Scientists have discovered a way to identify indicators of a mega earthquake using GPS-based information, an advance that may help improve early warning systems for quakes.
The researchers from University of Oregon in the US combed through databases of earthquakes since the early 1990s have discovered a possible defining moment 10-15 seconds into an event that could signal a magnitude seven or larger quake.
Likewise, that moment -- gleaned from GPS data on the peak rate of acceleration of ground displacement -- can indicate a smaller event.
GPS picks up an initial signal of movement along a fault similar to a seismometer detecting the smallest first moments of an earthquake.
Such GPS-based information potentially could enhance the value of earthquake early warning systems, said Diego Melgar, a professor in the University of Oregon.
The physics-heavy analyses of two databases detected a point in time where a newly initiated earthquake transitions into a slip pulse where mechanical properties point to magnitude.
Researchers were also able to identify similar trends in European and Chinese databases. Their study was detailed in the May 29 issue of the online journal Science Advances.
"To me, the surprise was that the pattern was so consistent. These databases are made different ways, so it was really nice to see similar patterns across them," said Melgar.
Overall, the databases contain data from more than 3,000 earthquakes. Consistent indicators of displacement acceleration that surface between 10-20 seconds into events were seen for 12 major earthquakes occurring in 2003-2016.
GPS monitors exist along many land-based faults, but their use is not yet common in real time hazard monitoring. GPS data shows initial movement in centimetres, Melgar said.
"We can do a lot with GPS stations on land along the coasts of Oregon and Washington, but it comes with a delay," Melgar said.
"As an earthquake starts to move, it would take some time for information about the motion of the fault to reach coastal stations. That delay would impact when a warning could be issued," he said.
This delay, he added, would only be improved by sensors on the seafloor to record this early acceleration behaviour.
Having these capabilities on the seafloor and monitoring data in real time, he said, could strengthen the accuracy of early warning systems.