May. 11, 2021
CWU Researchers Develop Space-Based System to Rapidly Characterize Large Earthquakes and Tsunamis
Researchers have developed a global earthquake monitoring system based on measurements of crustal deformation that can be detected by Global Navigational Satellite System (GNSS) receivers.
The monitoring system can rapidly assess earthquake magnitude and fault slip distribution within seconds for earthquakes of magnitude 7.0 and larger, making it a potentially valuable tool in earthquake and tsunami early warning for these damaging events, Central Washington University geophysicist Timothy Melbourne and colleagues report in the Bulletin of the Seismological Society of America.
GNSS can potentially characterize a large earthquake much more rapidly than the global seismic network, offering more time for evacuations, drop-and-cover and automatic shut-down of essential infrastructure.
“The imperative for doing it quickly is really about saving lives,” Melbourne said.
GNSS systems consist of Earth-orbiting satellites that send signals to receiver stations on Earth. The signals are used to determine the receivers’ exact locations through time. Earthquakes move and deform the crust underneath the receivers, so changes in their locations after an earthquake can be used to monitor and characterize the ruptures.
Seismic monitoring by GNSS is a “very blunt tool,” compared to seismometer-based networks capable of detecting minute seismic waves, Melbourne said.
A top-of-the-line seismometer is remarkably sensitive, he noted, able to detect seismic wave velocities as small as tens of nanometers per second. GNSS is more coarse—detecting displacements of centimeters.
But during a big earthquake, there is a trade-off between sensitivity and speed. Local seismic networks can be swamped with data during a large, complex event such as the 2016 magnitude 7.8 Kaikoura earthquake in New Zealand, where multiple faults are involved and waves from the original event reverberate through the crust.
To accurately determine magnitude and fault slip distribution, seismologists usually have to wait for the seismic wave data to reach distant stations before it can be accurately characterized, which entails tens of minutes of delay while the waves propagate across the planet.
The global system created by Melbourne and his colleagues is the first of its kind. It takes in raw GNSS data acquired at any Internet-connected receiver on Earth, positions these data, and then re-transmits the positioned data back to any Internet-connected device, within a second.
The researchers assessed their system over one typical week, using data from 1,270 receiver stations across the world. They found that the average time it took data to travel from a receiver to the processing center at CWU was about half a second—from anywhere in the world. It took an average of about 1/200th of a second to convert that data into estimates of GNSS position.
This means that the GNSS global monitoring system can detect changes well before the earthquake itself is done rupturing, since it can take tens of seconds—or even minutes, for the largest earthquakes—“for the fault to unzip and radiate all that energy into the planet,” Melbourne said.
The speed of a global GNSS seismic monitoring system might be even more important for tsunami warnings, he noted. At the moment, an international monitoring program uses data from a global seismic network combined with data from global tide gauges and buoys to detect a tsunami wave in the open ocean to determine whether a tsunami advisory should be sent to the public.
The seismic network could take 15 minutes or more to determine the magnitude of an earthquake that causes a tsunami, and the tidal gauges and buoys could take up to an hour to deliver data, depending on their proximity to the earthquake. GNSS receivers, on the other hand, could characterize an earthquake in tens of seconds with sufficient nearby stations.
“The real power of the GNSS for the tsunami is buying more time and greater accuracy from the get-go for the warnings that come out,” Melbourne said.
GNSS receiver stations are proliferating around the world as more people use them, especially for surveying in mining and construction. But the global GNSS monitoring system depends on open-source data, which has not expanded at the same rate. In some countries, data are sold to recover the costs of constructing and maintaining the receivers, Melbourne said, making their operators reluctant to make the data freely available.
“Part of what I do is trying to get countries in seismically active areas to open up their data sets for hazard mitigation purposes,” Melbourne said.
For instance, GNSS operators in New Zealand, Ecuador, Chile and elsewhere partner with Melbourne’s group, benefiting from the decade of work that the team has put into their GNSS positioning system. They send raw data from receivers in their countries to Central Washington, where Melbourne and colleagues position the data and send it back in under a second for their earthquake and tsunami monitoring.
• Reporter Becky Ham from the Seismological Society of America (SSA) wrote this piece. To receive a copy of the BSSA paper, email press@seismosoc.org. Melbourne can be reached at tim@geology.cwu.edu.
• “Global Navigational Satellite System Seismic Monitoring,” by Timothy I. Melbourne, Walter M. Szeliga, V. Marcelo Santillan, and Craig W. Scrivner at Pacific Northwest Geodetic Array (PANGA) at Central Washington University.
CWU media contact: David Leder, Department of Public Affairs, David.Leder@cwu.edu, 509-963-1518.