Predicting earthquakes -

9 Methods to Predict Earthquake are 1. Unusual Animal Behaviour, 2. Hydrochemical Precursors, 3. Temperature Change, 4. Water Level, 5. Radon Gas, 6. Oil Wells, 7. Theory of Seismic Gap, 8. Foreshocks, 9. Changes in Seismic Wave Velocity !

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Prediction is concerned with forecasting the occurrence of an earthquake of a particular intensity over a specific locality within a specific time limit. Normally prediction is of three types viz. long, medium and short range prediction.

While long range prediction is concerned with forecasting the occurrence of an earthquake a number of years in advance, medium term prediction is to be done a few months to a year or so and the short term prediction implies forecast ranging from a few hours to some days in advance.

Medium and short range predictions are very useful because they can help in saving the largest population from disaster in terms of life and property. Scientists believe that it is possible to predict major earthquakes by monitoring the seismicity caused by natural earthquakes, mining blasts, nuclear tests, etc.

However, no flawless technique has been developed to predict the earthquakes till date. Most of the methods and models are beyond the scope of the present work and only a few simple methods and models will be discussed here.

1. Unusual Animal Behaviour: 

It is a well established fact that animals are endowed with certain sensory perceptions denied to human beings. Some of the animals have much better power of sniffing, hearing, seeing and sensing than the human beings. The unusual behaviour of animals prior to earthquakes received wide publicity after the Haichang earthquake in Liaoning province of China, in February 4, 1975 was successfully predicted.

Although fluctuations in water levels and radon content in water were given due consideration, behaviour of animals was not overlooked in the process of earthquake prediction. On the morning of February 4, 1975, a moderate forestock hit the city of Haichang and by 2 p.m. a general alert was proclaimed.

Within six hours, the area was rocked by a devastating earthquake of 7.3 magnitude but almost all the one lakh residents were saved. Chinese are considered to be pioneers in recognising the unusual behaviour of animals preceding a quake as an important indicator to predict an impending earthquake, particularly since the accurate prediction of Haichang quake of 1975.

In fact, national war against earthquakes was launched in 1966 with an effective slogan, “Rather a thousand days with no earthquake than one day with no precaution.” Chinese report was presented at the Inter­governmental meeting convened at UNESCO, Paris in February 1976. This stimulated considerable interest among scientists.

However, it should be mentioned that abnormal behaviour of animals prior to a devastating earthquake was noticed earlier also in different parts of the world. In Japan large number of rats were seen every day in a restaurant in Nagoya City, which suddenly disappeared on the evening prior to Nobi earthquake of 1891.

Similar observations about rats were reported at two earlier occasions i.e., Kanto earthquake of 1923 and Sankriku earthquake of 1933. In China, unusual behaviour of rats was reported before 1966 Hsingtai earthquake in Hopei Province (300 km from Beijing).

In 1835 dogs escaped from the city of Talcahuano in Chile before the earthquake struck the city. Flocks of birds flew inland before the Chilean earthquakes of 1822 and 1835. Monkeys became restless a few hours before the Managua earthquake of 1972 in Nicaragua.

In summer of 1969, just before the Bahai quake (July, 1969), the custodians of Tientsin Zoo had observed that swans suddenly scrambled out of water and stayed away, a Manchurian tiger stopped pacing, a Tibetan yak collapsed, pandas held their heads in paws and moaned; and turtles were restless.

Hens and cocks were reported restless about an hour’s before in 1896 Ryakya earthquake in Japan. In Yugoslavia, birds in zoo started crying before 1963 earthquake. Deer gathered and cats disappeared from villages in northern Italy two or three hours before damaging earthquake of 1976.

Just before the earthquake which occurred in 1906 along the San Andreas Fault, horses whined and cows stampeded. In other cases cows about to be milked became restless before the shock. Bellowing of the cattle at the time of shock was very commonly reported. Howling by dogs was reported during the night preceding the earthquake.

Abnormal behaviour just before an earthquake has also been noticed among animals who live underground, like snakes, insects and worms, and those living in water (fishes). Abundant fishes were caught in just before the 1896 earthquake in north western coast of Japan and the Tango earthquake of 1927. However, in Kanto earthquake (1923) fishes were reported to have disappeared.

Just before the Edo earthquake (November 11, 1855), many grass snakes were reported to have come out of the ground near the epicentral areas even though it was severe cold winter. Very unusual behaviour of dogs was reported just before the Turkey earthquake (November 24, 1976). Barry Ralleigh of the U.S. Geological Survey noticed that the horses were fidget just before the earthquake of 28 November 1974 in Hollister (California).

In India, unusual behaviour of animals with respect to earthquake was noticed early in 1892. Animals were noticed to sniff the ground and exhibit nervousness such as a dog shows in the presence of an unaccustomed object, at the time of Govindpur (Manbhoom) a February 19, 1892. During the recent earthquakes of Uttarkashi (1991), Latur (1993), Jabalpur (1997), Chamoli (1999) and Bhuj (2001) there were isolated cases of unusual behaviour of pet dogs.

Extensive research is being carried on all over the world about the unusual behaviour of animals with respect to prediction of the earthquake. China and Japan are fore-runners in this regard. The USA has also shown keen interest in unusual behaviour of animals as a useful indicator of earthquake prediction.

The Stanford Research Institute, California, under the ‘Project Earthquake Watch’ has a network along the San Andreas Fault. This group keeps a watch on the behaviour of about 70 animal species. Dr. B.G. Deshpande has compiled a list of 87 animals which have been watched all over the world and whose behaviour might sense as an advance indicator of impending quake. Some of these which may be easily observed by the city dwellers are; cockroaches, crows, dogs, donkeys, ducks, fowls, frogs, geese, goats, horses, mice, monkeys, pigs, pigeons, rats, sheep, squirrels, swans and snakes.

The Group of Earthquake Research Institutes of Biophysics, China (1979) has arrived at the following conclusions after an extensive survey of animal behaviour before a strong earthquake.

(i) Most animals show increased restlessness before an earthquake.

(ii) The precursor time varies from a few minutes to several days, with increased restlessness at 11 hours which becomes still more marked about 2 to 3 hours before the earthquake. In general precursor times of various animals are mostly within 24 hours before the earthquake.

(iii) These observations have been noticed predominantly in high intensity or epicentral region close to active faults.

(iv) Abnormal behaviour of the animals is observed during earthquakes of magnitude 5 or more.

(v) More intensive response can be noticed with the increase of intensity of earthquakes.

2. Hydrochemical Precursors: 

Chemical composition of underground water was observed on a regular basis in seismically active regions of Tadzhik and Uzbekistan. These observations yielded following results.

(i) Concentration levels of dissolved minerals and gaseous components remained almost constant during seismically inactive period.

(ii) An appreciable increase in concentration of dissolved minerals was noticed 2 to 8 days before an earthquake. Variations in level of underground water, the pressure of artesian water, the discharge of water sources and temperature of underground water were also noticed during this period. These variations are large in the event of a strong earthquake.

(iii) After the earthquake, anomalies in concentrations of the gaseous and mineral components disappear.

According to India Meteorological Department report, significant pre-disaster and post disaster hydro geological changes rendering the ground water turbid were observed during the Jabalpur earthquake in Madhya Pradesh (1997).

3. Temperature Change:

There seems to be some relation between temperature and earthquakes. A considerable rise of temperature by 10°C and 15°C was reported before earthquakes in Lunglin in China (1976) and Przhevalsk in Russia (1970). The epicentral distances of these earthquakes where observations were taken in hot spring/well were 10 and 30 km and precursory periods were 42 and 72 days respectively.

4. Water Level: 

There are drastic changes in water level in several wells just before a major earthquake. There was a fall in water level a few days before the Nankai earthquake in Japan (1946). Rise of water level by 3 and 15 cm was reported before Lunglin (China) and Przhevalsk (Russia) earthquakes.

Similarly, water level rose by 3 cm a few hours before the earthquake in Meckering in Australia (1968). In China rise of water level in wells was observed before earthquakes of Haicheng (1975), Tangshan (1976), Liu- quiao and Shanyin (1979).

Experiments in water level variations have been conducted in Kurile Islands to predict the earthquakes of 4 and more on Richter scale. For this purpose wells upto 410-670 metres depth at epicentral distances upto 700 km are used. This is an effective technique for observing the deformation of the earth’s crust. The model on which the forecasts of earthquakes is based shows that 3 to 10 days before an earthquake, the water level begins to fall. After a short period, it starts rising when the earthquake strikes.

5. Radon Gas: 

Radon is a radioactive gas which is discharged from rock masses prior to earthquake. It is dissolved in the well water and its concentration in the water increases. Such an increase was reported in Tashkent in 1972 where increase in concentration varying from 15 to 200 per cent was noticed about 3 to 13 days prior to an earthquake.

In China, 50% and 70% increase in radon concentration was reported 18 and 6 days respectively before the Tangshan (1976) and Luhuo (1973) at Langfang and Guzan stations which were located 130 and 200 km epicentral distances for two cases. In 1995, a correlation in radon anomalies at four sites in Kangra and one site in Amritsar with the time of occurrence of Uttarkashi earthquake (1991) was reported.

6. Oil Wells: 

Large scale fluctuations of oil flow from oil wells prior to earthquakes were reported in Israel, northern Caucasus (Europe) and China. These earthquakes which occurred in 1969, 1971 and 1972 gave rise to increased flow of oil before their occurrence. It has been suggested that when the tectonic stress accumulates to a certain level, the pore pressure within a deep oil bearing strata reach its breaking strength causing oil to sprout along the oil wells.

7. Theory of Seismic Gap: 

Seismicity gap is a region where earthquake activity is less compared with its neighbourhood along plate boundaries. Soviet seismologist S.A. Fedotov studied the seismic record of 12 large earthquakes which rocked northern Japan between 1904 and 1963. By plotting the size of each tremor- struck area, he found that each quake segment abutted the next contiguous one without overlapping, as if each deep seated crack had been shut off by a barrier at the ends of the fracture zone.

Each large earthquake was in a segment that was quiet for the last 39 years or so. Fedotov predicted that those segments which were quiet for some time will be hit by earthquake sooner or later. Three of these blocks in Kurile Island were struck where according to Fedotov an earthquake was due. Thus evolved the theory of seismic gap in earthquake prediction.

Based on this theory Dr. Kiyo Mogi of Tokyo succeeded in predicting a few earthquakes in Japan. Three geophysicists—Masakazu Ohtake, Tosimatu Matumoto and Gary V. Latham—working at Taxas University’s Marine Science Institute had predicted a major earthquake in southern Mexico around the town of Puerto Angel based on the theory of seismic gap.

On 29 November, 1978, a severe earthquake measuring 7.9 on the Richter scale with an epicentre within a kilometre of the predicted site struck the area. A seismic gap predicted quake also occurred along the San Andreas Fault (Fig. 8.3).

In India, three seismic gaps have been identified—one in Himachal Pradesh which lies along the plate boundary between earthquakes of Kangra (1905) and Kinnaur (1975); the second called ‘Central gap’ between 1905 and 1934 earthquakes, third called ‘Assam Gap’ in northeast India between earthquakes of 1897 and 1950. Identification of these gaps can go a long way in predicting the earthquakes in these areas.

8. Foreshocks: 

Generally major earthquakes are preceded by minor shocks known as foreshocks. These foreshocks provide valuable dues to the occurrence of a strong earthquake. Some of the earthquakes have been successfully predicted on the basis of study of foreshocks. In addition to unusual behaviour of animals, the Haichang earthquake in China (February 4, 1975) was predicted by studying the increased seismicity from December 1974 to February 1975.

The Oaxaca, Mexico earthquake of November 1978 was also successfully predicted on the basis of foreshock observations. Foreshocks have been detected a few days to a month in advance with the help of closely located seismic stations in Himachal Pradesh for several earthquakes like Anantnag (1967), Dharmasala (1968), Kashmir (1973), Kinnaur (1975) and a few others. Uttarkashi earthquake of October 20, 1991 was preceded by foreshocks on October 15 and 16 with magnitude larger than 3.5 on Richter scale.

The most recent Bhuj earthquake of January 26, 2001 was also proceeded by foreshocks in December 2000. But there are some other earthquakes which are proceeded by foreshocks. Therefore, this is not a flawless method and has to be supplemented by other methods of earthquake prediction.

9. Changes in Seismic Wave Velocity: 

We know that P, S, and L waves originate from the focus of an earthquake. P and S are called body waves because they travel through the body of the earth, while L waves are known as surface waves because they move along the upper crust of the earth. P waves are faster than the S waves and reach seismographs first.

The time lag between the arrival of P and S waves is called lead time. Russian seismologists found that this lead time began to decrease significantly for days, weeks and even months before the earthquake. But just before the quake hit the area the lead time was back to normal. A longer period of abnormality in wave velocity presaged a larger quake.

Taking the cue from the Russians, Lynn Sykes, Scholz and Aggarwal conducted laboratory, experiments on rock samples in 1973. These experiments showed abnormal change of ratio of velocities of P waves and S waves before the earthquake.

This ratio is expressed as Vp/Vs. The duration of Vp/Vs anomaly depends upon the fault or dimensions of the aftershock area. After the Garm region of the former USSR, Vp/Vs anomalies were noticed in Blue Mountain Lake earthquake in the USA in 1973. The velocity anomaly period for this earthquake was about 5 days and the decrease in velocity was about 12 per cent.

Similar decrease in velocity ratio was reported before the damaging Haichang (February 4, 1975), Songpan-Perigwu (August 16, 1966) and bungling (1976) earthquakes in China. In Japan, 7 to 40% decrease in the velocity ratio ranging from 50 to 700 days before the main earthquakes were recorded. In Tehran 14% decrease in velocity was reported 1 to 3 days before three earthquakes in 1974.

Immediately after the Gujarat earthquake of 2001, the Survey of India mooted a network of 300 permanent Geographical Positioning System (GPS) stations all over the country to monitor earth movements round the clock—which help in predicting earthquakes.

If the GPS systems are located along the known active faults, it is possible to monitor movements of active faults or breaks in the earth’s crust. Though no precise prediction can be made about the location and magnitude of an earthquake, minor movements are an indication of an impending earthquake because it reflects the force coming from below the crust.