An earthquake is a series of vibrations on the earth’s surface caused by the generation of elastic (seismic) waves due to sudden rupture within the earth during release of accumulated strain energy.
Faulting may be considered as an immediate cause of an earthquake. Due to constant movement of plates, deformation is caused which results to generations of strain energy. Indian plate is moving in north-north-east direction and colliding with Eurasian plate along the Himalayas. All earthquakes, let it be the Gujarat Earthquake, Kutch (16 Jun, 1819, Magnitude 8), Shillong Plateau Earthquake (12 Jun 1897, Magnitude 8.7), Bihar Nepal Border Earthquake (15 Jan 1934, Magnitude 8.3), Arunachal Pradesh China Earthquake (15 Aug, 1950), Gujarat Earthquake, Bhuj (26 Jan 2001, Magnitude 7.7), Sumatra Earthquake (26 December, 2004, Magnitude 9.3), Kashmir Earthquake (08 October, 2005) have same story to tell about our destruction and annihilation.
The Recent Earthquake at Haiti (13 January, 2010, Magnitude 7) again repeats our helplessness to this mighty force of nature. Management of earthquake has become very crucial in this trouble times.
Severity of an Earthquake is measured by:
- Slight – Magnitude up to 4.9 in a Richter Scale
- Moderate – Magnitude up to 5 to 6.9 in a Richter Scale
- Great – Magnitude up to 7.0 to 7.9 in a Richter Scale
- Very Great – Magnitude up to 8.0 and more
A proactive stance to reduce the toll of disasters in the region requires a more comprehensive approach that encompasses both pre-disaster risk reduction and post disaster recovery. It is framed by new policies and institutional arrangements that support effective action. These types of approaches need the following set of activities:
- Risk analysis to identify the kind of risks faced by the people and development investments as well as magnitude
- Prevention and mitigation to address the structural sources of vulnerability
- Risk transfer to spread financial risks over time and among different actors
- Emergency preparedness and response to enhance a country’s readiness to cope quickly and effectively
- Post disaster rehabilitation and reconstruction to support effective recovery and to safeguard against future disasters.
There are different types of theories which states about the causes of an earthquake. Hence the true nature of an earthquake must be well understood before adopting any control measures.
Two models were suggested. One was the Dilatancy –Diffusion Theory developed in the USA and the other is the Dilatancy – Instability theory of the then USSR.
The interesting fact is that the first stage of both the models is an increase of elastic strain in a rock that causes them to undergo a dilatancy state, which is an inelastic increase in volume that starts after the stress on a rock reaches one half its breaking strength. Hence it is in this state the first physical change takes place indicating future earthquake.
The USA model suggests that the dilatancy and fracture of the rocks are first associated with low water containing dilated rock, which helps in producing lower 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 termed as an earthquake.
Now let us take the Russian Model: 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.
It is these areas which are thought to bring in tectonic strain and which are the candidates for future large earthquake. Any fault that has moved during quaternary can be called as active fault. It is generally assumed that these faults could get displaced at any time. Faults that have been inactive for the last 3 million years are generally classified as inactive fault.
Active fault are basically responsible for seismic shaking and surface rupture (Sinha et al.2000). 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 long fault plane. These vibrations may sometimes lead to the total collapse of large buildings, dams, tunnels, pipelines and other rigid structures.
Secondary effects of an earthquake include a variety of short range events: such as liquefaction landslides, fires, tsunamis and floods. Long range effects include regional phenomenon such as regional subsidence or emergence of landmasses, river shifting and regional changes in ground level.
The main objective of earthquake preventive measures should be to develop and promote knowledge, practices and policies that reduce fatalities, injuries and other economic losses from an earthquake. Geographic Information System and Remote Sensing provides a tool effective and efficient storage and manipulation of remotely sensed data and other spatial and non-spatial data types for both scientific management and policy oriented information. This can be used to facilitate measurement, mapping, monitoring and modeling of variety of data type’s related natural phenomenon.
The critical areas that need focus for effective Earthquake Management are:
• Lack of awareness among various stakeholders about the seismic risk;
• Inadequate attention to structural mitigation measures in the engineering education syllabus;
• Inadequate monitoring and enforcement of earthquake-resistant building codes and town planning
• Absence of systems of licensing of engineers and masons;
• Absence of earthquake-resistant features in non-engineered construction in suburban and rural
• Lack of formal training among professionals in earthquake-resistant construction practices; and
• Lack of adequate preparedness and response capacity among various stakeholder groups.
A number of organizations, like NGOs, self-help groups, CBOs, youth organizations, women’s groups, volunteer agencies, Civil Defense, Home Guards, etc. volunteer their services in the aftermath of any disaster. Large-scale natural disasters draw overwhelming humanitarian support from different stakeholders. The relief and response activities carried out by such stakeholder’s comply with the norms prescribed by the appropriate authorities. After an earthquake, accurate information is generally provided on the extent of the damage and the details of the response activities through electronic and print media.
The personal dos and don’ts at the time of an earthquake are given below for reference and awareness generation:
- Take shelter under a desk, table, bed or doorway during an earthquake.
- Provide help to others and develop confidence.
- Shut off kitchen gas.
- Keep stock of drinking water, food stuff and first aid arrangements.
- If you are in a moving vehicle, stop and stay in vehicle.
- Follow and advocate local safety building code for earthquake resistant construction.
- Heavy objects, glasses should be kept on lower shelf.
- Turn on transistor or T.V. to get latest information.
- Make plan and preparation for emergency relief.
- Do not get panicky
- Do not use candles, matches etc and do not switch any electric mains immediately after an earthquake.
- Do not spread and believe in rumors
- Do not run through or near buildings during an earthquake
Please send your feedback in the e-mail address given below.
Thanks and Regards,
Mr. Mainak Majumdar
Disaster Management Specialist and Consultant