Jussi Mattila

Stress-controlled fluid flow in fractures at the site of a potential nuclear waste repository, Finland

The relationship between present-day stress state and fluid flow within fractures in crystalline bedrock is investigated in the light of a comprehensive fracture database consisting of 38,703 fracture observations made during investigations at the site of a planned high-level nuclear waste repository in Finland. By combining fracture orientation data with detailed stress and fluid flow measurements, we observe that the orientations of conductive fractures display characteristic patterns attributed to the effect of the present-day triaxial stress state and that the highest transmissivities are associated with fractures having the lowest normal tractions. Our findings indicate that contemporary stress data combined with slip and dilation tendency analysis can be used in predicting the orientations and relative transmissivity values of conductive fractures.

LiDAR DEM detection and classification of postglacial faults and seismically-induced landforms in Finland: a paleoseismic database

Abstract During the last decades, postglacial faults (PGFs) have been found in northern Fennoscandia, the first fault scarps being discovered in western Finnish Lapland in the 1960s. With LiDAR-based digital elevation models (DEMs), a new and accurate remote sensing mapping methodology has been acquired. It allows the relatively rapid and low-cost detection and mapping of late- or PGFs and, for instance, mapping of landslides from areas where they have not previously been recognized. We describe the approach of the Geological Survey of Finland to the systematic search for (screening) and mapping of PGFs, paleolandslides, and other morphological features of Quaternary deposits related to post- and late-glacial seismic activity in Finland. The observations have been collected and classified into a file geodatabase with ArcGis (© ESRI) using a procedure that includes several steps. We also provide examples from western and northern Finland of how sites of late- and postglacial fault scarps and landslides have been detected and described from LiDAR DEM data.

Dating of paleolandslides in western Finnish Lapland: Dating of paleolandslides in western Finnish Lapland

The dating of landslide-buried organic materials potentially indicates non-stationary seismicity in northern Finland attributable to the release of lithospheric stresses during and after retreat of the Scandinavian Ice Sheet. The landslide age data reveals three episodes of increased slope instability and formation of landslides, from 9000 to 11 000 cal BP, from 5000 to 6000 cal BP, and from 1000 to 3000 cal BP. While a seismogenic origin cannot be unequivocally established, we interpret that at least the early Holocene episode reflects increased seismic activity in northern Finland in association with late-glacial and postglacial faulting. The foci of slope instabilities changes through time, implying that different segments of the postglacial fault systems were active at different times during the Holocene. We also show that the correlation of landslide ages with the surface roughness and backwall slope is complicated. The morphology of landslide scarps is significantly affected by thickness of glacial sediments, liquefaction during landslide formation, and accumulation of peat upon landslide scars and deposits, and thus, the time-dependent erosional smoothing of the surfaces should be considered as descriptive and non-qualitative. Copyright