Since 2002 the ROB paper inquiry has been complemented by the online internet « Did You Feel It? » (DYFI) macroseismic inquiry. The questionnaire that is used by the ROB is adapted from the United States Geological Survey (USGS) after DYFI pioneering work by David Wald and colleagues (Wald et al., 1999). The questionnaire has been translated in four languages (French, Dutch, German and English) to cover a wide area. Online DYFI inquiries allow rapid and automatic construction of community internet intensity macroseismic maps with which the authorities and the population can be quickly informed about the damage distribution and felt area of an earthquake. This information is complementary to the recordings by the seismic stations to study earthquakes and their impact in Belgium. In our system macroseismic maps are updated online every 5 minutes (Lecocq et al., 2009).
In 2011, the Erdbebenstation Bensberg (BNS, University of Cologne) joined our web-inquiry. German citizens can now submit their experience of a felt earthquake to the BNS network and based on the responses a Belgian – German macroseismic map is generated in real-time. This transfrontier macroseismic collaboration is a unique concept in the world!
In 2014, we developed an in-house geocoding algorithm to geolocate the submitted addresses of the responses to detailed geographical locations up to the street level or better. In a community macroseismic map, the intensity distribution is often spread inhomogeneously due to the irregular municipality shapes. Since 2015, the intensity of geocoded locations are grouped in equally-sized grid cells. To each grid cell, an intensity is assigned in a GIS environment. This representation (see Figure 5) allows us to map the felt effect in a more homogeneous way than in official communal or community internet macroseismic maps. Because people do not always provide their address, a grid cell map generally does not embody all reports (~80-90% of total data).
Since 2016, the ROB collaborates with the Bureau Central Sismologique Français (BCSF, Université de Strasbourg). Residents of France who felt an earthquake that occurred in France, can still submit their experience to our online system but the data are automatically transferred to the BCSF. This allows a real-time transfrontier intensity evaluation that strengthens the capacity of both institutes to analyse earthquake effects.
And what about your municipality?
All those paper questionnaires completed during the 20th century remained scattered across the ROB archives for decades. As part of his PhD, Ben Neefs brought them together, with Koen Van Noten, Kris Vanneste and Thierry Camelbeeck, into a single harmonised dataset: the Belgian Traditional Macroseismic (BTM) database (Neefs et al., 2024, Journal of Seismology). It contains 23,950 intensity values on the European Macroseismic Scale, for 80 felt earthquakes in and around Belgium with local magnitudes between 2.4 and 5.8.
The full dataset is freely available through our online platform MIDOP. You can use it to view the impact of each earthquake, and also to look up which earthquakes affected your own municipality. Curious how many earthquakes were felt in your municipality during the 20th century? Look them up! Please note: the absence of an observation for a municipality points to a lack of testimonies, not to an earthquake that was not felt there. Together with the online DYFI inquiries since 2002, the BTM database gives a detailed picture of 125 years of seismic impact in Belgium. This picture allows us to test the Belgian seismic hazard map and to assess which attenuation models best fit Belgian earthquakes.
Consult the database at: seismology.be/midop (dataset DOI: 10.24414/2b5w-j029).
References
- Lecocq, T., Rapagnani, G., Martin, H., De Vos, F., Hendrickx, M., Van Camp, M., Vanneste, K., Camelbeeck, T., 2009. B-FEARS: The Belgian Felt Earthquake Alert and Report System. Cahiers du Centre Européen de Géodynamique et de Séismologie.
- Wald, D.J., Quitoriano, V., Dengler, L.A., Dewey, J.W., 1999. Utilization of the internet for rapid community intensity maps. Seismological Research Letters 70(6), 680- 697.