Pre-loading effect on site response: Site amplification and soil properties mismatch

A new simulation-based site amplification model for shallow sites with thickness less than 30 m in Korea is developed. The site amplification model consists of linear and nonlinear components that are developed from one-dimensional linear and nonlinear site response analyses. A suite of measured shear wave velocity profiles is used to develop corresponding randomized profiles. A VS30 scaled linear amplification model and a model dependent on both VS30 and site period are developed. The proposed linear models compare well with the amplification equations developed for the western United States (WUS) at short periods but show a distinct curved bump between 0.1 and 0.5 s that corresponds to the range of site natural periods of shallow sites. The response at periods longer than 0.5 s is demonstrated to be lower than those of the WUS models. The functional form widely used in both WUS and central and eastern North America (CENA), for the nonlinear component of the site amplification model, is employed in this study. The slope of the proposed nonlinear component with respect to the input motion intensity is demonstrated to be higher than those of both the WUS and CENA models, particularly for soft sites with VS30 < 300 m/s and at periods shorter than 0.2 s. The nonlinear component deviates from the models for generic sites even at low ground motion intensities. The comparisons highlight the uniqueness of the amplification characteristics of shallow sites that a generic site amplification model is unable to capture.

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Estimation of Site Amplification from Geotechnical Array Data Using Neural Networks

Bulletin of the Seismological Society of America ◽

10.1785/0120200346 ◽

2021 ◽

Author(s):

Daniel Roten ◽

Kim B. Olsen

Keyword(s):

Neural Network ◽

Neural Networks ◽

Site Response ◽

Site Amplification ◽

Data Driven ◽

Vertical Array ◽

The Neural Network ◽

Simplifying Assumptions ◽

The Mean ◽

Fully Connected

ABSTRACT We use deep learning to predict surface-to-borehole Fourier amplification functions (AFs) from discretized shear-wave velocity profiles. Specifically, we train a fully connected neural network and a convolutional neural network using mean AFs observed at ∼600 KiK-net vertical array sites. Compared with predictions based on theoretical SH 1D amplifications, the neural network (NN) results in up to 50% reduction of the mean squared log error between predictions and observations at sites not used for training. In the future, NNs may lead to a purely data-driven prediction of site response that is independent of proxies or simplifying assumptions.

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Correspondence between Site Amplification and Topographical, Geological Parameters: Collation of Data from Swiss and Japanese Stations, and Neural Networks-Based Prediction of Local Response

Bulletin of the Seismological Society of America ◽

10.1785/0120210225 ◽

2021 ◽

Author(s):

Paolo Bergamo ◽

Conny Hammer ◽

Donat Fäh

Keyword(s):

Frequency Response ◽

Large Scale ◽

Site Response ◽

Low Frequency ◽

Field Measurements ◽

Site Amplification ◽

Local Response ◽

Regional Variability ◽

Individual Site ◽

Digital Elevation

ABSTRACT We address the relation between seismic local amplification and topographical and geological indicators describing the site morphology. We focus on parameters that can be derived from layers of diffuse information (e.g., digital elevation models, geological maps) and do not require in situ surveys; we term these parameters as “indirect” proxies, as opposed to “direct” indicators (e.g., f0, VS30) derived from field measurements. We first compiled an extensive database of indirect parameters covering 142 and 637 instrumented sites in Switzerland and Japan, respectively; we collected topographical indicators at various spatial extents and focused on shared features in the geological descriptions of the two countries. We paired this proxy database with a companion dataset of site amplification factors at 10 frequencies within 0.5–20 Hz, empirically measured at the same Swiss and Japanese stations. We then assessed the robustness of the correlation between individual site-condition indicators and local response by means of statistical analyses; we also compared the proxy-site amplification relations at Swiss versus Japanese sites. Finally, we tested the prediction of site amplification by feeding ensembles of indirect parameters to a neural network (NN) structure. The main results are: (1) indirect indicators show higher correlation with site amplification in the low-frequency range (0.5–3.33 Hz); (2) topographical parameters primarily relate to local response not because of topographical amplification effects but because topographical features correspond to the properties of the subsurface, hence to stratigraphic amplification; (3) large-scale topographical indicators relate to low-frequency response, smaller-scale to higher-frequency response; (4) site amplification versus indirect proxy relations show a more marked regional variability when compared with direct indicators; and (5) the NN-based prediction of site response is the best achieved in the 1.67–5 Hz band, with both geological and topographical proxies provided as input; topographical indicators alone perform better than geological parameters.

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Response Site Analyses of 3D Homogeneous Soil Models

Emerging Science Journal ◽

10.28991/esj-2018-01148 ◽

2018 ◽

Vol 2 (5) ◽

pp. 238 ◽

Cited By ~ 12

Author(s):

Davide Forcellini ◽

Marco Tanganelli ◽

Stefania Viti

Keyword(s):

Soil Type ◽

Soil Depth ◽

Site Response ◽

Soil Layer ◽

Shear Velocity ◽

Seismic Intensity ◽

Eurocode 8 ◽

Seismic Input ◽

Homogeneous Soil ◽

Response Site

The seismic excitation at the surface can be determined through Site Response Analyses (SRA) as to account for the specific soil properties of the site. However, the obtained results are largely affected by the model choice and setting, and by the depth of the considered soil layer. This paper proposes a refined 3D analytical approach, by the application of OPENSEES platform. A preliminary analysis has been performed to check the model adequacy as regards the mesh geometry and the boundary conditions. After the model setting, a SRA has been performed on various soil profiles, differing for the shear velocity and representing the different soil classes as proposed by the Eurocode 8 (EC8). Three levels of seismic hazard have been considered. The seismic input at the bedrock has been represented consequently, through as much ensembles of seven ground motions each, spectrum-compatible to the elastic spectra provided by EC8 for the soil-type A (bedrock). Special attention has been paid to the role of the considered soil depth on the evaluation of the surface seismic input. Different values of depth have been considered for each soil type and seismic intensity, in order to check its effect on the obtained results.

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Probabilistic Models for Uncertainty Quantification of Soil Properties on Site Response Analysis

ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems Part A Civil Engineering ◽

10.1061/ajrua6.0001079 ◽

2020 ◽

Vol 6 (3) ◽

pp. 04020030

Author(s):

Thanh-Tuan Tran ◽

Kashif Salman ◽

Seung-Ryong Han ◽

Dookie Kim

Keyword(s):

Soil Properties ◽

Uncertainty Quantification ◽

Probabilistic Models ◽

Site Response ◽

Site Response Analysis ◽

Response Analysis

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Significance of site natural period effects for linear site amplification in central and eastern North America: Empirical and simulation-based models

Earthquake Spectra ◽

10.1177/8755293019878198 ◽

2020 ◽

Vol 36 (1) ◽

pp. 87-110 ◽

Cited By ~ 1

Author(s):

Youssef M. A. Hashash ◽

Okan Ilhan ◽

Behzad Hassani ◽

Gail M. Atkinson ◽

Joseph Harmon ◽

...

Keyword(s):

North America ◽

Site Response ◽

Reference Conditions ◽

Site Amplification ◽

Empirical Models ◽

Response Analysis ◽

Eastern North America ◽

Natural Period ◽

Motion Models ◽

Simulation Based

This article evaluates linear simulation-based and empirical site amplification models including site natural period dependency parameters to account for the distinctive amplification behavior near site fundamental frequencies resulting from the sharp impedance contrast between soil and underlying hard bedrock in central and eastern North America (CENA). The simulation-based amplification models are developed using 581,685 frequency-domain linear analyses generated from a parametric study and include VS30-scaling and site natural period ( Tnat) parameters. The empirical models are derived from residuals analyses of ground-motion models for two reference conditions: B/C boundary ( VS30 = 760 m/s) and CENA hard-rock condition ( VS = 3000 m/s). The simulation-based and empirical models are compared for 8 site profiles in CENA to measured horizontal-to-vertical (H/V) component response spectral (RS) ratios, the mean of linear simulations for similar sites, and one-dimensional (1D) linear site response analysis for four of these sites. Comparisons between observed and estimated site amplification behaviors highlight model dependency on Tnat in CENA. Model consistencies and differences related to the distinct linear amplification features near site fundamental frequency are discussed.

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Nonlinear site amplification model for ergodic seismic hazard analysis in Central and Eastern North America

Earthquake Spectra ◽

10.1177/8755293019878193 ◽

2020 ◽

Vol 36 (1) ◽

pp. 69-86 ◽

Cited By ~ 4

Author(s):

Youssef M. A. Hashash ◽

Okan Ilhan ◽

Joseph A. Harmon ◽

Grace A. Parker ◽

Jonathan P. Stewart ◽

...

Keyword(s):

North America ◽

Site Response ◽

Epistemic Uncertainty ◽

Hazard Analysis ◽

Reference Conditions ◽

Site Amplification ◽

Eastern North America ◽

Ground Acceleration ◽

Uncertainty Model ◽

Nonlinear Amplification

This article presents recommendations for nonlinear site amplification models in Central and Eastern North America (CENA), which are developed from one-dimensional site response analyses results and accompanies linear site amplification model in a companion article. Two median nonlinear amplification models using identical functional forms are produced as a function of VS30 and peak ground acceleration for reference conditions ( PGAr) of VS = 3000 m/s and VS30 = 760 m/s. An epistemic uncertainty model on median nonlinear amplification is proposed as a piecewise functional form to generate reasonable variations of nonlinear amplification across the period and VS30 ranges of interest. Limitations of the models are based on both the methodology of the model derivation and assumptions of nonlinear amplification model forms.

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Repeatable Source, Path, and Site Effects from the 2019 M 7.1 Ridgecrest Earthquake Sequence

Bulletin of the Seismological Society of America ◽

10.1785/0120200008 ◽

2020 ◽

Vol 110 (4) ◽

pp. 1530-1548 ◽

Cited By ~ 6

Author(s):

Grace A. Parker ◽

Annemarie S. Baltay ◽

John Rekoske ◽

Eric M. Thompson

Keyword(s):

Los Angeles ◽

Ground Motion ◽

Site Response ◽

Ground Motions ◽

Warning System ◽

Site Amplification ◽

Earthquake Sequence ◽

Ground Acceleration ◽

Small Magnitude ◽

Earthquake Early Warning System

ABSTRACT We use a large instrumental dataset from the 2019 Ridgecrest earthquake sequence (Rekoske et al., 2019, 2020) to examine repeatable source-, path-, and site-specific ground motions. A mixed-effects analysis is used to partition total residuals relative to the Boore et al. (2014; hereafter, BSSA14) ground-motion model. We calculate the Arias intensity stress drop for the earthquakes and find strong correlation with our event terms, indicating that they are consistent with source processes. We look for physically meaningful trends in the partitioned residuals and test the ability of BSSA14 to capture the behavior we observe in the data. We find that BSSA14 is a good match to the median observations for M>4. However, we find bias for individual events, especially those with small magnitude and hypocentral depth≥7 km, for which peak ground acceleration is underpredicted by a factor of 2.5. Although the site amplification term captures the median site response when all sites are considered together, it does not capture variations at individual stations across a range of site conditions. We find strong basin amplification in the Los Angeles, Ventura, and San Gabriel basins. We find weak amplification in the San Bernardino basin, which is contrary to simulation-based findings showing a channeling effect from an event with a north–south azimuth. This and an additional set of ground motions from earthquakes southwest of Los Angeles suggest that there is an azimuth-dependent southern California basin response related to the orientation of regional structures when ground motion from waves traveling south–north are compared with those in the east–west direction. These findings exhibit the power of large, spatially dense ground-motion datasets and make clear that nonergodic models are a way to reduce bias and uncertainty in ground-motion estimation for applications like the U.S. Geological Survey National Seismic Hazard Model and the ShakeAlert earthquake early warning System.

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Empirical Linear Seismic Site Amplification in Central and Eastern North America

Earthquake Spectra ◽

10.1193/083117eqs170m ◽

2019 ◽

Vol 35 (2) ◽

pp. 849-881 ◽

Cited By ~ 8

Author(s):

Grace A. Parker ◽

Jonathan P. Stewart ◽

Youssef M. A. Hashash ◽

Ellen M. Rathje ◽

Kenneth W. Campbell ◽

...

Keyword(s):

North America ◽

Ground Motion ◽

Site Response ◽

Site Amplification ◽

Eastern North America ◽

Resonance Effects ◽

Bayesian Techniques ◽

Motion Data ◽

Motion Models ◽

Scaling Models

We present empirical linear site amplification models conditioned on time-averaged shear wave velocity in the upper 30 m ( VS30) for central and eastern North America. The models are derived from ground motion data and site condition information from the NGA-East project and are intended for use with reference rock ground motion models. Site amplification is found to scale with VS30 for intermediate to stiff site conditions ( VS30 > 300 m/s) in a weaker manner than for active tectonic regions such as the western United States. For stiff sites ( >800 m/s), we find differences in site amplification for previously glaciated and nonglaciated regions, with nonglaciated sites having lower amplification. The models were developed using a combination of least-squares, mixed effects, and Bayesian techniques; the latter show that accounting for predictor uncertainty does not appreciably affect the median model but decreases model dispersion. Our VS30-scaling models are modular and additive to simulation-based models for the nonlinear components of site response. A limitation of the present models is that they do not account for site-specific resonance effects.

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Uncertainty of linear earthquake site amplification via Bayesian inversion of surface seismic data

Geophysics ◽

10.1190/geo2012-0345.1 ◽

2013 ◽

Vol 78 (3) ◽

pp. WB37-WB48 ◽

Cited By ~ 6

Author(s):

Sheri Molnar ◽

Stan E. Dosso ◽

John F. Cassidy

Keyword(s):

Shear Wave ◽

Site Response ◽

Probability Distributions ◽

Site Amplification ◽

Text Structure ◽

Resonant Peak ◽

Probabilistic Seismic Hazard Assessment ◽

Uncertainty Distribution ◽

Surface Wave Dispersion ◽

Dispersion Data

We examine uncertainty in predicted linear 1D site amplification due to uncertainty in shear-wave velocity ([Formula: see text]) structure quantified from Bayesian (probabilistic) inversion of microtremor array dispersion data. Based on a sample of [Formula: see text] profiles drawn from the posterior probability density of the microtremor inversion, probability distributions are computed for common predictors of site amplification including [Formula: see text] (traveltime average [Formula: see text] to a depth [Formula: see text]) and amplification spectra based on seismic impedance variations and full transverse shear-wave effects. These methods are applicable for any site, but the resulting probabilistic site amplification analyses are specific to the two sediment sites studied here with strongly contrasting geology in high population centers of British Columbia, Canada. The site amplification probability distributions for the two sites are shown to be more informative than amplification estimated for a single best-fit [Formula: see text] profile by characterizing the uncertainty and therefore level of confidence in the predictions. The shear-wave amplification probability spectra are evaluated by comparison to empirical earthquake and microtremor spectral ratios, with generally good agreement in resonant peak frequencies and amplification levels, providing confidence that the primary influence of site-specific structure is accounted for appropriately. The wider implication here is that proper characterization of the [Formula: see text] profile uncertainty distribution from inversion of cost-effective surface wave dispersion data is beneficial in the application of said profiles to the prediction of earthquake site response and its uncertainty, as required for probabilistic seismic hazard assessment.

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