Printer Friendly Format

Page 1 of 4
| Next |

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

Dr. Jayant Sinha, Sri Sahendra Singh, Sri Indrajeet, Sri Tarun Kumar
*. Dept. of Geology, St.Xavier's College, Ranchi, Jharkhand, India
**. Vighneshwar E. BIZ Pvt. Ltd., Mumbai, India
***. Software Consultant, Bhubaneshwar, India 

Introduction:
Earthquakes are the most destructive among all the natural hazards. Most of the time, they occur without any warning, which makes them most feared and unpredictable natural phenomena. Globally, on an average two earthquakes of magnitude 8 are known to occur every year. Some of the countries like Japan, China and United States have suffered several damaging earthquakes in the past. India has also experienced a number of high intensity earthquakes in the recent past and more than 650 earthquakes of magnitude > 5.0 have been reported in India since 1890.

The recently occurred Bhuj earthquake of Gujrat State (India) has once again exposed our limitations in earthquake science and also our preparedness against such natural disasters. Earthquakes are known to occur at frequent intervals causing loss both in terms of economy and human life, the effect of which is not only felt at the local level but also at the national level. Still we have not been able to make enough inroads into the areas of their identifications, prevention and control, earthquake can still strike without any warning and there is no way to control them prior to its occurrence, except than some post earthquake rehabilitation measures. Off late there has been considerable advance in the delineation of earthquake prone areas and the whole world has been delineated into different seismic regions based upon their seismic characteristics. India has also been divided into five seismic zones from zone one to zone five, with the fifth one being of highest seismicity.

Earthquake causes:
The true nature of the causes of an earthquake must be fairly well understood before adopting any control measure. Two models are being tested to justify these control measures.

1. Dilatancy-diffusion theory developed in the U.S.
2. Dilatancy-instability theory USSR

The first stage of both models is an increase of elastic strain in a rock that causes them to undergo a dilatency state; which is an inelastic increase in volume that starts after the stress on a rock reaches one half its breaking strength. During Dilatancy State, open fracture developing the rocks. So it is in this state the first physical change takes place indicating future earthquake. Here the two models diverge. The U.S. model suggest that the dilatancy and fracture of the rocks are first associated with a low water containing dilated rock, which helps in producing lower seismic velocity, lower electrical resistivity and fewer minor seismic event.

The pore water pressure then increases due to influx of water into the open fracture, weakening the rock and facilitating movement along the fracture, which is recorded as an earthquake.

In contrast the Russian model state that the first phases is accompanied by an avalanches of fracture that release some stress but produce an unstable situation that eventually cause a large movement along a fracture.

Seismic gaps are defined as an area along active fault zones, capable of producing large earthquake but that have not recently produced an earthquake. These areas are thought to store tectonic strain and thus are candidate for future large earthquake.

Any fault that has moved during quaternary can be called as active fault. It is generally assumed that these faults can get displaced at any time. Faults that have been inactive for the last three million years are generally classified as inactive fault. Active faults are basically responsible for seismic shaking and surface rupture