N. Ackerley, K.K.S. Thingbaijam, S.K. Nath
Coverage of the Indian subcontinent is with the hazard model developed by Nath and Thingbaijam (2012). This model covers India, Bangladesh, Bhutan and Nepal. The model has been updated and translated from its original format into the OpenQuake (OQ) engine in collaboration with Natural Resources Canada. Additional information, material and documentation about the implementation of the model can be found at: https://github.com/nackerley/indian-subcontinent-psha
Information about the OQ model versions and input files can be found on the Results and Dissemination page.
The viewer below depicts the seismic sources and hazard results in terms of PGA for a return period of 475 years. Click on the menu in the upper right corner to select the layer.
The Indian subcontinent moves northward with respect to Eurasia and is colliding with the southern Asian margin at 35-45 mm/yr; this collision has contributed greatly to the uplift of the great mountain ranges of central and eastern Asia, including the Himalaya, the Tien Shan, the Pamir, and the Tibetan plateau. The Indian subcontinent is much stronger than the Asian continental crust with which it collides, though, so most of the deformation and seismicity that results from the plate collision is located in and north of the Himalaya outside of India. Exceptions include in northwest and northeast India where the Himalaya are within the national borders, and the Shillong region of eastern India, where some component of the plate convergence is accommodated on intraplate faults. The faults in the Himalayan belt take up at least half of the total plate convergence and represent the greatest source of seismic hazard to India; earthquakes on the Himalayan thrusts may be large enough that those in Nepal, Bhutan and Pakistan may still produce dangerous seismic shaking in densely-populated northern India.
Nonetheless, the strong Indian crust is capable of transmitting compressive stresses over great distances, and large, damaging earthquakes have occurred well within the Indian borders as a result. A prime example of this is the 2001 Mw 7.6 Bhuj earthquake in Gujarat, which killed over 2000 people (Bodin and Horton, 2004, Bulletin of the Seismological Society of America)
See Nath and Thingbaijam (2012) for a description of the datasets used for developing the hazard model.
Seismic Source Characterisation
Nath and Thingbaijam (2012) proposed three source models: a single set of areal seismogenic source zones, and two smoothed-gridded point source models. Epistemic uncertainty is considered through alternative values of b and Mmax in each source zone.
Ground Motion Characterisation
A wide range of tectonic regions are considered, and epistemic uncertainty is accounted for by using multiple GMPEs per tectonic region.
Hazard curves were computed with the OQ engine for peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2s, 0.5s, 1.0s, and 2s. The computation was performed on a grid of 55038 sites (spaced at approximately 10 km) with reference site conditions with shear wave velocity in the upper 30 meters (Vs30) of 760-800 m/s.
The hazard map for PGA corresponding to a 10% probability of exceedance in 50 years (475 year return period), can be seen using the interactive viewer. For a more comprehensive set of hazard and risk results, please see the GEM Visualization Tools.
Nath, S. K. and Thingbaijam, K. K. S. (2012). Probabilistic seismic hazard assessment of India. Seismological Research Letters, 83(1):135–149.