Rock block map analysis of southern Sweden

Abstract

Abstract The fracturing of the crust in southern Sweden has been investigated by means of topographical data, presented by the National Land Survey as the Relief Map of Sweden. Rock blocks of 3 different orders are presented in maps. On the basis of these maps, four regions have been distinguished, based on the character of the fracture pattern; southeastern Sweden with fairly regular pseudo-orthogonal patterns, southwestern Sweden with lensoidal patterns, the central belt with a penetrative north-southerly trend, and Skåne in the Fennoscandian Border Zone. Southeastern Sweden is dominated by a N10W grain, while the other regions, west of a line c. 30 km east of Lake Vättern, have a N20E grain. Rock block boundaries have been separated into 6 sets, according to their orientation. All sets show an arrangement of fractures into megalenses. The rate of the relative uplift of Fennoscandia is symmetric across southern Sweden, although the seismi-city is mainly confined to the western part. This implies that the differential movements in southeastern Sweden are aseismic, suggesting that the fracture pattern can accommodate applied strain. In southwestern Sweden, however, slip cannot occur along displaced curved fractures. The occurrence here of a late pseudo-orthogonal pattern in seismic areas, implies that new fractures form, if the crust cannot deform along existing fractures.