On seismotectonics of Northern Switzerland

Comparison of focal mechanisms with local neotectonic structures in Northern Switzerland shows, in many cases, a good correlation between the orientation of nodal planes of the fault-plane solutions and the orientation of fault systems observed at the surface. Focal depths of 10-30 km indicate that some of these fault systems cut deep into the crystalline basement and even through the whole crust. From the orientation of P-axes and T-axes it is concluded that the crust of northern Switzerland is undergoing a NNW-SSE maximum horizontal shortening and a WSW-ENE maximum horizontal extension. The orientation of the stress field which causes the present seismicity in northern Switzerland is very similar to that of the stress field of the last 5 to 8 million years which produced the neotectonic deformation. (author) 22 refs., 3 figs., 1 tab