Seasonal Seismic Velocity Variations in the Western Bohemian Massif Using Ambient-Noise Cross-Correlation

Abstract. Changes in surface and near-surface loads, such as temperature and precipitation, can perturb crustal stress and generate measurable responses, including triggered seismicity, transient strain, and seismic velocity changes. Quantifying these responses provides a means to track the spatiotemporal evolution of stress and its coupling to fault slip and subsurface fluid processes. Traditional approaches, relying on recurring earthquakes or controlled sources, are limited by poor repeatability and high operational cost. Ambient-noise–based imaging avoids these constraints by using fixed receivers and continuous records to enable near-continuous monitoring. Here, we investigate relative seismic velocity variations (δv/v) in the western Bohemian massif using four years of ambient-noise recordings from 20 stations. We estimate δv/v in the 0.1–0.5 Hz band across three coda windows and evaluate potential environmental drivers using cross-correlation. The strongest seasonal δv/v signal is observed for station pairs with interstation distances shorter than 20 km and azimuths of 60⁰-120⁰, indicating that path geometry and ambient-noise illumination strongly influence the stability of the measurements. Correlation estimates suggest that, δv/v is primarily associated with thermoelastic strain driven by atmospheric temperature variations, while groundwater-level fluctuations may contribute a weaker secondary hydrological signal whose mechanism remains ambiguous.