A magnitude 9 quake, centred east of Japan, on March 11 was one of the four or five most powerful quakes in the world since 1900. It generated a tsunami which killed more than 20,000 people and caused massive damage.
Dr Toy said the earthquake also involved the greatest movement of land - a 50m horizontal and 8m vertical displacement - recorded by scientists in any earthquake.
She was the only New Zealander aboard the 212m-long research vessel Chikyu, which during a two-month expedition, starting in April, went to the underwater subduction zone which triggered the tsunami.
International scientists were rethinking some of their ideas and trying to understand what mechanisms had caused the larger-than-expected movement, she said.
The vessel drilled to about 7740m below sea level and about 850m into underlying rock in a deep-sea trench area, about 6910m deep, off the Japanese east coast.
The initial expedition ended in late May at a drilling site about 200km east of the Oshika Peninsula, in northeast Honshu.
Technical problems meant planned installation of key temperature sensors at the drill site could not be carried out.
Dr Toy was yesterday relieved that a second expedition, also involving Chikyu, had recently returned to the drill site and succeeded in installing the sensors to glean more information about the quake.
And she began unpacking rock core samples recovered from the earlier expedition, which she had had sent back to her Dunedin office.
Dr Toy, who is co-principal investigator in an international Southern Alps quake-related drilling project, said by studying the Japanese samples she aimed "to further understand the mechanics of the earthquake faulting process at this unique site".
Such insights would also be applied to her New Zealand research.
