The Business Meeting at GEOSEA XII in Bangkok, on 8 March 2012 agreed that the Geological Societies of all 11 countries in Southeast Asia will be core members of GEOSEA. Where there are no Geological Societies, a relevant government department or institution will be invited to represent that country as an interim measure. Membership to GEOSEA is free of charge, voluntary and based on friendship and goodwill.

Core GEOSEA members will maintain affiliation with geological societies from East Asia and other parts of the world. The tradition of inviting geoscientists from East Asia and other parts of the world to participate in GEOSEA will be continued and strengthened.