Washington: Seismologists, using ultra sensitive instruments, have detected minute changes that preceded small quakes along California's famed San Andreas fault by as much as 10 hours.

If follow-up tests show that such signal is widespread, then it could be the basis of a robust early warning system for impending quakes, said researchers.

"We're working with colleagues in China and Japan on follow-up studies to determine whether this physical response can be measured in other seismically active regions," said Rice University seismologist Fenglin Niu, the study's co-author author.

"Provided the effect is pervasive, we still need to learn more about the timing of the signals if we are to reliably use them to warn of impending quakes."

Currently, state-of-the-art warning systems give only a few seconds warning before a quake strikes. These systems detect P-waves, the fastest-moving seismic waves released during a quake.

Like a flash of lighting that precedes thunderclap, the fast moving P-waves precede slower moving but more destructive waves.