correction: XML attribute vs30method is not required
correction: XML attribute vs30method is not required

Former-commit-id: 5f239e178cb66b2eb8230c1568be8c6f982a698b [formerly dd9e6fba500db2720db275149e4b0382e9f141fa]
Former-commit-id: 9d236faae2e80fc52ed7928b318d255427b7dce7
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine