This is done by means of vibration measurements at houses and buildings. The measurement and monitoring network can be used to investigate the relationship between vibrations in the subsurface, the movement of houses and buildings, and the final damage.
Research into earthquakes is carried out by the KNMI (Royal Netherlands Meteorological Institute), which has been using a seismic measurement network to determine the magnitude and location of the hypocentre for each registered earthquake since 1995. The KNMI's measurement network does not provide direct information on the consequences of the earthquakes for the buildings. However, such information is necessary in order to identify which buildings need preventive reinforcement, and in what way, in order to be able to withstand future earthquakes safely. TNO's measurement and monitoring network focuses specifically on the unambiguous determination of the consequences of future earthquakes on buildings by means of vibration measurements at houses and buildings. In the meantime, approximately 350 houses and buildings in and on the edges of the earthquake zone in the province of Groningen have been equipped with a vibration meter, which registers the actual vibration level in the houses and buildings in the event of each earthquake.
Measurement and monitoring network
By means of continuous observation it is possible to obtain as complete a picture as possible of the situation in the subsurface and its above-ground effects. The measuring points provide data on what actually happens to the houses and buildings when soil vibrations are measured. This is necessary because the vibrations measured by the KNMI in the subsurface are not transmitted to the buildings on a one-to-one basis. In addition to measuring the vibrations, each earthquake with a magnitude of 2.5 or more is recorded as an image of the damage caused by that earthquake to the houses and buildings within the measurement and monitoring network. These measurements are linked to KNMI data on soil vibrations. This makes it possible to establish a direct relationship between the actual vibration levels that occur and the resulting damage to houses and buildings.
Role of TNO
In the 1990s, the connection between earthquakes and gas production in Groningen was demonstrated. Research into earthquakes is carried out by the KNMI. The KNMI's measurement network does not provide direct information on the consequences of the earthquakes for the buildings. TNO has therefore set up a measurement and monitoring network on behalf of NAM (oil & gas producer) whereby a direct relationship can be established between the actual vibration levels that occur and the resulting damage to houses and buildings. Based on the results of the measurement and monitoring network, recommendations can be made about which houses need preventive reinforcement and in what way, in order to be able to withstand future earthquakes safely.