Hi I noticed for some blog providers in my country, which provide a sub-domian address for their blogs. the sub-domain authority is exactly as the main domain. Whereas, for some other blog providers  every subdomain has its different and lower authority. for example "ffff.blog.ir" and "blog.ir" both have domain authority of 60. It noteworthy to mention that the "ffff.blog.ir" does not even exist! This is while mihanblog.com and hfilm.mihanblog.com has diffrent page authority.