At the time it was reported he had pushed his sister out clear of the falling debris, saving her life, and later regained consciousness in hospital.
Last week, Prattley was sentenced to intensive supervision.
Judge David Saunders said Prattley's offending was very much at the lower end of the scale in terms of indecency offending, but the conviction automatically activated a first strike warning under the system which imposes heavier penalties on repeat violent offenders.
"Sometimes people have difficulty understanding why touching of an unwelcome nature would count as violence, but that is not my decision to make," Judge Saunders said.
Mental health reports had provided an insight into Prattley's offending and assisted in coming to a sentencing decision.
"I accept you have struggled with physical problems and mental health issues that came about because of the Canterbury earthquakes," Judge Saunders said.
"There is help available to you - which is why I am extending to you a rehabilitative sentence, to help you overcome these very real difficulties."
However Judge Saunders said Prattley carried the responsibility for taking advantage of the help offered.
"You have to be motivated to do better in the future," he said.
While subject to sentence, Prattley will also be under judicial monitoring to keep the court informed of his progress.
A year after the earthquake, Prattley told the Herald he carried his daughter's ashes around with him in a small cardboard box.
"They come everywhere with me. When I go to work, she usually stays in the car.
"She comes inside at night-time. It's just so that it feels as though she's still a part of me, she's still here with me."
He added: "Quite often, just out of the blue, I end up with tears in my eyes, thinking about it all. I still have the thoughts going through my head, 'How come I could help my sister, but there was no way I could help my partner and daughter?' That same thought keeps going over and over in my head."
His case follows that of John Howland whose 14-year-old son, Jayden Andrews-Howland, was killed by falling masonry in the February 22, 2011 earthquake.
In 2013, Howland was sentenced to eight months' home detention after being caught with thousands of images of child pornography on his computer.
Depression triggered by his teenage son's death - just a day before his 15th birthday - was behind his descent into the world of child pornography, Greymouth District Court heard.
Earlier this year, Howland was convicted of throwing muck over Minister Gerry Brownlee at the five-year memorial service for victims of the quake.
- Ashburton Guardian, NZ Herald staff
Where to get help:
• In an emergency: call 111
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633, or text 234 (available 24/7) or talk@youthline.co.nz or live chat (between 7pm and 11pm) http://livechat.youthline.co.nz/mibew/chat?locale=en&style=youthline
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155 (weekdays 11am to 5pm)
• NetSafe: 0508 NETSAFE (0508 638 723), www.theorb.org.nz
How parents can stop cyberbullying:
• Understand where your kids are going online, what they are doing and who they are talking to.
• Spend time in your child's online world.
• Accept and acknowledge how important technology is to your child.
• Don't ask your child if they're being cyberbullied. Use their language - have they seen mean texts circulating, humiliating photos or messages on others' Facebook walls?
• Don't downplay covert bullying. Don't dismiss it saying "don't worry ... it doesn't matter if you've been left out" or "just ignore the bullying". This tells the child that you don't take their situation seriously and can even convey that it's normal for others to treat them this way.
• Make it clear cyberbullying will not result in phone or internet access being taken away. Discuss this with your child and reassure them that's not how you'll deal with it.
• Teach your kids how to be good cyber citizens before they are in Year 4, when they may begin to venture online.
• Much of cyberbullying and face-to-face bullying is learned behaviour. Look at what behaviours you're modelling to your kids. Is sarcasm and point-scoring part of your family culture?
• Don't contact the other child but tell the school principal.
