Megacities face increasingly complex risks from the interaction of active faults and megathrust earthquakes, while a critical gap remains between scientific advances and their translation into effective disaster risk reduction. This session invites discussions to explores the Science-Policy-Action Nexus, highlighting how earth monitoring and observations, Early Warning Systems, and social exposure modeling can inform evidence based urban policies. Through international collaboration, technological innovation, and multi stakeholder engagement, the session aims to bridge science, policy, and action while advancing towards an International Platform for Risk Informed Development and Megacity Resilience.