Active normal faulting in the upper Rhine graben and paleoseismic identification of the 1356 Basel earthquake

We have identified an active normal fault in the epicentral area of the Bas el. (Switzerland) earthquake of 18 October 1356, the largest historical sei smic event in central Europe. The event of 1356 and two prehistoric events have been characterized on the fault with geomorphological analysis, geophy sical prospecting, and trenching. Carbon-14 dating indicates that the young est event occurred in the interval 610 to 1475 A.D. and may correspond to t he 1356 Basel earthquake. The occurrence of the three earthquakes induced a total of 1.8 meters of vertical displacement in the past 8500 years for a mean uplift rate of 0.21 millimeters per year. These successive ruptures on the normal fault indicate the potential for strong ground movements in the Basel region and should be taken into account to refine the seismic hazard estimates along the Rhine graben.