Abstract
An instrument capable of collocated measurement of three perpendicular ground velocity components (two horizontal and one vertical) and three seismic rotation rate components (around two horizontal axes and one vertical) in a high-frequency range of 2-100 Hz. Compared to the older prototypes, the maximum measurable frequency of seismic motions has been considerably increased by suppressing undesirable resonances due to a changed shape of the rigid metal frame of the instrument.
Moreover, the accuracy of the rotational measurement has been significantly increased by using more sensitive geophones at a higher number and in a substantially innovated arrangement.