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Site selection

Site selection for a permanent station is always a compromise between two conflicting requirements: infrastructure and low seismic noise. The noise level depends on the geological situation and on the proximity of sources, some of which are usually associated with the infrastructure. A seismograph installed on solid basement rock can be expected to be fairly insensitive to local disturbances while one sitting on a thick layer of soft sediments will be noisy even in the absence of identifiable sources. As a rule, the distance from potential sources such as roads and inhabited houses should be very much larger than the thickness of the sediment layer. Broadband seismographs can be successfully operated in major cities when the geology is favourable; in unfavourable situations such as in sedimentary basins, only deep mines and boreholes may offer acceptable noise levels.

Besides ground noise, environmental conditions must be considered. An aggressive atmosphere may cause corrosion, wind and short-term variations of temperature may induce noise and seasonal variations of temperature may exceed the drift specifications. Seismometers must be protected against these, sometimes by hermetic containers (see next section). As a precaution, cellars and vaults should be checked for signs of occasional flooding.


next up previous contents
Next: Seismometer installation Up: Seismic noise. Site selection. Previous: The USGS Low-Noise Model
Erhard Wielandt
2002-11-08