and the Netherlands, it consists of, from southwest to

Valley Rift System (RVRS) corresponds to the northern segment of the European Cenozoic rift system described by Ziegler (1988) (Fig 1). The Cenozoic RVRS developed upon pre-existing basins of Carboniferous (Campine foreland basin) and Mesozoic (rift) age. It is structurally closely related to the Mesozoic basin. During the Mesozoic, the area was characterized by several periods of subsidence and inversion which have reactivated the Variscan structural trends (Ziegler, 1990; Zijerveld et al., 1992; Winstanley, 1993). During the Cenozoic, the RVRS was affected by two periods of inversion named the Laramide phase (Earliest Tertiary) and the Pyrenean phase (Late Eocene-Early Oligocene) and by continuous subsidence since the beginning of the Oligocene (Geluk et al., 1994). Preservation of Late Oligocene-Early Miocene marine sediments on the Rhenish Massif demonstrates that the Roer Valley Graben (RVG) was connected to the URG (Sissingh, 1998), indicating a common evolution during at least this period. A close relationship between these two grabens is also suggested by the distribution of the earthquake focal mechanisms in the northern part of the URG and the RVG which indicate a present day NE-SW extension in both areas (Plenefisch and Bonjer, 1997). Structurally, the RVRS is the southwestern part of th