There was a "direct link" between the 2013 seismic activity and the injection of gas into a giant underground gas storage facility located in the Gulf of Valencia, the National Geographic Institute (IGN) confirmed in a yet-to-be published report.
Over 400 earthquakes struck the Gulf of Valencia, a zone not normally known for seismic activity, in September 2013, with the strongest a 4.2 magnitude quake. The quakes didn't cause damage but frightened residents.
Green groups blamed the earthquakes on the injection of gas into the gas storage facility operated by Castor. The plant aims to store gas in a depleted oil reservoir 1.7 kilometres (1.05 miles) under the Mediterranean Sea and send it via a pipeline to Spain's national grid.
In October, the Spanish Government agreed there appeared to be a link between the plant and the spate of earthquakes.
The new IGN report confirms this, revealing that seismic impact studies for the Castor plant were not adequate, Spain's Huffington Post reported on Monday.
Although the plant was known to be near a fault line, it was awarded the "lowest danger level" in terms of threats from earthquakes.
What that impact study did not take into account, however, was the threat of induced seismic activity. The study also revealed the presence of another, as yet unmapped fault line and called for this to be investigated by expert geologists.