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‘We must be ready for big earthquakes’

‘We must be ready for big earthquakes’
What is the biggest gap in our understanding about earthquakes in Himalayas?
The gap is not only for Himalayan earthquakes. It is a global gap. The fact remains that the “Plate Tectonics Hypothesis” was developed in the late 1960s and early 1970s. It provided, for the first time, the basis for a calculation of strain accumulation which results in earthquakes.

Take the example of the Fukushima earthquake of M 9.0 on March 11, 2011, in Japan that created an unprecedented tsunami, which was not anticipated. The maximum size of the earthquake expected on the host fault for the Fukushima earthquake was M 8. When a larger M 9.0 earthquake occurred, all estimates of the height and spread of the resultant tsunami went wrong.

Incidentally, on the magnitude scale, <g data-gr-id="80">increase</g> in magnitude by one unit increases the energy release 30 times. A magnitude 6 earthquake is something like the Hiroshima atom bomb. So, as of now, our knowledge about earthquakes is limited.

What kind of research is being carried out to find the answers to these questions?
There is a concentrated global effort to better understand the movements of the plates and accumulation and release of strains.

Thousands of Global Positioning Systems have been deployed globally at strategic locations. Seismic zoning is available for all major cities of the world. Efforts are on to develop <g data-gr-id="90">microzonation</g> maps so that the anticipated damage due to earthquakes is better understood and necessary measures are undertaken to construct earthquake-resistant structures.

Efforts on precursors are also continued. It has been realised that earthquakes re-occur where they have occurred earlier. Researchers are developing earthquake scenarios, where estimates are made of what would happen today if one of the earlier earthquakes repeats.

The National Disaster Management Authority (NDMA) and government of India undertook a major programme of developing scenarios for the repeat of the disastrous 1905 Kangra earthquake and the 1897 Shillong earthquake, both with a magnitude of more than 8.

A hypothetical earthquake of M 8 was considered to occur in Himachal Pradesh. Isoseismals were developed. On these isoseismals, if you place the building typology, you get a rough estimate as to how many houses would collapse and how many would be partially damaged. If you place the population density layer on top, you get a rough estimate of the number of people who would be killed and injured.

This exercise was carried out for the states of Himachal Pradesh, Punjab, Haryana and the Union Territory of Chandigarh. It was inferred that if this earthquake occurs in the middle of the night, it could claim up to one million human lives.

It may be noted that the Muzaffarabad (Kashmir) earthquake of October 8, 2005, some 300 km west of the hypothetical earthquake epicentre in similar local conditions, was M 7.6 and claimed some 75,000 human lives. It occurred at about 10 am <g data-gr-id="87">local</g> time when most of the people were out of their homes. Had it occurred in the middle of the night, the death toll would have been much higher.

This information was shared with state governments and ways to reduce this impact were shared with the public. Special emphasis was placed on the safety of lifeline buildings, such as hospitals, police stations, fire brigades and school buildings, to ensure that these structures are capable of withstanding the anticipated accelerations. The safety of school children received special focus.

After six months of preparation, the hypothetical earthquake was scheduled to occur at 11.30 am on February 13, 2013. In this mega mock drill, public and the state governments were totally involved.

The drill demonstrated the weaknesses of the system. It showed what the state and Central governments, as well as the public, would need to do to reduce the earthquake impact. This was a very successful exercise. The same approach was adopted for the repeat of the Shillong earthquake of 1897 for all the eight northeast Indian states on March 10 and 13, 2014.

What is your lab/ research team trying to find in the field of seismology and the seismology in Himalayas in particular?

The Ministry of Earth Sciences (MoES) has established multi-parametric laboratories in critical areas in the Himalayas to continuously observe several geophysical parameters and precursors that precede earthquakes. At the same time, a lot of efforts has been placed in <g data-gr-id="67">microzoning</g> of major cities.

Additionally, under a very popular programme, several schools in the Himalayan region have been provided with seismological laboratories so that students can see earthquakes being recorded and analysed. Another programme on the anvil is to install the earthquake early warning system at a critical location in the Kumaon Himalayas.

 
Anupam Chakravartty

Anupam Chakravartty

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