Ground Response Study Research Articles

Development of synthetic acceleration time histories for seismic ground response studies for site classes C to E for Bihar region: a case study

Development of synthetic acceleration time histories for seismic ground response studies for site classes C to E for Bihar region: a case study

Empirical nonlinear site effects in Japanese megathrust earthquakes

In the course of developing ground-motion models (GMMs) of peak ground acceleration (PGA) for Japanese megathrust earthquakes, we discovered that empirical nonlinear site effects from these events are very different from those found for shallow crustal earthquakes in California and other global active tectonic regions. In particular, nonlinearity in site response is much less prominent in Japan than these other regions, which is consistent with other empirical and theoretical ground-response studies using recordings from both crustal and subduction earthquakes. In this study, we used the residuals from Japanese megathrust GMMs that account for linear site response to develop a nonlinear site-response term that uses the value of PGA on rock as a measure of ground-motion severity and the value of time-averaged shear-wave velocity in the top 30 m of a site ( VS30) as a measure of site properties. The resulting residuals are unbiased and trendless over all PGA values of interest. We also investigated whether soil nonlinearity can be modeled using proxies for shear stress and shear strain. We found deviations from expected linearity unrelated to nonlinear site effects at small values of strain—believed to be due to network accelerograph trigger thresholds—and at large earthquake magnitudes, believed to be due to the shape of the source spectrum.

Reliability on ProSHAKE 2.0 in the Assessment of One Dimensional Ground Response Analysis through Verification Example

It is understood from the recent destructive earthquakes, topography, nature of the bedrock and geometry of the soil deposits are the prime factors that made modifications to the underlying earthquake motion. The influence of such confined soil states on the strong earthquake motion plays a significant task in accessing the uniqueness of ground action. In this paper, the response of the soil layers to the earthquake action of the bedrock directly under it is determined. The analysis is done through frequency domain approach. Pro-shake software 2.0 is used to arrive the reliability of the ground response study. A wide variety of output parameters such as time histories of acceleration, velocity, displacement, shear stress, shear strain, response spectra and maximum amplitude of various parameters with depth are plotted and the other scalar parameters such as peak acceleration, peak velocity, peak displacement, RMS acceleration, arias intensity, predominant period and bracketed duration was computed.

Dynamic soil properties and liquefaction potential of northeast Indian soil for non-linear effective stress analysis

This article presents a comprehensive study of dynamic soil properties [namely, initial shear modulus-Gmax; normalized shear modulus reduction (G/Gmax); and damping ratio (D) variation curves] and pore water pressure parameters of a river bed sand (Brahmaputra sand), sampled from a highly active seismic region (northeast India). Two independent high quality apparatus (resonant column-RC and cyclic triaxial-CTX) are adopted in the study. Resonant column apparatus was used to obtain the small strain properties (up to 0.1%) while CTX equipment was adopted to obtain the high strain properties along with the pore water pressure parameters. The results obtained from both the equipment are combined to provide a comprehensive data of dynamic soil properties over wide range of strains. A modified hyperbolic formulation was suggested for efficient simulation of G/Gmax and D variations with shear strain. Based on the CTX results, a pore water pressure generation model is presented. Furthermore, a nonlinear effective stress ground response study incorporating the pore water pressure generation, is performed using the recorded earthquake motions of varying peak bed rock acceleration (PBRA) in the region, to demonstrate the applicability of proposed dynamic soil properties and pore pressure parameters. High amplification for low PBRA ground motions (˂ 0.10 g) was observed and attenuation of seismic waves was witnessed beyond a PBRA of 0.10 g near the surficial stratum due to the induced high strains and the resulting high hysteretic damping of the soil. Also, increased excess pore pressure generation with increased PBRA of the input motion was observed and the considered soil stratum is expected to liquefy beyond a PBRA of 0.1 g. The established properties can be handy to the design engineers during seismic design of structures in the northeast Indian region.

Importance of Site-Specific Dynamic Soil Properties for Seismic Ground Response Studies

This article highlights the implication of site-specific properties on seismic ground response studies. One-dimensional equivalent linear ground response analysis was carried out using site-specific dynamic properties of locally available soils of Guwahati city, and the results are compared with those obtained using existing strain-dependent dynamic properties. Acceleration time histories from three strong motions were used. It was observed that an input motion having a higher peak bedrock acceleration, utilizing experimentally obtained dynamic soil properties, exhibits 38% and 24% lower peak ground acceleration and peak spectral acceleration, respectively, in comparison to the results obtained using standard VD-SI soil models. The amplification characteristics of the strong motions are observed to be significantly influenced by the degradation of damping ratio beyond 1% shear strain. The results highlight the necessity of conducting GRA of any region considering its regional dynamic soil properties to obtain more realistic outcomes.

Dynamic soil properties for seismic ground response studies in Northeastern India

Stiffness and damping properties of soil are essential parameters for any dynamic soil structure interaction analysis. Often the required stiffness and damping properties are obtained from the empirical curves. This paper presents the stiffness and damping properties of two naturally occurring sandy soils collected from a river bed in a highly active seismic zone in the Himalayan belt. A series of resonant column tests are performed on the soil specimens with relative densities representative of the field and with varying confining pressures. The test results are compared with the available empirical curves. Furthermore, a ground response analysis study is also carried out for a bridge site in the region using both the empirical curves and experimentally obtained curves. It has been observed that the application of empirical modulus and damping curves in ground response prediction often leads to underestimation of the seismic demands on the structures. The established soil curves can thus be utilized in performing seismic ground response studies for the design of new structures or requalification/reassessment of existing structures in the northeastern part of India.

Site-Specific Seismic Ground Response Study for Nuclear Power Plants and Ports in Mumbai

AbstractThe importance of characterizing site-specific free-field surface motion of facilities of national and worldwide economic influence [like ports and nuclear power plants (NPPs)] is well-realized, especially in Mumbai, the most important commercial city in India, with 40% of its land reclaimed from the Arabian Sea. In the research reported in this paper, site-specific seismic hazard and one-dimensional (1D) equivalent linear ground response analysis (GRA) of important sites in Mumbai [Jawaharlal Nehru Port (JNPT), Mumbai Port, Bhabha Atomic Research Center (BARC), and Tarapur Atomic Power Station (TAPS)] are attempted. The seismicity of the research region is modeled through delineation of 31 fault sources with an earthquake database of the past 418 years (years 1594–2012). The epistemic uncertainty in hazard estimation is accounted by employing seven different ground motion prediction equations developed for worldwide shallow crustal intraplate environments. The probabilistic seismic hazard analysi...

Liquefaction Hazard Assessment Using SPT and VS for Two Cities in India

The seismic behavior of a saturated soil depends on the potential for significant strains or strength loss that can contribute to ground deformations or instability during an earthquake. Historic large earthquakes throughout the world explain that the liquefaction related ground failure commonly causes extensive structural and lifeline damage in urban areas. Detailed assessment of liquefaction hazard is important for evaluating and reducing the risk through appropriate mitigation techniques. Soil liquefaction generally occurs in areas underlain by low density, saturated granular sediments. The liquefaction susceptibility can be mapped using specific, well established geologic and geotechnical criteria. Damages caused by liquefaction of saturated soil revealed that after liquefaction the ground failed, sand boiling occurred and the structure subsided unevenly causing tilting, cracking or even collapse. After the devastating 2001 Gujarat earthquake, the Government of India has paid serious attention to carry out the detailed site characterization and ground response studies which are very crucial in seismic microzonation and it is also accepted as a guiding tool in land use planning and safe construction practices to avoid the loss from the future earthquakes. Very preliminary process of reducing the effects of earthquake is by assessing the hazard itself. As part of the national level microzonation program, Department of Science and Technology, Govt. of India has initiated microzonation of 63 cities in India. In this research paper two urban centers Delhi and Vijayawada city which falls in seismic zones IV and III respectively are considered for liquefaction hazard assessment. Since these two cities are falling in the areas with high and moderate seismic probability, there is a great need for the assessment of liquefaction potential. An attempt has been made estimate the liquefaction hazard for these two cities considered using the measured shear wave velocities and SPT borehole data. From the detailed liquefaction assessment, it is observed that the possibility is severe in the north and north eastern side of Delhi and is very less in the western side of the city. In the south and central part of the area where shear wave velocities of the soil strata is ≥180 m/s the possibility of liquefaction is unlikely and in Vijayawada city, the occurrence of liquefaction is likely at several locations especially in Patamata, Autonagar and Kanuru.

The Aterno valley strong-motion array: seismic characterization and determination of subsoil model

The paper focuses on the strong motion array deployed in the upper Aterno River Valley, in the immediate outskirts north-west of the town of L’Aquila, which is part of the Italian Strong Motion Network operated by the Department of Civil Protection. The array is composed of six accelerometric stations located along a cross section of the valley. The importance of this array relies on the fact that a large amount of high-quality records were obtained during the 2009 L’Aquila seismic sequence, from both the mainshock and several aftershocks. These data are especially important to investigate site effects in sediment-filled valleys during moderate earthquakes in epicentral area because well-documented observational studies are very limited in the literature. However, the main drawback for the study of site effects in the Aterno valley is the lack of a detailed knowledge of the geometry of the valley, soil layering and dynamic properties of materials. The main motivation for this study stems from the need to provide a reliable subsoil model of the valley coupled with high-quality strong motion data. Based on the above, in the framework of S4 project, a major effort was undertaken to get a trustworthy cross section of the valley by an ad hoc investigation, comprising geological and geotechnical surveys as well as an extensive geophysical campaign, characterized by both active and passive measurements. These results were complemented by additional geological and geotechnical data available in the literature. By merging all the information acquired, a 2D subsoil model of the transversal section of the upper Aterno valley has been produced. The valley is characterised by an asymmetric shape with a shallower rock basement at the western edge of the valley that deepens at the valley centre. Moreover, based on the results of geophysical tests, representative Vs values were assigned to the different lithologic units forming the alluvial deposits filling the valley. Shear wave velocity is a fundamental parameter for ground response studies and it is also effective in classifying the accelerometric station from a seismic point of view. The 2D model may be therefore, considered a benchmark model for future studies of site effects. It will offer the possibility to examine site effects with a complex underlying geology and to validate the results of numerical simulations of site response analyses with the numerous observations from earthquake recordings, both for weak and strong ground motion conditions.

Geospatial contour mapping of shear wave velocity for Mumbai city

Shear wave velocity is one of the most important input parameter in the analysis of geotechnical earthquake engineering problems, particularly to estimate site-specific amplification factor and ground response study. Dynamic in situ tests such as spectral analysis of surface waves (SASW) or multichannel analysis of surface waves (MASW) are very expensive. Also due to lack of specialized personnel, these tests are generally avoided in many soil investigation programs. Worldwide, several researchers have developed correlations between the SPT ‘N’ value and shear wave velocity ‘Vs’, which are useful for determining the dynamic soil properties. In the present study, more than 400 numbers of soil borehole data were collected from various geotechnical investigation agencies, government engineering institutes and geotechnical laboratories from different parts of Mumbai city, which is financial capital of India with highest population density. In this paper, an attempt has been made to develop the correlation between the SPT ‘N’ value and shear wave velocity ‘Vs’ for various soil profile of Mumbai city and compared with other existing correlations for different cities in India. Using Geographical Information System (GIS), a geospatial contour map of shear wave velocity profile for Mumbai city is prepared with contour intervals of 25 and 50 m/s. The scarcity of database or maps of shear wave velocity profile for Mumbai city will make the present geospatial contour maps extremely useful and beneficial to the designer, practitioners for seismic hazard study involved in geotechnical earthquake engineering.

Spatial Variability of Rock Depth in Bangalore Using Geostatistical, Neural Network and Support Vector Machine Models

Geospatial technology is increasing in demand for many applications in geosciences. Spatial variability of the bed/hard rock is vital for many applications in geotechnical and earthquake engineering problems such as design of deep foundations, site amplification, ground response studies, liquefaction, microzonation etc. In this paper, reduced level of rock at Bangalore, India is arrived from the 652 boreholes data in the area covering 220 km2. In the context of prediction of reduced level of rock in the subsurface of Bangalore and to study the spatial variability of the rock depth, Geostatistical model based on Ordinary Kriging technique, Artificial Neural Network (ANN) and Support Vector Machine (SVM) models have been developed. In Ordinary Kriging, the knowledge of the semi-variogram of the reduced level of rock from 652 points in Bangalore is used to predict the reduced level of rock at any point in the subsurface of the Bangalore, where field measurements are not available. A new type of cross-validation analysis developed proves the robustness of the Ordinary Kriging model. ANN model based on multi layer perceptrons (MLPs) that are trained with Levenberg–Marquardt backpropagation algorithm has been adopted to train the model with 90% of the data available. The SVM is a novel type of learning machine based on statistical learning theory, uses regression technique by introducing loss function has been used to predict the reduced level of rock from a large set of data. In this study, a comparative study of three numerical models to predict reduced level of rock has been presented and discussed.

Geotechnical aspects and ground response studies in Bhuj earthquake, India

The extent of damage and affected areas in Bhuj earthquake (26th January 2001) has provided a unique opportunity to evaluate a wide range of geotechnical issues. A large area in the Rann of Kutch experienced massive liquefaction resulting in ground subsidence and lateral flow. A large number of dams in the Kutch district suffered moderate to severe damages. Many buildings were damaged and collapsed in the city of Ahmedabad situated on the bank of the Sabarmati River. In this paper, the ground response studies at a site in Ahmedabad City along with observations of geotechnical aspects such as ground cracking, sand volcanoes and liquefaction of soils associated with the Bhuj earthquake are discussed. The ground response studies indicate that the varying degree of damage to multistorey buildings in Ahmedabad in the close proximity of Sabarmati river area was essentially due to the collapse and undesirable settlement of partly saturated silty sand deposits. Large settlements are attributed to amplification of the ground and the near resonance condition.

Ground-response studies at the Alameda Naval Air Station : H. Carlisle & K. M. Rollins, US Geological Survey Professional Paper, 1551-A, 1994, pp 123–143

Ground-response studies at the Alameda Naval Air Station : H. Carlisle & K. M. Rollins, US Geological Survey Professional Paper, 1551-A, 1994, pp 123–143

Seismic ground-response studies in Olympia, Washington, and vicinity

AbstractRelative seismic ground-response characteristics in the cities of Olympia, Lacey, and Tumwater, Washington, were determined from analysis of instrumentally recorded ground motion induced by blasts at an open-pit coal mine near Centralia, Washington. A ground-response function (GRF), defined as the ratio of Fourier spectral amplitudes at an alluvium site to spectral amplitudes on hard rock, is a measure of amplification of seismic waves by localized site conditions. GRF values in three frequency bands (0.5 to 1.0 Hz, 1.0 to 2.0 Hz, and 2.0 to 4.0 Hz) were compared with observed Modified Mercalli (MM) intensities from the 29 April 1965, Puget Sound earthquake and with mapped surficial geologic units. Typically, the GRF values relate well with the surficial geological units.In addition, MM intensities within the V to VII range appear to be directly related to the frequencies within the 0.5 to 4.0 Hz bandwidth such that MM V intensity sites had a lower GRF value in the 2.0 to 4.0 Hz bandwidth as compared to the 0.5 to 2.0 Hz bandwidth, and the MM VII intensity sites had higher GRF values in the 2.0 to 4.0 Hz bandwidth as compared to the 0.5 to 2.0 Hz bandwidth. The set of GRF values determined for the city of Olympia and its vicinity should be useful in formulating a theoretical relative ground-response model for the southern Puget Sound area.

A comparative ground response study near Los Angeles using recordings of Nevada nuclear tests and the 1971 San Fernando earthquake

AbstractA comparative ground response study at sites in the Los Angeles region is based on the extensive strong-motion data set recorded in the 1971 San Fernando earthquake and 159 three-component recordings of distant nuclear tests in Nevada. Amplitude spectral ratios computed for the nuclear test data over those frequency bands for which there is an adequate signal-to-noise ratio provide statistically stable estimates of the local ground response related to the type of local geologic conditions. Comparison of the strong-motion data recorded from the 1971 San Fernando earthquake with that recorded at 28 of the same sites for the nuclear tests show that the corresponding amplitude spectral ratios are statistically equivalent for most sites, provided reference stations are chosen to minimize effects on the earthquake data of azimuthal source variations and crustal propagation path. Statistical equivalence of the spectral ratios for the two types of data sources suggests that amplitude spectral ratios computed with respect to the appropriate reference station provide a first-order estimate of local ground response.