Thermal tracking of upper crustal fluid flow in the Rhine graben

More than 52,000 temperature values from almost 10,000 boreholes in Germany have been incorporated into a data base since 1977. Due to petroleum‐oriented drilling, a large quantitity of temperature data (both German and French) is available for the Rhine Graben. A horizontal temperature contour map for 800 m depth and a vertical cross section support the concept that thermal anomalies in the Rhine Graben are caused by convection in the upper crust. At the local scale of a borehole, large changes of the temperature gradient to depths of 5 km can roughly be related to different hydraulic conditions of the formations. A better means to qualitatively characterize the convective regime, however, is the observed thermal equilibration in a well after drilling disturbances. The data base is well suitable for an application of temperature as a tracer for fluid flow.