Vanneste, Kris ; Onvani, Mahsa ; Camelbeeck, Thierry ; Lecocq, Thomas ; Rapagnani, Giovanni

Talk presented at IUGG 28th General Assembly, Berlin (Germany) on 2023-07-17

Abstract: In the frame of the BELSHAKE project, we collected all digital records by the Belgian seismic network of earthquakes with ML>2 in a dedicated waveform archive and the associated metadata in a database. We visually inspected all waveforms, calculated missing P- and S- arrival times from the Belgian velocity model, and defined noise, P-, S- and coda-windows. We also developed the tools to recompute local magnitudes and to compute new moment magnitudes. One of the main problems we encountered was missing instrument response information for older records. We tried to reconstruct this information based on information in our station database and/or the original data headers. Analysis of station ML residuals and PSDs of the noise window allowed to select the correct response or to identify unreliable cases. The definition of the Belgian ML scale is based on the Lg wave on the vertical component high-pass filtered at 1 Hz. It has been applied systematically since 1985, but unfortunately not all amplitude measurements are preserved in the database. Furthermore, the scale has not been calibrated for distances < 10 km and does not take into account hypocentral depth. These issues are problematic to determine ML of recent shallow geothermally induced seismicity. We will use our dataset to derive a better formulation of the Belgian ML scale. We also compute MW based on spectral fitting of P- and S-waves with the well-known sourcespec package. This will eliminate the need for empirical magnitude scale conversions to compute magnitude-frequency relations for seismic hazard assessment.

Funding: BRAIN_BELSHAKE/BRAIN_BELSHAKE/BRAIN_BELSHAKE