While a magnitude 9 could cause extensive damage, a magnitude 10 is almost unimaginable. There would be so much pressure on the Earth's crust that it would crack, causing uncountable volcanic...
The amplitude (height) of the seismic waves in a magnitude 8 earthquake will be ten times larger than in a magnitude 7 quake. This equates to approximately 31 times more energy.
There are many factors. One would be the distance a person is from the epicenter. A person who is further from a magnitude 7 earthquake would be less affected by the shockwaves than a person nearer...