Structural health monitoring (SHM) systems is a relatively new discipline, studying the structural condition of buildings and other constructions. Current SHM systems are either wired or wireless, with a relatively high cost and low accuracy. This thesis exploits a blend of digital signal processing methodologies, for structural health monitoring (SHM) and develops a wireless SHM system in order to provide a low cost implementation yet reliable and robust. Existing technologies of wired and wireless sensor network platforms with high sensitivity accelerometers are combined, in order to create a system for monitoring the structural characteristics of buildings very economically and functionally, so that it can be easily implemented at low cost in buildings. Well-known and established statistical time series methods are applied to SHM data collected from real concrete structures subjected to earthquake excitation and their strong and weak points are investigated. The necessity to combine parametric and non-parametric approaches is justified and to this direction novel and improved digital signal processing techniques and indexes are applied to vibration data recordings, in order to eliminate noise and reveal structural properties and characteristics of the buildings under study, that deteriorate due to environmental, seismic or anthropogenic impact. A characteristic and potential harming specific case study is presented, where consequences to structures due to a strong earthquake of magnitude 6.4 M are investigated. Furthermore, is introduced a seismic influence profile of the buildings under study related to the seismic sources that exist in the broad region of study.

Planet earth is restless and one cannot control its inside activities and vibrations those leading to natural hazards. Earthquake is one of such natural hazards that have affected the mankind most. Most of the causalities due to earthquakes happened not because of earthquakes as such, but because of poorly designed structures which could not withstand the earthquake forces. The improper building construction techniques adopted and the high population density are the major causes of the heavy damage due to earthquakes. The damage due to earthquakes can be reduced by following proper construction techniques, taking into consideration of appropriate forces on the structure that can be caused due to future earthquakes. The steps towards seismic hazard evaluation are very essential to estimate an optimal and reliable value of possible earthquake ground motion during a specific time period. These predicted values can be an input to assess the seismic vulnerability of an area based on which new construction and the restoration works of existing structures can be carried out. A large number of devastating earthquakes have occurred in India in the past. The northern region of India, which is along the plate boundary of the Indian plate with the Eurasian plate, is seismically very active. The north eastern movement of Indian plate has caused deformation in the Himalayan region, Tibet and the North Eastern India. Along the Himalayan belt, the Indian and Eurasian plates converge at the rate of about 50 mm/year (Bilham 2004; Jade 2004). The North East Indian (NEI) region is known as one of the most seismically active regions in the world. However the peninsular India, which is far away from the plate boundary, is a stable continental region, which is considered to be of moderate seismic activity. Even though, the activity is considered to be moderate in the Peninsular India, world’s deadliest earthquake occurred in this region (Bhuj earthquake 2001). The rapid drifting of Indian plate towards Himalayas in the north east direction with a high velocity along with its low plate thickness might be the cause of high seismicity of the Indian region. Bureau of Indian Standard has published a seismic zonation map in 1962 and revised it in 1966, 1970, 1984 and 2002. The latest version of the seismic zoning map of India assigns four levels of seismicity for the entire Country in terms of different zone factors. The main drawback of the seismic zonation code of India (BIS-1893, 2002) is that, it is based on the past seismic activity and not based on a scientific seismic hazard analysis. Several seismic hazard studies, which were taken up in the recent years, have shown that the hazard values given by BIS-1893 (2002) need to be revised (Raghu Kanth and Iyengar 2006; Vipin et al. 2009; Mahajan et al. 2009 etc.). These facts necessitate a comprehensive study for evaluating the seismic hazard of India and development of a seismic zonation map of India based on the Peak Ground Acceleration (PGA) values. The objective of this thesis is to estimate the seismic hazard of entire India using updated seismicity data based on the latest and different methodologies. The major outcomes of the thesis can be summarized as follows. An updated earthquake catalog that is uniform in moment magnitude, has been prepared for India and adjoining areas for the period till 2010. Region specific magnitude scaling relations have been established for the study region, which facilitated the generation of a homogenous earthquake catalog. By carefully converting the original magnitudes to unified MW magnitudes, we have removed a major obstacle for consistent assessment of seismic hazards in India. The earthquake catalog was declustered to remove the aftershocks and foreshocks. Out of 203448 events in the raw catalog, 75.3% were found to be dependent events and remaining 50317 events were identified as main shocks of which 27146 events were of MW ≥ 4. The completeness analysis of the catalog was carried out to estimate completeness periods of different magnitude ranges. The earthquake catalog containing the details of the earthquake events until 2010 is uploaded in the website the catalog was carried out to estimate completeness periods of different magnitude ranges. The earthquake catalog containing the details of the earthquake events until 2010 is uploaded in the website the catalog was carried out to estimate completeness periods of different magnitude ranges. The earthquake catalog containing the details of the earthquake events until 2010 is uploaded in the website A quantitative study of the spatial distribution of the seismicity rate across India and its vicinity has been performed. The lower b values obtained in shield regions imply that the energy released in these regions is mostly from large magnitude events. The b value of northeast India and Andaman Nicobar region is around unity which implies that the energy released is compatible for both smaller and larger events. The effect of aftershocks in the seismicity parameters was also studied. Maximum likelihood estimations of the b value from the raw and declustered earthquake catalogs show significant changes leading to a larger proportion of low magnitude events as foreshocks and aftershocks. The inclusions of dependent events in the catalog affect the relative abundance of low and high magnitude earthquakes. Thus, greater inclusion of dependent events leads to higher b values and higher activity rate. Hence, the seismicity parameters obtained from the declustered catalog is valid as they tend to follow a Poisson distribution. Mmax does not significantly change, since it depends on the largest observed magnitude rather than the inclusion of dependent events (foreshocks and aftershocks). The spatial variation of the seismicity parameters can be used as a base to identify regions of similar characteristics and to delineate regional seismic source zones. Further, Regions of similar seismicity characteristics were identified based on fault alignment, earthquake event distribution and spatial variation of seismicity parameters. 104 regional seismic source zones were delineated which are inevitable input to seismic hazard analysis. Separate subsets of the catalog were created for each of these zones and seismicity analysis was done for each zone after estimating the cutoff magnitude. The frequency magnitude distribution plots of all the source zones can be found at http://civil.iisc.ernet.in/~sitharam . There is considerable variation in seismicity parameters and magnitude of completeness across the study area. The b values for various regions vary from a lower value of 0.5 to a higher value of 1.5. The a value for different zones vary from a lower value of 2 to a higher value of 10. The analysis of seismicity parameters shows that there is considerable difference in the earthquake recurrence rate and Mmax in India. The coordinates of these source zones and the seismicity parameters a, b & Mmax estimated can be directly input into the Probabilistic seismic hazard analysis. The seismic hazard evaluation of the Indian landmass based on a state-of-the art Probabilistic Seismic Hazard Analysis (PSHA) study has been performed using the classical Cornell–McGuire approach with different source models and attenuation relations. The most recent knowledge of seismic activity in the region has been used to evaluate the hazard incorporating uncertainty associated with different modeling parameters as well as spatial and temporal uncertainties. The PSHA has been performed with currently available data and their best possible scientific interpretation using an appropriate instrument such as the logic tree to explicitly account for epistemic uncertainty by considering alternative models (source models, maximum magnitude in hazard computations, and ground-motion attenuation relationships). The hazard maps have been produced for horizontal ground motion at bedrock level (Shear wave velocity ≥ 3.6 km/s) and compared with the earlier studies like Bhatia et al., 1999 (India and adjoining areas); Seeber et al, 1999 (Maharashtra state); Jaiswal and Sinha, 2007 (Peninsular India); Sitharam and Vipin, 2011 (South India); Menon et al., 2010 (Tamilnadu). It was observed that the seismic hazard is moderate in Peninsular shield (except the Kutch region of Gujarat), but the hazard in the North and Northeast India and Andaman-Nicobar region is very high. The ground motion predicted from the present study will not only give hazard values for design of structures, but also will help in deciding the locations of important structures such as nuclear power plants. The evaluation of surface level PGA values is of very high importance in the engineering design. The surface level PGA values were evaluated for the entire study area for four NEHRP site classes using appropriate amplification factors. If the site class at any location in the study area is known, then the ground level PGA values can be obtained from the respective map. In the absence of VS30 values, the site classes can be identified based on local geological conditions. Thus this method provides a simplified methodology for evaluating the surface level PGA values. The evaluation of PGA values for different site classes were evaluated based on the PGA values obtained from the DSHA and PSHA. This thesis also presents VS30 characterization of entire country based on the topographic gradient using existing correlations. Further, surface level PGA contour map was developed based on the same. Liquefaction is the conversion of formally stable cohesionless soils to a fluid mass, due to increase in pore pressure and is prominent in areas that have groundwater near the surface and sandy soil. Soil liquefaction has been observed during the earthquakes because of the sudden dynamic earthquake load, which in turn increases the pore pressure. The evaluation of liquefaction potential involves evaluation of earthquake loading and evaluation of soil resistance to liquefaction. In the present work, the spatial variation of the SPT value required to prevent liquefaction has been estimated using a probabilistic methodology, for entire India. To summarize, the major contribution of this thesis are the development of region specific magnitude correlations suitable for Indian subcontinent and an updated homogeneous earthquake catalog for India that is uniform in moment magnitude scale. The delineation and characterization of regional seismic source zones for a vast country like India is a unique contribution, which requires reasonable observation and engineering judgement. Considering complex seismotectonic set up of the country, the present work employed numerous methodologies (DSHA and PSHA) in analyzing the seismic hazard using appropriate instrument such as the logic tree to explicitly account for epistemic uncertainties considering alternative models (For Source model, Mmax estimation and Ground motion prediction equations) to estimate the PGA value at bedrock level. Further, VS30 characterization of India was done based on the topographic gradient, as a first level approach, which facilitated the development of surface level PGA map for entire country using appropriate amplification factors. Above factors make the present work very unique and comprehensive touching various aspects of seismic hazard. It is hoped that the methodology and outcomes presented in this thesis will be beneficial to practicing engineers and researchers working in the area of seismology and geotechnical engineering in particular and to the society as a whole.

Local site conditions are known to influence ground motion during earthquake events and increase the severity of damage. Data from earthquakes are useful to study the response but they are available only from active regions. Ubiquitous ambient vibrations on the other hand offer a more practical approach to quantify site responses. This thesis explores the use of various methods for obtaining site responses. The primary area of study is the Kachchh rift basin, NW India, a Mesozoic rift that features significant lateral variations in surface geology and has experienced ground responses during 1819 and 2001 earthquakes. The Mw 7.6, 2001 event was followed by hundreds of aftershocks, which were recorded by temporary networks. In this study we have used earthquake signals as well as ambient vibrations to understand site response in various parts of the basin. In addition we have collected data from a few sites from the Indo-Gangetic plains and Kathmandu valley, both affected by large earthquakes, 1934 the M ~ 8 (Bihar) and 2015, Mw 7.8 (Nepal). Velocity and acceleration records from a network of eight stations in the Kachchh Rift were used to evaluate site responses using Standard Spectral Ratio (SSR) and Horizontal to Vertical spectral ratio (HVSR-E) methods. Ambient vibrations were analyzed following Nakamura’s H/V method (HVSR-AV), for data collected from 110 sites that represent different field conditions within the Kachchh Rift. Fundamental resonance frequency (f0) varied between 0.12 – 2.30 Hz, while the amplification factor (A0) was in the range of 2.0 – 9.1. We found that higher A0 and liquefaction index (Kg) values were mostly associated with higher liquefaction potential. Using a close network of stations, we studied the role of site response in damage to the Bhuj city that suffered maximum damage in 2001; our results suggest that site response was not a significant factor. Studies based on passive data were complemented by Multi-channel Analysis of Surface Waves (MASW) to map shear wave velocities of the various subsurface units up to depths of 10m (Vs10) and 30m (Vs30). Our results imply average Vs could be a good proxy to characterize site amplifications where sediment thicknesses are shallow. Power law relationship between f0 and thickness (h) suggest a strong positive correlation (r = 0.89) adding credence to HVSR-AV method, making it a cost-effective alternative to MASW to infer site conditions. Further, to understand the influence of topography on site effects, we analyzed data from hills, valleys and their edges, both from the Kachchh rift and Kathmandu valley. Sites on the edges of valleys showed multiple, fuzzy peaks in the low frequency range (< 1 Hz) and broad peaks attributable to sites prone to higher damage. Spectrograms generated through Huang-Hilbert Transforms (HHT) suggested focusing of energy in narrow frequency bands on the edges, while valleys tend to scatter energy over wide frequencies. Although our current results are based on limited observations, we recognize spectral analysis as a powerful tool to quantify site effects in regions with significant topography. It is known that coseismic liquefaction could lead to nonlinear behavior wherein the near-surface soil layer loses its shear strength, causing a reduction of its fundamental resonance frequency. We used data from selected sites of coseismic liquefaction to highlight the significance of nonlinear effects in site response. Earthquake signals and ambient vibrations from Umedpur, a region that experienced intense liquefaction during 2001 were used in this analysis. Here we followed an empirical decomposition method based on HHT and signals were decomposed as many intrinsic mode functions (IMFs) that showed characteristic peaks for events of various values of PGAs. Thus, the first IMF for events with relatively higher PGAs (0.03g) showed distinct peaks for the S wave coda part, which were not noted for those with lower PGA (0.01g). These observations in a region of coseismic liquefaction are useful in developing models for quantifying nonlinear behavior. In conclusion, site response studies using different types of data and processing techniques in regions affected by recent earthquakes brings out the scope and limitations of each of these sets of data and techniques. This study suggests that ambient vibrations provide reasonable estimates of site response and can be reliably used in regions where earthquake data are not available.