Shifts In Gravity May Detect Earthquakes Faster Than Seismic Waves Seismologists Say


Gravity signals that race through the ground at the speed of light could help seismologists get a better handle on the size of large, devastating quakes soon after they hit, a study suggests. The tiny changes in Earth’s gravitational field, created when the ground shifts, arrive at seismic-monitoring stations well before seismic waves.

Earthquakes are particularly troublesome among natural disasters because, unlike hurricanes and tornadoes, they cannot be reliably predicted or measured until after they have occurred. The best we can do is assess the magnitude of an earthquake as quickly as possible and allocate resources to relief efforts based on that data. Unfortunately, measuring magnitude using current methods takes long enough to muddy the process a bit.

However, according to a new Scientific American report, that could change in the near future. Seismologists hypothesize that studying minor shifts in the Earth’s gravitational field could help accurately measure devastating earthquakes faster than studying seismic waves, created by the energy of an earthquake. The difference is only a matter of minutes, but that is enough time to save lives when facing large enough earthquakes.

According to the report, seismologists in China and South Korea detected gravitational signals (which travel at the speed of light) right after the 2011 Tohoku earthquake, which along with the subsequent tsunami devastated Japan. At 9.1 magnitude, it was one of the largest earthquakes recorded in modern history. Scientific American says these gravitational readings showed up more than a minute before the seismic waves. The U.S. Geological Survey took 40 minutes to come up with an accurate reading of the Tohoku quake’s magnitude, so had they been using this technique, it could have cut down on that time significantly.

The more accurate our measurements, the more effectively we can assist in relief efforts, the report says. The problem with this method is that gravitational signals are weaker than seismic waves, and therefore harder to detect. These gravity signals are only detectable in earthquakes of a magnitude of 8.5 or greater. That means if an earthquake generates a signal at all, it is incredibly dangerous, but this method does not work for smaller earthquakes that still pose a threat.

As Scientific American points out, this is most useful in coastal areas where a massive earthquake almost certainly means a dangerous tsunami is on the way. Getting word out to the public a few minutes faster would help with evacuation and relief efforts immensely in those kinds of situations. Even more intriguing is that the signals could be detected as far as 2,000 kilometers from the Tohoku earthquake’s epicenter, before any seismic waves. That is the advantage of gravity signals moving at the speed of light.

Of course, unless technology for detecting shifts in gravity improves, this will not help much in measuring smaller earthquakes. The good news is those earthquakes, like the one off the coast of Delaware this week, generally do not cause much harm. Still, with earthquakes becoming distressingly more common in places like Oklahoma possibly due to fracking, any advantage seismologists can get in detection and measurement is for the benefit of everyone.


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