added reference velocity
added reference velocity


Former-commit-id: c35540473cd65b541bb13fc03fe05e4144a735d9 [formerly c35540473cd65b541bb13fc03fe05e4144a735d9 [formerly cffb4380661bcf4b0843207e200ae845516a3c24]]
Former-commit-id: db346befc556a1c30e0ec053a54aa141ca063244
Former-commit-id: fcac132443c19b3df2248896eba080ffe86824c1
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine