Abstract
This paper describes a means of combining the voltages from a three-component
seismometer so as to suppress noise waves arriving randomly from
all directions and to indicate the direction of arrival of any particular
wave-train, such as might be caused by an earthquake, explosion,
or moving vehicle. Each of the horizontal components of motion is
electronically multiplied by the vertical component, with or without
phase shift, and the two resulting products are displayed as a vector
pointing to the source of seismic waves. The equipment assembled
to perform these operations is referred to as the Motion Product
Detector. Mathematical analysis and small-scale tests of the Motion
Product Detector on the Research Center grounds look promising.