CHAPTER 1. INTRODUCTION 1.1 GENERAL Seismic hazard is defined as any physical phenomenon, such as ground shaking or ground failure, which is associated with an earthquake and that, may produce adverse effects on human activities. Many earthquakes in the past have given many lessons that still have to be learnt which are very essential to plan infrastructure and even to mitigate such calamities in future. Very preliminary process of reducing the effects of earthquake is by assessing the hazard itself. Till date Seismic hazard of the region has been represented in the form of zonation map. Seismic zonation is usually carried out in two parts, one at macro level and another at micro level. For a larger area like zonation of country or continent macro level is adopted. Macrozonation is carried out considering the seismicity, geology in larger scales without considering geotechnical aspects. But microzonation is carried out in smaller scale by considering regional seismicity, geology and local site conditions. Micro level zonations are becoming important for the cities and urban centers due to increasing population agglomeration in the cities, which result in rapid and unplanned constructions. The cities are more hazardous and high risk areas even for the moderate earthquakes. Seismic Microzonation is the first step to minimize seismic related loss of lives and damages. Microzonation has generally been recognized as the most accepted tool in seismic hazard assessment and risk evaluation and it is defined as the zonation with respect to ground motion characteristics taking into account the source and site conditions. Making improvements on the conventional macrozonation maps and regional hazard maps, microzonation of a region generate detailed maps that predict the hazard at much smaller scales. Seismic microzonation is the generic name for subdividing a region into individual areas having different potentials, hazardous earthquake effects, defining their specific seismic behavior for engineering design, land use and urban planning. The basic steps of seismic microzonation are to model the rupture mechanism at the source of an earthquake, evaluate the propagation of waves through the earth to the top of the bedrock, determine the effects of local soil profile and thus develop a surface hazard map indicating the vulnerability of the area to potential seismic hazards. Essentially microzonation is required to compile three essential components of seismology, geotechnical and structural engineering. Each component has to be dealt separately in detail and represent variation of the essential parameters and then compile in fashion to give final map for land use, city planning, disaster management and planning and post 3 earthquake relief work. Seismic Microzonation falls into the category of “applied research”. That is why it has to be upgraded and revised based on the latest information. Seismology component involves understating seismicity of region and compiling available geology data, deep geophysical data and earthquake data. Seismotectonic map has to be prepared to show seismic sources and with past earthquakes to depict seismology component. This is the base for seismic hazard analysis, where rock level hazard parameters in the form of spectral or peak ground acceleration are mapped. Second component consists of understanding geotechnical character of study area, estimating the modification of seismic waves and its induced effects. Basically this involves assessment of different effects due to seismic hazard identified in the seismology component. These two components will be dealt in detail and discussed with respect to the seismic zonation mapping. Third component involves assessment of damage potential of buildings in the region and cost assessment which are called as seismic vulnerability and risk assessment. SEISMIC ZONATION MAP OF INDIA Before 2002 (BIS, 1893-1970) 4 BIS, 2002 1.2 FACTORS AFFECTING SEISMIC HAZARD AT A LOCATION 1. Earthquake magnitude 2. The source-to-site distance 3. Earthquake rate of occurrence (return period) 4. Duration of ground shaking Earthquake Magnitude – The magnitude is a number that characterizes the relative size of an earthquake. Quantitative measure of its strength in terms of energy released at focus. It is a measure of the size of the earthquake source and is the same number no matter where we are or what the shaking feels like. Magnitudes can be based on any of the following: Ml - local magnitude is defined as the logarithm of the maximum trace amplitude recorded on a Wood-Anderson seismometer located 100km from the epicenter of the earthquake. The local magnitude is the best known magnitude scale, but it is not always the most appropriate scale for description of earthquake size. 5 2. Mb – Body wave magnitude is based on the longitudinal wave amplitude and their period. This magnitude scale becomes insensitive to the actual size of an earthquake for magnitudes of 6.4 or greater. 3. Ms - surface wave magnitude is based on the amplitude of maximum ground displacement caused by Rayleigh waves with a period of about 20 seconds and the epicentral distance of the seismometer measured in degrees. 4. Mw – Moment magnitude is bases on the seismic moment M0, which is a direct measure of the factors that produce rupture along the fault. This magnitude does not have an upper limit. Where Lf and Wf are the length and width of a fault area, Sf is the average slip on the fault during an earthquake in meters, μ is the shear modulus of the Earth crust. The source-to-site distance - Much of the energy released by rupture along a fault takes the form of stress waves. As stress waves travel away from the source of an earthquake, they spread out and are partially absorbed by the materials they travel through. As a result, the specific energy decreases with increasing distance from the source. The distance between the source of an earthquake and particular site can be interpreted in different ways. Earthquake rate of occurrence (return period) - A return period is an estimate of the interval of time between earthquakes. It is a statistical measurement denoting the average recurrence interval over an extended period of time, and is usually required for risk analysis. Duration of ground motion – The duration of ground motion is related to the time required for release of accumulated strain energy by rupture along the fault. As the length, or area, of fault rupture increases, the time required for rupture increases. As a result, the duration of ground motion increases with increasing earthquake magnitude. 1.3 REPRESENTATION OF SEISMIC HAZARD The seismic hazard can be expressed in different ways: from simple observed macroseismic fields, to seismostatistical calculations to analyse earthquake occurrences in time and space and assessing their dynamic effects in a certain site or region, to sophisticated seismogeological approaches to evaluating the maximum expected earthquake effects on the Earth surface. Representation of seismic hazard and ground motion includes 1) The selection and utilization of national ground motion maps; 2) The representation of site response effects; and 6 3) The possible incorporation of other parameters and effects, including energy or duration of ground motions, vertical ground motions, near source horizontal ground motions, and spatial variations of ground motions. Seismic hazard can be represented in different ways but most frequently in terms of values or probability distributions of accelerations, velocities, or Displacements of either bedrock or the ground surface. 1.4 SEISMIC HAZARD APPROACHES Two different seismic hazard maps have been generated, one using deterministic seismic microzonation map based on PGA from DSHA and another is the probabilistic seismic microzonation map based on PGA from PSHA. The major parameters used are PGA at rock level from deterministic and probabilistic approaches, site response parameters of amplification and predominant frequency, elevation levels to account topographical variation and factor of safety against liquefaction. In both the maps, only rock level PGA is changed and other parameters are kept similar. Deterministic Seismic Hazard Analysis:Deterministic Seismic Hazard Analysis (DSHA) is done for a particular earthquake, either assumed or realistic. The DSHA approach uses the known seismic sources sufficiently near the site and available historical seismic and geological data to generate discrete, singlevalued events or models of ground motion at the site. Typically one or more earthquakes are specified by magnitude and location with respect to the site. Usually the earthquakes are assumed to occur on the portion of the site closest to the site. The site ground motions are estimated deterministically, given the magnitude, source-to-site distance, and site condition. Probabilistic Seismic Hazard Analysis:Probabilistic seismic hazard analysis (PSHA) is the most widely used approach for the determination of seismic design loads for engineering structures. The use of probabilistic concept has allowed uncertainties in the size, location, and rate of recurrence of earthquakes and in the variation of ground motion characteristics with earthquake size and location to be explicitly considered for the evaluation of seismic hazard. In addition, PSHA provides a frame work in which these uncertainties can be identified, quantified and combined in a rational manner to provide a more complete picture of the seismic hazard. 7 1.5 METHOLOGY A general methodology in doing the seismic microzonation of a region can be divided into the following four major heads: 1. Estimation of the ground motion parameters using the historical seismicity and recorded earthquake motion data which includes the location of potential sources, magnitude, mechanism, epicentral distances. 2. Site characterization using geological, geomorphological, geophysical and geotechnical data. 3. Assessment of the local site effects which includes site amplification, predominant frequency, liquefaction hazard, landslides, tsunami etc. 4. Preparation of the seismic microzonation maps. 8 CHAPTER 2. LITERATURE REVIEW 2.1 SEISMIC RISK ANALYSIS Cornell (1968) introduces a method for the evaluation of the seismic risk of an engineering project. The method is based on the influence of all potential sources of earthquakes and the average activity rates. Arbitrary geographical relationships between the site and potential point, line, or areal sources can be modelled with computational ease. The results of this analysis presented in terms of ground motion parameter (such as peak acceleration) versus average return period. Gupta (2006) introduce Seismic hazard map for Northeast India based on the uniform hazard response spectra for absolute acceleration. This approach is free from regionalizing the seismotectonic sources to perform the hazard analysis. Also a developed a new attenuation model for pseudo-spectral velocity by using recorded accelerogram in Northeast India. The model is able to capture the frequency dependent variations in pseudo-spectral velocity (PSV), and properly accounts for the effects of earthquake magnitude, epicentral distance, and focal depth on the pseudo-spectral velocity (PSV) spectral shapes, for both horizontal and vertical motions. This analysis maps provide much more detailed and direct information about the seismic hazard. Malik (2006) carried out works to obtain seismic hazard and spectral strong ground motion on bed rock for the northeast Indian region using the complete and the extreme part of the earthquake catalogue. The region has been divided into four major seismogenic sources namely, the regional features in the Himalayas i.e., main boundary thrust and main central thrust, eastern syntaxis, shillong massif and the north south trending arakan yoma seismic belt. The seismic hazard is estimated for ten seismogenic zones which are further subdivisions of these four seismogenic sources based on the seismotectonics modeling of the area. The results of the probabilistic seismic hazard analysis may be used for the seismic microzonation and for earthquake engineering use. Kolathayar (2013) discussed seismic hazard analysis for the state of Tripura and Mizoram in North East India to evaluate the ground motion at bedrock level. It was done considering the available earthquake catalogs collected from different sources since 1731– 2010 within a distance of 500 km from the political boundaries of the states. Earthquake data were declustered to remove the foreshocks and aftershocks in time and space window and then statistical analysis is carried out for data completeness using the predictive ground motion equations given by Atkinson and Boore (Bull Seismol Soc Am 93:1703–1729, 2003) and Gupta (Soil Dyn Earthq Eng 30:368–377, 2010) for subduction belt. The results of this analysis were presented in the form of hazard curve, peak ground acceleration (PGA) and uniform hazard spectra. 9 2.2 MICROZONATION USING GIS APPROACH Nath (2004) introduced seismic ground motion hazard map in the Sikkim Himalaya with local and regional site conditions incorporated through geographic information system. The geological themes are united to form the basic condition coverage of the region. The seismological themes were assigned normalized weights and feature ranks following a pair-wise comparison hierarchical approach and later integrated to evolve the seismic hazard map. When geological and seismological layers are integrated together through GIS, microzonation map is prepared. The advantage of using GIS for seismic hazard mapping lies in its capability to calculate areas and lengths of geometric features. The hazard maps presented here may be useful for land use planning or for making hazard mitigation decisions. These maps are generally better representation of seismic hazard including site-specific analysis, and may be used for recognizing hazardous areas at a regional scale. The geologic site condition map is an initial model to describe areas that may exhibit different seismic shaking characteristics during future earthquakes. Pal (2007) prepared first order seismic microzonation map of Delhi using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types up to 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP). This study aimed at identifying tiny zones that would be vulnerable during earthquakes. Seismic microzonation is aimed for this reason.The seismic microzonation map thus generated will be of immense help for the Urban Development Authorities for planning of future construc-tion projects. It will also be of use for assessment of seismic risk to the existing construction, defense installation, heavy industry, and important structures like dams, nuclear power stations and other public utility services. Ganapathy (2011) produced first level seismic microzonation map of Chennai city in a GIS platform using the themes, Peak Ground Acceleration (PGA), Shear wave velocity at 3 m, Geology, Ground water fluctuation and bed rock depth. The near potential seismic sources were identified from the remote-sensing study and seismo-tectonic details from published literatures. The peak ground acceleration for these seismic sources were estimated based on the attenuation relationship. The analysis involved grid datasets (the discrete datasets from different themes were converted to grids) to compute the final seismic hazard grid through integration and weightage analysis of the source themes. The resultant map is useful information in construction planning of forthcoming buildings. Also it is helpful as a base material to identify seismic risk. 10 Manahiloh (2018) introduced Shear wave velocity and soil type microzonation using neural networks and geographic information system. A microzonation algorithm that combines neural networks (NNs) and geographic information system (GIS) is developed.In the field, standard penetration and downhole tests are conducted. Atterberg limit test and sieve analysis are performed on soil specimens retrieved during field-testing. The field and laboratory data are used as inputs, in the integrated NNs-GIS algorithm, for developing the microzonation of shear wave velocity and soil type of a selected site. The algorithm is equipped with the ability to automatically update the microzonation maps upon addition of new data.The approach could be adopted for microzonation of liquefaction potential, landslide risks, settlements, etc.The detailed soil condition maps generated with the proposed algorithm could be used in construction site selection, risk analysis, and geotechnical engineering designs. 2.3 MICROZONATION ASSESSMENT Ram (1997) discussed probabilistic assessment of Earthquake Hazards in the North-East Indian Peninsula and Hindukush Region. The probability of the occurrence of great earthquakes with magnitude greater than 7.0 during a specified interval of time was estimated on the basis of four probabilistic models, namely, Weibull, Gamma, Lognormal and Exponential for the NE Indian peninsula and Hindukush regions. The model parameters had been estimated by the method of Maximum Likelihood Estimates (MLE) and the Method of Moments (MOM). It should be mentioned that the result is related to the assumption that the process of earthquake occurrence is temporally stable. Sitharam (2014) described deterministic as well as probabilistic methods attempted for seismic hazard assessment of Tripura and Mizoram states at bedrock level condition. An updated earthquake catalogue is collected from various national and international seismological agencies. The homogenization, declustering and data completeness analysis of events have been carried out before hazard evaluation. Seismicity parameters have been estimated using G–R relationship for each source zone. Ground motion equations (Atkinson and Boore 2003; Gupta 2010) were validated with the observed PGA (peak ground acceleration) values before use in the hazard evaluation. Results are presented in the form of PGA using both DSHA (deterministic seismic hazard analysis) and PSHA (probabilistic seismic hazard analysis) with 2 and 10% probability of exceedance in 50 years, and spectral acceleration (T = 0. 2 s, 1.0 s) for both the states (2% probability of exceedance in 50 years). The hazard map developed using both the methods (DSHA and PSHA) provide a clear idea about the measure of variability or degree of uncertainty/errors involved in the estimated hazard values for a location in a quantitative manner/form. These maps can be used as a direct input in site response study to know the surface level hazard. These maps also provide useful information for other purposes, such as estimation of earthquake 11 insurance premium, identifying most vulnerable locations and selection of an appropriate location for important infrastructure and the most possible severe locations for detailed site specific evaluation of seismic hazards. The seismic hazard analysis presented here is an important step towards an accurate evaluation of seismic hazard potential in the area. Gandhi (2018) had given a methodoly to estimate the effect of soil on ground motion and to estimate the strong ground motion parameters at surface, soil modeling and the ground response analysis have been conducted along uniformly distributed boreholes drilled up to a depth of 50 m. The methodology is divided into three parts (i) Estimation of depth of Engineering Bed layer (EBL) (a layer with a shear wave velocity 400 m/ s≤Vs≤750 m/s, N value>80 and minimum soil variation below it) through soil modeling, (ii) Estimation of Ground Motion at EBL due to scenario earthquake at nearby active fault and (iii) Estimation of surface strong ground motion using 1D ground response analysis through SHAKE 2000 program. 2.4 MICROZONATION USING GEO-TECHNICAL METHODS Nakamura (1989) describe a new processing method that employ microtremor observation yet producing accurate estimation of characteristic of ground motion, investigation with boring. The method used vertical component and horizontal component. The method is based on the assumption that the ratio of horizontal and vertical spectra of surface treamor as an appropriate transfer function. The method can supplement the boring investigation results for proper and minute estimation of the characteristic of surface layer and it is expected to demonstrate validity in collection of fundamental data for estimation of detailed earthquake damage. Tokimatsu (2005) introduced a methodology for estimating the S-wave velocity profile of subsurface soils using both microtremor dispersion curve and H/V spectrum. In the inversion, both microtremor dispersion and H/V data are assumed to be the Rayleighwave dispersion curve and the surface (both Rayleigh and Love) wave H/V spectrum that have been theoretically derived by taking into account the effects of their fundamental and higher modes. Sensitivity analyses indicate that the surface-wave H/V ratio is sensitive to the bedrock VS structure more than the Rayleigh-wave phase velocity, confirming that the proposed joint inversion including H/V spectrum is promising. Boulanger (2006) discussed Semi-empirical procedures for evaluating the liquefaction potential of saturated cohesion less soils during earthquakes.The stress reduction factor (rd), earthquake magnitude scaling factor for cyclic stress ratios (MSF), overburden correction factor for cyclic stress ratios (Ks), and the overburden normalization factor for penetration resistances (CN) are discussed and modified relations are presented. These modified relations are used in re-evaluations of the SPT and CPT case history databases. Based on these re-evaluations, revised SPT- and CPT-based liquefaction correlations are recommended for use in practice. The reliability of any liquefaction evaluation depends directly on the quality of the site 12 characterization, including the quality (and not necessarily the quantity) of the in situ and laboratory test data. The importance of quality field and laboratory work cannot be overstated. Anbazhagan (2010) carried out the liquefaction potential analysis to estimate the liquefaction return period. The entire range of peak ground acceleration (PGA) and earthquake magnitudes was used in the evaluation of liquefaction return period. The seismic hazard analysis was done using probabilistic approach to evaluate the peak horizontal acceleration at bed rock level. The soil resistance for the area was characterized using the standard penetration test (SPT) values obtained from boreholes. These SPT data along with the PGA values obtained from the probabilistic seismic hazard analysis were used to evaluate the liquefaction return period for the area. The entire process of liquefaction potential evaluation, starting from collection of earthquake data, identifying the seismic sources, evaluation of seismic hazard and the assessment of liquefaction return period were carried out, and the entire analysis was done based on the probabilistic approach. Das (2018) carried out the liquefaction potential of Agartala City in Northeast India. The evaluation liquefaction potential are obtained using borehole SPT data were collected from geotechnical consultancy. Dynamic properties of soil are determined using SPT data. The cyclic shear stress of the soil layers are estimated considering the peak surface ground acceleration 0.36g. Idriss and Boulanger (2010)and Boulanger and Idriss (2015 and 2014) methodology are adopted to identify the liquefaction potential in terms of factor of safety and probability. The results are presented in maps on Geographical Information System (GIS) platform using the QGIS software. The liquefaction potential maps are much useful for the professional engineers, government agencies and disaster management authorities for future development and planning of the city against liquefaction failure. 13 CHAPTER 3. OBJECTIVES AND SCOPE SCOPE • Providing useful information for land use planning. • Providing basic seismic hazard information for regional damage potential estimate. • Providing information on site effects to be accounted for, in design of new structure. OBJECTIVE • • To define seismic actions for designing or improving the resistance of structure such as building, bridges and plants, To plan land use so as to reduce the level of hazard. 14 CHAPTER 4. CONCLUSION This report is prepared aiming towards the analysis of seismic microzonation. The seismic hazard analysis may be used for the seismic microzonation and for earthquake engineering use. It will also be of use for assessment of seismic risk to the existing construction, defence installation, heavy industry, and important structures like dams, nuclear power stations and other public utility services. Based on the literature study a summary has been framed. 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