Quake prone cities 'rock like jelly'
New Zealand's most earthquake-prone cities are just like Tokyo, and ''rock like jelly on a dinner plate'' when a quake hits, new research shows.
University of Canterbury senior hazards lecturer Dr Christopher Gomez has been studying Tokyo's rivers, which were found to be an area of concern after the 2011 Japanese earthquakes.
The research is believed to be of benefit to Christchurch and Wellington.
"Tokyo, like Christchurch and the lowland areas of Wellington, is built by the sea on young sediments that have been deposited mostly by rivers or by the sea that has receded," Gomez said in a University of Canterbury media statement.
"As with Christchurch, most of the city of Tokyo was underwater only a couple of thousands years ago and most of its underground is composed of unconsolidated sediments that are ready to rock like jelly on a dinner plate."
Rivers were seen as an accelerator of earthquake impacts in Tokyo and Christchurch.
When rivers moved laterally, they left abandoned channels filled by unconsolidated material.
"This unconsolidated sediment left in abandoned channels can dramatically increase ground acceleration during an earthquake, as observed in Christchurch in 2010 and 2011," Gomez said.
"There is a striking link between the amount of damage to buildings in central Christchurch and the location of abandoned and paleo-channel in the CBD area."
Tokyo was an excellent example of rapid urbanisation over coastal land, following its population explosion in the aftermath of World War II, Gomez said.
"The city's expansion has rapidly engulfed different types of ground including abandoned channels, rice fields drained from marshlands and mine pits.''
It was important to look at environmental risks in urban areas as in 2010 half the world's population was living in cities, Gomez said.
The ratio was projected to rise to 80 per cent by 2050.