The amplitude of a tsunami wave is defined in the same way as a seismic wave. It is the height from the median position to either the largest positive (crest) or negative (trough) value. In this case, the median position is the tide as shown by the smooth line (blue curve). You can use the scale on the coordinate (y) axis to determine the amplitude of the tsunami at any time. For example, the wave (labeled by the arrow), has an amplitude of about 1.25 feet. The absolute height of the water when this wave arrives is about 3.75 feet. 8. Look at the positive wave crests. What time (UTC) did the largest amplitude positive tsunami wave occur? Estimate the time to the nearest 15 minutes. 9. What is the amplitude (in feet) of the largest positive tsunami wave on this record? (Don't include the tide, this is just the largest tsunami wave.)