Barry,
Canie has made a very useful comment regarding the loading possibilities of flooding
as a trigger for earthquakes. I believe there was a study done several years ago
along the Mississippi on just this effect, however, cannot locate it in our archives
at this time, but will keep looking.
There are certainly several unusual earthquakes in the past 10 years which might
suggest that local flooding was responsible. During a previous flood in the Red River
valley in North Dakota/Minnesota a highly unusual earthquake occurred. The largest
flood recently in the Rio Grande area was followed by a Ml 5.8 on April 14, 1995.
There are some areas where earthquake seem to occur only during certain times
of the year like some areas of So. Colorado where earthquakes are generally confined
to mid-April to mid-May in the San Luis Valley.
The easiest (and dirtiest) way to answer your question is in a statistical sense.
Look at the number of earthquakes which have occurred each month in the general
area of Memphis. I have attached a listing of numbers of earthquakes per month
to this comment. The first group is for the general Memphis area, the second for
the region up-river. This listing does not include aftershocks from the New Madrid
earthquakes of 1811-1812 as this would considerably bias the data towards
December and January having more events. The result as seen below shows
that there is a tendency for the number of recorded earthquakes in the region
of Memphis to decline during the spring months of March through June when
all earthquakes are considered and also, but less so, when only larger earthquakes
are considered.
Since floods occur preferentially in this area in the spring, it would appear that
flooding is not a major factor in the seismicity of the area. In fact, the number
of monthly earthquakes is almost half in the Spring months what it is in the
Winter months, so one could argue that something is happening in the area
in the Springtime which is retarding the occurrence of earthquakes (maybe flooding).
At any rate, the statistics do not seem to suggest that spring flooding is
responsible for a higher risk of seismicity in the Memphis area.

88-92W 34-36N ALL EVENTS
MON # events
1 66
2 50
3 38
4 32
5 39
6 35
7 41
8 48
9 53
10 46
11 50
12 61

88-92W 34-36N ML>=2.0
MON # events
1 29
2 31
3 16
4 20
5 16
6 17
7 21
8 17
9 25
10 25
11 21
12 32

88-92W 34-36N ML>=3.0
MON # events
1 12
2 11
3 8
4 9
5 5
6 8
7 8
8 5
9 11
10 7
11 9
12 16

92-100W 37-50N ALL EVENTS
MON # events
1 52
2 32
3 28
4 21
5 18
6 33
7 39
8 23
9 24
10 24
11 23
12 37

92-100W 37-50N ML>=2.0
MON # events
1 31
2 19
3 10
4 12
5 15
6 19
7 24
8 19
9 17
10 19
11 13
12 28

92-100W 37-50N ML>=3.0
MON # events
1 27
2 14
3 7
4 7
5 11
6 8
7 14
8 10
9 12
10 17
11 13
12 18