Original paper

Aims and First Results of the TIMO Project - Tiefenstruktur des mittleren Oberrheingrabens

Ritter, Joachim R.R.; Wagner, Michael; Wawerzinek, Britta; Wenzel, Friedemann

Abstract

The Upper Rhine Graben (URG) in Southwest Germany is a branch of the European Cenozoic Rift System. The natural seismicity in the region is moderate, however, the seismic hazard for the about 6 million people in the region may be significant due to the high concentration of inhabitants, infrastructure and industry. As there are still few and only coarse data-based models for the deep structure of the URG, the TIMO project (Iiefenstruktur des mittleren Qberrheingrabens - Deep Structure of the Central Upper Rhine Graben) is conducted mainly to improve the resolution of the subcrustal lithosphere and asthenosphere. This will allow us a better understanding of the geodynamic evolution as well as provide constraints for seismichazard evaluation. From December 2004 until May 2006 a passive seismological experiment was conducted with 32 mobile and 5 permanent broadband stations. Additionally recordings from up to about 20 short-period stations from regional networks can be used. A study of the local seismicity indicates normal faulting across the entire crust inside the central URG. The determined anisotropy in the upper mantle shows only a smooth variation of the direction with fast wave propagation. This pattern is interpreted as preferred mineral alignment in the upper mantle due to flow-induced shearing. An anomaly in anisotropy associatedwith the URG could not be found, and therefore we infer that there is currently no distinct asthenosphericflow associatedwith this rift as well as no distinct lithosphericanisotropic signature.