Hello Pat,
yesterday I posted the symbol :
"M"**+>
If you read in explanation you'll see that to "M" correspond swarm of shockes or large EQ.
Seeing the quaint moment, maybe it is better more to say.
The exact table of perception in day feb/23/00 is:
11.00h---------"m"
12.00h---------"M"
12.01h---------"M"*,--"M"*
12.03h---------"M"**,----"M"**
12.08h to 12.12h---"M"**,--"M"*,--"M"*,--"M"**,--"M"*,--"M"*
13.40h---------"M"
13.42h---------"M"
13.44h---------"M"*
13.46h---------"M"*
13.48h---------"M"*,"M"*,"M"*
13.50h---------"M"*+>
13.51h---------"M"**
15.00h---------"M"
23.00h---------"M","M"

It is not a thing of nothing!
Doing an analysis from a past experiences, after a group of "M" I'm noting three evidences:
or Etna after seven days about;
or numerous EQs at the same time in Italy and near Italy after ten days about;
or(only two cases, probable coincidence) after 13 or 15 days California and China a strong EQ.