Morphotectonics and past large earthquakes in eastern belgium

Abstract

Tectonic landforms are generally modest in stable plate interiors characterized by low strain rates and rare earthquakes. Nevertheless, specific investigations identified such landforms in Belgium, which is located in the most seismically active region of stable Europe northwest of the Alps. Here, we present two active fault zones among the best documented in continental Europe, and whose geomorphology is related to earthquake activity in eastern Belgium. The 12-km-long Bree fault scarp is readily identified in the flat alluvial landscape of the Campine. It results from the activity since the Middle Pleistocene of the Geleen fault bounding the Roer Valley Graben (RVG) to the west. At its base, a ~1-m-high scarplet corresponds to the surface rupture associated with a Holocene large normal-faulting earthquake. Combined geomorphological and paleoseismic investigations allowed evaluating the average slip rate and the return period of large earthquakes on the Geleen fault during the Late Pleistocene. Extending across a more animated landscape in NE Ardenne, owing also to lower slip rates, the Hockai Fault Zone (HFZ) is morphologically less conspicuous. Microseismicity, geology and geomorphology provide consistent evidence of recent activity of this fault zone. The location of the M = 6 ¼ 18 September 1692 earthquake, the largest historical earthquake recorded in this part of Europe, on the northern HFZ suggests that the fault morphology could have resulted from sporadic bursts of large earthquakes.