Train conductor Brett McCullough and conductor Donald Dinnie have been confirmed as two of the three victims of the fatal crash.
A passenger, who has not yet been named, also died in the incident, while six others were treated in hospital with minor injuries.
The Aberdeen service to Glasgow Queen Street on Wednesday at 6:38 a.m. crashed near Stonehaven, an area that had been affected by heavy rains and flooding.
Emergency service workers were called to the scene at around 9.40 a.m., with dozens of emergency service vehicles – including an air ambulance – present.
Aerial shots showed a cart completely overturned, with a landslide the suspected cause of the crash.
Kevin Lindsay, Scottish organizer of the Aslef Train Drivers’ Union, described how Mr McCullough “thought the world of his family and his colleagues thought the world of him”.
The 45-year-old leaves behind his wife Stéphanie and three children, two girls and a boy.
The former gas engineer is said to have serviced an Aberdeen train conductor’s boiler when they started discussing the job and Mr McCullough then decided to join the railroads.
Following the fatal derailment, Network Rail perform emergency inspections on high-risk railway embankments as an immediate precautionary measure.
Checks – which will also involve a helicopter survey – will take place on areas of railroad with earthen cuttings similar to Stonehaven.
Network Rail chief executive Andrew Haines visited the crash site on Thursday after allegedly cutting short a family vacation to Italy.
“I have come in mourning because the whole rail industry mourns the loss of a precious passenger and two respected dear colleagues,” he said.
“Viewing the site only arouses this sense of real concern for those who have suffered such a tragic loss.
“We have the best safety record in Europe and it is not an easy thing to achieve.
“It’s been through years and decades of safety improvements – but we weren’t good enough yesterday. ”
Last month, Network Rail was warned not to follow extreme weather conditions events after an annual report noted a peak in landslides on UK railways, demonstrating the “vulnerability” of the network.
Mr Haines said, “We have a very extensive dialogue with the Office of Roads and Railways and this report only confirmed the conversation we had, as we are concerned about the increase in landslides.
“We have been very important over the past 10 years, but this winter we had the second wettest winter on record and there is evidence that climate change can actually have a real impact on safety.
UK Transport Secretary Grant Shapps and Scottish Transport Secretary Michael Matheson also visited the site on Thursday and met with members of the emergency services.
Mr Shapps spoke to the police who arrived at the scene first, as well as seeing the “absolutely heartbreaking” scene of the crash from a helicopter.
“My heart goes out to the friends and family of everyone who has been involved,” he said.
“It’s a terrible accident and we have to get to the bottom of what exactly happened. ”
Mr. Shapps said the derailment “appears to be likely related to a landslide of some form. ”
In addition to emergency checks on other lines, Mr Shapps revealed he had also ordered Network Rail to provide an interim report by September 1 on the wider resilience of the UK rail network.
Mr Matheson told Sky News that there is “no doubt that climate change and these types of intense weather events are impacting the transportation network, which was not designed to cope with this type of incident ”.
He pointed to how parts of Scotland experienced a month of rain between Tuesday evening and Wednesday morning,
An ongoing investigation into the Stonehaven derailment is being led by the Crown Office and the Procurator Fiscal Service (COPFS), who are working with a team of inspectors from the Railway Accident Investigation Branch and the Highway Bureau and of the rail.
Anyone who is concerned about friends or family involved in the derailment is urged to call the NHS Grampian helpline on 01224 319519 for advice and assistance.
ScotRail warned its network remains severely disrupted due to recent weather conditions and the Stonehaven incident.