Geophone

The deviation of this measured voltage from the base line is called the seismic response and is analyzed for structure of the Earth.

Geophones have historically been passive analog devices and typically comprise a spring-mounted wire coil moving within the field of a case-mounted permanent magnet to generate an electrical signal.

[1] Recent designs have been based on microelectromechanical systems (MEMS) technology which generates an electrical response to ground motion through an active feedback circuit to maintain the position of a small piece of silicon.

Although waves passing through the Earth have a three-dimensional nature, geophones are normally constrained to respond to single dimension - usually the vertical.

It can be assumed that small signals that register uniformly at all geophones in an array can be attributed to a distant and therefore significant event.

In such an application there is an area of interest which when penetrated a system operator is to be informed, perhaps by an alert which could be accompanied by supporting photographic data.