I've seen large drops before (like the drop mentioned in this question), but I've never seen a drop like this before and am concerned that something is seriously wrong with our site's relationship with google.

enter image description here (the last day displayed above is monday Nov. 10th)

To confound things further we, as of today, are now ranking higher in google for some our key search terms than we ever have before. My question is two fold:

a) What could this possibly be?

  • Our site has been live for this hold period
  • It's been performing faster than normal (can see this with new relic)
  • There's been no surge in 500 errors or 404s on google webmaster tools
  • Our users haven't seen a surge in 500 errors (can tell because we're using Airbrake)
  • We haven't restructured our urls or changed our pages over this period
  • We are not using any blackhat SEO techniques (and if we were and being penalized, I presume we wouldn't be ranking so high in search, right?)

b) How long should I expect it take a decrease in crawl volume like this to precipitate a change in our SERP rankings, if it precipitates a change at all?

Edit: I reference the question which this has been marked as a duplicate of in the first line of my question. In that question, crawl volume drops by about 50%. Here crawl volume has dropped by 98.5%. I think the difference in the magnitude of the drop makes this a sufficiently different question.