Sunday Times 2
Earthquakes, predictions and lies
“The information about how big an earthquake’s going to be may not be in the earth’s crust BEFORE the earthquake begins.” This line by Lucy Jones, a prominent senior seismologist at the United States Geological Survey, aptly sums up our current understanding of earthquakes. It is a highly nonlinear process with agonisingly limited predictability. This restriction stems from the fact that, to predict an earthquake, physical conditions in and around the potential rupture area should be known precisely before an earthquake. Acquiring this knowledge is beyond
the reach of current geophysical capabilities.
Moreover, the ground on which we stand (lithosphere — Earth’s rigid outermost shell) is laced with a myriad network of faults. This is especially true near plate boundaries. Most of these faults, including those that can produce large earthquakes whose recurrence interval is several times the human lifetime scale, remain hidden from us. These can slip whenever the conditions are right. Even when a fault has been identified, there is no guarantee that it will slip in a predictable periodic manner as tectonic stress builds on it. Perhaps the most famous example of this is the Parkfield section of the San Andreas Fault in California, which slipped with a mean repeat time of 22 years (in 1857, 1881, 1901, 1922, 1934, and 1966) to produce magnitude 6 or greater earthquakes. The next big earthquake in this sequence was expected between 1988 and 1993, but it came more than a decade later in 2004!
With the benefit of hindsight, numerous precursors to earthquakes have been proposed; variations in seismic wave speeds near the source region, emission of radioactive elements, variations in seismic activity, changes in groundwater level and spring flow, changes in surface displacement/elevation, anomalous animal behaviour etc. These, however, have never been proven to be causally related to earthquakes through repeatable observations, which is the cornerstone of science.
Prediction versus forecast
So then, have not we made any progress? Ambitious research efforts requiring large sums of money have been made to better understand earthquakes and develop new methods to provide better forecasts. One should not confuse prediction with forecast. A prediction is the ability to foretell the exact magnitude, location and time of an earthquake, whereas a forecast is a complex statistical calculation that takes into account many geophysical parameters and determines the probability of an earthquake of a certain magnitude occurring at a given location and time frame. Conceptually this is not that different from the weather forecast you see on the TV on a daily basis.
With the advent of geodesy — satellite-based millimeter-scale measurements of displacements on the Earth’s surface — in recent times, significant improvements have been made to earthquake forecasting models. For sure, there is still a large margin of error in these forecasts precisely due to the aforementioned reasons. Nonetheless, earthquake forecasts, valid usually on decadal time-scales, provide useful information to guide earthquake preparedness; building codes, designing rapid response schemes, and deciding where to site hospitals, schools, power plants, and dams.
Liars and their insidious lies
Charles Richter, after whom the famous Richter Scale is named, once said “Journalists and the general public rush to any suggestion of earthquake prediction like hogs toward a full trough, [Prediction] provides a happy hunting ground for amateurs, cranks, and outright-publicity seeking fakers”. This has exactly been the case in Sri Lanka after the temblors in Indonesia and Nepal.
A couple of years ago, a group of pseudo-scientists, none of whom has any qualification in earthquake science, claimed that they were able to “predict” earthquakes by considering planetary alignment (astrology). They even suggested a fake instantaneous interaction between the Earth’s liquid iron core and the surface to justify their claim. Their deceitful “predictions” unsettled vulnerable masses during the April festive season in 2011 quite unnecessarily.
Several rigorous statistical studies conducted by international scientists suggest that only a weak correlation (not causation!) exists between Earth’s tides induced by the moon and small shallow earthquakes. The moon’s gravitational force can pull Earth’s solid surface up about a foot as the moon passes over the Earth daily. This shift in mass induces very small stresses (0.05 – 0.5 bar) whose effects are mainly felt in the top 10-20 km of the Earth. This is the possible origin of weak correlation between tides and small shallow earthquakes. The only other body that can induce notable tidal stresses on Earth is the Sun, yet its influence is much less than that of the moon. No other planetary body can induce appreciable tidal force on Earth.
Another pseudo-scientist recently claimed that he can predict earthquakes by inspecting the colour changes in soils. He also claimed that the 2004 tsunami did not originate in the Indonesian region, but near Sri Lanka. Firstly, the shallowest earthquakes nucleate several kilometres below the Earth’s surface, where the rock is hard enough to be broken by tectonic stresses. There is no instantaneous link between the surface soils and earthquake processes active at depth. Soils acquire the characteristics of the rock, from which they are derived through a process called weathering. This takes thousands of years. Rapid changes in the soil that this pseudo-scientist claims to have observed signalling impending earthquakes are unheard of in credible earthquake science.
Secondly, the question regarding the location of the 2004 great earthquake, shown in the figure, has been put to rest long ago by advanced seismological and geodetic modeling. An excellent source of information about this particular earthquake can be found at www. iris.iris.edu/sumatra/. In this day and age of advanced technology, the general public should remain wary of a dubious pseudo-scientist crouching around wearing a stethoscope at the crack of dawn, searching for earthquake signals — this scene is taken directly from a dim-witted cartoon.
The Conclusion
Earthquakes cannot be predicted at present. Period! Anyone claiming to have solved the “Holy Grail” problem in modern global seismology MUST publish his results in a high impact international journal under thorough peer-review. Anyone falling short of this is lying through his teeth. It is disheartening to see national media, both print and electronic, giving valuable air time to individuals who have little understanding of natural phenomena. These media organisations have a grave responsibility to check the credentials and the track record of “experts” before running outrageous stories that harm society. Readers’ trust is paramount in the wake of a natural hazard, during which time national media can play a critical role in building social resilience. I, therefore, advocate for a new brand of journalism well grounded in proper science to combat the menace of pseudo-science in Sri Lanka.
About the author: http://www.sundaytimes.lk/150524/