Recalibration of the local magnitude scale of the Belgian seismic network: Improved models of geometrical spreading and path duration

Authors

  • Kris Vanneste Royal Observatory of Belgium (ROB), Ringlaan 3, B-1180 Brussels, Belgium
  • Thierry Camelbeeck Royal Observatory of Belgium (ROB), Ringlaan 3, B-1180 Brussels, Belgium
  • Thomas Lecocq Royal Observatory of Belgium (ROB), Ringlaan 3, B-1180 Brussels, Belgium https://orcid.org/0000-0002-4988-6477

DOI:

https://doi.org/10.26443/seismica.v5i2.2123

Keywords:

local magnitude, geometrical spreading, anelastic attenuation, path duration

Abstract

The current local magnitude ML scale for local and regional earthquakes recorded by the Belgian seismic network was developed in 1985 using Lg-wave amplitudes measured on paper seismograms from vertical seismographs, and has been applied to records from digital seismometers installed progressively since then. However, the seismic attenuation in this scale does not properly reflect the relative contribution of geometrical spreading and anelastic attenuation of crustal S-waves at distances < 150 km. Furthermore, the scale is not well constrained at distances < ~ 20 km, encumbering magnitude evaluation of shallow small earthquakes (e.g., induced seismicity) recorded only by nearby stations. We recalibrate the Belgian ML scale as a function of hypocentral distance, paying particular attention to short distances, while keeping good agreement with the original scale at larger distances. The recalibrated scale features a segmented powerlaw geometrical spreading model, shows improved residuals, and yields lower magnitudes for earthquakes with ML < ~ 1.5. We also performed a calibration using horizontal components, but residuals are significantly higher, hampering adoption. Nevertheless, these results have led to improved models of geometrical spreading and path duration for horizontal S-waves, which are important components in many seismological applications. Finally, we also derive an empirical relation between ML and moment magnitude.

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Published

2026-10-03

How to Cite

Vanneste, K., Camelbeeck, T., & Lecocq, T. (2026). Recalibration of the local magnitude scale of the Belgian seismic network: Improved models of geometrical spreading and path duration. Seismica, 5(2). https://doi.org/10.26443/seismica.v5i2.2123

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Vol. 5 No. 2 (2026)

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Copyright (c) 2026 Kris Vanneste, Thierry Camelbeeck, Thomas Lecocq

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