S T G Raghukanth

This paper deals with the estimation of spectral acceleration for Manipur based on probabilistic seismic hazard analysis (PSHA). The 500km region surrounding Manipur is divided into seven tectonic zones and major faults located in these zones are used to estimate seismic hazard. The earthquake recurrence relations for the seven zones have been estimated from past seismicity data. Ground motion prediction equations proposed by Boore and Atkinson (2008 Earthq. Spectra 24 99-138) for shallow active regions and Atkinson and Boore (2003 Bull. Seismol. Soc. Am. 93 1703-29) for the Indo-Burma subduction zone are used for estimating ground motion. The uniform hazard response spectra for all the nine constituent districts of Manipur (Senapati, Tamenglong, Churachandpur, Chandel, Imphal east, Imphal west, Ukhrul, Thoubal and Bishnupur) at 100-, 500- and 2500-year return periods have been computed from PSHA. A contour map of peak ground acceleration over Manipur is also presented for 100-, 500-, and 2500-year return periods with variations of 0.075-0.225, 0.18-0.63 and 0.3-0.1.15g, respectively, throughout the state. These results may be of use to planners and engineers for site selection, designing earthquake resistant structures and, further, may help the state administration in seismic hazard mitigation. © 2012 Sinopec Geophysical Research Institute.

This article presents site-specific probable seismic hazard of the Himachal Pradesh province, situated in a seismically active region of northwest Himalaya, using the ground motion relations presented in a companion article. Seismic recurrence parameters for all the documented probable sources are established from an updated earthquake catalogue. The contour maps of probable spectral acceleration at 0, 0.2, and 1 s (5% damping) are presented for 475 and 2475 years return periods. Also, the hazard curves and uniform hazard response spectrums are presented for all the important cities in this province. Results indicate that the present codal provision underestimates the seismic hazard at cities of Bilaspur, Shimla, Hamirpur, Chamba, Mandi, and Solan. In addition, regions near Bilaspur and Chamba exhibit higher hazard levels than what is reported in literature.

This article presents probabilistic seismic hazard analysis (PSHA) of India and adjoined region, carried out to develop a new national seismic hazard map for India. The hazard map is developed using fault oriented spatially smoothed seismicity approach. A catalog of earthquakes has been compiled for the region (Latitude 50N − 400 N and Longitude 650E − 1000E) from 2600BCE to 2019CE to estimate the seismicity parameters. Eighteen suitable ground motion prediction equations in the logic tree framework are used for the four major geological regions of the country. The hazard is estimated at rock sites (B-C boundary type) conditions in terms of peak ground acceleration (PGA), short-period (0.2 s), and long-period (1s) spectral acceleration maps and uniform hazard spectra, with 2% and 10% probabilities of exceedance in 50 years. Higher hazard values are observed in the Hindukush-Pamir regions and Northeast India, whereas central India and the southern peninsular regions are less prone to seismic threat. The proposed maps find their application in the seismic design of structures, risk assessment, and as an input for updating the existing code provisions.

This article presents four regional site-specific ground motion relations developed for the state of Himachal Pradesh in northwest Himalaya, situated in a seismically active region. These relations are developed from synthetic free surface ground motion databases obtained from a calibrated stochastic seismological model considering the characteristic properties of this specific region. The adopted methodology incorporates the site effects characterised through active MASW tests conducted in 22 important cities. The estimated ground motion levels from the developed relations are found to be in reasonable agreement with the recorded data.

The present work aims at developing the first probabilistic fling hazard map of India and adjoined regions. First, we developed a new ANN-based ground motion prediction equation (GMPE) for fling corresponding to horizontal and vertical directions. The developed GMPE is based on permanent ground residual displacement form 556 scenario events considered consistent with the regional characteristics. The corresponding simulations are performed by suitably combining the Okada’s solutions. Developed GMPE is comparable with the existing relations and the few available data which contained fling characteristics. Further, the developed GMPE, along with the other two available prediction equations for the fling, is incorporated to represent the ground motion characteristics in the estimation of hazard using a suitable logic tree. In addition to the fling prediction equations, the evaluation of regional fling hazards requires identifying the location of all the probable seismic sources and their seismicity characteristics. In this study, we used the linear-fault model, as the fling is a near field phenomenon. We report the resultant probabilistic fling hazard map for 10%,2% 1%, and 0.5% probability in 50 Years for the region. The maps showed that the active regions in Himalayas, North-Eastern India, and Andaman experience higher values for fling than stable Peninsular India. Thus, this study develops the fling hazard map for the first time, and the results are essential in the design and rehabilitation of important structures in the region.