Our Subdomains were Removed from Google's Index

[delsoijj]

Is anyone else noticing Google removing sub domains from their index? We have a high profile website and are traffic tanked recently. Did some investigation and noticed that non of our sub domains are indexed (when they've been indexed for years). Is Google shifting their algo remove sub domains from their index?

[edited by: tedster at 5:07 pm (utc) on Sep 25, 2010]
[edit reason] moved from another location [/edit]

[tedster]

I work with sites whose subdomains are not removed - so I'm pretty sure this wouldn't be something Google does across the board. For instance. if we think about a site like wordpress.com, where every hosted blog is a subdomain, it seems clear.

So the question becomes why your subdomains were removed and if anyone else is seeing the same thing.

How many URLs did these subdomains have, on average?

[Robert Charlton]

Where were your subdomains getting most of their link juice...

a) from your main domain (the one whose traffic recently tanked), or...
b) from outside independent pages?

What was the cross-linking like between the subdomains and the main site? What was the cross-linking like between subdomains?

I ask because if the link juice source for your subdomains was primarily from the main domain, and that domain has run into difficulty, then it makes sense that the subdomains, further down the chain, would have run into even more difficulty.

[delsoijj]

@ tedster: This is very weird and not sure why our sub-domains was removed. What's weird is that the main sub-domain e.g. http://example.mydomain.com is removed but interior pages e.g. http://example.mydomain.com/content-1/ is indexed and ranked. PR is still the same on sub-domains so it's not a Google penalty. About a good 30-40% of the URLs are sub-domains.

@ Robert Charlton: Subdomains were getting most of their link juice from our internal links (roughly 85%). The rest are coming from external sites. The main domain has not run into difficulty and it is still ranking high for its terms. What could be the cause of this?