The seismic event that caused a fatal collapse at Codelco’s biggest mine in Chile is likely to have been caused by mining activity rather than nature, according to a person with direct knowledge of the matter.

The probable scenario being used inside Codelco is that the incident was caused by geological stresses resulting from the project’s own extraction processes rather than any naturally occurring shifting of tectonic plates, the person said, asking not to be identified given an investigation is ongoing.

El Teniente, one of the world’s biggest underground copper mines, has been halted since July 31, when six workers died and nine others were injured following a 4.2-magnitude event that caused part of the operation to collapse. The tremor affected a newly developed area known as Andesita.

The accident has rocked the mining industry in Chile, where projects need to be built to withstand frequent and sometimes massive seismic activity. State-owned Codelco has filed a request to restart parts of the mine while it carries out an investigation into the cause of the incident.

The scenario that Codelco is leaning toward is one shared by many industry experts. Nicolas Munoz, a copper supply analyst from consultancy CRU, also thinks the seismic activity was likely self-induced.

As the so-called panel-caving method used at El Teniente routinely involves the controlled collapse of depleted areas of the mine, this, combined with simultaneous mining activities in other areas, could have increased stress within the ore-body, said Munoz, who previously worked as an engineering contractor on projects including El Teniente.

“In some cases, parts of the rock cannot accommodate the new stress regime and fail suddenly, releasing stored energy as seismic events,” Munoz said. These so-called rock-bursts are very hard to predict in deep and highly active mines, he said.

Other than the nature of the seismic event, a major question is whether it is safe to restart underground mining at El Teniente, which accounts for a quarter of Codelco’s copper output. A one-day suspension could bring a loss of 750 tons copper, or about $7.5 million of revenues, according to CRU.

If Chilean authorities order the massive mine to remain closed until investigations are complete, the lost production may exacerbate supply strains in the global market. It would also heap financial pressure on indebted Codelco, which has major spending commitments and faltering output.

To restart the mine, Codelco has to satisfy regulators and unions that the whole of the underground operation is stable, not only the affected areas. A comprehensive review of the mine’s current plans, particularly the design assumptions and safety criteria applied in all key zones will be needed, Munoz said.

In May, seismic activity leading to flooding at Kamoa Kakula — the biggest copper mine in Africa — was also found to be self-induced, according to its operator Ivanhoe Mines Ltd. Ivanhoe plans to stabilize the flooded section of the mine by installing larger structural pillars, while speeding up construction in another section to keep producing copper.

But Munoz said this solution is not applicable at El Teniente, which reaches depths of 1,200 meters and had seen significant rockfalls in areas like Andesita.