Black box recordings revealed that the train was travelling at 192kph (119mph) when the brake was applied; the train derailed at 153kph. The speed limit at the spot where the train derailed was set at 80kph an hour.
"Seconds before the accident the brakes were activated. It is estimated that at the time of the derailment the train was travelling at 153 kilometres an hour," the High Court of Galicia which is leading the investigation said.
The driver of the train was speaking on his work phone at the time of the accident and appeared to consult a map or other document, the court added in a statement.
"Minutes before the train came off the tracks he received a call on his work phone to get indications on the route he had to take to get to Ferrol.
From the content of the conversation and background noise it seems that the driver consulted a map or paper document," it said.
The eight-carriage train was travelling from Madrid to Ferrol on Spain's northwestern coast when it flew off the tracks last Wednesday on a bend and ploughed into a concrete siding about four kilometres (2.5 miles) from the pilgrimage city of Santiago de Compostela.
Examining judge Luis Alaez on Sunday charged the driver, Francisco Jose Garzon Amo, 52, with 79 counts of reckless homicide and released him under court supervision.