Symmetric Triaxial Seismometers

Synonyms

Galperin configuration seismometer; Homogeneous triaxial seismometer

Introduction

Of the class of seismic instruments measuring ground motion known as triaxial seismometers, most provide three signal outputs that represent mutually orthogonal motions in the East, North, and Vertical (or X, Y, and Z) directions (see entry “Broadband Seismometers”). Of these, some are designed with three independent internal sensors that are respectively sensitive to motions in the three XYZ directions, and so directly measure the single vertical and two horizontal motion degrees of freedom. Some triaxial seismometers use a different configuration known as a Galperin arrangement (Galperin 1955), also known as a “symmetric triaxial” or “homogeneous” design (Melton and Kirkpatrick 1970). In the Galperin configuration, the sensing elements are also arranged to be mutually orthogonal, but instead of one axis being vertical, all three are inclined upwards from the horizontal at precisely the same...