[Rockhounds] Gravity signals could detect earthquakes at the speed of light

[Kreigh Tomaszewski]

Two minutes after the world’s biggest tectonic plate shuddered off the
coast of Japan, the country’s meteorological agency issued its final
warning to about 50 million residents: A magnitude 8.1 earthquake had
generated a tsunami that was headed for shore. But it wasn’t until hours
after the waves arrived that experts gauged the true size of the 11 March
2011 Tohoku quake. Ultimately, it rang in at a magnitude 9—releasing more
than 22 times the energy experts predicted and leaving at least 18,000
dead, some in areas that never received the alert. Now, scientists have
found a way to get more accurate size estimates faster, by using computer
algorithms to identify the wake from gravitational waves that shoot from
the fault at the speed of light.

“This is a completely new [way to recognize] large-magnitude earthquakes,”
says Richard Allen, a seismologist at the University of California,
Berkeley, who was not involved in the study. “If we were to implement this
algorithm, we’d have that much more confidence that this is a really big
earthquake, and we could push that alert out over a much larger area
sooner.”

Scientists typically detect earthquakes by monitoring ground vibrations, or
seismic waves, with devices called seismometers. The amount of advance
warning they can provide depends on distance between the earthquake and the
seismometers, and the speed of the seismic waves, which travel less than 6
kilometers per second. Networks in Japan, Mexico, and California provide
seconds or even minutes of advance warning
<https://www.science.org/doi/10.1126/science.362.6414.514>, and the
approach works well for relatively small temblors. But beyond magnitude 7,
the earthquake waves can saturate seismometers. This makes the most
destructive earthquakes, like Japan’s Tohoku quake, the most challenging to
identify, Allen says.

Recently, researchers involved in the hunt for gravitational waves—ripples
in space-time
<https://www.science.org/content/article/ripples-spacetime-sciences-2016-breakthrough-year>
created
by the movement of massive objects—realized that those gravity signals,
traveling at the speed of light, might also be used to monitor earthquakes.
“The idea is that as soon as mass moves anywhere, the gravitational field
changes, and … everything feels it,” says Bernard Whiting, a physicist at
the University of Florida who worked on the Laser Interferometer
Gravitational-Wave Observatory. “What was amazing was that the signal would
be present even in seismometers.”
https://www.science.org/content/article/gravity-signals-could-detect-earthquakes-speed-light