves that continue for many hours.
b. The 1st wave height may not be the largest.
c. The largest wave may not occur at the station closest to the earthquake.
d. Tsunami signals arriving at coastal stations are affected by local conditions,such as the
e. Tsunami wave periods can vary from minutes (5-10) to one hour.
Record length is about 25 hrs, with tick marks every 5 hours. Amplitude scale of each record
varies and normalized. Shown are high-frequency, low-amplitude wind-generated
Showing of the tides is useful because you can determine if the tsunami will arrive at high
3. Tsunami warnings are cancelled when signals become small on many stations. In this
a. The earthquake rupture determines the initial character of the tsunami wave.
In theory, for a subduction zone thrust earthquake, the thrusting plate moves the ocean
In reality, seafloor topography between the tsunami source and affected coast will modify
Left:The 1st tsunami wave arrival will be an advancing wave (wall of water) toward China,
and a receding wave at Luzon, Philippines.
Right:With time, the wave character is changed by seafloor topography. The trailing trough
catches up to crest in the north (A), but not in the south (B).
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