Mihnea-Corneliu Oncescu, Thierry Camelbeeck, and Henri Martin. “A Note on the Foreshock of the 1992 Roermond Earthquake, the Netherlands”. Netherlands Journal of Geosciences, vol. 73, Jan. 1994, pp. 229-33, https://njgjournal.nl/index.php/njg/article/view/12468.