Earthquakes: The Prediction

The common toad (Bufo bufo) can detect seismic activity, days in advance of a quake.
A 2010 study published in Journal of Zoology found that 96 percent of male toads in a population abandoned their breeding site five days before the earthquake that struck L’Aquila, Italy, in 2009, about 46 miles (74 kilometers) away.
Researchers aren’t certain how the toads do this, but it is believed that they can detect subtle signs, such as the release of gases and charged particles, that may occur before a quake.
At Least The Toads Will Be Safe.But what about the people?
Scientists can predict where major earthquakes are likely to occur, based on the movement of the plates that make up the surface of the Earth, and the location of fault zones (areas where cracks or holes have developed in the plates).
They also can make general guesses about when earthquakes might occur in a certain area, by looking at the history of earthquakes in the region and detecting where pressure is building along fault lines.
But these predictions may not turn out to be reliable because, when strain is released along one part of a fault system, it may actually increase strain on another part.
Another area of study is the relationship between earthquakes and the magnetic and electrical charges in rock material. Some scientists have theorized that these electromagnetic fields change in a certain way just before an earthquake.
Seismologists are also studying gas seepage and the tilting of the ground as warning signs of earthquakes.
There do exist real-time earthquake warning systems, which, upon detection of a severe earthquake, can provide neighboring regions a few seconds warning of potentially significant shaking.
Let’s face it, though; most earthquake predictions are vague at best.
Scientists have had more success predicting aftershocks, additional quakes following an initial earthquake (the so-called mainshock). These predictions are based on extensive research of aftershock patterns.
Seismologists can make a good guess of how an earthquake originating along one fault will cause additional earthquakes in connected faults.
That’s great. After the event.
So, what can we do to increase our chances of survival?Good question.
With over 7,000 earthquakes around the world each year of magnitude 4.0 or greater, one that’s relevant to a whole bunch of people.
To be useful, an earthquake prediction must be precise enough to warrant the cost of increased preparations (including disruption of ordinary activities and commerce), and timely enough to allow preparations to be made.
Predictions must also be reliable, as false alarms are not only economically costly, but seriously undermine confidence.
Small problem, though:
While many scientists still hold that – given enough resources – prediction might be possible, many others maintain that earthquake prediction is inherently impossible.
Various approaches have been considered, and several notable (alleged) predictions have been made.
Those Toads, Again?Maybe.
Precursors, based on animal behavior.
An earthquake precursor could be any anomalous phenomena that can give effective warning of the imminence or severity of an impending earthquake in a given area. Phenomena anecdotally reported as possible precursors number in the thousands, some dating back to antiquity.
One of the earliest is from the Roman writer Claudius Aelianus concerning the destruction of the Greek city of Helike by earthquake and tsunami in 373 BC:
‘For five days before Helike disappeared, all the mice and martens and snakes and centipedes and beetles and every other creature of that kind in the city left in a body by the road that leads to Keryneia. … But after these creatures had departed, an earthquake occurred in the night; the city subsided; an immense wave flooded and Helike disappeared….’
Such reports are often given wide exposure by the media, and almost always with the spin that animals predicted the subsequent earthquake – often with the suggestion of some “sixth sense” or other unknown power.
Any Proof, Though?Scientific observation of such phenomena is limited because of the difficulty of performing an experiment, let alone repeating one.
It is extremely important to note the time element: how much warning did the animals give?
Earthquakes radiate multiple kinds of seismic waves. The “p” (primary) waves travel through the earth’s crust about twice as fast as the “s” (secondary) waves, so they arrive first. The greater the distance, the greater the delay between them.
For an earthquake strong enough to be felt over several hundred kilometers (approximately M > 5) this can amount to some tens of seconds difference.
The P waves are also weaker, and often go unnoticed by human beings.
So, for example, the signs of alarm reported in the animals at the National Zoo in Washington, D.C., some five to ten seconds prior to the shaking from the M 5.8 2011 Virginia earthquake, was undoubtably prompted by the p-waves. This was not so much a prediction, as a warning of shaking from an earthquake that had already happened.
Seismic Waves, Perhaps?Possibly.
Vp is the symbol for the velocity of a seismic “P” (primary or pressure) wave passing through rock, while Vs is the symbol for the velocity of the “S” (secondary or shear) wave.
Small-scale laboratory experiments have shown that the ratio of these two velocities – represented as Vp/Vs – changes when rock is near the point of fracturing.
In the 1970s it was considered a significant success and likely breakthrough when Russian seismologists reported observing such changes in the region of a subsequent earthquake.
Study of this phenomenon near Blue Mountain Lake (New York) led to a successful prediction in 1973. However, additional successes there have not followed, and it has been suggested that the prediction was only a lucky fluke.
Foreshocks, Then.Maybe.
Foreshocks are medium-sized earthquakes that precede major quakes.
An increase in foreshock activity (combined with other indications like ground water levels and strange animal behavior) enabled the successful evacuation of a million people one day before the February 4, 1975 M7.3 Haicheng earthquake.
The Xiuyan M5.3 earthquake (29 November 1999) is another example where a successful prediction was issued, based on the correct interpretation of an earthquake swarm as foreshocks.
However, while 50% of major earthquakes are preceded by foreshocks, only about 5-10% of small earthquakes turn out to be foreshocks, leading to false warnings.
The Giuliani Option?Potentially.
As you may recall, Giampaolo Giuliani was the – let’s call him “independent researcher”, to be polite – who claims to have predicted the 2009 earthquake in L’Aquila (but couldn’t speak up at the time, due to a court order stemming from a previous prediction which didn’t pan out), by studying the emission of radon.
Most rock contains small amounts of gases that can be distinguished from normal atmospheric gases. There are reports of spikes in the concentrations of such gases prior to a major earthquake; and this has been attributed to release due to pre-seismic stress or fracturing of the rock.
One of these gases is radon, an element produced by radioactive decay of the trace amounts of uranium present in most rock.
Radon is attractive as a potential earthquake predictor because being radioactive, it is easily detected, and its short half-life (3.8 days) makes it sensitive to short-term fluctuations.
A 2009 review found 125 reports of changes in radon emissions prior to 86 earthquakes since 1966.
Another review concluded that in some cases changes in radon levels preceded an earthquake, but a correlation is not yet firmly established.
So, the jury’s still out.Indeed.
But rest assured, the scientific community is out there, working on it.
I’ll let you get back to whatever you were doing.
Till next time.