The 1992 Roermond earthquake, the Netherlands, and its aftershocks

Abstract

On April 13,1992 an MW = 5.4 normal dip-slip earthquake occurred 5 km south-west of theDutch town Roermond. It was located at a depth of 17 km near the Peel Boundary Fault in the Roer Valley Graben. Belgian, Dutch, German and French seismologists installed 29 mobile seismograph stations for a period of two months after the main shock. Both the mobile and the permanent stations recorded more than 200 aftershocks. High-quality hypocentral locations were obtained for 55 aftershocks. Hypocenters that occurred in the vicinity of the main shock hypocenter coincide with one of the focal mechanism nodal planes, i.e. strike 127°, dip 70°. The Roermond earthquake also triggered seismic activity in the graben as far as 40 km to the southeast. Focal mechanisms were determined for 20 aftershocks. Out of the 14 with a predominantly normal fault solution, eight have a strike direction parallel, and six a strike perpendicular to the strike of the main event. A stress inversion using the 13 best constrained fault plane solutions of aftershocks located near the main shock hypocenter indicates a direction for the principal stress that is similar to that of the regional stress field. From our experience in analyzing the data we recommend the upgrading of the existing regional recording systems to high-dynamic range seismograph stations and the installation of a number of accelerometers in the Roer Valley Graben and its surroundings.