Online material : Data files for seismogenic source zones (polygons), smoothed-gridded seismicity models, and hazard curves at 0.2° regular grid spacing over the study region.

Earthquake disasters occur mainly due to the collapse of buildings and structures triggered by ground motions. It is, therefore, important to predict ground-shaking levels in order to determine appropriate building code provisions for earthquake-resistant design of structures. This involves extensive analyses and development of appropriate seismological models; namely, seismogenic sources, seismic site conditions, and ground motion predictions. The hazard products, viz . data and maps, constitute important tools for framing public policies toward land-use planning, building regulations, insurance, and emergency preparedness.

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Table 1 
Major Earthquake Casualties during 1900–2008 in India and Adjoining Regions



In India, several events during the last 100 years, as listed in Table 1, indicate that even moderate earthquakes ( MW < 7.0) can cause significant devastation. On one hand, ongoing urbanization and unprecedented population growth have considerably aggravated the prevailing seismic risk. On the other hand, the available seismic hazard maps covering the entire country are about a decade old. Consequently an updated seismic hazard model for the country is imperative and necessitated by new data, recent findings, and methodological improvements. In the present study, we make a case for new probabilistic seismic hazard analysis (PSHA) of India. The fundamental studies have been carried out to deliver the hazard components, including seismogenic source zonation and seismicity modeling in the Indian subcontinent (Thingbaijam and Nath 2011), assessment of site conditions across the country (Nath, Thingbaijam, Adhikari et al. 2011), and a suitability test for the ground-motion prediction equations in the regional context (Nath and Thingbaijam 2011). These components are integrated to deliver a preliminary model consisting of spatial distributions of peak ground acceleration (PGA) and 5%-damped pseudo spectral acceleration (PSA).

Initial attempts at …

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Probabilistic Seismic Hazard Assessment of India

Ground motion prediction equation considering combined dataset of recorded and simulated ground motions

Proper selection and ranking of Ground Motion Prediction Equations (GMPEs) is critical for successful logic-tree implementation in probabilistic seismic hazard analysis. The present study explores this issue in predicting peak ground accelerations at the rock sites in India. Macroseismic intensity data complemented with limited strong ground-motion recordings are used for the purpose. The findings corroborate the possible conformity between the GMPEs developed for tectonically active shallow crust across the globe. On the other hand, the relevant GMPEs in the intraplate regions cluster into two different groups with the equations of lower ranks catering to higher ground motions. The earthquakes in the subduction zones have significant regional implications. However, affinity in the ground-motion attenuations between the major interface events (MW > 7.4) in Andaman-Nicobar, Japan and Cascadia, respectively, is noted. This can be also observed for the intraslab events in the Hindukush and Taiwan respectively. Overall, we do not observe any significant advantage with the equations developed using the regional data. These findings are expected to be useful in probabilistic seismic hazard analysis across the study region.

Peak ground motion predictions in India: an appraisal for rock sites

Many older unreinforced masonry (URM) buildings feature timber floors and solid brick masonry. Simple equivalent frame models can help predicting the expected failure mechanism and estimating the strength of a URM wall. When modelling a URM wall with an equivalent frame model rather than, for example, a more detailed simplified micro-model, the strengths of the piers and spandrels need to be estimated from mechanical or empirical models. Such models are readily available for URM piers, which have been tested in many different configurations. On the contrary, only few models for spandrel strength have been developed. This paper reviews these models, discusses their merits, faults and compares the predicted strength values to the results of recent experimental tests on masonry spandrels. Based on this assessment, the paper outlines recommendations for a new set of strength equations for masonry spandrels.

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Review of strength models for masonry spandrels

The seismic performance of stone masonry buildings is known to be generally poor with respect to other structural typologies. However, significant differences can be observed for different architectural configurations, structural details and masonry mechanical properties. In particular, the seismic vulnerability of existing stone masonry structures is often governed by local failure modes, typically consisting of out-of-plane overturning of structural portions or crumbling of outer wythes in multi-leaf walls. In buildings with an adequate masonry quality, an overall behaviour controlled by the in-plane capacity of walls can develop and govern the global failure mode, provided that proper connections between perpendicular walls and between walls and floors are effective in contrasting the activation of early local failures. In these cases, the in-plane stiffness of diaphragms (typically vaults and timber floors/roofs) can play a significant role in coupling the response of the different walls, hence controlling the global building capacity. Recent experimental testing campaigns carried out in different laboratories have focused on several aspects of the seismic response of stone masonry buildings and on the effect of several strengthening techniques. The availability of such experimental results allowed validation and improvement of analysis tools and procedures for the assessment of the seismic capacity of existing stone masonry structures. In order to make them available to all practitioners, the research achievements need to be incorporated in codes and guidelines for the assessment and strengthening of existing stone masonry buildings. The procedures currently proposed in several codes are already based on a rational approach, which starts from the acquisition of an adequate structural knowledge level and allows for using nonlinear analysis procedures. They could straightforwardly include new research findings and practical developments.

Seismic assessment of existing and strengthened stone-masonry buildings: critical issues and possible strategies

The south Indian state of Tamil Nadu in the peninsular shield is a zone of low to moderate seismic activity with a sparse historical record of significant earthquakes. The current intensity-based zoning adopted by the Indian seismic code stipulates an effective peak ground acceleration (PGA) of either 0.10 or 0.16 g for different parts of the state, for the maximum considered earthquake (MCE), and the service life of a structure. In the current study, probabilistic seismic hazard contour maps for Tamil Nadu and the union territory of Pondicherry, in terms of the ground-motion parameters, PGA and spectral accelerations, at 0.1, 0.5, and 1.0 sec for 2%, 5%, and 10% probabilities of exceedance in a 50 yr period, have been produced. Hazard computations have been performed over a grid of sites covering the territory at an interval of 0.2°. A comprehensive earthquake catalog has been compiled for the region extending between 2 and 20.7° N latitude and 68 and 88° E longitude and spanning ∼950 yrs. The hazard maps are produced by suitably accounting for epistemic uncertainty in the hazard computations within a logic-tree framework incorporating parameters such as different probabilistic hazard analysis methods (classical Cornell–McGuire and zone-free approaches), catalog completeness estimation methods, maximum cutoff magnitude, and ground-motion predictive equations for shallow crustal intraplate environments. The hazard maps are compared to the zoning prescribed by the seismic code. The current estimations show that the potential seismic hazard in considerable parts of the state is underestimated by the broad zoning adopted by the Indian Standards.

Probabilistic Seismic Hazard Macrozonation of Tamil Nadu in Southern India

Response of masonry walls to out-of-plane excitation is a complex, yet inadequately addressed theme in seismic analysis. The seismic input expected on an out-of-plane wall (or a generic “secondary system”) in a masonry building is the ground excitation filtered by the in-plane response of the walls and the floor diaphragm response. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. The current article delves into the details and results of several nonlinear dynamic time-history analyses executed within a parametric framework. The study addresses masonry structures with rigid diaphragm response to lateral loads. The scope of the parametric study is to demonstrate the influence of inelastic structural response on the seismic response of secondary systems and eventually develop an expression to estimate the seismic input on secondary systems that explicitly accounts for the level of inelasticity in the primary structure in terms of ...

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: I. Parametric Study

The seismic input expected on an out-of-plane wall (or a generic secondary element) in a URM building is the ground excitation filtered by the in-plane response of the walls and the response of the floor diaphragms. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. Inelastic response of the primary structure can alter the secondary system response considerably in comparison to that under elastic structural response. The current article proposes a semi-analytical formulation to estimate the acceleration demand on an out-of-plane URM wall that explicitly takes into account the level of inelasticity in the primary structure in terms of the displacement ductility demand. A simplified approach to determine the acceleration profile over the height of a structure is also introduced. The formulation is based on statistical evaluation of the results of several inelastic time-history analyses treated within a parametric framework, which a...

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: II. Formulation

Role of diaphragm flexibility modelling in seismic analysis of existing masonry structures

The Minaret of Jam in Afghanistan was recently included in UNESCO's List of World's Endangered Monuments. The minaret is the world's second tallest (∼60 m) after the Qutub Minar in New Delhi and it is also one of the oldest (∼800 years). It is situated at the centre of the Hindukush range in the Ghor Province at the junction of Rivers Hari-Rud and Jam-Rud, at an elevation of 1900 m. The Minaret of Jam is in danger of collapse due to a 3.4° northward inclination inducing high stresses in its deteriorated brick masonry. The precarious conditions of the monument render it highly vulnerable to earthquakes. Therefore prior to any intervention to protect it, an assessment of the seismic hazard at the site, followed by an evaluation of the tower's seismic vulnerability, is of foremost importance. This article illustrates the results of the seismic hazard assessment of the archaeological site of Jam using both the probabilistic explanation (PSHA) and the deterministic explanation (DSHA) approaches. Uncertainty in...

Arun Menon

Papers

Probabilistic Seismic Hazard Macrozonation of Tamil Nadu in Southern India

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: I. Parametric Study

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: II. Formulation

Role of diaphragm flexibility modelling in seismic analysis of existing masonry structures

Seismic hazard assessment of the historical site of Jam in Afghanistan and stability analysis of the minaret