Wait a minute...!
This comet is basically in the
same direction from the Sun in all those plots, because of the shape of its orbit, right? As it approaches perihelion from far away, the Earth and Sun will be almost in alignment with it
every 6 months (probably on some other set of dates 6 months apart, we'll be in alignment with some other comet; you can always find an alignment if you look hard enough). So what those dates have in common is just that we make roughly the same line with the Sun, irrespective of what else happens to be along that line
(there's always something). What's more interesting about those dates is that they're all close to the equinoxes, when the seasons change. I'm not a planetary scientist, but I believe people have studied this and concluded that earthquakes are not generally seasonal -- so that might arouse some curiosity... However, the magnitudes of these events are between 7-9 and I understand from past reading that there is typically one magnitude 8 or larger earthquake somewhere in the World each year. You can probably pick the closest out of a few different magnitude 7s to fill in the third point (eg. the mag. 7 Haiti earthquake and the mag. 7 off the coast near Valdivia a few months ago didn't make it onto your list). So the coincidence here is 2 earthquakes of a size that happens anually, one year apart. Hmmm...

(OK, I don't actually have stats. for the probability of a comet alignment, but there are thousands of them known and they mainly have eccentric orbits, so this doesn't seem unlikely).
Cheers,
James.