The invention concerns a measuring instrument, a combined seismic sensor system that can measure 9 components of seismic motion, i.e. 3 orthogonal translational components, 3 components of rotation around orthogonal axes and 3 strain components at the measuring point. The system according to the invention comprises a solid undeformable frame, horizontal and vertical seismic sensors and optical dilatometers. The invention also includes a method of seismic measurement using the instrument. The instrument is suitable for measuring wavefields generated both by artificial sources (mine blasts, generators of rotational motions) and by natural sources (e.g. local earthquakes, rockbursts etc.)