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Seeks to examine risk assessment of human settlements due to seismo‐tectonic setting of a populated area in the Himalayas, so that mitigation measures may be taken before…
Seeks to examine risk assessment of human settlements due to seismo‐tectonic setting of a populated area in the Himalayas, so that mitigation measures may be taken before the next earthquake takes its toll.
Keeping in view the seismic vulnerability of the Himalayan ranges, an earthquake scenario is considered for the Narendranagar block of Tehri Garhwal District which lies in Seismic Zone IV of the seismic zoning map of India (BIS, 1893‐2002). Damage of MSK Intensity VIII and peak accelerations of 0.25 g are expected here at any time. The hypothetical epicenter is placed near Tapowan at 30°08′10″N and 78° 20′30″E on the crest of the meandering River Ganga, where three large thrusts, viz. Garhwal, Tons Nayar and Krol, congregate. Iso‐acceleration contours plotted for the entire Narendranagar block for earthquakes of magnitude 7.0 and 7.5 are elongated along the main boundary fault.
Almost 59 percent population of the Narendranagar block was found to be vulnerable to damage associated with higher accelerations of 0.41 g.
The topographic effects influencing the risk of settlements have not been taken into account.
Implications of such an earthquake on housing stock; roads; infrastructure; awareness and time of occurrence are discussed. Strategies are suggested for long‐term earthquake preparedness and short‐term action plan for emergency management.
The methodology evolved can be extended for other Himalayan regions.
For a state like Uttarakhand, which is located in the seismically active Himalayan region and in the vicinity of plate boundaries, estimation of seismic hazards and the…
For a state like Uttarakhand, which is located in the seismically active Himalayan region and in the vicinity of plate boundaries, estimation of seismic hazards and the preparation of a zoning map are an urgent necessity. This paper aims to focus on this hazard.
In total, 32 potential seismo‐tectonic source zones were identified in a very wide area in and around the state, on the basis of seismicity and tectonics, and the longer ones were segmented. The maximum magnitude that each seismo‐tectonic source zone can support was then estimated. The seismic hazard due to each seismo‐tectonic source zone was assessed at 180 sites, in terms of peak ground acceleration (PGA).
The maximum PGA at each site varied between 0.06g and 0.50g. The seismic hazard was highest around the main central thrust and the main boundary thrust, and five other thrusts between these two thrusts. This assessment was adapted to make a seismic zoning map of Uttarakhand, with five distinct zones.
If seismo‐tectonic source zones from the contiguous regions of Nepal and Tibet were included as part of this assessment, then a higher hazard would be expected in Uttarakhand.
Threat perceptions of a potential earthquake disaster can be assessed in this zoning map. Disaster mitigation strategies will vary geographically, with priorities defined by the zoning map presented here. The methodology evolved has the potential to be extended to other vulnerable states in the Himalayan arc.
The seismic hazard assessed has been adapted to formulate a seismic zoning map of Uttarakhand.