Seismometer network investigates earthquakes
It is well known that deep geothermal energy can cause earthquakes. These are usually mild earthquakes that can only be recorded using sensitive measurement equipment. The injection of cooled water appears to be a significant cause of these. By determining the location of the earthquakes, we are able to establish how the substrate responds to differences in pressure in connection with the injection. This allows us to become more familiar with the substrate.
Seismometer network
The injection of water into the deep substrate causes small movements that give rise to earthquakes. Artificially induced earthquakes are a focal point in the development of every deep geothermal energy project and are an important topic of research. It is for this reason that VITO has further developed a seismometer network. The network allows us to pinpoint the soil movements to within several tens of metres.
By comparing the locations of consecutive earthquakes, we can calculate the direction in which the pressure effects of the injection continue. We are therefore able to monitor whether they occur in proximity to major fracture systems. By monitoring the injection (pressure and temperature), VITO is hoping to guarantee the safe operation of the geothermal energy plant.
Traffic Light System (TLS)
In the geothermal power plant, we use a traffic light system (TLS) based on four parameters:
-
the calculated magnitude of an earthquake;
-
the distance to the fault;
-
the number of earthquakes per unit of time;
-
the maximum measured peak ground velocity in the seismometers of the monitoring network.
Threshold values are defined for each parameter, delineating a green, orange, and red zone. If one or more parameters fall within the orange zone, the operational conditions in the geothermal power plant, such as flow rate and injection pressure, are gradually reduced. If one or more parameters fall within the red zone, the plant is temporarily shut down in a controlled manner.
The map below provides an overview of earthquakes in the past 90 days and the current status of the traffic light system (TLS).
Newly detected earthquakes appear on the map within 15 minutes. The time, location, and magnitude of newly detected earthquakes may be slightly adjusted afterward based on additional data processing. The event times are displayed in local time (Belgian time).
For each earthquake, the local magnitude (Richter scale) is shown. This value is calculated using the seismometers in the monitoring network on and around the geothermal power plant and takes into account the proximity of these seismometers. Earthquakes with a local magnitude of 1.0 or higher are also picked up by seismometers located further away. For such events, the Royal Observatory of Belgium (KSB) also calculates the local magnitude, which may differ from the magnitude calculated by VITO. These differences are partly due to the use of different networks. For the traffic light system (TLS), we use the magnitude calculated by VITO.
