How can we know seo updates for Google? Please give url.

Not sure what you mean. Google releases new algorithm updates just about daily. Every so often, there are some big ones that happen, but Google doesn't release official announcements about them. The SEO community finds out because people begin to notice large shifts in their traffic overnight and so they announce it and get confirmation from others experiencing the same thing at the same time.

Last update of google panda in 23 augest 2012 which effect on website ranks.

google has recently updated google panda and google pengiun which bans useless sites and effect ranking..
in response to ur question there is no such officail site of google where it updates its new rules..
only the seo or experience webmasters reaserch and get to knw abt latest updates which r furtur convey to other webmasters.
happy blogging..!!

This is the big problem that we can't have any authentic source where we go and find the updates , you have to get it with the webmasters and the other seo experts and keep reading .

Jus regularly visit this site seomoz.org/google-algorithm-change to get the updated seo results. Hope it will be useful

I am agree with angelinwilliams

there are few seo site, you can join them for latest seo updates or participate in forum discussions

googleblog.blogspot.com you will google from this blog. i hope this is what you comming to ask. correct?

I too agree with (angelinwilliams).