You didn't supply an image of how ideally this would look, so how about something like:

ggplot(data=SO) +
   geom_rect(aes(xmin=date,xmax=date+1,ymin=min(latitude),ymax=max(latitude), 
      fill=eqx.effect)) +
   geom_line(aes(x=date,y=latitude),color="yellow")