Himalayan Geology, Vol. 40 (1), 2019, pp. 78-82, Printed in India
Assessment of seismic hazard in Kumaun-Garhwal region
AJAY PAUL1*, VATSAL JOSHI2
1Wadia Institute of Himalayan Geology, Dehradun, 248001, India
2Birla Institute of Technology and Science, Pilani, 333031, India
*Email (Corresponding author): ajaypaul@wihg.res.in
Abstract: The Garhwal-Kumaun region of northwest Himalaya lies between the two great earthquakes (i) 1934 Bihar-Nepal earthquake and (ii) 1905 Kangra earthquake. This unruptured region between the two great earthquakes, where the accumulated strain energy is sufficient to generate a great earthquake, has been termed as the Central Seismic Gap (CSG). The data set comprises of the earthquake events recorded between July 2007- February 2016 from a ten station broad-band seismic network installed in CSG. The peak ground accelerations (PGA), have been evaluated using probabilistic approach and the contour maps are drawn to show its variation. The analysis has been carried out for (i) checking the consistency of the attenuation relation and (ii) calculating PGA values to draw its contour map. The contour map of PGA, drawn from the current seismicity shows that the trends of peak values follows the trend of MCT traverse and the narrow zone of microseismicity prevailing in the region. The peak values of 21.5 gals and 13.7 gals have been obtained for the Uttarkashi and Chamoli regions from the observed current seismicity. These values are far too low as compared to the observed PGA values of the two moderate earthquakes of recent past in this region (i) 268 gals at Uttarkashi for Mw 6.8, 1991 Uttarkashi earthquake and (ii) 262 gals at Gopeshwar for Mw 6.6, 1999 Chamoli earthquake.
Key words: Peak ground acceleration, seismic gap, contour map.
