Thermo-hydrological and thermo-mechanical modeling of freezing soil and frost quake occurrence

Abstract. Frost quakes are seismic events originating in frozen ground, traditionally attributed to ice expansion when air temperature decreases rapidly, the soil is saturated and has little or no snow cover. However, novel observations presented here question the necessity of some of the previous assumption and meteorological conditions, driving us to consider alternative mechanisms. This study investigates frost quake formation through numerical modeling and seismological and hydrological observations in Tähtelä, Finland, during winter 2022–2023. We analyzed soil and atmospheric conditions during frost quake occurrences, noting a strong correlation with rapid air temperature decrease below -20 °C, and with varying snow cover. We modeled the thermo-hydrological (TH) processes, such as cryosuction-driven ice lens growth, using Amanzi-ATS, while the thermo-mechanical (TM) evolution was modeled with OpenGeoSys (OGS). The ATS TH simulation results suggest an important role of cryosuction for the appearance of frost quakes. Focusing on volumetric effects, the OGS TM simulation results reveal tensional and shear stress rates in the soil, both of which are able to cause fracturing leading to frost quakes. Future work should integrate fully-coupled thermo-hydro-mechanical simulations and laboratory experiments to refine predictive models and assess infrastructure risks in cold climates.