I have to know!!

I have to know when is an earthquake an earthquake? I mean at what magnitude do you feel it or notice things moving? I've been viewing this U.S. website that tracks the worlds earthquakes and it's amazing to me how many there are. Albeit there are alot between 2 and 3 magnitude but many more that are 4 and above! Fortunately I live in a "safe" area but it has felt the odd one now and again. Not like you fellas on the coast!


teejtc's picture

I believe the commonly accepted numbers are that some people can begin feeling an earthquake if it's a 2 on the Richter scale... most don't until it's a 3. There are something like a hundred thousand earthquakes (worldwide) each year in the 2-3 range.

Damage usually begins at about 4.5; a 6 is roughly equivalent of a hydrogen bomb (in the amount of energy it releases).

My understanding is that the Richter numbers aren't of consistent size, the larger they get, the more energy it takes to get to the next one. (In other words, there's a bigger difference between a 7 and an 8 than between a 1 and a 2.

Of course, it isn't exactly my area of expertise.... :-)

Grace and Peace,

bkeith's picture

Right. As I remember, Richter is a logarithmic scale. So 2 isn't twice as big as 1, it's 10 times as big. 3 is 10 times as big as 2, 4 is 10 times as big as 3, etc. So the difference between 7 and 8 is vastly more than the difference between 1 and 2.

MMario's picture

The richter scale is logorithmic; a two is 10 times a one. a three is 100 times a one.


YOu don't usually get noticiable shaking until over the 4.0 mark.

there are about 6200 earthquakes per year that are between 4.0 and 4.9 in magnitude. somthing like 8000 a DAY of the

MMario - I'm not divorced from reality - we're having a trial separation

steve kadel's picture

in l.a. we get hundreds a day under 3. we can feel some 4s but not all. 5s are hard to miss depending on how close the epicenter is. the northridge quake in 94 was terriifying and it was under 7.

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Wow home insurance rates must be phenomenol! My knit hat is off to you guys