Seismicity in Flanders

Abstract

This study aimed to review seismicity in Flanders. Although generally described as a region of low seismicity, in recent years Flanders has been confronted with seismic activity related to a deep geothermal project. Prior to this project, seismic activity in the deep subsurface of Flanders was not specifically monitored and the detection sensitivity of the national monitoring network did not allow recording of small quakes everywhere. The natural microseismicity and the risk of induced (micro)seismicity in subsurface applications in Flanders is insufficiently known. The Flemish Government is confronted with a series of open questions and uncertainties within this topic. In order to be able to impose adequate measurement plans on exploitations and to get a better picture of the natural (micro)seismicity and the role of faults in view of a well-founded licensing, Flanders wished to contract a targeted study. This study therefore needed to focus on i) the (partial) reconstruction of a natural earthquake baseline as far as data are preserved that can reflect it, ii) a better understanding of the role of faults in the context of the (potential) applications in the deep subsurface of Flanders, iii) the setting up of adequate seismic monitoring of such activities and of the natural baseline, and iv) an evaluation of the induced earthquakes in the deep geothermal project. In addition to reporting the research findings, policy recommendations were to be formulated. This included the request to apply lessons already learned abroad to the situation in Flanders. The study conducted comprises three parts. In the first part, an earthquake catalogue is compiled as complete as possible for Flanders and surrounding areas. In addition, the current regional fault model is compared with the Flemish catalogue and fault mechanisms are investigated. In the second part, a revision of the induced seismicity at the deep earthquake project is made. In the third part, recommendations are made for managing risks of induced seismicity in deep subsurface activities in Flanders.