More than a thousand earthquakes in a region no one had labeled a risk zone. The culprit isn’t a tectonic plate but a field, Groningen, in the northeast of the Netherlands, exploited since 1963. Gas is drawn from a sandstone formation located about 3 km below the surface, and the site long ranked among Western Europe’s major suppliers.
For nearly three decades, however, the subsurface remained quiet.
The first earthquake was recorded in 1991, near Middelstum: magnitude 2.4, nothing dramatic. That prolonged silence had reinforced the idea of a northern Netherlands that was safe. Then the number and the strength of the quakes increased, until they exceeded a thousand in total.
- The Groningen field has been exploited since 1963.
- The first recorded earthquake dates to 1991, near Middelstum.
- The Huizinge earthquake of August 16, 2012 reached a moment magnitude of 3.6.
- Normal extraction ended on October 1, 2023, and a complete ban took effect on October 1, 2024.
A sandstone that settles, faults that slide
The mechanism is simple in its principle. This porous sandstone traps gas under high pressure; by pumping it out, the pressure falls, and the rock compacts under the weight of the layers above. This compaction slides faults already present in the rock. Groningen’s earthquakes originate on faults known within the reservoir, between 2,800 and 3,500 m deep.
What remains to be understood is why modest magnitudes cause so much damage. The seismic foci are close to the surface, and the ground, made of clay and peat, is soft: a small area shakes, but intensely. In a region with no natural earthquakes, houses were never built to withstand such shaking.
In a seismic zone, a magnitude of 3.6 would be considered a modest tremor. Here, the mining safety authority notes that quakes strong enough to collapse vulnerable houses remain possible for this type of reservoir, even if none of that scale has occurred to date.
Huizinge, the evening of August 16, 2012
On the August 16, 2012, in the evening, the ground trembles near the village of Huizinge, in the former municipality of Loppersum. The moment magnitude reaches 3.6, while the initial local magnitude calculation yielded 3.4. The focus lies at a depth of roughly 3 km.
Within the field, no quake measured had ever been this strong. The fault slipped by about 5 cm on a disk with a radius of about 390 m, i.e., nearly 48 hectares, more than 60 football pitches.
Two numbers for the same quake can be confusing. The local magnitude, 3.4 on the initial calculation, comes from the ground motions recorded by the measurement network. The moment magnitude, however, is derived from the size of the ruptured fault and the distance it slipped, namely the 5 cm and the 390 m mentioned above. According to studies, the local magnitude is given as 3.4 or 3.6, and the moment magnitude as 3.6 within a 0.1 margin.
More than 2,000 compensation claims were filed.
The damage isn’t limited to cracked walls. The work to reinforce homes and resolve damages moves forward slowly, and the waiting, with the uncertainty about the state of dwellings, triggers health complaints among some residents. The mine safety authority itself acknowledges this in its pages dedicated to the former field.
In 2013, the mine safety authority recalculated and called for a substantial reduction in production. Huizinge was a turning point, not the endpoint. From 2014 onward, the production cap set by the state steadily declined. On January 8, 2018, Zeerijp was jolted as well, with a magnitude of 3.4.
Shutting off the tap does not stop the tremors
On October 1, 2023, normal production ends; the field remains in standby. It still produced for two days in January 2024, during a cold spell. In April 2024, the law for definitive closure was passed, after a postponement once contemplated by the Senate, concerned about supply security. The ban on extraction takes effect from October 1, 2024.
The earthquakes continue, but become increasingly rare, as the pressure balances out in the subsoil. They do not stop simply because a law has been enacted.
In 2024, the field recorded 36 quakes.
Counting the earthquakes from year to year requires a stable reference. The measurement network has expanded and now detects smaller tremors, but all quakes with a magnitude of 1.5 or greater have been measured since 1991, which allows year-to-year comparisons.
These 36 tremors account for most of the 40 induced earthquakes recorded in the Netherlands in 2024, and 6 of them reached magnitude 1.5 or higher. The strongest induced quake of the year, at Garsthuizen on October 31, reached 2.2, far from Huizinge’s 3.6. The previous year, the field counted 43.
What continues to hold the subsurface in check is a pressure imbalance. Around the clusters of Loppersum, where extraction stopped in 2018, pressure remains relatively high, while it is lower in the south, which was exploited until 2024. The mining authority estimates a 1% probability of a magnitude 4.0 or greater, a low risk that continues to diminish.
Source: aveva.com
