HR: 0800h
AN: T51D-0771    [Abstracts]
TI: Earthquake relocation in the Ardenne (Belgium) : identification of active structures in intraplate context
AU: * Lecocq, T
EM: Thomas.Lecocq@oma.be
AF: Royal Observatory of Belgium, Avenue Circulaire, 3, Brussels, B-1160, Belgium
AU: * Lecocq, T
EM: Thomas.Lecocq@oma.be
AF: Universite Libre de Bruxelles, Departement des Sciences de la Terre et de l'Environnement Avenue Franklin Roosevelt, 50, Brussels, B-1050, Belgium
AU: Petermans, T
EM: Toon.Petermans@oma.be
AF: Royal Observatory of Belgium, Avenue Circulaire, 3, Brussels, B-1160, Belgium
AU: Alexandre, P
EM: Pierre.Alexandre@oma.be
AF: Royal Observatory of Belgium, Avenue Circulaire, 3, Brussels, B-1160, Belgium
AU: Camelbeeck, T
EM: Thierry.Camelbeeck@oma.be
AF: Royal Observatory of Belgium, Avenue Circulaire, 3, Brussels, B-1160, Belgium
AB: The Ardenne region, although in intraplate context, presents a moderate seismic activity. Seismic pattern and structural knowledge of the region are not only keys to regional seismotectonic framework, but also to a better understanding of the regional seismic hazard prevention. In 1692 a magnitude 6¼ earthquake destroyed the city of Verviers (East of Belgium) and caused damages as far as Dover (UK). Still ongoing historical researches are getting the location of this event more and more precise. The research for the fault responsible for the 1692 quake has lead to preliminary surveys in the Verviers region. The recent study along the Vesdre river gives good confidence that its terraces are displaced by at least one major fault and maybe some more smaller faults. Recent subsurface geophysical study of the supposed fault trace gives clues to assess for its presence but no certitude for it, further analyses will be necessary. Elsewhere in the Ardenne, the precise location of every event of an earthquake swarm that occurred in 1989-- 1990 in the Hockai Faulted Zone (HFZ) allowed us to map a fault plane with great resolution. This shows the importance of having precise earthquakes locations. These two elements show the necessity to search for major active faults, which will benefit from a complete seismotectonic analysis. In this study, we focus on a region broader than the HFZ or the Verviers area, ranging 5° to 8° East and 49.5° to 51.5° North. The aim of this work is, on one hand, to identify seismically active structures and on the other hand, to analyse the focal mechanisms that will better constrain the regional tectonic setting. The active structures will be analysed later using different means : from aerial photographs or satellite imaging to geomorphological and geophysical surveying in the field. The belgian numerical data dates back to 1985. We recorded over 1100 earthquakes located in Belgium and the neighbouring regions for this period. Each event for the last 22 years has been routinely located using HYPO2000 (a local version of HYPO71). This dataset has never been relocated all at once. The relocation process is achieved by adapting and using different tools commonly used worldwide, among which HypoDD and COMPLOC. The main advantage is that all the data are processed at once, which greatly improves the relative location accuracy as the corrections for each station are computed for a whole dataset. We also evaluate the relative movement between each event's old and new location to search for a response that could be due to the seismic network geometry. Focal mechanisms are also calculated when possible, based on P-wave first motion and also based on P, SH and SV amplitudes. The newly located events evidence at least 5 interesting small-scaled zones which present well aligned events or at least earthquakes concentrations. Even though the analysis of focal mechanisms is still incomplete, we can already show the main trends and some heterogeneities in the present-day regional brittle deformation field.
DE: 7205 Continental crust (1219)
DE: 7209 Earthquake dynamics (1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting