Innovative methods for microseismic monitoring

Research article in Seismological Research Letters - May 2023

Seismic Noise Reduction as a Function of Depth Recorded by a Vertical Array Installed in a 285-m-Deep Borehole at a Gas Storage Field in Northern Italy

Camilla Rossi^1,2,3, Francesco Grigoli⁴, Paolo Gasperini², Stefano Gandolfi³, Timur Gukov⁵, Chiara Cocorullo^1,6, Paolo Macini³

The background seismic noise can be generated by different sources such as, oceanwaves (microseisms), atmospheric disturbances (strong wind and storms), and anthropogenic activities, temperature changes and magnetic field variations. Such disturbances are characterized by specific frequency bands, time occurrence (diurnal and seasonal variation), and site location (close to populated areas or to the coasts). Reducing the pernicious effect of these noise sources is one of the main challenges that seismologists and engineers need to face when designing seismic monitoring networks and, more specifically when selecting the hosting site of a seismic station. A solution to partially attenuate the seismic noise effect is achieved by deploying seismic stations in boreholes. A general law estimating the sufficient depth to gain to detect even low seismic events, highly masked by background noise, is fundamental for defining the capability ofmicroseismic network.

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

JpGU 2023, May 21-26, Chiba (Japan)

Estimation of amplitude noise reduction and SNR variation as a function of depth recorded by a vertical array of seismometers

Camilla Rossi^1,2,3, Francesco Grigoli⁴, Paolo Gasperini², Stefano Gandolfi³, Timur Gukov⁵, Chiara Cocorullo^1,6, Paolo Macini³

This work is focused on the mitigation of the background seismic noise effect in detection capability of seismic monitoring network, especially when we deal with low magnitude events. A solution to partially attenuate the background seismic noise is deploying seismic station in boreholes. It this sense, a general law estimating the minimum depth to place seismometers can be very useful. Here, we focused on an area close to two industrial sites, highly influenced by noise and where seismicity occurs. By using three years of continuous seismic data recorded by a vertical array, we estimate a noise attenuation relationship and SNR variation for 18 seismic events with different magnitude and hypocentral distances.

Our results show:

the noise attenuation relationship follows a logarithmic trend;
the mean amplitude attenuation within 135 m depth is about 0.16 dB/m;
the mean SNR trend increases according to depth with a more marked change between 0 and 85 m, a slightly slower increase between 85 and 235, and no evident change below 235 m depth;
the magnitude has more influence on SNR variation than the hypocentral distance;
5. an optimal installation depth could be found between 85 and 235 m.

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

EGU 2023, April 23-28, Vienna

DOI

Estimation of amplitude noise reduction as a function of depth with data recorded by a vertical array (Northern Italy)

Camilla Rossi^1,2,3, Francesco Grigoli⁴, Paolo Gasperini², Stefano Gandolfi³, Timur Gukov⁵, Chiara Cocorullo^1,6, Paolo Macini³

The background noise level of potential installation sites is one of the main factors limiting the detection capability of the monitoring infrastructures. To improve the seismic network capability in detecting microseismicity characterized by a low signal to noise ratio (SNR), is thus necessary to mitigate the effect of seismic noise. Here we analyse continuous seismic noise from January 2019 to December 2021 recorded at underground gas storage site of S. Potito-Cotignola in the Po Valley (Italy).

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

EGU 2022, May 23-27, Vienna

DOI

Microseismicity monitoring with SeisComP and 3D local velocity model

Camilla Rossi¹, Chiara Cocorullo¹, Timur Gukov², Francesco Grigoli³

In this work we show how SeisComP can be optimized for real-time data-processing for microseismic monitoring of an Underground Gas Storage field in Northern Italy.

We analysed to 2-years of continuous seismic data recorded by a network composed of 15 (surface and borehole) stations.

Our processing routine for this seismic network is the first application in Italy where a 3D velocity model is fully integrated within the real-time microseismic monitoring operations, as suggested by the Italian Guideline for Microseismicity Monitoring on Industrial activities.

¹ Seismix srl, Palermo
² Edison Stoccaggio S.p.A.
³ Department of Earth Sciences, University of Pisa

Innovative methods for microseismic monitoring

Seismix develops innovative methods for microseismic monitoring. Learn about our work published in peer-reviewed journals.

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