We used a broadband (BB) seismic station at surface and a vertical array composed by 6-short period 3-components seismometers installed at depth ranging between 35 to 285 m in borehole at the same location of the BB sensor.
We found that:
- an evident noise reduction with depth for frequencies from 1 to 10 Hz;
- for some frequencies, the noise level is below the NHNM only at depth larger than 85 m;
- most of the noise reduction occurs between 0 and 35 m;
- the decrease of noise level (dB) as function of depth follows a logarithmic trend
1 Seismix srl, Palermo
2 Department of Physics and Astronomy, Alma Mater Studiorum University of Bologna
3 Department of Civil, Chemical, Environmental and Materials Engineering, Alma Mater Studiorum University of Bologna
4 Department of Earth Sciences, University of Pisa
5 Edison Stoccaggio S.p.A.
6 Solgeo Srl