Japan was considered more prone to earthquakes and volcanic eruptions. But the country developed scientific process of constructing houses that faced the quake tremors without loss to life and property.
India too has a long history of earthquakes. But we have not been able to develop a perfect warning system nor have we been able to identify areas that may experience this natural calamity. The worst earthquake that killed more than 3 lakh people was in Calcutta more than two centuries back on October 11, 1737. 300 people were killed in Mathura and Kumaon Hills on September 1, 1803 and 1,000 on June 6, 1828 in Srinagar. Thousands were killed in Kangra in H.P. on April 4, 1905. Records are not available for deaths in Earth tremors that were experienced in Assam, Andamans, Nepal border, Maharashtra, A.P., Kinnaur, Maharashtra, Goa, Srinagar and J & K between 1981 and 1993. But the Indo-Nepal border quake of January 15, 1934 took atoll of 10,700. In 1950, 1,530 died in Assam. But the worst was on May 31, 1935 in which 30,000 died in Quetta.
According to a report a thousand quakes occur daily in the world. The intensity is measured on Richter scale developed by Charles F. Richter, an American seismologist in 1935.
Most of the earthquakes that occur daily are of a magnitude of 2R and are not hazardous. Most of the damaging ones measure more than 5. Those that cross 7 are most serious. Each (lumber on the Richter scale represents an intensity of ten times more than the previous number i.e. the intensity of a quake measuring 7 is ten times stronger than that measuring 6.
Most of the damaging earthquakes in India have been between 6 and 8.5 (Assam in 1950). Worldwide, the Mexico quake of 1985 measured 8.1, of Japan in 1933 and Colombo Equator border in Pacific Ocean in 1906 measured 8.9 the highest recorded anywhere. Richter scale has been considered a traditional system. The modified Mercalli Intensity Scale (MM) classifies earthquakes into 12 categories. The Mexico (1985) earthquake had an MM intensity of VIII to IX. It took 5,000 lives and injured 10,000.
There may be a million quakes a year. But only those that occur in surface in populous areas cause death and devastation. Most of these million are much beneath the surface of earth or the sea. The energy released by a considerably large earthquake is about 180 million metric tons of TNT i.e. near about 10,000 times more than the Hiroshima atom bomb.
There are a number of theories about the reasons of earthquakes. The most prevalent is the 'plate tectonics' theory. It says that earth's surface consists of seven large rigid plates. There are an equal number of small plates. These plates move slowly past one another.
The motion stretches or squeezes rocks at the edge of the plates. If the force is great the rocks break and shift. This causes an earthquake. These ruptures (breaks) are known as faults. Only a few of them are visible like the San Andrea Fault in California. The place where the fault occurs is known as epicenter. The energy released in an earthquake travels away in the form of waves. These are called 'seismic waves' and can be recorded in seismographic stations throughout the world if the quake is a large one. Seismic waves have three types. 'Compressional’ or longitude waves are sound waves that travel at a speed of eight kms a second. As the rocks vibrate in the direction of the movement of waves it causes the rocks to change volume. 'Shear' or transverse waves travel at half the speed of compressional waves. The rocks vibrate at right angles to the direction of the movement of waves. This results a change in the shape of rocks. The speed of 'Surface' waves is lesser than that of shear' waves. They are limited to the surface of the Earth. Seismic waves pass through the earth in 21 minutes.
The focus of most earthquakes is less than 40 kms under the Earth's surface. While some may take place at the surface of the Earth a few occurs 640 kms below the surface. What is important to note is that generally earthquakes occur at the place where plates collide, separate or slide past each other. These places are deep ocean trenches, new mountain ranges or volcanoes.
The earthquakes are generally limited to two beltg i.e. the "circumpacific belt' and the 'Alpine belt' that follows plate boundaries in Southern Europe and Asia. California may expect a devastating earthquake once in 50 to 100 years.
Thus they have developed buildings that can face the onslaught of even a severe earthquake. Prediction of an earthquake depends on two systems—The devices that record small movements along a fault. The other way is by measuring the speed of the seismic waves. Although successful to some extent these require more research to have an exact and perfect system.
The four latest earthquakes that occurred in India were more than a thousand kms away from each other. October 1991 saw a devastating earthquake in Uttarkashi in the Himalayan ranges in Uttar Pradesh killing more than 1500. It was the most devastating after 1950 quake on the Indo- Nepal border thattookthe life of 10,700 people.
The Maharashtra earthquake of September 30, 1993 in Latur and Osmanabad districts bordering Andhra Pradesh crossed all the records except the one in Calcutta two and a half centuries back killing 3 lakh people. Marathwada tremors began at 3.56 a.m. By 7.45 the area experienced 5 tremors killing more than 30,000 people and injuring an equal number.
The tremors that were recorded 6.4 on the Richter scale shook Satara, Sangti, Nasik, Sholapur, Nanded and Aurangabad districts killing only nine people. Seismic waves travelled to Karnataka killing 13 and to A.P., Kerala, Tamil Nadu, Gujarat and Goa. Many parts of Bombay too were rocked. The epicentre was at latitude 18.2 North and longitude 76.7 East in the Maharashtra-Karnataka -Andhra Pradesh region about 500 km from Bombay. Vidarbha too experienced the shocks. 21 villages in Latur and Osmanabad were completely wiped out. In many cases there was none to conduct funeral rites as all in the family were killed.
A large number of NRIs, individuals, humanitarian organizations came to the rescue and help. 15,000 troops did yeoman's service in providing food and water. As usual RSS people were the first to help extricate dead bodies from the debris. Centre provided Rs. 10 crore for the quake-affected. Femandes thought it inadequate when the government, spends Rs. 20 crore a year on the security of M.Ps. The worst aspect could be seen on October 2 when some vandals (rogues) indulged in a looting spree in the area.
The third earthquake was experienced in Chamoli region of Garhwal in Uttar Pradesh on April 1, 1999 in which more than 400 lost their lives. The fourth and the most devastating one was experienced in Bhuj and Ahmedabad in Gujrat which according to George Fernandes took a toll of one lakh. It took place on 26th of January 2001. Bhuj, Anjar, Bhaehau and Rapar were the most affected areas. In Ahmedabad too 78 multistoreyed buildings fell like house of cards killing most of the families.
It was only three and a half month later that the Indian community living in Los Angeles in USA suffered from a devastating earthquake that took no lives but was responsible for a great loss of property.
According to Christ Browitt of the Global Seismology Unit in the Geological survey opened that the earthquake in Maharashtra released energy equivalent to a hydrogen bomb explosion. The region (Latur & Osmanabad) is dominated by structures not designed to withstand seismic convulsions. James Jackson of the Department of Earth Sciences sees that although the 1897 and 1905 earthquakes along the foothills of Himalayas were 8 R or more yet the loss in Maharashtra was more.
NJG Negi and Krishnabrahaman of the National Geophysical Research Institute (NGRI) have a bit different view. According to them it was because of reactivation of Kurudwadi fault that they had discovered in 1973 on the basis of gravity data. The gravitational force differs from place to place and it gives clue to the faults. According to them gravity anomaly over the Bombay region 'is the highest' in India.
Earthquakes have been occurring for thousands of years. European countries have evolved methods of predicting. Vinod K Gaur, former Director of National Geophysical Research Institute complained that Indian Meteorological Department has not perfected the system of predicting earthquakes. According to him "The Indian plate, which is one of the fastest moving plates in the world, moving about five and half centimeters every year is steadily moving northward towards the Himalayas and parts of it are already bent under the great range of mountains. The plate is getting the push from the Karsberg Ridge in the Arabian sea." It might have caused the earthquake.
According to Gaur "In other countries, they have instruments which record and send information immediately after a quake to a central station which can help one understand a lot of things. But in our country 50 national laboratories all overthe country are equipped with instruments which are four generations behind and therefore cannot do any effective monitoring." "Compared to China, which is also in that category our equipment is simply primitive again." What we require is Very Long Base
Interpherometry (VLBI). "It is used in astronomy to measure the distance between two stars and record changes. But in seismology, the same can be used to detect even a one centimetre movement. With the help of this we can tab on the Faults, which are in the thousands in India." It would not cost -lore than Rs. 10 crore.
In 1975 China used the system and evacuated a large area before the earthquake occurred, preventing damage and deaths. At least now when we have entered the new millennium let the people and the government has more consciousness to work out means and ways to check such calamities.