Electric and magnetic fields in the ULF band
were monitored at two sites adjacent to the San
Andreas Fault near Parkfield and
Hollister, California. A data window enclosing the
September 28, 2004 M6 Parkfield earthquake, was
analyzed to determine if anomalous electric or
magnetic fields, or changes in ground conductivity,
occurred before the earthquake. Three
main statistical techniques were employed to separate
local anomalous electrical or magnetic fields from
the dominant coherent natural fields: transfer
function and residual field estimates between
components at each site; principal...