Ask A Scientist General Science Archive

Question:
California had a lot of rain last year.  We also had a pretty
nasty earthquake recently.  Do you suppose there may be a
correlation between seismic activity and rainfall?  More
specifically, would it be possible that heavy rainfall
causes fault movement because of increased weight of soil
from the increased water content?
 Jim G

Answer:
It is pretty unlikely that there is any connection between
rainfall and earthquakes.  Earthquakes usually occur
pretty deep within the earth.  For example, the depth
of the latest earthquake in Los Angeles was about 12
miles.  The weight of any added rainfall would be small
compared to the weight of 12 miles of earth.
 
However, some people do believe in a connection between
weather and earthquakes.  For centuries, people
have referred to hot weather as "earthquake weather."
The idea is that earthquakes are more likely to occur
during hot weather.  A scientist, Jerome Namias, from
the Scripps Institution of Oceanography, published
a paper in 1989 suggesting that earthquakes do occur
more often in hot weather.  I would say that most
seismologists (people who study earthquakes) are
skeptical of the connection between weather and
earthquakes.  But there might be something to it.

Also you will be interested to know that the weight of
water can definitely cause earthquakes.  Water impounded in a
resevoir can sometimes trigger an earthquake.  For example,
the filling of the Oroville Dam in northern California
probably triggered the magnitude 5.7, 1975, Lake Oroville,
California earthquake.  The triggering of earthquakes
by the filling of dams can be a major concern in
seismically active areas.  There is the possibility
that the triggered earthquake will cause the dam to
fail leading to a serious flood.  Engineers who
build dams sometimes have to consider this possiblity
in the design of the dam.
-Grant