Earthquake prediction has been a goal of scientists for centuries, and efforts in this direction have been mostly successful. Despite considerable research by seismologists, scientifically reproducible predictions cannot yet be made to a specific hour, day or month but for well-understood faults, seismic hazard assessment maps can estimate the probability that an earthquake of a given size will affect a given location over a certain number of years. Scientific evaluations of prediction claims look for the following elements in a claim: 1. A specific location or area; 2. A specific span of time; 3. A specific magnitude range; and 4. A specific probability of occurrence. Statistical methods also have been tried with populations of regional earthquakes. Approach to the statistical occurrence of earthquakes involves analysis of past earthquakes in a particular place and the periodicity between those quakes. Geologic methods of extending the seismicity record back from the present also are being explored. Field studies indicate that the sequence of surface ruptures along major active faults associated with large earthquakes can sometimes be constructed. For example, the series of large earthquakes in Turkey in the 20th century, which were caused mainly by successive westward ruptures of the North Anatolian fault. Liquefaction effects preserved in beds of sand and peat have provided evidence, when radiometric dating methods are used for large paleoearthquakes extending back for more than 1,000 years in many seismically active zones, including the Pacific Northwest coast of the United States.

For many years prediction research has been influenced by the basic argument that strain accumulates in rock masses in the vicinity of a fault and results in crustal deformation. The Elastic Rebound Theory, formulated by US seismologist Harry F Reid in 1911, mainly utilizes this principle to give rough prediction of the occurrence of large shallow focus earthquakes. Deformations can be measured in the horizontal direction along active faults (by trilateration and triangulation) and in the vertical direction by precise leveling and tiltmeters. Reid himself gave a crude forecast of the next great earthquake near San Francisco (the theory also predicted, of course, that the place would be along the San Andreas or an associated fault). The geodetic data indicated that during an interval of 50 years relative displacements of 3.2 metres had occurred at distant points across the fault. The maximum elastic-rebound offset along the fault in the 1906 earthquake was 6.5 metres. Therefore, in (6.5/3.2)x50 or about 100 years would again elapse before sufficient strain accumulated for the occurrence of an earthquake comparable to that of 1906. Such strain rates are now being more adequately and precisely measured along a number of active faults such as the San Andreas, using networks of GPS sensors. In the year 2005, GSI carried out such studies entitled ‘Prediction of earthquake from spatial/temporal clusters by statistical analysis’. A paper on this research was worked out by Basab Mukhopadhyay and Sujit Dasgupta titled ‘Temporal and Spatial Clustering of Earthquakes in Burmese-Andaman Arc and Himalaya’. This particular method of predicting earthquakes was also stated by seismologist Prof Surya Kanta Sarma in an article titled ‘Experts differ on possibility of major quake’ that was published in the September 24, 2009 edition of The Assam Tribune.

There are also other techniques adopted by geoscientists to give earthquake predictions. The theory of dilatancy of rocks prior to rupture once occupied a central position in discussions of premonitory phenomena of earthquakes. For earthquake prediction the significance of dilatancy, if real, is in its effects on various measurable quantities of the Earth's crust, such as seismic velocities, radon gas emission rates and ground water levels. Strain buildup in the focal region may have measurable effects on other observable properties, including electrical conductivity and gas concentration. Because the electrical conductivity of rocks depends largely on interconnected water channels within the rocks, resistivity may increase before the cracks become saturated. As pore fluid is expelled from the closing cracks, the local water table would rise and concentrations of gases such as radioactive radon would increase. No unequivocal confirming measurements have yet been published.

VAN is a method of earthquake prediction proposed by professors Varotsos, Alexopoulos and Nomicos in the 1980s; it was named after the researchers' initials. The method is based on the detection of ‘seismic electric signals’ (SES) via a telemetric network of conductive metal rods inserted in the ground. The method stems from theoretical predictions by P Varotsos, a solid-state physicist at the National and Capodistrian University of Athens. It is continually refined as to the manner of identifying SES from within the abundant electric noise the VAN sensors are picking up. Researchers have claimed to be able to predict earthquakes of magnitude larger than 5, within 100 km of epicentral location, within 0.7 units of magnitude and in a 2-hour to 11-day time window.

An increase in foreshock activity (combined with purported indications like ground water levels and strange animal behaviour) enabled the successful evacuation of a million people one day before the February 4, 1975 7.3 magnitude Haicheng earthquake by the China State Seismological Bureau. While 50% of major earthquakes are preceded by foreshocks, only about 5-10% of small earthquakes turn out to be foreshocks, leading to many false warnings.

According to new research to be published by Prof Shlomo Havlin, of Israel’s Bar-Ilan University, earthquakes form patterns that can improve the ability to predict the timing of their recurrence. The November 11, 2005 issue of the journal Physical Review Letters, published by the American Physical Society, had an article by researchers from Israel and Germany that says that there is a way to predict when the next earthquake will hit. Prof Havlin in collaboration with Prof Armin Bunde of the Justus-Liebig University in Giessen, Germany and Bar-Ilan University graduate student Valerie Livina used the ‘scaling’ approach from physics to develop a mathematical function to characterize earthquakes of a wide range of magnitudes in order to learn from smaller magnitude earthquakes about larger magnitude earthquakes. The team's findings reveal that the recurrence of earthquakes is strongly dependent on the recurrence times of previous earthquakes.

One possible method for predicting earthquakes, although it has not yet been applied yet, is fractoluminescence or ‘earthquake lights’ also known as EQL. Before the 1995 Kobe earthquake in Japan, many people reported seeing flashes of red and blue light in the sky up to an hour before the earthquake. Studies at the Chugoku National Industrial Research Institute by Yoshizo Kawaguchi has shown that upon fracturing, silica releases red and blue light for a period of about 100 milliseconds. Kawaguchi attributed this to the relaxation of the free bonds and unstable oxygen atoms that are left when the silicon oxygen bonds have broken due to the stresses within the rock. It has been suggested that methane escaping from underground during earthquakes is ignited somehow and burns near the surface, giving off EQL. This as well as the VAN method of predicting earthquake using natural electrical and electromagnetic effects may also be related to piezoelectricity, where some materials are able to generate an electric potential in response to applied mechanical stress. As we know that magnetic field is associated with electric field, so may be certain low frequency electromagnetic pulse waves are released prior to the sudden release of strain energy in a particular fault. There have also been cases in which electromagnetic waves caused by the earthquake interfered with radio transmissions, such as during the Great Chilean Earthquake of 1960. On May 12, 2008, 30 minutes prior to the Sichuan Earthquake, a cell phone captured footage of multi-coloured clouds in the sky. The footage was uploaded to YouTube. There is also footage from Meixian, Shaanxi, approximately 550 km northeast of the epicentre, recorded 10 minutes before the earthquake. However, the footage appears to show a circumhorizontal arc, which is caused by refraction of the sun's light through ice particles in a cirrus cloud, similar to a rainbow. Earthquake lights were also spotted in Tianshui, Gansu, approximately 400 km north-northeast of the epicentre.

Since 1994, Zhonghao Shou, a retired Chinese chemist living in New York, has made dozens of earthquake predictions based on cloud patterns in satellite images, and claims to have a 70% accuracy. Stress and friction in the ground can vaporize water long before the earthquake happens, according to Shou, and clouds formed through these mechanisms are distinctively shaped. He has identified five different types of earthquake cloud, including ‘line-shaped’, ‘feather-shaped’, and ‘lantern shaped’ clouds. He claims that an earthquake will take place within 103 days of the appearance of one of these clouds, and that the average time is 30 days. Historical records have indicated a possible correlation between clouds and earthquakes in the ancient civilizations of Rome, India and China. Mysterious earthquake clouds were spotted before the 7.9 magnitude quake of May 12, 2008 that struck Sichuan Province of China.

The Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (Demeter) satellite, constructed by CNES, has made observations which show strong correlations between certain types of low frequency electromagnetic activity and the seismically most active zones on the Earth, and have shown a sharp signal in the ionospheric electron density and temperature near southern Japan seven days before a 7.1 magnitude earthquale occurred there (on August 29 and September 5, 2004, respectively). Quakesat is an earth observation nanosatellite based on 3 CubeSats. It was designed to be a proof-of-concept for collecting extremely low frequency earthquake precursor signals from space. The primary instrument is a magnetometer housed in a 2-foot telescoping boom. ESPERIA is an equatorial space mission mainly conceded with detecting any tectonic and preseismic related signals. More in general, it has been proposed for defining the near-Earth electromagnetic, plasma, and particle environment, and for studying perturbations and instabilities in the ionosphere-magnetosphere transition region.

Another, modern method of predicting earthquakes based upon so-called ‘Syzygy Effect Theory’ adopted by some groups (although this technique is often discarded by majority of world’s geoscientists, because of its non-standard methods) uses calculations regarding the positions of sun and moon as well planetary positions with respect to earth’s volatile seismic zones. Historically, there have been some great earthquakes whose timing coincides with tidal forces near their maximum as well as with total solar eclipses. In fact, according to some archaeological researches, Mayan people prepared themselves for an earthquake just after observing a total solar eclipse.

The notion that animals can sense earthquakes before they occur may have originated in ancient Greece in 373 BC. But precisely what animals do sense, if they feel anything at all, is a mystery. One theory is that wild and domestic creatures feel the Earth vibrate before humans. Other ideas suggest they detect electrical changes in the air or gas released from the Earth. According to the chief conservator of forests of Tamil Nadu, a few minutes before the killer tsunami waves generated by an underwater earthquake hit the Indian coastline in December 2004, a herd of 500 blackbucks rushed away from the coastal areas to the safety of a nearby hilltop, although there is little evidence for animals being able to sense earthquakes before they happen. Besides, the peculiar behaviour of birds may be attributed to the fact that, since birds highly rely upon earth’s magnetic field, certain changes related to electromagnetic disturbances before an earthquake may cause some imbalance in their biological system. So keeping a special notice on their pets (dogs, cats, fishes, especially birds, etc) and trying to figure out their strange behaviours (distinguishable from those displayed commonly) people can remain alert and have some rough idea about a coming earthquake, without panicking.

Finally, with a hope of dissipating the earthquake fear from the minds of people, especially Guwahatians, in view of the recent tremors, I would like to present a little idea of mine about earthquake prediction, which I once read in the website of National Geographic Channel. There should be a particular reporting station in every earthquake-prone area where people may report their observations of strange animal behaviours or other phenomena like peculiar or unseen cloud patterns, strange lights in the sky or even changes in groundwater level. If the recorded data of such observations becomes unexpectedly high in a specific zone, that data can be analysed and correlated to other data collected through geophysical measurements like seismicity, ground tiltations, radon levels, etc in that zone within the same time period. Based upon the equations and their results we can come up with a particular decision. I hope our scientific community will try to think over my idea.

Dipankar Pathak