Answer:The frequency of the echo is slightly decreased
Explanation:
Given
speed of boat 
cliff is 
away
when boat is still , suppose t is the time taken by the echo to reach observer on the boat
But as soon as boat starts moving the distance between cliff and boat decreasing and time for echo to reach observer also decreases
and we know 
therefore frequency of the echo slightly decreased.
This is my opinion so don't really take my word for it, but we as humans are an evolved species of mammals. So we are a lot more complex in our structure than most animals or insects, but then again through history we made lots of discoveries because we created new technology or out of pure curiosity tried new thing like building better civilizations, even though ours today is destroying the earth but besides the point, and new materials that we can use and all that. So we have made mistakes but that doesn't always mean we are a mistake as a whole
Tensional forces which is associated with normal faults
4x time 10x (I think)
Here, this will help-
http://www.cas.miamioh.edu/mbiws/microscopes/Magnification.html#totalmagnification
