HR: 1330h
AN: S12B-0383    [PDF]
TI: Integrated Seismic Imaging of the Carlsberg Fault in the Copenhagen City Center
AU: * Nielsen, L
EM: ln@geo.geol.ku.dk
AF: Geological Institute, Univ. Copenhagen, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AU: Thybo, H
EM: thybo@geo.geol.ku.dk
AF: Geological Institute, Univ. Copenhagen, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AU: Jorgensen, M I
EM: gf97mj@geo.geol.ku.dk
AF: Geological Institute, Univ. Copenhagen, Oester Voldgade 10, Copenhagen K, 1350 Denmark
AB: Images of the Carlsberg Fault in the area of the Copenhagen city center, Denmark, are obtained from normal incidence and refraction seismic data collected along a 3 km long E-W trending profile, which is oriented approximately perpendicular to the strike of the fault. The integrated seismic data set provides the most detailed images to 500 m depth so far obtained of this fault. The fault zone appears as a flower structure in the normal incidence section, and an abrupt change in the P-wave velocity structure across the fault zone further indicates that significant lateral movements have taken place along the fault. Vertical movements of up to 90 m are evident in the fault zone. Even the shallowest layers that can be imaged by the seismic data (approximately 30 m depth) are clearly vertically offset by the fault. In order to constrain the strike of the fault zone through the Copenhagen area we use shots detonated inside the fault zone, which are recorded by geophones distributed along arcs of circles situated up to 7 km away from the shots. Ground penetrating radar measurements are conducted to image the fault structures in the topmost 10 m. Geodetic measurements conducted in the Copenhagen area during the last 165 years indicate that the fault may still be active with horizontal displacements of about 5 cm over a 73-year period. Small cracks in walls and displacements of buildings may further indicate that the fault is still playing an active role in forming the Copenhagen area. However, no earthquakes are detected along the fault, and the seismicity of the study area is very weak. The formation of the Carlsberg Fault may be related to extensional stresses in a strike-slip system associated with the Sorgenfrei-Tornquist zone, which is situated only 40 km east of the study area. The Sorgenfrei-Tornquist zone is a major tectonic element in southern Scandinavia where it is situated close to the boarder between the Danish Basin to the southwest and the Baltic Shield to the northeast.
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: 2003 Fall Meeting