Seismic Instruments

Seismometers 

• A seismometer is the detecting and recording parts of a larger apparatus known as seismograph. Seismometers are pendulum type devices mounted on the ground that measure the displacement of the ground with respect to a stationary reference point.

•  Since a seismometer records the motion in only one orthogonal direction, three seismometers are needed to record all components of ground motion.

Vertical Component Seismometer

Horizontal Component Seismometer

Creep meter

Creep meter measures minute gradual movement along a fault. In the past, such meters used to use wire stretched across a fault. Current creep meters use laser technology.

Creep Meter

Gravimeter

Gravimeter measures the variations in the local force  of gravity. Such variations are the result of changes in  underground rock density.

Gravimeter

 Laser

Laser can measure the round-trip travel time of a light  beam between two points. When the relative positions of the two points changes as a direct result of an earthquake, the travel time also changes.

Accelerometer

• An accelerometer (accelerograph) is a seismometer which records large accelerations, thus they are also known as strong motion seismometer. 
• An accelerometer located in a building does not run continually. It is triggered by a P-wave and runs for a fixed period of time. 

Accelerometer

 

Scintillation Counters 

• Scintillation counters are installed in wells to measure amount of radioactive radon gas in the water. Minute amounts of radon are released into well water by rocks under stress. 

Scintillation Counter