A team led by Dr. Geoffrey Blewitt of the Nevada Bureau of Mines and Geology and Seismological Laboratory, University of Nevada, Reno, demonstrated that a large quake's true size can be determined within 15 minutes using GPS data. This is much faster than is possible with current methods.
Using just 15 minutes of GPS data of ground movement at multiple ground monitoring stations, scientists were able to determine the Sumatra earthquake's true size and tsunami generation potential. Image credit: University of Nevada, Reno
"Tsunami warning is a race against time," said co-author Dr. Seth Stein, Department of Geological Sciences, Northwestern University, Evanston, Ill. "Tsunamis travel at jet speed, so warning centers must accurately decide, within minutes, whether to issue alerts. This has to be done fast enough for the warning to be distributed to authorities in impacted areas so they can implement response plans. Together with seismometer and ocean buoy data, GPS adds another tool that can improve future tsunami danger assessments."
"We'll always need seismology as the first level of alert for large earthquakes, and we'll need ocean buoys to actually sense the tsunami waves," added Blewitt. "The advantage of including GPS in warning systems is that it quickly tells how much the ocean floor moved, and that information can directly set tsunami models into motion."
The new method, called GPS displacement, works by measuring the time radio signals from GPS satellites arrive at ground stations located within a few thousand kilometers of a quake. From these data, scientists can calculate how far the stations moved because of the quake. They can then derive an earthquake model and the quake's true size, called its 'moment magnitude.' This magnitude is directly related to a quake's potential for generating tsunamis.
As illustrated by the magnitude 9.2-9.3 Sumatra quake of December 2004, current scientific methods have difficulty quickly determining moment magnitude for very large quakes. That quake was first estimated at 8.0 using seismological techniques designed for rapid analysis. Because these techniques derive estimates from the first seismic waves they record, they tend to underestimate quakes larger than about 8.5. That is the approximate size needed to generate major ocean-wide tsunamis. The initial estimate was the primary reason warning centers in the Pacific significantly underestimated the earthquake's tsunami potential.
The potential of GPS to contribute to tsunami warning became apparent after the Sumatra earthquake. GPS measurements showed that quake moved the ground permanently more than 1 centimeter (0.4 inches) as far away as India, about 2,000 kilometers (1,200 miles) away from the epicenter. "With signals like that, an earthquake this huge can't hide," said Blewitt. "We hypothesized that if GPS data could be analyzed rapidly and accurately, they would quickly indicate the earthquake's true size and tsunami potential."
To test the feasibility of their approach, the scientists used NASA's satellite positioning data processing software to analyze data from 38 GPS stations located at varying distances from the Sumatra quake's epicenter. The software pinpoints a station's precise location to within 7 millimeters (0.3 inches). Only data that were available within 15 minutes of the earthquake were used. Results indicated most of the permanent ground displacements occurred within a few minutes of the arrival of the first seismic waves. Their analysis inferred an earthquake model and a moment magnitude of 9.0, very near the earthquake's final calculated size.
"Modeling earthquakes with GPS requires a robust, real-time ability to predict where GPS satellites are in space with exacting precision, which our software does," said Dr. Frank Webb, a JPL geologist. "This technique improves rapid estimates of the true size of great earthquakes and advances real-time tsunami modeling capabilities."
Results of the study are published in Geophysical Research Letters.
Other media contacts include Jill Boudreaux, University of Nevada, Reno, 775-784-4611; Megan Fellman, Northwestern University, 847-491-3115; and Harvey Leifert, American Geophysical Union, Washington, 202-777-7507.
JPL is managed for NASA by the California Institute of Technology.
Jill Boudreaux | EurekAlert!
Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute
Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine