scholarly journals Checking the site categorization criteria and amplification factors of the 2021 draft of Eurocode 8 Part 1–1

2021 ◽  
Author(s):  
Roberto Paolucci ◽  
Mauro Aimar ◽  
Andrea Ciancimino ◽  
Marco Dotti ◽  
Sebastiano Foti ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Shear Wave ◽  
Ground Motion ◽  
Shear Wave Velocity ◽  
Soft Soil ◽  
Site Amplification ◽  
Soil Conditions ◽  
Eurocode 8 ◽  
Site Specific ◽  
Amplification Factors

AbstractIn this paper the site categorization criteria and the corresponding site amplification factors proposed in the 2021 draft of Part 1 of Eurocode 8 (2021-draft, CEN/TC250/SC8 Working Draft N1017) are first introduced and compared with the current version of Eurocode 8, as well as with site amplification factors from recent empirical ground motion prediction equations. Afterwards, these values are checked by two approaches. First, a wide dataset of strong motion records is built, where recording stations are classified according to 2021-draft, and the spectral amplifications are empirically estimated computing the site-to-site residuals from regional and global ground motion models for reference rock conditions. Second, a comprehensive parametric numerical study of one-dimensional (1D) site amplification is carried out, based on randomly generated shear-wave velocity profiles, classified according to the new criteria. A reasonably good agreement is found by both approaches. The most relevant discrepancies occur for the shallow soft soil conditions (soil category E) that, owing to the complex interaction of shear wave velocity, soil deposit thickness and frequency range of the excitation, show the largest scatter both in terms of records and of 1D numerical simulations. Furthermore, 1D numerical simulations for soft soil conditions tend to provide lower site amplification factors than 2021-draft, as well as lower than the corresponding site-to-site residuals from records, because of higher impact of non-linear (NL) site effects in the simulations. A site-specific study on NL effects at three KiK-net stations with a significantly large amount of high-intensity recorded ground motions gives support to the 2021-draft NL reduction factors, although the very limited number of recording stations allowing such analysis prevents deriving more general implications. In the presence of such controversial arguments, it is reasonable that a standard should adopt a prudent solution, with a limited reduction of the site amplification factors to account for NL soil response, while leaving the possibility to carry out site-specific estimations of such factors when sufficient information is available to model the ground strain dependency of local soil properties.

Seismic soil class map for Italy according to European and Italian codes map

2020 ◽  
Author(s):  
Giovanni Forte ◽  
Eugenio Chioccarelli ◽  
Melania De Falco ◽  
Pasquale Cito ◽  
Antonio Santo ◽  
...  
Keyword(s):  
Shear Wave ◽  
Ground Motion ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Large Scale ◽  
Soil Conditions ◽  
Site Classification ◽  
Soil Class ◽  
Topographic Slope ◽  
Geological Maps

<p>Soil conditions affect ground motion amplification. Thus, seismic site classification is a critical issue to predict ground motion parameters in the context of both probabilistic seismic hazard analysis and real-time generation of shaking maps. Especially on large areas, simplified procedures for estimating the seismic soil amplification can be advantageous. In order to account for these local effects, some proxies which account for the soil behaviour can be identified; e.g., the average shear-wave velocity of the upper 30 m (VS,30), or the equivalent shear-wave velocity from the depth of the seismic bedrock (VS,eq). <br>In this study, two maps of seismic shallow soil classification for Italy according to Eurocode 8 (EC08) and the new Italian Building Code (ItBC2018) are presented. The methodology from which the maps are derived is described in Forte et al. (2019) and accounts for two sources of information: site-specific measurements and large-scale geological maps. The soil maps are obtained via a four-step procedure: <br>(1) a database of about four-thousand shear-waves velocity (Vs) measurements coming from in-hole tests, surface geophysical tests and microtremors is built, covering (unevenly) the whole national territory; <br>(2) twenty geo-lithological complexes are identified from the available geological maps; <br>(3) the investigations are grouped as a function of the geo-lithological complex and the distribution of measured VS,30, VS,eq are derived;<br>(4) medians and standard deviations of such distributions are assumed to be representative of the corresponding complexes that are consequently associated to soil classes. <br>The EC08 soil class map and the available database of Vs measurements were compared with the seismic soil map provided by the USGS based on a topographic slope-proxy (Allen and Wald, 2007). The latter is obtained by the correlation between topographic slope and VS,30, assuming morphometrical characteristics of the terrain as representative of the lithology. The slope-based method appears less reliable than the proposed approach, because its predictions resulted in a slight but systematic overestimation of the measured soil classes. Therefore, the proposed map can be more suitable for large-scale seismic risk studies, despite it is not a substitute of seismic microzonation and local site response analyses.<br>To make the results of the study available, a stand-alone software “SSC-Italy” has been developed and is freely available at http://wpage. unina.it/iuniervo/SSC-Italy.zip. </p>

Site characterisation of GeoNet stations for the New Zealand Strong Motion Database

2017 ◽  
Vol 50 (1) ◽  
pp. 39-49 ◽  
Author(s):  
Anna Kaiser ◽  
Chris Van Houtte ◽  
Nick Perrin ◽  
Liam Wotherspoon ◽  
Graeme McVerry
Keyword(s):  
New Zealand ◽  
Shear Wave ◽  
Ground Motion ◽  
Shear Wave Velocity ◽  
Strong Motion ◽  
Motion Prediction ◽  
Ground Motion Prediction ◽  
High Quality ◽  
Site Specific ◽  
Strong Motion Database

The New Zealand Strong Motion Database provides a wealth of new strong motion data for engineering applications. In order to utilise these data in ground motion prediction, characterisation of key site parameters at each of the ~497 past and present GeoNet strong motion stations represented in the database is required. Here, we present the compilation of a complete set of site metadata for the New Zealand database, including four key parameters: i) NZS1170.5 site subsoil classification, ii) the time-averaged shear-wave velocity to a depth of 30 m (Vs30), iii) fundamental site period (Tsite) and iv) depth to a shear-wave velocity of 1000 m/s (Z1.0, a proxy for depth to bedrock). In addition, we have assigned a quality estimate (Quality 1 – 3) to each numerical parameter to provide a qualitative estimate of the uncertainty. New high-quality Tsite, Vs30 and Z1.0 estimates have been obtained from a variety of recent studies, and reconciled with available geological information. This database will be used in efforts to guide development and testing of new and existing ground motion prediction models in New Zealand, allowing re-examination of the most important site parameters that control site response in a New Zealand setting. Preliminary analyses, using the newly compiled data, suggest that high quality site parameters can reduce uncertainty in ground motion prediction. Furthermore, the database can be used to identify suitable rock reference sites for seismological research, and as a guide to more detailed site-specific references in the literature. The database provides an additional resource for informing engineering design, however it is not suitable as a replacement for site-specific assessment.

Identification of Engineering Bedrock in Taiwan based on Site Amplification and Velocity Structures of Strong-motion Stations

2020 ◽  
Author(s):  
Che-Min Lin ◽  
Jyun-Yan Huang ◽  
Chun-Hsiang Kuo ◽  
Kuo-Liang Wen
Keyword(s):  
Shear Wave ◽  
Ground Motion ◽  
Wave Velocity ◽  
Earthquake Engineering ◽  
Shear Wave Velocity ◽  
Receiver Function ◽  
Ground Surface ◽  
Strong Motion ◽  
Site Amplification ◽  
Velocity Profiles

<p>There are two kinds of bedrocks that are widely used in seismology and earthquake engineering respectively. The seismology field uses the “seismic bedrock” to define an interface that has a practically lateral extent. The strata deeper than this interface is much more homogeneous in comparison with the shallower one. It is common to set the seismic bedrock within the upper crust has 3000 m/sec of the shear wave velocity. In contrast, the earthquake engineering prefers the shallower interface which dominates the main seismic site amplification, especially the predominant frequency of ground motion. The interface is called “Engineering Bedrock”, which the underlying stratum has the shear wave velocity from 300 to 1000 m/sec for different purposes. But, the reference shear wave velocity of the engineering bedrock is mostly defined as 760 m/sec for ground motion prediction and simulation. In Taiwan, the Central Weather Bureau (CWB) constructed and operates a dense strong-motion network called TSMIP (Taiwan Strong Motion Instrument Program), which provides numerous ground motion data for seismology and earthquake engineering. In our previous studies, the shallow shear wave velocity profiles of over 700 TSMIP stations were estimated by the Receiver Function method. The velocity profiles are from the ground surface to the depth with the shear wave velocity of at least 2000 m/sec. It allows us to compare the theoretical site amplification of the velocity profile of TSMIP stations with their observed one from the seismic records. The variance of fitness between theoretical and observed amplifications through shear wave velocity is analyzed to evaluate which reference velocity can appropriately define the depth of engineering bedrock, where the most site amplification occur beneath, in all of Taiwan. The difference between local geology is also discussed. Finally, an engineering bedrock map is proposed for further applications in earthquake engineering.</p>

scholarly journals Nonlinear Site Amplification as Function of 30 m Shear Wave Velocity

2005 ◽  
Vol 21 (1) ◽  
pp. 1-30 ◽  
Author(s):  
Yoojoong Choi ◽  
Jonathan P. Stewart
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Active Regions ◽  
Site Amplification ◽  
Site Factors ◽  
Empirical Relationships ◽  
Amplification Factors ◽  
Attenuation Relationships ◽  
Average Shear

We develop empirical relationships to predict nonlinear (i.e., amplitude-dependant) amplification factors for 5% damped response spectral acceleration as a continuous function of average shear wave velocity in the upper 30 m, Vs-30. We evaluate amplification factors as residuals between spectral accelerations from recordings and modified rock attenuation relationships for active regions. Amplification at low- and mid-periods is shown to increase with decreasing Vs-30 and to exhibit nonlinearity that is dependent on Vs-30. The degree of nonlinearity is large for NEHRP Category E (Vs-30<180 m/s) but decreases rapidly with Vs-30, and is small for Vs-30>∼300 m/s. The results can be used as Vs-30-based site factors with attenuation relationships. The results also provide an independent check of site factors published in the NEHRP Provisions, and apparent bias in some of the existing NEHRP factors is identified. Moreover, the results provide evidence that data dispersion is dependent on Vs-30.

scholarly journals Variability of Ground Motion Amplitudes Recorded in Bucharest Area during Vrancea Intermediate-Depth Earthquakes

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Florin Pavel
Keyword(s):  
Shear Wave ◽  
Ground Motion ◽  
Site Amplification ◽  
Peak Ground Velocity ◽  
Eurocode 8 ◽  
Intermediate Depth ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Normal Probability ◽  
Normal Probability Distribution

This study focuses on the assessment of the correlation and variability of ground motion amplitudes recorded in Bucharest area during Vrancea intermediate-depth earthquakes from a database of 119 pairs of horizontal components. Empirical models for the evaluation of the peak ground velocity and displacement from spectral accelerations are proposed in this study. The distribution of the shear wave velocities from 41 boreholes at specific depths appears to follow a normal probability distribution. The analysis performed in this study has also shown that the variability of peak ground velocities and displacements does not appear to be influenced by the earthquake magnitude. In addition, it was observed that the variability in terms of shear wave velocities at specific depths is smaller than the variability of the spectral amplitudes of the recorded ground motions. The empirical site-amplification factors from the Eurocode 8 draft fail to capture the long-period spectral amplifications observed in Bucharest area during large magnitude Vrancea intermediate-depth earthquakes.

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