By IANS,
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.
Findings from the new study indicate that the stresses measured by the new instruments precede the temblor itself, so a warning system using the new technology would be radically different from current warning systems.
“Detecting stress changes before an earthquake has been the holy grail in earthquake seismology for years and has motivated our research,” said co-author Paul Silver of the Carnegie Institution of Science.
“Researchers have been trying to precisely and continuously measure these velocity changes for decades, but it has been possible only recently, with improved technology, to obtain the necessary precision and reliability.”
For example, when rocks are compressed, the stress forces air out of tiny cracks in the rock. This causes seismic waves to travel slightly faster through the rock.
Niu said the variations are so slight that they can only be measured with very precise instruments. For example, though the Parkfield instruments were more than a half mile below ground, the set-up was sensitive enough to measure fluctuations in air pressure at the Earth’s surface.
The findings of the study appear in this week’s edition of the journal Nature.