The BELSHAKE Database of Earthquake Ground Motion in Belgium

Abstract The BELSHAKE database compiles ground-motion data from Belgium and surrounding regions in northwest Europe, a region characterized by low-to-moderate seismicity. It currently contains ∼6400 digital records from 344 tectonic and induced earthquakes with ML≥2, recorded since 1985 with short-period, broadband, and accelerometric sensors operated by the Royal Observatory of Belgium. The database consists of a waveform archive with the raw and processed seismograms for each event–station pair, and a relational database containing the associated metadata, as well as the derived ground-motion intensity values. All records have been visually inspected to identify, and if possible correct, problematic waveforms. Missing arrival times are computed from the local velocity model and interactively adjusted if necessary. We use a combination of two windowing procedures, one to isolate P, S, and coda windows, and a more sophisticated method for the noise window. The waveform data were processed in a uniform way using a semiautomated workflow based on schemes in other ground-motion databases. A suite of intensity measures was computed from the processed data that were evaluated as reliable, taking into account the usable frequency range. These are computed for different signal windows and components, including the geometric mean and orientation-independent percentiles. Data consistency was validated using different methods. Fitting a generic ground-motion model (GMM) using mixed-effects regression shows that residuals are well behaved and have a similar range as the database for France. Analysis of the evolution of residuals for each station allowed identifying additional issues related to instrument response and location changes, which were addressed. Finally, we also determined moment magnitudes from displacement spectra for most events. The BELSHAKE database complements existing databases by increasing the coverage of low-seismicity zones. It will not only help evaluating or calibrating GMMs specifically for Belgium but will also be useful for other seismological applications.