How do they measure tsunamis?
Today, it said on the news that a tsunami would hit the pacific ocean side of Japan due to a 8.1 magnitute somewhere. Then later on, it was making announcements that a 10cm, 40cm, 50cm, and 1 meter tsunamis either "hit" this city or that.
Whenever they make tsunami announcements, I often see these really low "tsunamis". I thought a tsunami was a huge wave...so I have a hard time comprehending why they make warning announcements for a "10cm tsunami". If a boat passes by, that alone would cause more than a 10cm wave, right?
Any ideas on why they call a 10cm wave a "tsunami"?