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要旨:
In this study the analysis of continuous seismic data is used to investigate the processes related to seismic events generated through the release of accumulated thermal stresses in the upper water-saturated soils during freezing and melting. Under certain conditions, the stresses are released as a swarm of small-scale magnitude impulses, called cryoseismic emission, which have no or very little effect on the infrastructures. In some cases, however, this stress release can result in seismic events called frostquakes. Such events can be of relatively large magnitude, and they are capable to produce cracks on the ground surface and damage infrastructures such as buildings and roads. To understand what combinations of weather and ground conditions results in these different stress release mechanisms, we installed two seismic arrays with co-located soil stations in two geographically different sites in Northern Finland characterized by different weather, geological and hydrogeological conditions. The first site is located in the municipality of Sodankylä at the latitude of 67.36 deg. and the second one in the city of Oulu at the latitude of 65.04 deg. Based on local inhabitants ‘eyewitness’ reports of ground shaking and unusual ‘seismic noise’ near the Oulu site on 06.01.2023, we identified several frostquakes in seismic records. The analysis of continuous seismic records allowed us to recognise two different stress release mechanisms: frostquakes and cryoseismic emission. Our results support the conclusion that stress release by different mechanisms is defined mainly by certain meteorological and groundwater conditions.
