* Yen rockets to 76.25 vs dollar, pulls back to 79.00
* G7 to meet, traders on guard for Japan intervention
* Japan retail trader margin calls blamed for volatility
(Adds comment, updates; previous TOKYO/SINGAPORE)
By Anirban Nag
LONDON, March 17 (Reuters) - The yen hovered near a record high against the dollar on Thursday, with speculators building more bearish bets in the U.S. dollar and keeping alive the risk of intervention by the Japanese to stem the yen's rise.
As the shock of Friday's massive earthquake and tsunami worsened into a nuclear crisis, the yen has climbed as investors cut back on carry trades and positioned for Japanese investors selling overseas assets to bring home funds.
A break through the previous record of 79.75 triggered a cascade of stop-loss and algorithmic selling of the dollar, sending the yen surging in illiquid trade in the hours between the U.S. and Asian trading days.