Wiktionary
underdrag
n. (context geology English) The tensile stress exerted by an overthrust rock mass upon overlying rocks which themselves are not under compressive thrusting stress and therefore tend to be stretched and broken by normal faulting. vb. 1 (context transitive English) To exert pull on the underside of (something). 2 (context intransitive English) To undergo a pull from the underside.