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Evaluation of parameters controlling Earthquake Management System : An analytical approach using 3S' Technology

Effects of earthquake:
Like all other natural hazards earthquakes also produce primary and secondary effects. Primary effects include surface vibration, which may be associated with surface rupture and displacement along fault plane. These vibrations may sometimes lead to the total collapse of large buildings, dams, tunnels, pipelines and other rigid structures. Deterministic ground motion analysis is one of the tools to determine the spatial distribution of surface vibration. Secondary effects of earthquake include a variety of short-range events; such as liquefaction, landslides, fires, tsunamis and floods. Long range effects include regional phenomena such as regional subsidence or emergence of landmasses, river shifting and regional changes in ground water level.

Liquefaction results from transformation of water-saturated granular material from solid to liquid state as a result of increase in pore water pressure. It may result in three types of failure.

1. Landslide on moderate slope.
2. Landslide occurring on gentle or nearly flat slopes.
3. Quick condition failure.

Landslide of all varieties in addition to those associated with liquefaction, are triggered or directly caused by earthquake. Earthquakes also cause catastrophic destruction from fires due to disruption of electrical power lines and broken gas lines. Coastal or submarine earthquake also generate tsunamis or seismic sea waves. Other secondary effects of large earthquake are regional changes in land elevation. The destruction of critical facilities may cause catastrophic losses of life, property damage or disruption of society, e.g. large dams, nuclear power plant and liquid natural gas.

Earthquake hazard reduction:
For any modern nation public safety concern are of prime importance and India is of no exception. In view of this concern there should be adequate thrust towards understanding earthquakes the science of which is known as seismology. These studies may be helpful in seismic hazard assessment and mitigation

A comprehensive earthquake hazard reduction programme should include

1. Prediction
2. Control measure.
3. Post earthquake rehabilitation measure.

a) Prediction:
First successful prediction of a major earthquake was made in 1975. The earthquake took place in China ( Haichung) on Feb 4 1975. The intensity of the earthquake was 7.3 on ritcher scale and about ninety percent of the structure was destroyed in a city of 90,000 people. In this case thousand of people were saved by the massive evacuation from unsafe housing just before the earthquake. The short-term prediction was possible primarily on a series of foreshock that began four days prior to the main shock. Unfortunately these types of short-range prediction on the basis of foreshock are not always reliable.
Earthquake prediction by any geoscientist is far from success, however a detailed and systematic investigation may lift haze in its prediction. Earthquake prediction in an area may be carried out under following heads:

1. Lithological characterization and structural setting of the region
2. Crustal deformational studies
3. Frequency of fore shock
4. Repetitive land level survey
5. Water tube tiltmeters
6. Geomagnetic observation.
7. Geothermal gradient.
8. Gravity survey
9. Hazard mapping

Lithological Characterization and Structural Setting of the region

Geological mapping of an area is the first step towards the surface and subsurface investigation of a region. The accuracy of these investigations decides the prediction accuracy before an earthquake and also the post earthquake control and reduction measures.

The advent of Geoinformatics has brought revolutionary change in these investigations. Now a day number of geological softwares are available in the market for the geological mapping of the area. These softwares are highly useful in the speedy and accurate execution of mapping work. The arrival of GPS has the capability of recording spatial co-ordinates with accuracy level up to millimeter.

Remote sensing and air photogrammetry is of immense potential at the reconnaissance stage of the mapping. Now it is possible to map the inaccessible regions through the satellites.

Structural setting indicates the future earthquake by giving enough information regarding the palaeoseismology of the area. It is also helpful in the hazard mapping of the area to take preventive and control measures.

"Earthquake don't kill people, but the unsafe building". Carrying out systematic lithological mapping of the terrain can very well minimize the magnitude of seismic destruction. The Bhuj quake aftermath is an ideal example since such a high magnitude of destruction was possible mainly because of unconsolidated basement of the structures. It has been observed that the structures on a consolidated foundation, e.g. igneous and metamorphic rocks, are more safe than those on unconsolidated basements, viz. Alluvial, sand and loamy soil. Different surface materials behave differentially in response to seismic shaking of various frequencies. Unconsolidated earth materials (mud alluvium and bedrock) vibrate more in compare to hard bedrock. Therefore an area sensitive to earthquake hazards must be mapped for it to be available to land-use decision maker.

So a highly accurate geological map can be prepared with the help of recent geomatic tools and they can be analysed through GIS to use it for the prediction or the preparation of action plan during the post earthquake rehabilitation measures.