"The problem is the building quality and the buildings are extremely, extremely vulnerable," he said.
"We have been expecting a big earthquake in the region, the only question was when."
Mr Bothara was part of a team which developed Building Code for Nepal in 1992-1994, and also sits on the New Zealand Society for Earthquake Engineering panel.
Two New Zealand Red Cross aid workers have also left for Nepal today.
Donna Collin, a nurse and midwife from Whangarei, will join an International Federation of Red Cross (IFRC) team supporting Nepal Red Cross to carry out health assessments in villages outside the Kathmandu Valley.
Jacqui Dixon, an aid worker from Morrinsville, will coordinate staff safety and security for Red Cross teams across Nepal.
It came as the IFRC called for increased urgent aid, saying it was "extremely concerned" about the welfare of hundreds of thousands of people, particularly those in remote areas outside the Kathmandu Valley.
"One of our teams that returned from Chautara in Sindupalchowk district reported that 90 per cent of the homes are destroyed," said IFRC Asia Pacific operations director Jagan Chapagain.
"The hospital has collapsed, and people are digging through the rubble with their hands in the hope that they might find family members who are still alive.
"We can expect the situation to be the same if not worse in many other places where aid has not yet been delivered."
The amount of emergency aid needed for such a large-scale disaster outstripped the capacity of Kathmandu's small international airport, which was receiving an extremely high volume of aid flights now coming into Nepal, Mr Chapagain said.
Caritas New Zealand said agencies were coming up against challenges to distribute aid, including the government asking agencies to hand over relief supplies to the government to distribute.
"Aid is coming in, but the airport is very busy and clearance of relief items is taking time. With the arrival of more and more aid organisations, prices are skyrocketing and there is rapidly expanding competition for transport and relief goods," Fr Pius Perumana SJ, director of Caritas Nepal, said.
Oxfam has warned of "widespread destruction" in the Gorkha district close to the epicentre of the large earthquake, and said people in remote villages which had yet to be accessed could run out of supplies within a week.
Medical functions across the entire district are largely gone.
"No one is getting formal health care in Gorkha. Medicin Sans Frontiers [Doctors Without Borders] is active, which is a great benefit, but with the lack of sanitation facilities, it is likely more people will fall sick," Oxfam India's humanitarian programme manager Andrio Naskar said, speaking from Gorkha.
Oxfam aid workers in remote Gorkha villages say 80 per cent of houses are destroyed and almost everyone has been forced to live and sleep outside.
"This is not sustainable especially for the sick, elderly and children. Women - especially those who are pregnant or breast-feeding - are desperate for private spaces to wash and bathe, while rudimentary sanitation systems have been wrecked," Mr Naskar said.
The Leprosy Mission New Zealand said its hospital in Kathmandu was treating a large number of earthquake victims, who were "streaming in, despite having much of the building and staff quarters destroyed".
Meanwhile, New Zealanders were today warned to be on the alert for "unscrupulous people who exploit the public's generosity" after the earthquake.
"I encourage New Zealanders to donate to well-established registered charities that have the experience and infrastructure needed to provide disaster-relief assistance," Community and Voluntary Sector Minister Jo Goodhew said.
"This way you can be sure that your donation is going directly to the people in Nepal who have been affected by the earthquake, and that your contribution is making the greatest possible difference."
To make a donation
• World Vision: Nepal Earthquake Appeal worldvision.org.nz on 0800 90 5000
• Unicef: unicef.org.nz/nepal or call 0800 243 575
• Oxfam: oxfam.org.nz or call 0800 600 700
• Red Cross: redcross.org.nz or call 0800 RED CROSS (0800 733 276)
• ChildFund New Zealand: childfund.org.nz/Nepal-Earthquake-Appeal or call 0800 808 822
• Caritas Aotearoa New Zealand: caritas.org.nz or call 0900 4 11 11
• New Zealand Nepal Society: Donations can be made to bank account number 01-0142-0053378-00
• Himalayan Trust Rebuild Appeal: givealittle.co.nz/cause/nepalearthquake
• Save the Children: Visit savethechildren.co.nz or call 0800 167 168
• TEAR Fund: tearfund.org.nz or call 0800 800 777
• International Nepal Fellowship: inf.org/earthquake-appeal-new-zealand
• The Leprosy Mission New Zealand: leprosymission.org.nz/nepal or 0800 862 873
Key facts about the earthquake
• 5600 dead.
• 11,200 injured.
• 3 million in need of food assistance.
• 8.1 million in need of humanitarian assistance.
• 130,033 houses destroyed and 85,856 partially damaged.
• US$22 million ($29 million) in bilateral contributions from UN Member States and private organisations has been received for the Nepal earthquake response.
• US$415 million ($547 million) sought by the UN to provide life-saving assistance for the next three months.
-Source: United Nations Office for the Coordination of Humanitarian Affairs)
