Subtle Signals Could Help Forecast Earthquakes

Satellite system analyzes thermal anomalies

9 September 2013

Earthquakes strike suddenly, almost without warning. There were 80 quakes in the first six months of this year with a magnitude of 6 or greater, according to the European Mediterranean Seismological Centre. Countries where they struck include Colombia, Greece, Indonesia, and the United States. Earthquakes can cause loss of life and structural damage in populated areas. Poorly designed buildings are destroyed, walls tumble, and furniture is smashed.

Because earthquakes strike seemingly at random, they are among the most difficult disasters to forecast, but that hasn’t stopped scientists from trying to decipher the clues that may foretell an occurrence.

One area of research relies on images from satellites to analyze thermal anomalies caused by the stress in fault lines and the energy buildup that occurs before an earthquake. The anomalies alter several electromagnetic radiation signals, including outgoing longwave radiation, which is thermal infrared energy leaving Earth; microwave radiation; and surface latent heat flux, or the heat that moves from Earth’s surface to the atmosphere—all of which can be tracked by remote-sensing systems.

A number of observation systems are taking images of the anomalies, some with higher resolution than others, and scientists are using different methods of analysis. So far, inconsistent results have prompted questions about how useful the anomalies are as forecasters.

But confident that the anomalies are, in fact, valid indicators, IEEE Members Li-Xin Wu and Shan-Jun Liu and Graduate Student Member Kai Qin have developed a method to study them using data from GEOSS, the Global Earth Observation System of Systems. The network brings together data gathered by thousands of sensors aboard buoys, weather stations, and satellites, measuring conditions across the land, water, and atmosphere. GEOSS is supported by dozens of nations and scientific organizations, including IEEE through its Committee on Earth Observation.

Wu is chief professor with the Academy of Disaster Reduction and Emergency Management at Beijing Normal University and with the School of Environment Science and Spatial Informatics at the China University of Mining and Technology, in Xuzhou. He is the IEEE Geoscience and Remote Sensing Society’s liaison with the Group on Earth Observation’s User Interface Committee.

Liu is a professor and vice head of the Institute of Geoinformatics and Digital Mine Research at Northeastern University, in Shenyang, China.

Qin received his Ph.D. in March in photogrammetry and remote sensing at the College of Geosciences and Surveying Engineering at China University of Mining and Technology, in Beijing, and Wu was his thesis advisor. Now Qin is a lecturer at the School of Environment Science and Spatial Informatics at the university’s Xuzhou campus.

Their paper, “GEOSS-Based Thermal Parameters Analysis for Earthquake Anomaly Recognition,” was published in the October 2012 Proceedings of the IEEE special edition on remote sensing of natural disasters.

“We can use the multiple thermal parameters from this integrated Earth observation system for seismicity analysis and earthquake anomaly recognition,” Wu says.

the method

The group’s project—a deviation-time-space thermal (DTS-T) earthquake anomaly recognition method—is what they call a spatiotemporal statistical analysis, based on notable deviation, quasi-synchronism, and geo-adjacency. It mines data from GEOSS, looking for multiple thermal parameters and observations in the important interface between the lithosphere—the solid outer covering of Earth itself—and the atmosphere.

The theoretical basis behind the project, Wu says, is the coupling effect between the lithosphere, the coversphere (which includes soil, bodies of water, and vegetation), and the atmosphere that occurs before an earthquake. Precursor anomalies include changes in ground stress, temperature, moisture, groundwater, and electromagnetic radiation.

The researchers also look at the energy balance and the thermal radiation from Earth’s surface and analyze surface latent heat flux, thermal infrared radiation, outgoing longwave radiation, diurnal temperature range (DTR), atmospheric temperature, and radiometric surface temperature.

“The advantage of the DTS-T method,” Wu says, “is its synergistic analysis of multiple thermal parameters from GEOSS.” It takes into account “the inherent correlations among different thermal parameters so as to avoid bias and misjudgments if we took a single parameter and particular anomaly.”

precursors

To test their theory, the researchers examined data from GEOSS in the days preceding seven medium-to-large earthquakes. Those included the Wenchuan earthquake, with a magnitude (M) of 8.0 that struck China on 12 May 2008 [see photo] and the M7.1 quake that hit Darfield, New Zealand, about 40 kilometers west of Christchurch, New Zealand, on 4 September 2010.

Their analysis of the Wenchuan quake showed that on 6 May there were abnormal changes near the epicenter in the DTR, outgoing longwave radiation, atmospheric temperature, and surface temperature.

In studying the 2010 Christchurch earthquake, they found changes to the surface latent heat flux, atmospheric temperature, surface temperature, and DTR during July and August. Strong anomalies occurred near the epicenter.

The group will soon develop a software system built around parallel computing techniques, as well as analysis tools and a reliability index, which they will make available free to Group on Earth Observation (GEO) members, Wu says. GEO is a partnership among 90 countries and 67 international organizations that helped build GEOSS.

“With the DTS-T method and the software system,” Wu says, “it will be possible to provide a practical way to make earthquake prewarning and short-term forecasts, at least to some extent, for specific active seismic regions.”

This article has been corrected from an earlier version.

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