add ref soil velocity
add ref soil velocity


Former-commit-id: 653dafb9c43e4736c208519d03e6def6418b1b8e [formerly 546e36e4896ea929197ba7c234938014ad2ad7b5]
Former-commit-id: 9757780bc910b42f472905868728c3f6a291adb0
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine