A Late Glacial surface rupturing earthquake at the Peel Boundary faultzone, Roer Valley Rift System, and its morhologic response by the Meuse river

In a trench along the central part of the Peel Boundary fault zone (PBFZ), Roer Valley Rift System (RVRS), southeastern Netherlands, evidence was found for a large faulting event that occurred around 14 ka. The event caused a fault scarp in unconsolidated sediments of ~1 meter. A colluvial wedge was formed next to the scarp. A second faulting event offsets this colluvial wedge by 0.2 - 0.1m. This event can be tentatively dated at ~13 ka. During or immediately after the second event, a large clastic dyke intruded along the fault plane. The dyke is not faulted, but its emplacement did cause some minor thrust faulting around the injection. The sudden character of the main faulting event, the brittle deformation style of loam layers, the lack of growth faulting in the colluvial wedge, the clastic dykes and the flame structures demonstrate that the main faulting event was a surface rupturing earthquake. Based on the scarp height, the estimated moment magnitude is about 6.8±0.3. Similar observations in a previous trench site suggest that the length of the surface rupture was at least 32 km, which is in agreement with the inferred magnitude. In general, glacio-isostatic movements might explain the earthquake events in the RVRS, like in northern Germany and Denmark. The Maas river crosses the PBFZ and shows several morphodynamic responses that are synchronous with the fault displacement. This forms a unique example of a transient river response to abrupt, surface-rupturing faulting and it is different to what classical models predict