Today google deindexed more than half of my pages! I used to have 15k+ pages now it's 5k pages. Is this normal? will it grow back up? my site is a year old so it's not a brand new site. My traffic dropped by half =[
Make sure you're using a structured sitemap, also start link building campaign to get backlinks to your inner pages which you want to get indexed.
there may be several reasons, either your site is not authorized by google(trust of google), or u never upgrade your pages, or no backlinks to ur inner pages. or may b all of those deindexed pages are newly added to ur website, google give newly added pages more weight in the beginning, but later it removes some of them which according to google are of no use, also check your PR, possibly it may be decreased. it generally takes three weeks to show your actualy PR. but lower position in serp is the solid symptom that ur PR is dropped, so search ur main keyword in google, if ur position is lower than actual, then after three weeks u will also see the decreased in PR which is also a possible reason 4 decrease of indexed pages.
check your sitemap, all links are available or not and make link building for those pages which are not crawled yet, start building links with book markings and link exchanges.
Check on google webmaster tools for any problems in crawling your website. If you have broken links somewhere on your site, that could stop the crawlers in their track and they wouldn't bother crawling the rest of your site. I checked the other day and found a page on my site that had 60 inbound links was returning a 404 error! fixed that straight away!
Many Dynamic (query string) site have been "gray barred" due to "duplicate content". This resultes from having a template that contains most of the code and content (common code) and very little data base, unique content. But when it comes to images, then G considers them all the same now and they are removed. Work-around. Each image must have a unique text string describing it. Remove as much of the common code and content as possible. Consider taking some of the "text content" and making it an image. And finally, verify that all basic SEO elements are unique (Title and Description). Also, it would help to have the URL to look at.
This is perfectly normal activity for google. Dont worry about it. And your only down 10k pages? I had problems with my site map about 6 - 8 weeks ago and lost around 300,000 pages. Give it a couple of weeks and google will find your pages again.
15k pages is no joke. is your content unique? if not, then that would explain the reason behind de-indexing. google will not index page with duplicate content or will deindex later on