That actually varies a lot depending on ones' distance to the epicenter, the depth of the quake, the local geology, the structure one is in, and so on. A recent 2.6 near LaCenter, KY, was surprisingly "noisy", and was felt by quite a few people who were right on top of it.
http://www.wpsdlocal6.com/news/ky-state-news/Earthquake-shakes-stirs-up-questions-242286401.html
“That actually varies a lot depending on ones’ distance to the epicenter, the depth of the quake”
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Yes, if your on the epicenter, you can feel most any tremor.
I am referring to quakes that are 50-100 miles away.
If I am sitting perfectly still in my chair, I might feel a
very slight 2 second vibration from a mag 4 quake on Bohol, which is about 50 km from me. I can see Bohol from my beach.
Judging by the chart, they seem to consider anything over a 4 to be significant, as they highlight the magnitude in a darker black.
By the way, one can register for the USGS Earthquake Notification System. http://earthquake.usgs.gov/
They will email you when there is a significant quake anywhere in the world. I have been a member for about five years.