The damaging 1932 Uden Earthquake in the Netherlands – revision of cross-border macroseismic data and its impact on source parameters

A re-assessment of the macroseismic intensity data was conducted for the second-largest instrumentally recorded event in the Netherlands: the 20 November 1932 Uden earthquake. This event was felt across the Netherlands, Belgium and Germany. Intensity values on the EMS98 scale were assigned based on original data (reports/enquiries/letters), manually for the Netherlands and automatically for Belgium, with existing German data added for completeness. The updated dataset was used to calculate macroseismic location and magnitude using the Bakun and Wentworth (1997, 1999) algorithm. To capture epistemic uncertainty, four newly calibrated intensity attenuation relations were applied and their results averaged. The results using only intensity data from the Netherlands provided stable solutions within the region of maximum observed intensity (Imax = VII). However, including Belgian and German data shifted the source location outside this region and becomes less reliable, likely due to differences in data collection methods and local/regional site effects. Comparison of confidence levels from the BW method with bootstrap modelling showed that almost all bootstrap results fall within the 50% confidence region. A more realistic estimate for the location uncertainty was derived from the bootstrap analysis. The revised source parameters are 51.63°N and 5.61°E ± 7.3 km for the source location and ML = 5.1 ± 0.3 (MS 4.9 ± 0.3) for the magnitude.