GEOLOGY

Detailed explanation-1: -To completely characterize the earth’s movement, the motion must be measured in three perpendicular directions. Consequently, seismographs often employ three sensors, recording in each of the north-south, east-west and vertical (up and down) directions.

Detailed explanation-2: -Modern seismometers include three (3) elements to determine the simultaneous movement in three (3) directions: up-down, north-south, and east-west. Each direction of movement gives information about the earthquake.

Detailed explanation-3: -A seismograph is a device for measuring the movement of the earth, and consists of a ground-motion detection sensor, called a seismometer, coupled with a recording system. A simple seismometer that is sensitive to up-down motions of the earth can be understood by visualizing a weight hanging on a spring.

Detailed explanation-4: -A seismometer is the internal part of the seismograph, which may be a pendulum or a mass mounted on a spring; however, it is often used synonymously with “seismograph". Seismographs are instruments used to record the motion of the ground during an earthquake.

Detailed explanation-5: -Instruments come in three main varieties: short period, long period and broadband. The short and long period measure velocity and are very sensitive, however they ‘clip’ the signal or go off-scale for ground motion that is strong enough to be felt by people.