Innovative methods for microseismic monitoring

Here,we aimto characterize the seismic noise level at S. Potito-Cotignola in the Po Valley, Italy, from January 2019 to December 2021 recorded by a broadband seismic station at surface and a vertical array composed by six short-period three-component seismometers installed at depth ranging between 35 and 285min borehole.
We compute the amplitude noise reduction as a function of depth for different frequencies and we evaluate the depth dependency of the signal to noise ratio for 18 seismic events, with different magnitude (from −0.1 to 2.9) and hypocentral distances (from 12.9 to 37.2 km).
Results show that:

• the dependence of noise level with depth follows a logarithmic empirical trend;
• most of the selected seismic events show that signal to noise ratio increases with depth.

The empirical relationships we estimated can be used to help the design of microseismic monitoring networks in similar geological settings.

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

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