Went through a stack of EOS Transaction AGU...June 3 2008 vol. 89 no 23 has a letter from Antony C. Fraser-Smith titled " Ultralow-frequency magnetic fields preceding large earthquakes.

I think it was him who recorded the signal before the Loma Prieta (1989) quake. He mentions a forgotten paper by Moore from 1964 that there were strong signals 1 to 2 hours before the Great 1964 Alaska quake. He says there were signals before a couple other large (M7+) quakes.
Chris