Explained | Joshimath crisis: A brief history of India’s seismic zone maps

Joshimath is located in Zone V of India’s seismic zonation scheme, which denotes a high-risk area.

The story so far: Joshimath, a small but busy town in Uttarakhand’s Chamoli district, is in the midst of a crisis as 723 houses in all nine of the town’s wards have developed major or minor cracks on the floors, ceilings and walls. Beams have also been dislodged in many houses.

The first cracks appeared in a few houses in October 2021, but the administration failed to take adequate steps. After more cracks appeared in buildings this January, 145 families have been temporarily relocated to safer locations within the town while a debate on the future of Joshimath rages.

Joshimath is located in Zone V of India’s seismic zonation scheme, which denotes a high-risk area.

It is also worth noting that the Indian Space Research Organisation (ISRO) said in a report that the town in Uttarakhand sank 5.4 cm between December 27, 2022, and January 8, 2023. However, the report and the satellite images were later withdrawn from the ISRO website. The National Disaster Management Authority (NDMA) has directed all departments and organisations associated with survey and data collection in Joshimath not to interact with the media or share any data on social media.

A seismic zone is an area where there is a high probability of earthquakes due to the area’s geology. Seismic zonation, which involves dividing areas based on expected ground motion, assesses the hazards related to earthquakes in such areas to provide inputs for safer constructions and other practices.

A published in the Journal of theInternational Society for the Prevention and Mitigation of Natural Hazards said that almost 65% of India falls in high to very high seismic zones.

According to the 2002 version of India’s seismic zone map, earthquake-prone regions in the country are divided into four zones – zone II, III, IV, and V – based on intensity levels during past earthquakes. However, this is not the version of the map that has always been in use.