Skip to main content

Visualizing blind faults with shear-wave seismic reflection surveys: a case study from the Sorgenfrei-Tornquist Zone, northern Denmark

So-called ‘blind’ faults, which are not visible at the Earth’s surface may be the source of unexpected and potentially disastrous earthquakes and thus represent a major hazard, especially in urban areas. Detecting such hidden faults is highly important for the seismic hazard assessment of a region, but often remains a challenge, because the faults are covered by young sediments. To overcome this limitation, we visualize blind faults in the area of the Sorgenfrei-Tornquist Zone in northern Denmark with shear-wave seismic reflection surveys. The faults on the seismic surveys are interpreted based on systematic reflector offsets, the presence of continuous transparent zones that separate individual fault blocks, abrupt lateral changes in the reflector pattern, and the presence of fault shadows. The seismic surveys give evidence for a near-surface strike-slip fault system, based on the presence of flower structures and the dominance of steep faults. The distribution of the faults on the seismic surveys and the occurrence of fault-related shear-deformations bands that occur in outcrops along the nearby seas-cliff, together with fault-related basins that are developed in the study area, indicate that the northern boundary fault of the Sorgenfrei-Tornquist Zone is not an isolated fault, but a wider fault array. The study demonstrates that the shear-wave reflection seismic method is a powerful tool to image near-surface faults and is very suitable for palaeoseismological studies. The significantly improved resolution of shear-wave seismic surveys compared to those of the common P-wave reflection method is an advantage, especially in the case of small fault displacements.


Christian Brandes1, Ulrich Polom2, Jutta Winsemann1, Sandersen Peter3
1Institut für Geologie, Leibniz Universität Hannover, Callinstr. 30, 30167 Hannover, Germany; 2Leibniz Institut für Angewandte Geophysik, Stilleweg 2, 30655 Hannover, Germany; 3Geological Survey of Denmark and Greenland, Department of Near-surface land and marine geology, University City 81, Building 1872, 8000 Århus C, Denmark
GeoBerlin 2023