After their defeat in 928 AD by Samanid empire Alavids dispersed into three main branches: the main brunch was absorbed into the conquering Samanid empire; second moved up north following the caspian sea to present day Azerbaijan; the third branch took refuge in northern part of Armenia (what is now Dzoramut/Norashen territories).
The Tahirids were in turn replaced in Merv by the first the Saffarids, then the Samanids and later the Ghaznavids.