Researchers find mathematical patterns to forecast earthquakes

These are seismogenic areas of Spain and Portugal. The study focused on the areas 26 and 27. -  Martínez-Álvarez et al.
These are seismogenic areas of Spain and Portugal. The study focused on the areas 26 and 27. – Martínez-Álvarez et al.

Researchers from the Universidad Pablo de Olavide (UPO) and the Universidad de Sevilla (US) have found patterns of behaviour that occur before an earthquake on the Iberian peninsula. The team used clustering techniques to forecast medium-large seismic movements when certain circumstances coincide.

“Using mathematical techniques, we have found patterns when medium-large earthquakes happen, that is, earthquakes greater than 4.4 on the Richter scale,” Francisco Martínez Álvarez, co-author of the study and a senior lecturer at the UPO revealed to SINC.

The research, which will be published this month by the journal Expert Systems with Applications, is based on the data compiled by the Instituto Geográfico Nacional on 4,017 earthquakes between 3 and 7 on the Richter scale that occurred on the Iberian Peninsula and in the surrounding waters between 1978 and 2007.

The scientists applied clustering techniques to the data, which allowed them to find similarities between them and discover patterns that will help to forecast earthquakes.

The team concentrated on the two seismogenic regions with the most data (The Alboran Sea and the Western Azores-Gibraltar fault region) analysing three attributes: the magnitude of the seismic movement, the time elapsed since the last earthquake and the change in a parameter called the b-value from one earthquake and the other. The b-value reflects the tectonics of the region under analysis.

A high b-value means earthquakes are predominantly small in size and, therefore, the land has a low level of resistance. In contrast, a low value indicates that there are a relatively similar number of large and small seismic movements, which implies the land is more resistant.

Successful Forecast Probability Greater than 80%

“We have discovered the strong relationship between earthquakes and the parameter b-value, recording accuracy rates of more than 80%,” Antonio Morales Esteban, another of the co-authors of the study and a senior lecturer at the US highlighted. “After the calculations had been performed, providing the circumstances and sequences we have determined to be forerunners occur, we obtain a significant success probability”.

The technique summarises the forecasts in two factors: sensitivity (probability of an earthquake occurring after the patterns detected occur) and specificity (probability of an earthquake not occurring when no patterns have occurred).

The results reflect a sensitivity of 90% and specificity of 82.56% for the Alboran Sea region and 79.31% and 90.38% respectively for the seismogenic region of the Western Azores-Gibraltar Fault.

That is, there is a high probability of an earthquake in these regions immediately after the patterns discovered occur (high sensitivity) and, moreover, on most of such occasions, they only occur after the patterns discovered (high specificity).

At present the team is analysing the same data using their own algorithms based on “association rules”, other mathematical techniques used to discover common events or those which fulfil specific conditions within a set of events.

“The results are promising, although I doubt we will ever be able to say that we are capable of forecasting an earthquake 100% accurately,” Martínez Álvarez conceded.

Researchers reveal way in which possible earthquakes can be predicted

This is Professor Jay Fineberg of the Racah Institute of Physics at the Hebrew University of Jerusalem. -  The Hebrew University of Jerusalem
This is Professor Jay Fineberg of the Racah Institute of Physics at the Hebrew University of Jerusalem. – The Hebrew University of Jerusalem

Researchers at the Hebrew University of Jerusalem who have been examining what happens in a “model earthquake” in their laboratory have discovered that basic assumptions about friction that have been accepted for hundreds of years are just wrong. Their findings provide a new means for replicating how earth ruptures develop and possibly enabling prediction of coming severe earthquakes.

“The findings have a wide variety of implications for materials science and engineering and could help researchers understand how earthquakes occur and how severely they may develop along a fault line,” said Jay Fineberg, the Max Born Professor of Natural Philosophy at the Racah Institute of Physics at the Hebrew University.

The work by Fineberg, his graduate student Oded Ben-David and fellow researcher Gil Cohen, has been published in an article in Science magazine. An article based on their work also has been published online in Wired magazine.

For centuries, physicists have thought that the amount of force needed to push an object in order to make it slide across a surface is determined by a number called the coefficient of friction, which is the ratio between the forces pushing sideways and pushing down (basically, how much the object weighs). First described by Leonardo da Vinci in the 15th century and redefined a few hundred years later, these laws are so widely accepted that consistently appear in introductory physics textbooks.

But, when Ben-David tried to check whether these “laws” work at different points along a block’s contact surface, the laws fell apart. In carefully controlled lab experiments, Ben-David found that points along the contact surface could sustain up to five times as much sideways force as the coefficient of friction predicted, and the object still wouldn’t budge.

The experiments actually studied two contacting blocks as they just start to slide apart. Although the blocks look like they are smoothly touching, in reality they are only connected by numerous, discrete, tiny contact points, whose total area is hundreds of times less than the blocks’ apparent contact area. Performing sensitive measurement of the stresses at contacting points, the researchers noted that the strength at each point along the contact surface could be much larger than the coefficient of friction allows before the contacts ruptured and the block began to slide.

Furthermore, the contacts don’t all break at the same time. They, instead rupture one after another in a cadence that sets the rupture speed. These rapidly moving ruptures are close cousins of earthquakes, Fineberg said. The blocks in effect represent two tectonic plates pushing one against each other, and when the force between them is enough to disengage the plates, the resulting contact surface rupture sends shock waves through the blocks, exactly as in an earthquake.

The team found that ruptures come in three distinct modes: slow ruptures that move at speeds well below the speed of sound; ruptures that travel at sound speed; and “supershear” ruptures that surpass sound speeds. Which type of wave one gets is determined by the stresses at the contact points, which provide a measure of how much energy would be released if an actual earthquake were to occur. These different types of earthquakes have all been seen in the earth, but these experiments provide the first clue of how the earth “chooses” how to let go.

“An earthquake is the same system as in the Hebrew University experiments, just scaled up by factors of thousands,” Fineberg said. “We can watch how these things unfold in the lab and measure all of the variables that might be actually relevant in a way that you could never observe under the earth.”

How an earthquake “chooses” to rupture is not simply an academic question. Each type of rupture mode determines how the earth releases the enormous pressures that are locking tectonic motion and is intimately related to the potential hazards embodied within an earthquake. Whereas sonic earthquakes are destructive, their supersonic cousins are potentially much more dangerous as they release the enormous stored energy within the earth as a shock wave. In contrast, slow ruptures create negligible damage for the same amount of stress release.

And while it is still impossible to make detailed measurements of the stresses along a real fault, the Hebrew University results suggest a method by which stresses can be tracked as an earthquake is under way, and how one earthquake can set the stage for the initial conditions for the next one. This new understanding has the potential to provide unprecedented predictive power, estimating both the rupture mode and extent of a future earthquake.

Scientists look deeper for coal ash hazards

Duke scientists have been sampling the Kingston spill since it happened. Photo Credit: Avner Vengosh
Duke scientists have been sampling the Kingston spill since it happened. Photo Credit: Avner Vengosh

As the U.S. Environmental Protection Agency weighs whether to define coal ash as hazardous waste, a Duke University study identifies new monitoring protocols and insights that can help investigators more accurately measure and predict the ecological impacts of coal ash contaminants.

“The take-away lesson is we need to change how and where we look for coal ash contaminants,” says Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School of the Environment. “Risks to water quality and aquatic life don’t end with surface water contamination, but much of our current monitoring does.”

The study, published online this week in the peer-reviewed journal Environmental Science and Technology, documents contaminant levels in aquatic ecosystems over an 18-month period following a massive coal sludge spill in 2008 at a Tennessee Valley Authority power plant in Kingston, Tenn.

By analyzing more than 220 water samples collected over the 18-month period, the Duke team found that high concentrations of arsenic from the TVA coal ash remained in pore water — water trapped within river-bottom sediment — long after contaminant levels in surface waters dropped back below safe thresholds. Samples extracted from 10 centimeters to half a meter below the surface of sediment in downstream rivers contained arsenic levels of up to 2,000 parts per billion – well above the EPA’s thresholds of 10 parts per billion for safe drinking water, and 150 parts per billion for protection of aquatic life.

“It’s like cleaning your house,” Vengosh says of the finding. “Everything may look clean, but if you look under the rugs, that’s where you find the dirt.”

The potential impacts of pore water contamination extend far beyond the river bottom, he explains, because “this is where the biological food chain begins, so any bioaccumulation of toxins will start here.”

The research team, which included two graduate students from Duke’s Nicholas School of the Environment and Pratt School of Engineering, also found that acidity and the loss or gain of oxygen in water play key roles in controlling how arsenic, selenium and other coal ash contaminants leach into the environment. Knowing this will help scientists better predict the fate and migration of contaminants derived from coal ash residues, particularly those stored in holding ponds and landfills, as well as any potential leakage into lakes, rivers and other aquatic systems.

The study comes as the EPA is considering whether to define ash from coal-burning power plants as hazardous waste. The deadline for public comment to the EPA was Nov. 19; a final ruling — what Vengosh calls “a defining moment” — is expected in coming months.

“At more than 3.7 million cubic meters, the scope of the TVA spill is unprecedented, but similar processes are taking place in holding ponds, landfills and other coal ash storage facilities across the nation,” he says. “As long as coal ash isn’t regulated as hazardous waste, there is no way to prevent discharges of contaminants from these facilities and protect the environment.”