Earth Movements

The occurrence of earthquakes in India is due to the drifting of the so-called Indian Plate. Scientists divide the globe into a number of major tectonic plates* that drift very slowly. Whenever and wherever these plates slide against each other a tremendous amount of energy is released and causes the terrific destructions. The recent earthquakes in Maharashtra and Gujarat give us a good estimate of how damaging they could be.

Earthquake

There was a time – some 225 million years ago – when the continents were not separated by oceans. The earth’s surface knew only one massive continent, called Panagea. The some 200 million years ago, Panagea split into two major continents, one of them Gondwanaland (which contains Africa, South America, India and Australia). Gondwanaland continued to split into smaller land masses, one of them is the Indian plate. It drifted at a speed of 9 metres per century towards the Eurasian plate. Where these giant plates met under enormous pressure, the Himalayans were formed.

How Earthquakes Occur?

There are many fault-lines in the Earth’s crust. A fault is where blocks of crust on either side are moving relative to one another. The typical average rate is around a millimetre per year. If this movement happened gradually it would pose few problems for people living near by. Unfortunately rocks do not behave that way. Instead, they tend to stick. Strain builds up for decades or centuries until it reaches a critical level, and then everything gives at once.

Once a fault has given way at one point, slip movement may occur along its whole length, which may be hundreds or thousands of kilometres, though movement is usually restricted to a much shorter portion of the whole fault. The strongest seismic waves are generated at the initial break-point. The closer to the break-point, the greater the energy and the greater the potential for destruction, especially if the break-point is near the surface. Technically, the break-point is called the earthquake focus, and the point on the surface directly above it is referred to as the epicentre. Slip further along the fault and readjustments close to the focus usually cause a series of smaller aftershocks, which continue for days (even years in extreme cases) after the initial earthquake. Such kind of energy release are called waves because of the way they move.

Most of the damage caused by an earthquake is not done by the P-waves and S-waves. These waves travel through the body of the Earth, and their energy is spread over a rapidly increasing volume as they propagate. It is other waves of the sort that travel along the surface of the ground that do most of the harm. These include up-and-down waves (like waves on the ocean) and strong side-to-side shaking waves. The P- and S-body waves travel faster than the surface waves, and, if felt, can give a few seconds (minutes, if further away) warning of the arrival of the more damaging surface waves.

What next?

Scientists can't predict earthquakes but they know in which regions earthquakes are most likely to occur. Taking into account the speed and direction of the drift of the plates, the structure of the land masses and in particular the measurements of the tensions between different areas almost accurate probabilities can be calculated. Gujarat and the whole of Northern India are areas, with a high probability of experiencing severe earthquakes. Based on tension measurements and past movements of the Indian plate scientists know that a very major earthquake is going to hit the shillong plateau in the north-eastern part of the country before 2010. There is a very high probability - but it is absolutely impossible to predict an exact date or the epicentre of this quake.

Research on Quakes

Important research on earthquakes is carried out by the National Geophysical Research Institute in Hyderabad. Since its foundation in 1961, the institute carried out applied and basic research in the frontier areas of solid earth geophysics. It seeks to devise new methods and instruments for the exploration of mineral and groundwater resources. Other aims include natural hazard assessment, geophysical instrumentation, research on mobile zones of the lithosphere, analysis of the edges of the crust, earthquakes and volcanoes.

During the last few years intensive cooperation between Geo-forschungszentrum (Germany) and National Geophysical Research Institute has evolved. Together with the Indian scientists, German colleagues are analysing the structure and seism of the Indian plate, one of the oldest regions of the earth. In this area rock strata of an age of the earth. In this area rock strata of an age of upto 3.5 billion years exist. There are only few regions in the world better suited for scientists to find clues leading to a profound understanding of the history of earth.

Scientists from India and Germany are developing mathematical models of the seismic speeds which can be determined by measuring the shock waves after an earthquake. In their joint project, the Indian and German scientists are measuring only natural and not man-made quakes. A network of mobile stations covers the whole of India to gather very high digital quality data and also to measure aftershocks following every big earthquakes. The interpretation and evaluation of these data are done jointly using the long experience of the scientists of the Geoforschungszentrum Potsdam.

Seismic Scale
Richter Scale

The Richter scale is a logarithmic scale, devised in 1935 by geophysicist Charles Richter, for representing the energy released by earthquakes. A figure of 2 or less is barely perceptible, while an earthquake measuring over 5 may be destructive. More relevant as a measure of earthquake strength is the intensity, for which the modified Mercalli scale is widely used.

Richter Magnitudes--------------Earthquake Effects

2.5-------------------------------Generally not felt, but recorded

4.5-------------------------------Local damage.

6.0-------------------------------Can be destructive in populous region.

7.0-------------------------------Major earthquake. Inflicts serious damage. Roughly ten occur -----------------------------------each year.

>8.0------------------------------Great earthquakes. Occur once every 5-10 years; produce -------------------------------------total destruction to nearby communities.

Volcanoes

A volcano is a mountain or hill with an opening on top known as a crater. Hot melted rock (magma), gases, ash, and other material from inside the Earth mix together a few kilometres underground, rising up through cracks and weak spots in the mountain. Every once in a while, the mixture may blast out, or erupt, through the crater. The magma is called lava when it reaches the air. Lava may be as hot as 1000 degree Centigrade. Gradually the lava cools and solidifies on the earth surface making new landforms. In some eruptions, huge fiery clouds rise over the mountain, and glowing rivers of lava flow down its sides. In other eruptions, red-hot and cinders shoot out from the mountain top, and large chunks of hot rock are blasted high into the air. A few eruptions are so violent they blow the mountain apart. Some eruptions occur on volcanic islands. Such islands are the tops of volcanic mountains that have been built up from the ocean floor by repeated eruptions. Other eruptions occur along narrow cracks in the ocean floor. In such eruptions, lava flows away from the cracks, building up the sea bottom.

Ring of Fire

The hundreds of active volcanoes found on the land near the edges of the Pacific Ocean make up what is called the Ring of Fire. They mark the boundary between the plates under the Pacific Ocean and the plates under the continents around the ocean. The Ring of Fire runs all along the west coast of South and North America, from the southern tip of Chile to Alaska. The ring also runs down the east coast of Asia, starting in the far north in Kamchatka. It extends down past Australia.

*-The concept of Continental Drift was first described by the German geophysicist Alfred Wegener in 1910 and later reinvigorated as the Theory of Plate Tectonics in early 1960’s