Why is it being de-indexed?

One of my sites used to have 400K+ pages at google but it decreased over three months to be 32K+ only.
SERPs are almost the same except for the most important and most competitive term.
Traffic is the constant (at a middle point for 4 months or so).
Any explanation or reason for that? Thank you.

 

Hi ... although not on the same scale, much the same has happend to my main site. Seems about 99% of pages de-indexed, with SERPs and traffic about the same. I suspect this is a short term shocker. Let us know when your site rebounds. Good luck.

 

Google does always evaluate each site value all the times. It is including the page value analyze too. If your site index dropped then you should build up some links to inner pages. It can be done by social bookmark but the topic on that page should be worthwhile to being listed too. You should also check if someone did scrape content on your site and out ranked your original page.

 

continues link building can help SEs bots to crawl and index your site more often..

 

I had the same issue but on a smaller scale.. was 2200 pages and now 120 pages indexed only .. Maybe google looked at your site and thought that 400,000 pages was just too much for any one site and decided it was time for a trim. I Hope you get it back , I have not thus far but I am ever hopeful

 

The reasons could be many. You can post your url if you wish to and then people over here can help you solve the problem.

Also you can use Google Webmasters forum to ask queries like this.

 

Have you submitted xml sitemap on Google webmaster tools? If not you should try so that Google will continue to index your site pages.

 

Internal linking may fix this problem. You should create internal link while writing a new article. You should rebuilt sitemap and resubmit it to webmaster tool.

 

submit sitemap.xml