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.

In this article, analytic expressions for the frequency wave number spectra are derived for the displacement and rotational components at the ground surface of a micropolar elastic half-space. The ground motion is caused by buried sources described in terms of unit impulsive force and micro-moments. Closed-form analytic expressions for both plane strain and anti-plane strain conditions are established. In the sequel, Green's functions for reduced micro polar half-space where the couple stresses are zero and the stress tensor is nonsymmetric are also presented. Numerical results are presented for anti-plane strain case. The derived expressions can be used to simulate rotational and displacement components of ground motion during earthquakes.

In this article, a predictive model for ground motion characteristics is developed using the artificial neural network (ANN) technique. This model is developed to predict peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), spectral acceleration at 0.2 and 1 s. The input parameters of the model are moment magnitude (Mw), closest distance to rupture plane (Rcd), shear wave velocity in the region (Vs30), and focal mechanism (F). The updated NGA-West2 database released by Pacific Engineering Research Center (PEER) is employed to develop the model. A total of 13,678 ground motion records are used to develop the model. The ANN architecture considered in the study has four input nodes in the input layer, three neurons in the hidden layer, and three output nodes in the output layer. The ANN is trained by a hybrid technique combining genetic algorithm and Levenberg–Marquardt technique. The results of the study are found to be comparable with the existing relation in the global database. The model developed can be further used to estimate seismic hazard.

In the analysis and design of important structures with relatively long life spans, there is a need to generate strong motion data for possible large events. The source of an earthquake is characterized by the spatial distribution of slip on the fault plane. For future events, this is unknown. In this paper, a stochastic earthquake source model is developed to address this issue. Here, 1D and 2D stochastic models for slip distribution developed by Lavallée et al. (2006) are used. The random field associated with the slip distribution is heavy-tailed stable distribution which can be used for large events. Using 236 past rupture models, the spectral scaling parameter and the four stable or Levy’s parameters against empirical relationship for known quantities like magnitude or fault length are developed. The model is validated with data from 411 stations of 1999 Chi-Chi earthquake. The simulated response spectrum showed good agreement to actual data. Further the proposed model is used to generate ground motion for the 1993 Killari Earthquake where strong motion data is not available. The simulated mean peak ground velocity was in turn related to the intensity (MSK) and compared against values in the literature.

The present study aims at developing a model for simulating ground motion for earthquakes in the Sumatran region where one of the most devastating earthquakes took place in 2004 with a moment magnitude (Mw) of 9.1. With advancements in instrumentation, the three-dimensional material properties, topography and bathymetry of the region are available in the global database. These parameters are used as inputs in Spectral Finite Element Method to simulate ground motions. The model is first validated with the IGCAR broadband velocity data for 2012 Mw 8.6 Sumatra Earthquake. Due to favourable comparison, our model is also used to generate ground displacement characteristics of Mw 9.1 event. The source uncertainties are accounted by using three finite fault slip models available in the global database. The simulated time histories showed that the ground motion is sensitive to input slip models. The peak ground displacement (PGD) and ground residual displacement (GRD) in both horizontal and vertical directions are presented as contour plots. PGD obtained from various slip models in the epicentral region is of the order of 14-22 m in horizontal direction and 7-16 m in vertical direction. GRD in the epicentral region is of the order of 6-17 m in East-West (E-W) 4-17 m in the North-South (N-S) directions. The vertical uplift obtained from various slip models is around 2-8 m. The developed model can be used to simulate ground motion time histories, which can be further used in hazard analysis, tsunami simulations, etc.

Great earthquakes in the past (e.g. 1869 Cachar earthquake, 1897 great Assam earthquake) have caused large scale damage and ground liquefaction in the Guwahati city. Moreover, seismologists are of opinion that a great earthquake might occur in the unruptured segment of the North-East Himalaya that is near to Guwahati city. In this paper, the liquefaction hazard due to these events have been simulated. The obtained results are in general agreement with the reported damages due to the past earthquakes. The central part of the city (i.e. Dispur, GS road), that has large thickness of soft soil deposit and shallow ground water table, is highly vulnerable to liquefaction. © 2009 Springer-Verlag.

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.

In this article, stochastic finite-fault simulation combined with site response analysis is used to understand the spatial distribution of ground motion in Guwahati city due to three damaging earthquakes. The rock level ground motion for the scenario earthquakes is generated based on the stochastic finite-fault methodology. These simulated motions are further amplified up to the surface by equivalent linear site response analyses using the available borelog data at 100 different locations in Guwahati city. A set of twenty simulated rock level time histories for each event, are used to compute the surface level ground motion. Response spectra are computed and the results are presented in the form of contour maps, at selected natural periods. The mean amplification due to local soil deposit is as high as 2.2 at most of the sites in Guwahati city. Based on these simulated motions, an average site correction factor is obtained for soil sites in Guwahati city. The standard error in the simulated response spectra is also reported. The contour maps obtained will be useful in identifying vulnerable places in Guwahati city.

The 2011 great Japan Tohoku earthquake is not only the most devastating but also, one of the best recorded earthquakes in the history of seismology. A thorough study of strong motion characteristics of this earthquake is conducted using 20 well established ground motion parameters (GMPs). The behaviour of these parameters with fault distance and average shear wave velocity is examined and attenuation relationships are developed using the 1172 surface level strong motion records. In addition, all GMPs are categorized on a statistical basis using principal component analysis, which is further used to rate the damage potential of ground motion records.

This paper is motivated by the desire to derive seismic hazard maps for the Indian subcontinent. The most up-to-date earthquake data has been collected to estimate the hazard parameters for quantifying seismicity. An earthquake catalog for the entire country from 1250 B.C.-A.D. 2008 has been compiled from various sources in the literature (Figures 2 and 3). The entire country and its neighboring region is divided into 930 nodes at a spacing of 1° × 1° in the N-S and E-W directions. Seismicity data in 300-km regions around each grid point is assembled to quantify the seismic activity. The earthquake catalogs for each node are first evaluated for their completeness. Based on the completeness test of Stepp (1972), the seismicity data is divided into complete and extreme parts. The maximum likelihood procedure of Kijko and Sellevol (1989), which utilizes the information in both the complete and extreme parts of the catalog, is used for estimating the seismicity parameters (λ, b, Mmax). The parameters are obtained at each node, and the final results are shown in the form of contours (Figures 9, 10, and 11). The obtained b-values for grid points in the Himalayas, northeast India, and the Gujarat regions are lower when compared with peninsular India. The λ-value, and Mmax are lower in PI when compared with rest of the country, indicating moderate seismicity. In this study, the spatial variation of seismicity parameters has been obtained by discretizing the entire region into equally spaced grid points. The derived seismicity parameters are to be interpreted as the characterization of seismic activity around each node. Alternatively, one can derive the spatial variation of seismicity by identifying probable source zones based on the seismotectonic features and association of seismicity with these sources (Gupta 2006). In regions where seismicity is low, such as PI, considerable care is necessary in defining source zones. It should be mentioned here that in the present analysis past seismicity has been used to estimate the seismicity parameters. The use of geological data such as strain rate or the rate of seismic moment release to constrain the seismicity parameters would increase confidence in using the obtained results (Field et al. 1999). However, with the existing limitations such as non-availability of geological data, the results obtained in the present study are the best possible. The results obtained from the present study have several uses in engineering construction and design. These results can be used to rank available construction sites for important projects. The estimated seismicity parameters combined with the fault map (Figure 1) can be used to prepare hazard curves for peak ground acceleration and response spectra at different return periods by PSHA.