The Seismicity of the Rhinegraben Rift System — Source Parameters, Propagation- and Site Effects —

Extended Abstract

In the last two decades seismological investigations of the Rhinegraben Rift System considerably improved the knowledge about the manifold menu presented by the seismotectonic regime acting today. One of the earliest findings was the consistency of the direction of the stress field having a prevailing NW-SE trending strike (Ahorner, 1970). The Lower Rhine Embayment, the Rhenish Massif and the northernmost part of the Upper Rhinegraben — approximately up to the latitude of Heidelberg — still experience active rifting (Ahorner et al., 1983). The middle and southern part of the Upper Rhinegraben dominantly show strike slip dislocations (Schneider et al., 1966; Ahorner, 1970; Ahorner and Schneider, 1974; Bonjer, 1979; Bonjer et al., 1984) as displayed in Fig. 1. However, in the southern Rhinegraben — Black Forest area very recent observations (e.g. in Fig. 2) indicate that normal faulting may play a similar intrinsic role like in the northern Upper Rhinegraben area (Bonjer and Apopei, 1984), as already found and postulated by geological investigations (e.g. Illies, 1981).

As far as the epicenter distribution and the focal depth in the Upper Rhinegraben area are concerned some peculiarities have been found (Bonjer et al., 1984). The comparison of historical and instrumental data (Fig. 3) reveals three facts. Firstly, local source areas exhibit a significant geographical consistency for the past millennium. Secondly, short-time but high sensitivity observations show that most of these focal areas are marked by persistent microseismicity which already reflects the general pattern of the Rhinegraben seismicity.