Changes in gravity signals could help assess size of devastating earthquakes faster, save more lives

In a new study, a group of seismologists have suggested that detecting shifts in gravity signals could help assess the magnitude of devastating earthquakes sooner than current methods.

Generally, when an earthquake occurs, seismic waves are produced that help researchers estimate how big the quake actually is. But, much before these waves arrive, another type of signal passes through the surface at the speed of light -- signal generated from the shift in Earth's gravitational field.

These signals reach seismic monitoring stations more than a minute earlier than seismic waves show up and could make a big difference in saving lives. According to a report in Nature, in case of a large, devastating earthquake, quicker detection could help first-responders allocate their resources effectively and save as many lives as possible using that data.

Though many have argued that signals from gravity shift, which are detected as tiny accelerations on seismic recording devices, are weak and not a big game changer, the seismologists behind this work believe it could still save numerous lives, particularly in coastal areas where a massive earthquake can trigger a Tsunami in the following minutes.

As per the report, seismometers in China and South Korea immediately picked up the change in gravity signals after the devastating 2011 Tohoku earthquake in Japan. But, as nobody looked for these shifts, there was not an accurate estimate soon after the quake struck. The United States Geological Survey took some 40 minutes to update its magnitude estimate of 7.9 to 8.8, while Japan Meteorological Agency took some 3 hours.

On the other side, gravity signals shift detection could have made a big difference. The signals were clearly detected at monitoring stations located some 1,000-2,000km from the quake's epicentre.

Until improved measurement technologies are developed, these signals cannot be used an accurate method for all types of quakes -- small and medium ones -- but they could still be a good indicator for quakes with a magnitude of 8.5 or above.

"We can look before the seismic waves arrive," says Martin Vallée, a seismologist at the Paris Institute of Earth Physics and an author of this study. "If we see nothing, we can say that the quake that made these was maybe large, but not huge. If we see the signals, it means we really have a very big quake."