Based on the analytical and numerical solutions as well as unexpected observed damages to the buildings and long-span structures in the epicentral zone of large shallow earthquakes, structural engineers have concluded that coseismic vertical ground motion play a major role in the damages. Recent researches have revealed the generation of high frequency Rayleigh wave with large amplitude in the epicentral zone of shallow earthquakes. Further, there is meta-response of a building at its longitudinal resonance frequency as compared to flexural resonance frequency during interaction with the Rayleigh waves. This paper presents the physics behind Rayleigh wave generation in the homogeneous half-space due to an incident SV-wave at the free surface and numerical quantification of variation of dominant frequency and spectral amplitudes of the generated Rayleigh waves with focal depth, Poisson's ratio and the rise-time of the point earthquake. It is concluded that the coupling of evanescence P-wave with the critically reflected SV-wave at/just after the critical point generates Rayleigh waves. Further, generation process is not immediate just after the critical point, but, it occurs over a span at least equal to one wavelength. A relation is established between depth of point earthquake and dominant wavelength of Rayleigh wave and this relation is unaffected by the change of Poisson’s ratio, rise-time and depth of point earthquake source. There is an exponential decrease of percentage conversion of the critically incident SV-wave energy in to the Rayleigh wave energy with an increase of focal-depth. Further, this percentage conversion increases with decrease of Poisson’s ratio and an increase of rise-time of the earthquake.

The paper presents quantification of site-city-interaction (SCI) effects on buildings and free-field motion under earthquake loading. The obtained reduction in the response of buildings in wide bandwidth conflicts with the reported splitting of the bandwidth of fundamental frequency in past SCI studies, which used a simple plane wave-front. However, the achieved reduction in fundamental-frequency and free-field motion corroborates with past studies. Obtained largest SCI effect was highly dependent on building type, city, and basin-heterogeneity in contrast to general perception. It is recommended that city should be homogeneous and fundamental-frequency of buildings should be less than 1.4 times to that of basin and buildings should preferably be of steel.

This paper presents the physics based ground motion synthetics and its earthquake engineering consequences in the National Capital Territory (NCT) Delhi, India due to the Mw8.2 scenario earthquake on the Nahan segment of the western Himalaya. In order to fulfill the aim, a state-of-the-art pseudo-dynamic rupture is implemented in a 3D fourth-order staggered-grid viscoelastic time-domain finite-difference code. The ground motion is simulated in a frequency bandwidth of 0–2.5 Hz at the basement level at 158 locations of the NCT Delhi. The computed transverse component of velocity time series at the basement level is numerically transferred to the free surface taking into account the rheological parameters of the sediment deposit. Upon first inspection, the estimated range of peak ground acceleration, between 0.017–0.12 g, indicates that all the buildings in the NCT Delhi will remain safe in the event of an Mw8.2 Nahan earthquake, provided they are constructed in accordance with Indian building codes. But, the computed acceleration response spectra (Sa) depicts that some of the high-rise buildings of the NCT Delhi may suffer minor damage to collapse under partial or complete double resonance condition due to Sa exceeding the DBE and MCE levels. The obtained range of pseudo-spectral displacements (Sd) reveals the need of performance-based design for high-rise buildings in the NCT Delhi, so that they can withstand under partial or complete double resonance condition during the occurrence of Nahan earthquakes. The developed contour maps of Sa and Sd at different periods can be used for the retrofitting and forced-based and displacement-based designs of the high-rise buildings.

The paper presents the response of cluster of buildings located on soft sediment in double resonance situation. In order to comprehend the influence of Site-city interaction on the response of the buildings, two symmetrical models–Cluster 1 (9 buildings) and Cluster 2 (25 buildings) situated on trapezoidal shaped basin are simulated using Finite Difference algorithm. The analysis of FDM simulation for 3D SCI reveals a reduction in spectral amplitude at natural frequency of building which increases with the number of buildings. The reduction of spectral amplitude is of the order of 65% in the case of cluster 2 with 25 buildings as compared to standalone building located at the center of closed 3D trapezoidal basin. The S-wave response of buildings shows much larger value of spectral amplitude (approx. 180) for standalone building for 3D analysis in comparison with that of 2D analysis for SH and SV-wave and also there is larger reduction of Spectral Amplification Factor (SAF) at fundamental frequency with the splitting of bandwidth for both Cluster 1 and Cluster 2. These findings call for the urgent need of 3D Site-City Interaction studies in urban environment in development of the seismic resilient and sustainable city.

This paper presents the effects of randomization of slip and the parameters of source time function on the pseudo-dynamically simulated ground motion characteristics. In the case of numerical simulations, the radiation of seismic energy from the rupture plane as per Brune’s model as well as to avoid the coherency effects is a challenging job for the simulators. The randomization of slip, rise time, and peak time of the source time function and the rupture arrival time, as well as the incorporation of fault roughness and damage zone, play important roles in seismic energy release from the rupture plane as well as in the reduction of coherency effects on the high-frequency seismic radiations. Inversion of earthquake data or statistical analysis of dynamic rupture simulations is used to estimate the slip distribution. The statistical approach assumes that the earthquake slip follows a random distribution on the fault plane. The simulation of pseudo-dynamic ground motion has been carried out using a fourth-order accurate staggered-grid time-domain 3D finite sdifference method. The ground motions are simulated taking ten different slip patterns for a hypothetical strike-slip Mw 6.0 earthquake. In addition, for each slip pattern, a stochastic perturbation in the parameters of the source time function is introduced. The simulated results have been analyzed based upon some important parameters such as arias intensity, peak ground acceleration, peak ground velocity, and peak ground displacement. Considerable variation in the computed values for the aforesaid parameters is obtained with the change of slip patterns and parameters of the STF. A good match of the computed average pseudo-spectral acceleration (PSA) using the simulated ground motion with that obtained using NGA West2 GMPEs is obtained in the frequency range 0.1–5.0 Hz and at an epicentral distance of 11 km.

<p>This paper presents the effects of 3D conical topography on the pseudo-dynamically simulated ground motion characteristics. The simulation of pseudo-dynamic ground motion has been carried out using a fourth-order accurate staggered-grid time-domain 3D finite-difference method. In the case of numerical simulations, the radiation of seismic energy from the rupture plane as per Brune’s model as well as avoiding the coherency effects is a challenging job for the simulators. The randomization of slip, rise-time, and peak-time of the source time function and the rupture arrival time, as well as the incorporation of fault-roughness and damage zone, play important roles in seismic energy release from the rupture plane as well as in the reduction of currency effects on the high-frequency seismic radiations. Firstly, the ground motions have been simulated for a hypothetical strike-slip Mw 6.0 earthquake. The efficacy of the presented code has been validated with a good match of the computed average pseudo-spectral acceleration (PSA) using the simulated ground motion with that obtained using NGA-West2 GMPEs in the frequency range 0.1–5.0 Hz. The code has been able to correctly incorporate the rupture directivity effect. Further, the effect of 3D conical topography has been estimated with azimuthal coverage of receivers. The effect of the direction of the source on the topographic amplification has also been estimated. It has been observed that topography plays an important role in the amplification of earthquake ground motion. Also, the direction of the source plays an important role in estimating the pattern of topographic amplification.</p>

Earthquake engineers continually face challenges in how to implement ridge/hill amplification to transfer predicted peak horizontal acceleration (PHA) near the base using a ground motion prediction equation (GMPE) to the desired location on the ridge to compute the design forces. There are very few relations available for the prediction of 2D ridge amplification only, irrespective of geometry. This paper presents the development of relationships for the prediction of ridge amplification based on the numerically simulated seismic responses of the 2D triangular and elliptical and 3D conical and ellipsoidal ridge models for different shape ratios. The variation in ridge effects with the change of azimuth of a site on a hill is also considered in the development of relationships. The analysis of simulated results revealed very large amplitude and spectral amplifications as well as average spectral amplifications (ASA) in the case of 3D ridges as compared to the corresponding 2D ridges. An increase in ridge amplification with an increase in shape ratio is observed for both the 2D and 3D ridge models. An increase in the fundamental frequency of ridges with an increase in shape ratio is observed for a particular width. The analysis of snapshots of the seismic wave field reveals the need for computation of amplitude amplification and associated strain within the hill mass for a tunnel design. It is concluded that the estimated ridge amplification using earthquake records and standard spectral ratio method gives an overestimate due to the de-amplification at the reference station as well as a false fundamental frequency. The developed relations for the 2D and 3D ridges predict amplitude amplification as well as ASA for a particular value of normalised elevation and shape ratio. These relations can be conservatively used by the field earthquake engineer to predict the PHA at any location on a hill (taking into account the dimensionality and shape of the real hill mass), if the same is available at the base of that hill mass using a GMPE.

This paper quantifies the impact of ridge-weathering on the simulation of ground motion across 2D and 3D topographical models. The models are excited with plane wave-fronts of Gabor wavelet. The seismic responses of a 3D ellipsoidal ridge topography having shape ratio 1.0 and one of its cross-Sect. (2D model) are simulated for different thickness and velocity of weathered layer. The SH- and SV-waves responses of a 2D cross-section of 3D topography are computed to understand the effect of dimensionality on the amplification pattern. The analysis of simulated responses reveals very large spectral amplifications and ASA in the case of 3D topography as compared to 2D. An increase of weathering effect on ground motion is inferred with an increase of weathering-thickness and a decrease of weathering velocity. A considerable variation of topography amplification with elevation is obtained. Finally, it is concluded that the shape of ridge topography and rheological parameters of the weathering layer should be taken in to account for the quantification of topographical effects on the ground motion characteristics.

Tehri dam with a height of 260.5 m is the highest earth and rock fill dam in India. It is situated on the confluence of the Bhagirathi and the Bhilangana rivers in the Garhwal Himalaya and located in the highly strained region of the north-western Himalaya. The region around Tehri dam lies in zone IV and V as per the seismic zoning map of India where the 1991 Uttarkashi earthquake Mb ~ 6.6 and the 1999 Chamoli earthquake Mb ~ 6.4 have occurred. The local seismicity in the environs of Tehri dam is being monitored for last more than two and half decades. For this purpose, a local seismological network was deployed by the Department of Earthquake Engineering in September 1993 under the scheme of Department of Science and Technology (DST). The network has been upgraded time to time. Presently, 18 stations of state-of-the-art seismological network is being operated around Tehri dam reservoir area. The spatial variation of local seismicity follows the trend of surface trace of MCT in the Garhwal Lesser Himalaya. The focal depth distribution of seismic events along and across the strike direction of the regional tectonic features reveal the confinement of activity within 10 to 15 km. In the present paper, attributes of local seismicity for more than two and half decades have been presented for Tehri dam. In addition, the changes in seismicity due to dam reservoir as a part of reservoir-induced seismicity (RIS) has been studied and no correlation of seismicity activity with the dam reservoir filling has been observed even after about seventeen years filling/drawdown of dam reservoir.

The paper presents implementation of state-of-the-art pseudo-dynamic rupture in a 3D viscoelastic fourth-order staggered-grid time-domain finite-difference code for the physics-based broadband strong ground motion synthetics. The achieved quantitative improvements in the efficacy of the considered reference pseudo-dynamic rupture model (comprising of random distribution of slip, rake, rise-time of source time function, peak-time as 0.13 times rise-time and rupture arrival time) after the explicit addition of damage zone, fault-roughness and perturbation to the peak-time are highly stimulating in proficient broadband seismic energy radiation and reduction of coherency effects on the high frequency radiations. A final pseudo-dynamic rupture model is implemented with random distribution of all the source parameters along with damage-zone and fault-roughness. An excellent match of the computed pseudo-spectral acceleration using the simulated ground motion by means of the final pseudo-dynamic rupture model with that obtained using NGA-West2 GMPEs for a hypothetical Mw6.5 strike-slip earthquake validates the efficiency of final implemented rupture model. Further, the obtained average of spectral ratio of fault normal and fault parallel ground motions of the order 1.28 (around 1.0) for frequencies 0.8–10 Hz reflects the efficacy to reduce the coherency effect on the high frequency radiations. The observed good match of the simulated ground motion due to the 2004 (Mw6) Parkfield, California earthquake with the earthquake records on rock further validates the efficiency of the implemented final-pseudo-dynamic rupture model in the 3D finite-difference code.

Transient stability analysis is emerging as one of the most critical evaluations in the electrical power grid for assuring stability of the system and the ability to sustain major disturbances. To reduce the impact of faults in the grid and to ensure transient stability, faults must be cleared within the critical clearing time. For this purpose a rapid response of the protection system is required in order to clear the faults in the system. The dynamic simulation is carried out to examine transient stability aspects based on terminal voltage, machine rotor angle, and output electrical power, with application of different types of faults. The paper provides a case study by considering actual Mumbai grid with equivalents of neighbouring system provides glimpse into various aspects of studies to determine critical clearing time of large power grids using PSS/E software.

This paper presents the quantification of the role of structural parameters and impedance contrast in the insulation and meta-capacity of a city for Rayleigh waves at an earthquake engineering scale. The feasibility of developing heterogeneous and homogeneous meta-cities in a soft sediment deposit is investigated using the meta-behavior of structures and meta-blocks in the epicentral zone of shallow crustal earthquakes. The Rayleigh wave and horizontally propagating plane SH-wave responses of the city with different structural parameters and impedance contrast are simulated at the top of the structure as well as at the free field after crossing the city. It is concluded that the structures act as a meta-structure for the Rayleigh waves but not for the Love waves, and the meta-capacity of the city increases with the increase in the number and stiffness of structures and decrease in damping and impedance contrast. An increase in the width of bandgaps at different longitudinal modes of vibration of structures is obtained with a decrease in impedance contrast, particularly when it is less than 15. It is concluded that meta-blocks can be developed using appropriate ceramic material considering the half-space impedance to develop a desired bandgap for Rayleigh waves. Based on the obtained increase in the city's insulation capacity for Rayleigh waves with the increase in the number and width of structures and decrease in impedance contrast, it is recommended that engineers consider the urban layer as lying in the path of Rayleigh waves for the estimation of seismic hazard in the epicentral zone of shallow crustal earthquakes.

This paper presents numerical quantification of depth-dependent free surface effect on ground motion characteristics for the earthquake-resistant design of underground structures. The SH-wave responses of homogeneous half-space model are computed on the vertical arrays using different central frequency in the Gabor wavelet for various angles of incidence. The analysis of simulated results reveals that the obtained free surface effect at the free surface as 2.0 is not affected by the angle of incidence and the magnitude of earthquake. On the other hand, depth-dependent free surface effect in homogeneous half-space depends on both the magnitude of the earthquake and the angle of incidence. However, in the case of layered earth model, it is conservatively concluded that the free surface effect almost linearly decreases from 2 at the free surface to 1 at a depth equal to one-eighth of wavelength of the corner frequency of earthquake. It is recommended to transfer the predicted peak ground acceleration at the free surface to the desired depth using a linear reduction factor from 1.0 at free surface to 2.0 at a depth equal to one-eighth of the wavelength of the corner frequency of the postulated earthquake for economical earthquake resistant design of the underground structures.

A deterministic seismic microzonation of the NCT Delhi (The capital of INDIA) and its earthquake engineering implications is presented in this paper. The NCT Delhi with population density around 21,000/sq. Km has experienced several severe earthquake shakings in the past due to earthquake occurrences in its vicinity and in the Great Himalaya. The exposed central quartzite ridge, Badarpur-Okhala hillocks and River-Yamuna are responsible for the very large spatial variation of sediment thickness (10 m to more than 300 m) in the NCT Delhi. The dynamic properties of sediment layers over the quartzite basement at 158 sites, well distributed in the NCT Delhi, are considered for seismic microzonation. First, we have finalised the maximum credible earthquake (MCE) for each considered site based on the deterministic seismic hazard analysis. Thereafter, acceleration time history at basement level is computed at each site using stochastic finite-fault method with dynamic corner frequency and the geometry as well as rupture-dimension of the respective MCE. The basement ground motion is numerically transferred to the free surface using the rheological parameters and thickness of sediment layers overlying the quartzite basement. Different maps of earthquake engineering interest like peak ground acceleration (PGA), peak ground velocity (PGV) and peak ground displacement (PGV) at basement level and the free surface level are developed and analysed for earthquake implications. The obtained range of PGA (0.08-0.30g), PGV (3.34-26.58cm/s) and PGD (0.55-7.2cm) at the free surface and fundamental frequency of the sediment deposit (0.4-7.0Hz) reveals that the NCT Delhi needs special attention by the planners, engineers and decision makers for earthquake disaster preparedness.

The paper presents the quantification of site-city-interaction (SCI) effects on the responses of buildings of a city and free field motion under realistic earthquake loading for the economic development of a smart city. The state of the art pseudo-dynamic earthquake rupture is implemented in the existing fourth-order viscoelastic staggered-grid SH-wave finite-difference program, and simulated results validated. SH-wave responses of various homogeneous and heterogeneous cities situated on horizontal sediment layer as well as in 2D heterogeneous basins are simulated and analyzed for different dynamic parameters of the buildings. The simulated SCI effects using realistic earthquake loading reveals a reduction of transfer function (TF) of buildings in a wide frequency bandwidth. This finding is conflicting with the reported splitting of bandwidth of the F o SB in the past SCI studies, carried out using simple plane incident wave-front with a single zero-phase wavelet. The obtained largest SCI effects on a building was highly dependent on the building type, city and basin heterogeneity in contrast to the general perception that it should be maximum at centre of city. It is also obtained that SCI effects are always beneficial to buildings when fundamental frequency of building on rock F o SR <1.4F o B ( F o B is the fundamental frequency of basin/sediment layer). The obtained reduction of of building of city as well as free field motion due to the effects of SCI corroborates with the past SCI studies. The increase of coupling between the buildings and basin due to an increase of building density causes an increase of SCI effects on the responses of both the buildings and free field motion. The SCI effects in the case of buildings with low damping are beneficial during an earthquake. It is recommended that the smart city should be homogeneous in nature and of buildings should be less than around 1.4 times the of the underlying basin/sediment deposit and buildings should preferably be a steel one.

In this paper, the computation of seismic responses of complex ridge topography is documented that can provide a reliable scenario of ridge amplification. This research work is inspired by the topography of the great Himalaya, wherein the increase of height from the south to north is in form of ups (anticlines) and downs (synclines). The viscoelastic SH- and SV-wave responses of triangular and elliptical complex ridge topography models are simulated using fourth-order finite-difference method. The complexity in the model is augmented by adding more number of sub-ridges and sub-valleys along the flanks of the reference mega-ridge. An increase in ridge amplification is obtained with an increase of complexity in both the triangular and elliptical ridge models for both the polarization of S-wave. The increase of amplification with complexity is drastically very high for the horizontal components of the SV-wave in the case of triangular ridges. It is concluded that the horizontal ground motion simulated at the crest of ridge very much depends on the shape and complexity of the topography as well as the polarization of the incident S-wave. It is concluded that the computed topography effects using the spectral ratio of earthquake records at the top and near its base generally overpredicts spectral amplifications and may not be reliable. In this paper, the increase of S-wave amplification at the crest of sub-ridges as well as the base of subvalleys with an increase of complexity in the topography models is observed. The increase of amplification of the horizontal components of the SV-wave with complexity was larger to that of the SH-wave in the case of triangular sub-ridges. The predicted ridge amplification using earthquake records at the top and base of a ridge generally over-predicts the ridge amplification.

In this paper, seismic responses of 2D complex valley topography are computed to provide a reliable scenario of valley de-amplification. Most of the cities in hilly regions are located in the valleys surrounded by high mountains and ridges. The 2D topography effects intended using the analytical formulae to determine the amplification in case of ridge and de-amplification in case of valley might not reliable for complex topography. The viscoelastic SH-wave responses of triangular complex valley topography models are simulated using finite difference method. The complexity in the model is increased by increasing the number of sub-valleys and sub-ridges along the flank of the reference mega-valley. In case of sub-valleys, the reduction in spectral amplification is less at the trough instead of increase in de-amplification with an increase of complexity in the triangular valley models, and increase in amplitude at crest of sub-ridges is obtained. The numerically computed topography effects using the spectral ratio of earthquake records at the trough and flat surface near the valley generally under predict spectral amplification and may not be reliable. It is concluded that the ground motion simulated at the trough of valley and the crest of the ridge very much depends on the complexity of the topography.

In Indian metro cities like Bangalore, Delhi, and Mumbai etc, the rapid growth of the population made the realty developers to construct housing complexes, high rise commercial and residential structures at locales like sites close to the river beds and lakes. The expansion of these metropolises has pressurized builders to fill many lakes and terrains with loose soil, resulting land reclamation as a regular practice. These reclaimed lands, pose a grave threat to the human life and damage of structures during an earthquake, as subsurface basement topography (SSBT) can play a major role. In order to document the seismic response, we studied the effects of depth of SSBT on ground motion characteristics in both the quantitative and qualitative manners. The numerically computed P-SV-wave of various 2D SSBT models (bounded) is shown in this paper. The investigation of simulated results revealed a major alteration in ground motion and generation of new seismic phases. The curves for average spectral amplification are not symmetrical and smooth. These outcomes represent that consideration of depth of SSBT impact is very significant in seismic hazard analysis for the development of smart city. This study provides a way to differentiate between a risky and safe construction site in relative terms and can be utilized as a guide in earthquake readiness.

This paper presents the role of impedance contrast (IC) at the base of 2D deep elliptical basin (shape-ratio > 0.25) in the site-city-interaction (SCI) effects on both the SH- and SV-wave responses of buildings and basin. The obtained SCI effects in the form of reduction of fundamental frequencies of building (F02DSB) and basin (F02DB), corresponding amplification and splitting of the bandwidth of fundamental mode of vibrations of both the building and basin corroborates with the findings in the past SCI studies. The F02DB of basin and F02DSB of building are unaffected by an increase of IC during site-city-interaction, even though, there is an increase of F02DB of basin with an increase of IC in the absence of city. A drastic increase of SCI effects on the basin response but only minor increase of SCI effects on the building response with an increase of IC is observed for both the polarizations of the S-wave. However, the rate of increase of SCI effects with IC is more in the case of SV-wave responses of buildings and basin. The obtained larger % reduction of F02DB and corresponding amplification in the case of SH-wave responses as compared to those in the case of SV-wave responses may be due to the larger height of B16-buildings compared to B12-buildings used in the SV-wave simulations or due to the buildings behaving as a shear beam for the SH-wave or may be due to both.

This paper presents a scenario for the spatial variation of the fundamental frequency of the sediment deposits above the basement and the corresponding amplification as well as the average spectral amplification in different frequency bandwidths for the National Capital Territory Delhi (the capital of India). The exposed central quartzite ridge and the Yamuna River channel are responsible for very large spatial variations of the fundamental frequency in the eastern part of the National Capital Territory Delhi. At 20% of the considered sites, a good match is obtained between the fundamental frequency computed numerically using available S-wave velocities to a certain depth and their extrapolation and that obtained experimentally. The computed fundamental and dominant frequencies reveal that both medium-rise (5–10 storey) and high-rise (> 10 storey) buildings in the western part and medium-rise buildings lying in the localities east of or very near to the Yamuna River may suffer heavy to very heavy damage due to the occurrence of the double resonance phenomenon. Furthermore, 1–2-storey buildings lying on the weathered exposed quartzite rock may also suffer heavy damage during local earthquakes because of the occurrence of double resonance. The possible reasons behind the lack of earthquake damage to the Qutab Minar, the tallest brick masonry minaret in the world, over the last 800 years may be the nonoccurrence of double resonance and almost no amplification in the low frequency range. There are two localities in the western part of the National Capital Territory Delhi, namely Kanganheri-Chhawla and Buradi, wherein all sorts of buildings are highly vulnerable to earthquake damage. For the closed Chhatarpur Basin and a semiclosed basin to its northeast, formed due to exposed quartzite rock, three-dimensional (3D) simulations are required to predict the characteristics of basin-generated surface waves and their focusing effects in the Chhatarpur Basin. The average spectral amplification map developed for the 0–10 Hz bandwidth depicts a range of 2.25–4.82 in the National Capital Territory Delhi and may be directly used to transfer the estimated seismic hazard at basement to the free surface.