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

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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3D Nonlinear Ground‐Motion Simulation Using a Physics‐Based Method for the Kinburn Basin

Bulletin of the Seismological Society of America ◽

10.1785/0120180201 ◽

2019 ◽

Cited By ~ 1

Author(s):

Amin Esmaeilzadeh ◽

Dariush Motazedian ◽

Jim Hunter

Keyword(s):

Shear Wave ◽

Ground Motion ◽

Seismic Waves ◽

Peak Ground Velocity ◽

Ground Acceleration ◽

Low Frequencies ◽

Wave Velocities ◽

Shear Wave Velocities ◽

Nonlinear Viscoelastic ◽

Finite Fault

Abstract We used a finite‐difference modeling method, developed by Olsen–Day–Cui, to simulate nonlinear‐viscoelastic basin effects in a spectral frequency range of 0.1–1 Hz in the Kinburn bedrock topographic basin, Ottawa, Canada, for large earthquakes. The geotechnical and geological features of the study area are unique: loose, postglacial sediments with very low shear‐wave velocities (<200 m/s) overlying very firm bedrock with high shear‐wave velocities (>2000 m/s). Comparing records and simulated velocity time series showed regular viscoelastic simulations could model the ground motions at the rock and soil sites in the Kinburn basin for the Ladysmith earthquake, a local earthquake occurred on 17 May 2013 with Mw 4.7 (MN 5.2). The Ladysmith earthquake was scaled to provide a strong level of shaking for investigating the nonlinear behavior of soil; therefore, a new nonlinear‐viscoelastic subroutine was introduced to the program. A modeled stress–strain relationship associated with ground‐motion modeling in the Kinburn basin using a scaled Ladysmith earthquake event of Mw 7.5 followed Masing’s rules. Using nonlinear‐viscoelastic ground‐motion simulations significantly reduced the amplitude of the horizontal component of the Fourier spectrum at low frequencies and the predicted peak ground acceleration and peak ground velocity values compared with regular linear viscoelastic simulations; hence, the lower soil amplification of seismic waves and the frequency and amplitude spectral content were altered by the nonlinear soil behavior. In addition, using a finite‐fault model to simulate an earthquake with Mw 7.5 was necessary to predict the higher levels of stresses and strains, which were generated in the basin. Using a finite‐fault source for the nonlinear‐viscoelastic simulation caused decreases in the horizontal components because of the shear modulus reduction and increase of damping.

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

Bulletin of Earthquake Engineering ◽

10.1007/s10518-021-01118-9 ◽

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.

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Implications of the Mw9.0 Tohoku-Oki Earthquake for Ground Motion Scaling with Source, Path, and Site Parameters

Earthquake Spectra ◽

10.1193/1.4000115 ◽

2013 ◽

Vol 29 (1_suppl) ◽

pp. 1-21 ◽

Cited By ~ 17

Author(s):

Jonathan P. Stewart ◽

Saburoh Midorikawa ◽

Robert W. Graves ◽

Khatareh Khodaverdi ◽

Tadahiro Kishida ◽

...

Keyword(s):

Ground Motion ◽

Ground Motions ◽

Site Amplification ◽

Low Frequencies ◽

High Frequencies ◽

Wave Velocities ◽

Shear Wave Velocities ◽

Active Tectonic ◽

Motion Scaling ◽

Ground Motion Scaling

The Mw9.0 Tohoku-oki Japan earthquake produced approximately 2,000 ground motion recordings. We consider 1,238 three-component accelerograms corrected with component-specific low-cut filters. The recordings have rupture distances between 44 km and 1,000 km, time-averaged shear wave velocities of VS30 = 90 m/s to 1,900 m/s, and usable response spectral periods of 0.01 sec to >10 sec. The data support the notion that the increase of ground motions with magnitude saturates at large magnitudes. High-frequency ground motions demonstrate faster attenuation with distance in backarc than in forearc regions, which is only captured by one of the four considered ground motion prediction equations for subduction earthquakes. Recordings within 100 km of the fault are used to estimate event terms, which are generally positive (indicating model underprediction) at short periods and zero or negative (overprediction) at long periods. We find site amplification to scale minimally with VS30 at high frequencies, in contrast with other active tectonic regions, but to scale strongly with VS30 at low frequencies.

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Review article "Remarks on factors influencing shear wave velocities and their role in evaluating susceptibilities to earthquake-triggered slope instability: case study for the Campania area (Italy)"

Natural Hazards and Earth System Science ◽

10.5194/nhess-12-2147-2012 ◽

2012 ◽

Vol 12 (7) ◽

pp. 2147-2158 ◽

Cited By ~ 4

Author(s):

V. Paoletti

Keyword(s):

Shear Wave ◽

Slope Failure ◽

Site Amplification ◽

Review Article ◽

Slope Instability ◽

Careful Evaluation ◽

Wave Velocities ◽

Shear Wave Velocities ◽

Factors Influencing

Abstract. Shear wave velocities have a fundamental role in connection with the mitigation of seismic hazards, as their low values are the main causes of site amplification phenomena and can significantly influence the susceptibility of a territory to seismic-induced landslides. The shear wave velocity (Vs) and modulus (G) of each lithological unit are influenced by factors such as the degree of fracturing and faulting, the porosity, the clay amount and the precipitation, with the latter two influencing the unit water content. In this paper we discuss how these factors can affect the Vs values and report the results of different analyses that quantify the reduction in the rock Vs and shear modulus values connected to the presence of clay and water. We also show that significant results in assessing seismic-induced slope failure susceptibility for land planning targets could be achieved through a careful evaluation, based only on literature studies, of the geo-lithological and geo-seismic features of the study area.

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