An earthquake occurred on Monday evening near the village of Usquert in the province of Groningen. It had a magnitude of 0.9, which was too weak to be felt. The Netherlands has now recorded its 2,000th earthquake caused by gas extraction. The first such tremor took place in 1986 near Assen.
Human activity drives these earthquakes, known as induced earthquakes. According to Läslo Evers, a seismologist at the Royal Netherlands Meteorological Institute (KNMI), the real number is far higher than 2,000. In earlier years, only a few sensors were available, and they could detect tremors of magnitude 1.5 or greater. Today, more measuring equipment is in place, and it is far more sensitive. As a result, the system now records tremors close to magnitude 0.0, which previously went unnoticed.
Most induced earthquakes occur in the heart of Groningen province, in the middle of the Groningen gas field. The municipalities of Eemsdelta and Midden-Groningen have experienced more than 1,300 earthquakes together, accounting for two‑thirds of all induced tremors in the country. “That is where the shrinkage of the gas reservoir is greatest, and the subsidence is highest. This is also where the most tension has built up,” Evers said.
Risk of major earthquakes
The number of earthquakes is falling as gas extraction winds down. Last year, the KNMI recorded 37 induced earthquakes, compared with 42 the year before. Ten to fifteen years ago, gas extraction caused more than one hundred tremors each year. “You see a decrease in the number of earthquakes, but unfortunately, the risk of earthquakes remains,” Evers said. “The subsurface has not yet settled down; the earthquakes will continue for years to come.”
Evers added that the risk of relatively large earthquakes also remains. “In November, there was a magnitude 3.4 earthquake near Zeerijp. That was the third‑largest earthquake ever recorded in Groningen.”
Exceptional
Such stronger tremors are rare. Nine out of ten recorded tremors have a magnitude below 2.0, which is too weak to feel.
Evers said he cannot predict when the tremors will stop. “Gas extraction started in the 1960s, and the first tremor was around 1990. It took thirty years for enough tension to build up in the ground and for tremors to become noticeable. The tremors became increasingly severe and more intense. Nobody knows how long it will take.”
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