A Probabilistic Seismic Hazard Analysis of Northeast India

Geophysical Journal International, 2003

A seismic hazard map of the territory of India and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases. The input data set consists of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. There are few probabilistic hazard maps available for the Indian subcontinent, however, this is the first study aimed at producing a deterministic seismic hazard map for the Indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation, the level of seismicity and wave propagation in anelastic media. Synthetic seismograms at a frequency of 1 Hz have been generated at a regular grid of 0.2°× 0.2° by the modal summation technique. The seismic hazard, expressed in terms of maximum displacement (Dmax), maximum velocity (Vmax), and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory. The estimated values of the peak ground acceleration are compared with the observed data available for the Himalayan region and are found to be in agreement. Many parts of the Himalayan region have DGA values exceeding 0.6 g. The epicentral areas of the great Assam earthquakes of 1897 and 1950 in northeast India represent the maximum hazard with DGA values reaching 1.2-1.3 g. The peak velocity and displacement in the same region is estimated as 120-177 cm s-1 and 60-90 cm, respectively.

The present research paper reviews on the different seismic hazards variations in the country. All the thirty-two source zones of country covered into seven geological regions. A brief highlights of return period along with a review of past PSHA effects for estimating seismic hazard in India. Earthquake catalogue containing all unknown events of medium to large magnitudes are 4≤Mw<5, 5≤Mw<6, 6≤Mw<7, 7≤Mw<8 and 8≤Mw<9. After collecting earthquake raw data following process carried out to the preparation of earthquake data, Z-map used for declusturing the data, completeness of the catalogue and recurrence relation of Gutenberg-Richter's derived a frequency-magnitude recurrence relationship. Seismic hazard analysis describes the potential for earthquake related natural phenomena such as ground shaking, rupture of fault and soil liquefaction, Seismic hazard may be assessed deterministic and probabilistic approach. Deterministic Seismic Hazard Analysis (DSHA) involves the development of a particular seismic scenario consisting of an earthquake of a specified size occurring at a specified location in other words provides a straightforward frame work for evaluation of worst-case ground motion. The Peak Horizontal Acceleration (PHA), Peak Vertical Acceleration (PVA) and Peak Ground Acceleration (PGA) values obtained in the past study matches well with the values obtained by other authors studied for different area of the country.

Current Science, 2005

Seismic hazard maps have been prepared for Northeast India in the form of uniform hazard contours for pseudo-spectral acceleration at stiff sites. These maps are for the horizontal component of ground motion and for different values of exposure time, confidence level and natural ...

Geomatics, Natural Hazards and Risk, 2013

Earthquakes constitute among the most feared natural hazards and these occur with no warning which can result in great destruction and loss of lives, particularly in developing countries. One way to mitigate the destructive impact of such earthquakes is to conduct a seismic hazard assessment and take remedial measures. This article aims at demonstrating significant contributions in the field of seismic zonation and microzonation studies in the Indian subcontinent. The contributions in the field of earthquake hazard have been very valuable and beneficial not only for science but also for society. The historical seismicity and seismic zonation studies as well as the present scenario of seismic hazard assessment in the Indian subcontinent, whether through probabilistic or deterministic approaches, are discussed. It has been found that many parts of the Himalayan region have peak acceleration values exceeding 0.6g. The epicentral areas of the great Assam earthquakes of 1897 and 1950 in northeast India represent the maximum hazard with acceleration values reaching 1.2-1.3g. The peak velocity and displacement in the same region is estimated as 120-177 cm s 71 and 60-90 cm, respectively. To mitigate seismic risk, it is necessary to define a correct response in terms of both peak ground acceleration and spectral amplification. These factors are highly dependent on local soil conditions and on the source characteristics of the expected earthquakes. This article will also present the findings of site-specific hazard assessment in megacities.

Acta Geophysica

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.

Pure and Applied Geophysics, 2008

The maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of NW Himalaya and the adjoining regions. For this purpose, we have prepared a reliable, homogeneous and complete earthquake catalogue during the period 1500-2010. The technique used here allows the data to contain either historical or instrumental era or even a combination of the both. In this study, the earthquake hazard parameters, which include maximum regional magnitude (M max ), mean seismic activity rate (k), the parameter b (or b = b/log e) of Gutenberg-Richter (G-R) frequency-magnitude relationship, the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900-2010. The uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters. The earthquake hazard in the whole NW Himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level, tectonics and focal mechanism. The annual probability of exceedance of earthquake (activity rate) of certain magnitude is also calculated for all seismogenic source zones. The obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters. It is observed that seismic hazard level is high in Quetta-Kirthar-Sulaiman region in Pakistan, Hindukush-Pamir Himalaya region and Uttarkashi-Chamoli region in Himalayan Frontal Thrust belt. The source zones that are expected to have maximum regional magnitude (M max ) of more than 8.0 are Quetta, southern Pamir, Caucasus and Kashmir-Himanchal Pradesh which have experienced such magnitude of earthquakes in the past. It is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity.

Bulletin of the Seismological Society of America, 2007

Peninsular India (10.0Њ N-28.0Њ N; 68.0Њ E-90.0Њ E) is one of the oldest and seismically most stable landmasses of the Indian plate. Recent seismic history, however, shows that more than five damaging earthquakes with magnitudes greater than M w 6.0 have occurred in this region, highlighting the importance of seismichazard assessment for the region. This article estimates the probabilistic seismic hazard associated with peninsular India with a zoneless approach incorporating the observed seismic activity and known geological characteristics of the region. The seismicity parameters for hazard assessment have been estimated incorporating completeness criteria for various spans of the catalog data. The spatial and temporal variations of seismic activity have been modeled using different source models. Seismic source zones for the region have been defined on the basis of large-scale geological features, which are used for assigning the maximum possible earthquake potential. Due to the poorly known attenuation characteristics of the study region, three appropriate attenuation models have been used for the estimation of groundmotion parameters. Hazard maps for peninsular India have been developed using a convolution scheme based on weighting and incorporating various uncertainties involved while modeling different parameters. The comparison of the probabilistic seismic-hazard map developed herein with the hazard map specified in the Indian Standards shows that the design parameters in the Indian Standards may significantly underestimate the seismic hazard in some regions of peninsular India.

Journal of Geophysics and …, 2012

This paper deals with the estimation of spectral acceleration for Manipur based on probabilistic seismic hazard analysis (PSHA). The 500 km 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 Bull. Seismol. Soc. Am. 93 1703 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 0.3-0.1.15 g, 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

In view of the major advancement made in understanding the seismicity and seismotectonics of this region in recent times, an updated probabilistic seismic hazard map of India covering 6°–38° N and 68°–98° E was prepared and presented in this paper. In present analysis, three types of seismic sources, viz. linear, areal and zoneless models were considered and different attenuation relations were used for different tectonic provinces. The study area was divided into small grids of size 0.1° x 0.1° and the PHA and Sa values were evaluated at the centre of each grid point. A MATLAB code has been developed to estimate the hazard using linear sources and zoneless approach whereas CRISIS software was used to model areal sources. Comparison of different methodologies is presented in the paper. The linear source model predicts higher hazard compared to other two source models and Zoneless approach gives the lower value of hazard at a particular grid point. For most of the cities, gridded sei...