also in danger are over 400 public venues and dependent care facilities .
study estimates 77 % of communities have the 15-25 minutes required to evacuate safely after an earthquake hits .
some communities in washington , the most at-risk state , could increase chance of survival simply by walking faster .
but certain communities along the coast are too far from high ground for a safe evacuation - no matter how fast they walk .
they will need to build special evacuation structures instead .