Question 470224
you should do a google search on earthquakes to get your answer, unless you have a textbook that describes what is being asked.
I did a google search and came up with some interesting tidbits you might find useful.
here's what I found.
Read up and you should find your answers in here.
<a href = "http://www.geo.mtu.edu/UPSeis/intensity.html" target = "_blank">http://www.geo.mtu.edu/UPSeis/intensity.html</a>
<a href = "http://www.geography-site.co.uk/pages/physical/earth/richt.html" target = "_blank">http://www.geography-site.co.uk/pages/physical/earth/richt.html</a>
<a href = "http://pubs.usgs.gov/gip/earthq4/severitygip.html" target = "_blank">http://pubs.usgs.gov/gip/earthq4/severitygip.html</a>
<a href = "http://science.howstuffworks.com/nature/natural-disasters/earthquake7.htm" target = "_blank">http://science.howstuffworks.com/nature/natural-disasters/earthquake7.htm</a>
These are just some of the references out there.
There's a wealth of information on the internet.
All you need to do is a search and pick the articles that look like they will be most meaningful to what you are studying.
From what I learned in a very short period of time:
Richter Scale is a scientific method of measuring the magnitude of an earthquake.
Mercali Scale is a perceptive scale based on observations of the effect of an earthquake.
Both are usually reported.
The earthquake in Japan was about 8 on the Richter Scale.
Reports of the devastation by eyewitnesses was that the earthquake was highly catastrophic, especially when taking into account the impact of the tsunami.
These observations are more in line with the Mercali Scale.
A magnitude 8 earthquake does not release millions of times more energy than a magnitude 4 earthquake.
It's roughly 10 times as strong for every increase of 1 on the Richter Scale.
There's also a factor between ground movement and energy that comes into play.
Something about the energy being 1.5 times the ground movement, while the ground movement is based on the magnitude.
Read the references for more information.
Based on the logarithmic scale along, a magnitude 8 earthquake would register 10 thousand times more energy than a magnitude 4 earthquake.
The math is 10^8 / 10^4 = 10^4 = 10 thousand times more.
This is far from millions.
If I were to look for the impact of the earthquake, the Mercali Scale would be more descriptive of the actual damage than the Richter Scale, even though it might not be as scientific.  
What we know of the devastation caused by the Japan Earthquake was through eye witness reports.  
There are many factors that go into how much damage the earthquake will cause, such as how close the epicenter is to the area, how deep the epicenter is in relation to the area, the construction of the buildings in the area, the type of geology inherent in the area, plus many more.
The Richter Scale doesn't tell you much except how much energy was released.  The effects are what has been observed (Mercali Scale).