Residents of affected areas want answers, as seismic activity increases

The undersea gas–storage facility at which the government has this week halted activity due to a series of earthquakes in the coastal area of Vinarós, Castellón province, is positioned right on top of an active fault. The 51-kilometer fault in the Mediterranean’s Amposta trench is known to scientists and registered by Spain’s Geological and Mining Institute.

There are two other major faults in the area, measuring 18 and 35 kilometers, which have not been fully mapped.

The company that runs the plant, Escal UGS, sees no problem in this fact, arguing that the fault forms part of the underground facility, helping to seal the gas in. But the recent increase in seismic activity in the now seem set to become the object of official scrutiny after the Industry Ministry’s decision to investigate the Castor Project storage plant.

Meanwhile, residents of coastal towns located near the offshore gas facility are having trouble sleeping, thanks to a series of tremors, some reaching as high as 4.2 on the Richter scale.

"I was sleeping and the door of the closet that's just behind my bed started to shake," explains Ricard Fuster, a resident of Alcanar, Tarragona. "It gave me such a shock that I woke up straight away. It was very strange, like nothing I've ever experienced."

Pietat Subirats, aged 47, has a similar story to tell. "I spent half the night tossing and turning," she explains. "I woke up startled. The two strongest earthquakes were very noticeable in my house [...]. We're very angry, because this is starting to be genuinely disturbing. I want the politicians and the company to take responsibility."

If the intensity rises much further, there is the chance of small tsunamis

While the cause of the tremors is yet to be officially confirmed, local residents and experts have no doubt that the root is the Castor gas-storage facility, which is located 30 kilometers off the coast of Vinaròs. The EU-backed facility, which is the largest of its kind in Spain, makes use of a depleted oil field, located 1,800 meters below sea level. The plant, which was due to open this summer, is designed to be injected with gas from the national grid for storage, and pumps it back as and when it is required.

But the gas, which is treated and compressed into liquid form before being pumped into the facility, does not end up in a kind of empty underground cave. Instead the fluid is injected into porous rock, which previously held the hydrocarbons that were extracted in the 1970s and 1980s.

Ángel Cámara, the dean of the Mining Engineering College, explains what can go wrong with the process. "When the petroleum is extracted, the pressure in the rock, which is partially flexible, reduces, causing it to contract. Then, when the gas is injected, it expands once more," he says. "That is when there is a risk that microfractures are caused."

Comparisons with the fracking technique are inevitable. But, as the experts explain, the processes are very different. "Fracking is based on the injection of fluids," explains Cámara. "The aim is to fracture the ground to ease the extraction of gas or petroleum. In contrast, the Castor facility is being injected with liquids, which are pushing the rock closer to [unwanted] fracturing."

If the cracks in the rock are not located next to a fault in the Earth's tectonic plates, then the worst that could happen is a sudden collapse. But if they are near a fault, then they "propagate the fracture, creating an earthquake," Cámara explains.

According to Spain's Civil Protection service, the seismic activity in the area is originating near a fault line off the coast of Castellón. While major earthquakes are unlikely, if the intensity of the tremors rises much further, there is the chance of small tsunamis. But given that the injection of gas into the subterranean store was halted on September 16, under orders from the Industry, Energy and Tourism Minister José Manuel Soria, the seismic activity should last "just a few days," according to Cámera, until the ground settles.

Given that the tremors have lasted much longer, the Industry Ministry has sent a team of engineers to investigate whether Escal UGS correctly complied with the order to shut down the project. The president of the company, Recaredo del Potro, told radio station Cadena Ser that they had "radically" brought the plant to a halt, but that personnel were still on the platform in order to guarantee its safety. Del Potro said that he was surprised by the seismic activity — tremors measuring just one or two on the Richter scale were expected.

"We are using all of the means possible to investigate the exact origin," he said, adding that they "are hoping" that within a week they can "discard or confirm a cause-effect relationship between the seismic activity and the plant."