There are so many factors that affect how destructive an earthquake is, and how widespread it is felt.
Obviously the magnitude of the earthquake is a significant Factor, however the depth of the earthquake is equally if not more important. (I'm no expert! Just repeating what I've learnt over the years)
Other factors also affect how destructive it is. The primary wave that an earthquake sends out is felt like a short, sharp, shock, and it travels in a vertical motion. But it's the secondary waves that do the damage. They travel perpendicularly. They are big rolling waves, kind of like massive waves at the beach, curling in under themselves as they hit.
It's when they hit the surface that it really gets nasty. Surface waves come in two types: version 1 rock from side to side - believe it or not they're called Love waves. Again though it's the churning waves that are the most destructive. I forget what they're called.
And of course there's timeframe - sometimes it's over and done with in a matter of a second or two, others can go on for for several minutes. They're scary. And I do not say that lightly.
Another major factor that affects both the destructive power of the earthquake and how widespread its felt is of course geology. Is the local geology predominantly rock - if so what kind? Or is it mainly sand and sediment? (In which case it could well liquefy, which is extremely destructive).
Whilst most of us talk about the intensity of an earthquake in terms of the richter scale, I believe most countries that routinely experience them - for example New Zealand and the United States - use a far more useful system called 'The Modified Mercalli (MM) Intensity Scale' . It describes how destructive an earthquake is, and is a far better measure than the Richter scale in terms of ascertaining how severe and earthquake has been. The New Zealand version measures earthquakes in 12 steps: numbers 1 and 2 are not noticeable, 3 and 4 noticeable but no big deal, 5 and 6 vary from mild anxiety to a bit scary, and stuff starts to break. Seven and eight go from hard to stand and your furniture dancing, to full-on panic and structural damage occurring to well-built buildings; weaker ones are destroyed.
Worst case, people start to die.
9 and upwards - believe me, you really don't want to know.
Incidentally those are my descriptions not the official ones!
There are numerous excellent online articles so I won't go on any more.