How well can we predict earthquake site response so far? Site-specific approaches

Earthquake site responses or site effects are the modifications of surface geology to seismic waves. How well can we predict the site effects (average over many earthquakes) at individual sites so far? To address this question, we tested and compared the effectiveness of different estimation techniques in predicting the outcrop Fourier site responses separated using the general inversion technique (GIT) from recordings. Techniques being evaluated are (a) the empirical correction to the horizontal-to-vertical spectral ratio of earthquakes (c-HVSR), (b) one-dimensional ground response analysis (GRA), and (c) the square-root-impedance (SRI) method (also called the quarter-wavelength approach). Our results show that c-HVSR can capture significantly more site-specific features in site responses than both GRA and SRI in the aggregate, especially at relatively high frequencies. c-HVSR achieves a “good match” in spectral shape at ∼80%–90% of 145 testing sites, whereas GRA and SRI fail at most sites. GRA and SRI results have a high level of parametric and/or modeling errors which can be constrained, to some extent, by collecting on-site recordings.

Seismic Ground Response Analysis of Input Earthquake Motion and Site Amplification Factor at KUET

Ground motion is the movement of the earth's surface due to explosions or the propagation of seismic waves. In the seismic design process, ground response analysis evaluates the impact of local soil conditions during earthquake shaking. However, it is difficult to determine the dynamic site response of soil deposits in earthquake hazard-prone areas. Structural damage has a great influence on the selection of input ground motion, and in this study, the importance of bedrock motion upon the response of soil is highlighted. The specific site response analysis is assessed through “DEEPSOIl" software with an equivalent linear analysis method. Furthermore, four input motions including Kobe, LomaGilroy, Northridge, and Chi-Chi were selected to obtain normalized response spectra. This study aims to obtain the site amplification of ground motion, peak spectral acceleration (PSA), and maximum peak ground acceleration (PGA) based on shear wave velocity from the detailed site-specific analysis of Bangabandhu Sheikh Mujibor Rahman hall at Khulna University of Engineering & Technology. The maximum shear wave velocity obtained was 205 m/s while the amplification factor varied from 4.01 (Kobe) to 1.8 (Northridge) for rigid bedrock properties. Furthermore, the Kobe earthquake produced the highest (4.3g) PSA and the Northridge earthquake produced the lowest (1.08g) PSA for bedrock, with Vs=205 m/s. The surface PGA values were acquired in the range of 0.254g (Northridge) to 0.722g (Kobe), and the maximum strain values for Kobe earthquakes were in the range of 0.016 to .303. Therefore, the surface acceleration values were very high (>0.12g) for the Kobe earthquake motion.

Equivalent-linear seismic ground response analysis in Palu area

The 7.5 Mw Palu earthquake on September 28, 2018, was caused by the Palu Koro fault. This earthquake produced forceful wave propagation in the soil layer and generated enormous surface damage in Balaroa, Petobo, and Jono Oge. Estimations of soil amplification at a specific location are helpful as guidance for infrastructure development. This study examined the effect of local soil in modifying the one-dimensional linear soil response in Balaroa, Petobo, and Jono Oge regions, considering the data of various sites in those regions. The soil response was observed to obtain the synthetic input motion and its effects in the time history of surface acceleration, the ratio of shear stress to effective vertical stress to spectrum response time, and the Fourier amplitude versus frequency ratio. Amplification is standard for ground acceleration, which considers the strong ground motion with the acquired frequency and duration of the content. The results showed that the peak of ground acceleration amplification factors for Balaroa, Petobo, and Jono Oge was around 1.49, 2.05, and 1.27 times, respectively. With a lack of information at the particular site, designers will use the response spectrum obtained along the soil layer to develop earthquake-resistant geotechnical structures in locations close to Palu.

Seismic Ground Response Estimation Based on Convolutional Neural Networks (CNN)

One of the purposes of earthquake engineering is to mitigate the damages in buildings and infrastructures and, therefore, reduce the impact of earthquakes on society. Seismic ground response analysis refers to the process of evaluating the ground surface motions based on the bedrock motion. On the other hand, deep learning techniques have been developing fast, and they are establishing their application in the civil engineering field. This study proposes two convolutional neural network (CNN) models to estimate the seismic response of the surface based on the seismic motion measured at 100 m level beneath the surface, and selected the one which outperforms the other as the main model. The performances of the main model are compared with those of a physical software SHAKE2000. Twelve sites that include 100 earthquake datasets, whose moment magnitude is higher than 6 and PGA is higher than 0.1 g were selected. In addition, the corresponding earthquake datasets are used for the CNN model. Whereas the conventional software overestimated the values of the amplitudes for most of the sites, the proposed CNN model predicts fairly well both the values of the amplitudes and the natural periods where responses amplify the most with few exceptions. The proposed model especially outperforms the conventional software when the natural periods range from 0.01 to 0.3 s. For specific sites, the average mean squared errors of the proposed model are even dozens of times lower than those of the physical conventional software.

Numerical investigation of seismic behaviour of railway embankments in cold regions

To investigate more fully seismic behaviour of the Qinghai-Tibet railway embankment, a comprehensive discussion and a781nalysis is conducted in this paper by applying a numerical technique. Specifically, the one dimensional equivalent linear ground response analysis was conducted in permafrost regions. On this basis, the seismic response of a typical railway embankment was further studied by applying the nonlinear dynamic finite element analysis method. As a result, nonlinear behaviour of permafrost sites was determined, and the dynamic acceleration, velocity and displacement of the embankment was discussed and the quantitative assessment was approximately estimated. The results indicate that the dynamic response of the embankment has distinct nonlinear characteristics. The peak ground acceleration coefficient at the embankment shoulder is larger than the natural ground surface, marking a 73% increase compared to the coefficient on the natural ground surface. When the seismic intensity reaches a certain value, a plastic zone gradually appears in the embankment, and a continuous extension of the plastic zone can be noted with an increase in peak acceleration of the input seismic wave. The findings of this research may provide an additional insight and have significant implications for further research of cold regions.

Evaluation of Seismic Site Amplification Using 1D Site Response Analyses at Ba Dinh Square Area, Vietnam

This study presents a case study on ground response analysis of one of the important cultural heritages in Hanoi, Vietnam. One-dimensional nonlinear and equivalent linear site response analyses which are commonly applied to solve the problem of seismic stress wave propagation are performed at the Ba Dinh square area. A measured in-situ shear wave velocity profile and corresponding geotechnical site investigation and laboratory test data are utilized to develop the site model for site-specific ground response analysis. A suite of earthquake records compatible with Vietnamese Design Code TCVN 9386: 2012 rock design spectrum is used as input ground motions at the bedrock. A few concerns associated with site-specific ground response evaluation are analyzed for both nonlinear and equivalent linear procedures, including shear strains, mobilized shear strength, and peak ground acceleration along with the depth. The results show that the mean maximum shear strains at any soil layer are less than 0.2% in the study area. A deamplification portion within the soil profile is observed at the layer interface with shear wave velocity reversal. The maximum peak ground acceleration (PGA) at the surface is about 0.2 g for equivalent linear analysis and 0.16 g for nonlinear analysis. The ground motions are amplified near the site natural period 0.72 s. The soil factors calculated in this study are 1.95 and 2.07 for nonlinear and equivalent linear analyses, respectively. These values are much different from the current value of 1.15 for site class C in TCVN 9386: 2012. A comparison of calculated response spectra and amplification factors with the local standard code of practice revealed significant discrepancies. It is demonstrated that the TCVN 9386: 2012 soil design spectrum is unable to capture the calculated site amplification in the study area.

Site Response Analysis of S2 Soil Deposits Focusing on the Effects of Liquefaction and Pore-Pressure Dissipation on the Ground Surface Response Spectrum

A numerical algorithm for executing non-linear ground response analysis of layered sites is developed, capable of reproducing liquefaction phenomena, considering the simultaneous dissipation of the excess pore water pressure through soil grains. Τhe wave propagation algorithm is based on the plasticity constitutive model for sand Ta-Ger expressed in a one dimensional p-q space form, which exhibits remarkable versatility in representing complex patterns of sand cyclic behavior, such as stiffness decay and decrease in strength due to build-up of pore-water pressure. Its calibration is based on shear modulus reduction and damping curves for drained loading conditions and liquefaction resistance curves for undrained conditions. A detailed presentation of the numerical model formulation is provided, indicating the numerical approach of the wave propagation and consolidation differential equations. The recorded seismic ground response of the Port Island array from Kobe 1995 earthquake is used as a benchmark for testing the validity of model predictions. The model is finally applied to estimate the elastic response spectra at the surface of soil profiles with liquefiable layers (ground type S2) as per EC8:2004. The investigation study involves the ground response analysis of diverse soil profiles, all including a liquefiable zone, excited with a suite of earthquake motions at their base. The acceleration time histories were extracted from the PEER Ground Motion Database having characteristics compatible with the NGA-estimated response spectrum at the bedrock and with key seismological parameters such as the earthquake magnitude Mw and horizontal distance from the fault RJB. Two different methods are applied regarding the selection of base excitations: Amplitude scaled records (to match a target response spectrum) and spectral matched records. From the results an idealized response spectrum is deduced in terms of the design spectrum parameters S, η, ΤΒ and TC. It is shown that the idealized ground surface response spectrum is marginally sensitive to method of base excitation selection.

The Use of Ground Motion Parameters to identify the Liquefaction during a Strong Earthquake in Northern Thailand

This paper presents a ground response analysis to simulate the liquefaction phenomenon during the 2011 Tarlay Earthquake in northern Thailand. The site investigation data and geophysical measurements on 7 sites in northern Thailand were collected. The multi-springs element model was implemented in finite element ground response analysis. Several parameters, such as peak ground acceleration, peak ground velocity, amplification factor, excess pore pressure ratio, were observed. Furthermore, the correlation from the ground motion parameters was generated to estimate liquefaction potential, which was represented by excess pore pressure ratio. The result showed that the excess pore pressure ratio was relatively well correlated with several ground parameters, such as amplification factor, velocity-acceleration ratio, and factor of safety against liquefaction. The results could be also used for the engineering practice in predicting liquefaction potential in Northern Thailand.