Dear 許銘凱,
Are you asking about calculating the damage/losses due to a single earthquake? If so, the feature you are asking for is already available in the OpenQuake-engine for both the scenario_damage and scenario_risk calculators, and documented in the user manual. You can input an observed or pre-calculated ground motion field using the parameter gmfs_file, and use it to compute damage or losses for that earthquake.
On the other hand, if you are asking about probabilistic risk calculations starting from ground motion fields, that feature is currently being implemented, as Michele mentioned in his previous reply.
Regards,
Anirudh