▁contrast , ▁fast - sp reading ▁rid ges ▁( gre ater ▁than ▁ 9 0   mm / yr ) ▁such ▁as ▁the ▁East ▁Pacific ▁R ise ▁lack ▁r ift ▁valle ys . ▁The ▁spread ing ▁rate ▁of ▁the ▁North ▁Atlantic ▁Ocean ▁is ▁~ ▁ 2 5   mm / yr , ▁while ▁in ▁the ▁Pacific ▁region , ▁it ▁is ▁ 8 0 – 1 4 5   mm / yr . ▁The ▁highest ▁known ▁rate ▁is ▁over ▁ 2 0 0   mm / yr ▁in ▁the ▁Mi oc ene ▁on ▁the ▁East ▁Pacific ▁R ise . ▁R id ges ▁that ▁spread ▁at ▁rates ▁< 2 0   mm / yr ▁are ▁referred ▁to ▁as ▁ul tras low ▁spread ing ▁rid ges ▁( e . g ., ▁the ▁G ak kel ▁R idge ▁in ▁the ▁Ar ctic ▁Ocean ▁and ▁the ▁South west ▁Indian ▁R idge ). ▁ ▁The ▁spread ing ▁center ▁or ▁axis , ▁commonly ▁connect s ▁to ▁a ▁transform ▁fault ▁orient ed ▁at ▁right ▁angles ▁to ▁the ▁axis . ▁The ▁fl anks ▁of ▁mid - o cean ▁rid ges ▁are ▁in ▁many ▁places ▁marked ▁by ▁the ▁in active ▁sc ars ▁of ▁transform ▁fault s ▁called ▁f ract ure ▁zones . ▁At ▁faster ▁spread ing ▁rates ▁the ▁axes ▁often ▁display ▁over la pping ▁spread ing ▁cent ers ▁that ▁lack ▁connecting ▁transform ▁fault s . ▁The ▁depth ▁of ▁the ▁axis ▁changes ▁in ▁a ▁system atic ▁way ▁with ▁shall ower ▁depth s ▁between ▁off sets ▁such ▁as ▁transform ▁fault s ▁and ▁over la pping