Ask A Scientist General Science Archive

Question:  How many earthquakes are there usually in a year?
 brandon s pincus

Answer:
Nobody knows exactly how many earthquakes there are per
year since many of the really small earthquakes go
unrecorded.  Generally, an earthquake must be at
least magnitude 5 to assure that it is recorded by
a seismograph somewhere on earth.  Over the last
ten years or so, there have been an average of 1656
magnitude 5 or larger earthquakes each year.
(This information is from the National Earthquake
Information Center of the U.S. Geological Survey
in Golden, Colorado.)
 
As a rule of thumb, for every magnitude you drop down,
there are roughly ten times more earthquakes.  So,
if there are 1656 magnitude 5 or larger earthquakes
per year, there are about 16,560 magnitude 4 or larger
earthquakes per year.  Nobody is sure how far down
this rule of thumb applies, but just for fun, let's
take it down to magnitude 1.  We would expect 10,000
times more magnitude 1 earthquakes than magnitude
five earthquakes following our rule of thumb; this
would give 16,560,000 earthquakes larger than
magnitude 1 each year.  Yikes!
 
-Grant