Christchurch bounced during deadly earthquake
PAUL GORMAN
Last updated 12:41 17/03/2011
Christchurch turned into a huge trampoline during the February 22 earthquake, GNS Science research has revealed.
Seismologist Dr Bill Fry said a recently discovered physical phenomenon called "slapdown" caused the trampoline-like effect felt by residents as violent upward jolting.
Layers of sediments under the city had separated during the quake, with weak top layers bouncing higher than stronger ones below them. When the top layer fell back and hit the next layer, they slapped and caused the high impacts felt, he said.
Ground accelerations in Christchurch, the largest ever recorded for a New Zealand earthquake, were as much as four times higher than the highest accelerations measured in last Friday's magnitude 9.0 earthquake off the east coast of Japan.
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