Guralp Systems CMG-EDU - Manual (Page 6)

CMG-EDU
2 Installing the CMG-EDU
2.1 Installing in vaults
The CMG-EDU is a sensitive instrument designed to measure
extremely small movements of the ground. These movements are the
sum of all the vibrations arriving at the instrument: as well as distant
earthquakes and nearby tremors, the ground responds to surf on
nearby beaches, quarry blasts, heavy machinery, traffic, and even
people moving around the building. Temperature changes and air
currents in the same room as the sensor can also affect its output.
2.1.1 Choosing a location
When studying natural earth movements, any other effects introduce
unwanted noise into the system. It is therefore important to choose an
appropriate site for the instrument, ideally in an underground vault
with the sensor installed on a concrete pier that is in direct contact
with the bedrock.
This setup has a number of advantages:
•
It is installed below ground. Most man-made noise tends to
travel along the surface, and natural microseisms (tiny natural
flexings of the Earth's crust) also occur near the surface.
•
Good contact with bedrock means that the signals accurately
reflect earth motions; seismic waves do not have to travel
through layers of soft soil and sediment.
6 Issue A