Name: Vonisha L.
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: March 22, 2004
Question:
What is the effect of the moon's gravitational pull in producing
"land tides" similar to ocean tides? Do seismologists think this could be triggering
earthquakes?
Replies:
The short answer is generally not. According the web page of the
Seismological Laboratory at University of California at Berkeley:
"The question often arises as to whether astronomical events, such as
planetary alignments, can significantly influence the occurrence of
earthquakes. The moon, sun, and other planetary bodies in our solar system
influence the earth in the form of perturbations to the gravitational field.
The relative amount of influence is proportional to the objects mass and
inversely proportional to the cube of its distance from the earth. The
general idea is that strains in the earths crust caused by perturbations in
the gravitational field may influence when an impending earthquake will
occur (like the straw that broke the camel's back). If this were indeed the
case we would expect to see a correlation between the rate at which
earthquakes occur and the perturbations to the gravitational field. The
dominant perturbation in the earth's gravitational field generates the
semi-diurnal (12 hour) ocean and solid earth tides which are primarily
caused by the moon (due to its proximity) and the sun (due to its large
mass). No significant correlations have been identified between the rate of
earthquake occurrence and the semi-diurnal tides when using large earthquake
catalogs. There have, however, been some small but significant correlations
reported between the semi-diurnal tides and the rate of occurrence of
aftershocks in some volcanic regions, such as Mammoth Lakes."
You can read the entire commentary on this question at
www.seismo.berkeley.edu/seismo/faq/planets.html.
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