1. A method for determining reflection travel times of seismic events picked on 3D records of seismic data corresponding to signals picked up by seismic receivers distributed along an acquisition line in response to the emission in the subsoil of waves from source points, this data having been previously converted to cylindrical wave data and interpreted, characterized in that it comprises the following stages: a) defining a slowness vector ({right arrow over (p)}) whose component (p x ) in a direction parallel to the acquisition line defines the slope of the cylindrical wave; b) for a seismic receiver situated at abscissa (x R ) on the acquisition line, seeking abscissa (&xgr;) of the source point on the acquisition line such that a ray starting from the seismic receiver and reflecting on a picked event emerges at the source point, with a slowness vector ({right arrow over (p)}) whose component in the direction of the acquisition line is (−p x ); c) determining a travel time (t e (x R )) by adding to the value of the travel time along said ray a time equal to the product of the slope of the cylindrical wave by the abscissa of the source point; d) repeating stages b) and c) for all the positions of the receivers for which a demigration result is wanted; and e) repeating stages a) to d) for all the values taken by parameter (p x ) for which an event has been picked in the corresponding migrated data.