Earthquakes and the time of day and moon phase

Earthquakes and the time of day and moon phase

Question:

Over the years I have noticed that most major earthquakes seem to happen in the early morning hours between 

12:00 midnight and 6:00 a.m. Is there any truth in this observation? Could there be a correlation between full 

and new moon and the frequency of earthquakes (land tides)? The Sylmar and the Northridge earthquake fit 

this model and the Tehachipe in 1952 occured in the early morning but I do not know what the phases of the 

moon was in 1952.  wayers

Answer:

Ah, so you've noticed that earthquakes tend to occur in the early morning hours, have you?  You mentioned the 

Northridge, Sylmar, and Tehachpi earthquakes--some recent southern California earthquakes that fit the pattern are:

Earthquake	Magnitude	Time of Day
----------	--------	----------
1994 Northridge	6.7	4:31 AM
1992 Landers	7.5	3:57 AM
1992 Big Bear	6.5	7:05 AM
1991 Sierra Madre	5.4	6:43 AM
1987 Superstion Hills	6.1	5:15 AM
1987 Whittier Narrows	5.9	6:42 AM
1986 North Palm Springs	5.6	1:20 AM

The California Institute of Technology has a catalog of earthquake times and locations for

southern California that is fairly complete back to 1933.  Of 44 magnitude six or larger earthquakes 

in that catalog, 28 occurred in the morning and 16 occurred in the evening.  The odds of 28 or more 

earthquakes occurring in the morning by random chance is about 5%. 

If this is a real effect, it is probably related to earth tides as you suggest.  I have been planning to look into 

it in more detail, but haven't had the time yet.  

Sounds like a good project for a science fair for an enterprising student.

-Grant

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