Seasonal variations in seismic velocities within the Swiss Jura using Ambient Noise Interferometry

In recent years, seismic ambient noise interferometry has become a promising non-invasive time-lapse monitoring tool for near-surface studies. Indeed, researches have revealed that the coda of ambient noise cross-correlations can detect subsurface velocity changes (dv/v) as small as 0.01%. Seismic interferometry applications have been demonstrated for monitoring natural processes (groundwater cycle, volcano eruption dynamics) and human operations affecting the subsurface (e.g. geothermal, wastewater disposal). In such applications investigating human-induced effects, careful consideration must be given to site-specific natural background fluctuations to confidently determine if observed velocity changes can be attributed to human interventions. 

An upcoming Enhanced Geothermal System will be developed in the Swiss Jura mountains. Before seismic interferometry can be deployed to monitor geothermal operations, it is important to understand seasonal variations of the noise field. Hence, we are conducting a seismic interferometry study to investigate natural dv/v fluctuations in the area of the future geothermal plant. Using four years of continuous seismic data (August 1, 2017 to June 1, 2021) recorded by four triaxial high-gain broadband stations part of the Swiss national seismic network, we are applying both the moving window cross-spectral (MWCS) and stretching techniques across multiple cross-components. The objective is to quantify the range and magnitude of seasonal seismic velocity changes in the subsurface. Furthermore, our investigations involve exploring correlations between observed velocity changes and specific environmental factors, such as precipitation, groundwater level variations, and temperature fluctuations.