Amplification Effects of Thin Soft-Surface Layers

2016 ◽  
Vol 32 (4) ◽  
pp. 2109-2126 ◽  
Author(s):  
W. D. Liam Finn ◽  
Francisco Ruz
Keyword(s):  
Soft Soil ◽  
Soil Layer ◽  
Tohoku Earthquake ◽  
Response Spectra ◽  
Surface Layers ◽  
Soft Layer ◽  
The 2011 Tohoku Earthquake ◽  
Amplification Factors ◽  
Soft Surface ◽  
Using Data

The amplification effects of shallow soft-surface layers with respect to an underlying hard-soil layer or rock are studied using data recorded from the 2011 Tohoku earthquake. Twenty-four sites have been studied with depths to rock ranging from 4–30 m. At each site, two records were available: one in rock at the bottom of the borehole at depths of 100–500 m and one on the surface of the soft-soil layer. Analyses of the soil-rock columns were conducted using the program SHAKE. Good agreement was found between calculated and recorded surface spectra, which demonstrated the reliability of SHAKE analyses for the sites under study. Therefore, SHAKE analyses were used to determine the outcrop motions at the top of rock. Amplification factors were determined by comparing characteristics of the surface and outcrop motions such as Fourier and response spectra. Computed amplification factors were correlated with V S30, V soil, and soft layer period, T = 4 H/ V soil. The results show clearly that the most reliable correlations for estimating the amplification of soft shallow surface layers less than 30 m are those based on V S30 and soft layer period, T.

Erdbebenantwortspektren einer weichen Bodenschicht auf einem Halbraum/Earthquake response spectra of a soft soil layer underlain by a halfspace

Bauingenieur ◽  
2016 ◽  
Vol 91 (04) ◽  
pp. 131-139
Author(s):  
Horst Werkle
Keyword(s):  
Soft Soil ◽  
Soil Layer ◽  
Response Spectra ◽  
Earthquake Response ◽  
Earthquake Response Spectra

Weiche Bodenschichten, wie sie beispielsweise als Tonschichten über steifen Sedimentböden auftreten, beeinflussen die Form eines horizontalen Erdbeben-Antwortspektrums aufgrund von resonanzartigen Effekten der einfallenden SH-Wellen erheblich. Daher werden etwa im EC 8 (deutsches NAD) für weiche Böden mit Scherwellengeschwindigkeiten unter 150 m/s besondere Untersuchungen gefordert. Auf der Grundlage einer intensiven Parameterstudie wurden für das Modell einer homogenen viskoelastischen Bodenschicht auf einem homogenen viskoelastischen Halbraum Gleichungen zur Beschreibung des zugehörigen horizontalen Beschleunigungsantwortspektrums entwickelt. An der Oberfläche des Halbraums wurde ein Antwortspektrum nach EC 8, Boden-/Untergrundklasse C-S angenommen. Die mit den Gleichungen erhaltenen Antwortspektren stimmen mit den nach der Theorie für eindimensionale Scherwellen erhaltenen Ergebnissen gut überein. Sie können unmittelbar zur Ermittlung der Erdbebenbeanspruchungen von Gebäuden auf einer weichen Bodenschicht nach EC 8 verwendet werden.

scholarly journals Seismic Response of Soft Soil Deposit Using Simplified Models

2019 ◽  
Vol 92 ◽  
pp. 16008
Author(s):  
Miguel Villalobos ◽  
Celso Romanel
Keyword(s):  
Seismic Response ◽  
Seismic Station ◽  
Soft Soil ◽  
Linear Method ◽  
Tohoku Earthquake ◽  
Site Classification ◽  
The 2011 Tohoku Earthquake ◽  
Soft Soils ◽  
Near Surface ◽  
The Real

Near surface soils can greatly influence the amplitude, duration, and frequency content of ground motions. Surveys of the damage caused by earthquakes indicates that the lowest levels of damage occur in structures founded on rock or hard soil, while most of the damage occurs usually in structures founded in soft soil sites. With the aim to understand better the seismic response of soft soils deposits, not susceptible to liquefaction, this study made a comparison between the real seismic response registered in soft soil deposit in the 2011 Tohoku earthquake (Mw=9.1), with the response predicted by a propagation analysis with the equivalent linear method using the computer program SHAKE2000 [1]. An additional comparison is made applying the simplified method of Carlton (2014), developed specifically for soft soils. The site chosen for this analysis was a soft soil deposit, with NEHRP site classification type F, monitored by the seismic station TKCH07 of the KiK-net network located in Hokaiddo, Japan. The estimated response showed and acceptable approximation with the real response, although the response calculated with SHAKE2000 predicted high levels of amplification near the natural frequencies of the soft soil deposit.

Evaluation of local site effects and their removal from borehole records observed in the Sendai region, Japan

1995 ◽  
Vol 85 (6) ◽  
pp. 1770-1789 ◽  
Author(s):  
Toshimi Satoh ◽  
Hiroshi Kawase ◽  
Toshiaki Sato
Keyword(s):  
Site Effects ◽  
Soft Soil ◽  
Standard Penetration Test ◽  
Response Analysis ◽  
S Wave ◽  
Surface Layers ◽  
Local Site Effects ◽  
Amplification Factors ◽  
Wave Velocities ◽  
Local Site

Abstract We present results from a borehole observation network composed of 12 borehole sites deployed in a 20 × 20 km area in the Sendai region, Japan. The subsurface Quaternary layers vary with each site, but a Pliocene layer is commonly underlying at a depth of 0 to 80 m throughout the Sendai region. We define this Pliocene layer, whose S-wave velocity is larger than 500 m/sec and whose N value of the standard penetration test is greater than 50, as an engineering bedrock in the region. Once we characterize ground motions at the engineering bedrock, we can either use these motions directly in the response analysis of whole soil-building systems or use them in the nonlinear analysis of soft soil layers as an input. The purpose of this study is to evaluate the local site effects due to surface layers overlying the engineering bedrock and to remove them by using one-dimensional (1D) soil models whose properties are determined by weak-motion records of 18 events. First we identify S-wave velocities and frequency-dependent quality factors Q from amplification factors between surface records and borehole records observed at 10 sites at depths of several tens of meters. The identified S-wave velocities are very close to S-wave logging values. The identified Q values show strong frequency dependence, proportional to f(0.46 to 1.16), where f is frequency. We confirm that the observed amplification factors in the frequency range from about 0.1 to 20 Hz can be explained well by the theoretical ones based on the 1D wave propagation theory with the identified S-wave velocities and Q. Then we estimate the so-called engineering bedrock waves, which are supposed to be observed on the outcrop of the engineering bedrock, from borehole records by using the 1D models with these identified soil constants. We confirm that local site effects due to surface layers overlying the engineering bedrock are properly removed so that we have similar characteristics in the resultant engineering bedrock waves from records at different sites.

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.

Evaluation of floor acceleration demands from the 2017 Mexico City code seismic provisions using a continuous elastic model and records of instrumented buildings

2020 ◽  
Vol 36 (2_suppl) ◽  
pp. 213-237
Author(s):  
Miguel A Jaimes ◽  
Adrián D García-Soto
Keyword(s):  
Mexico City ◽  
Seismic Design ◽  
Soft Soil ◽  
Response Spectra ◽  
Elastic Model ◽  
Ground Acceleration ◽  
Nonstructural Components ◽  
Floor Response Spectra ◽  
Instrumented Buildings ◽  
Floor Acceleration

This study presents an evaluation of floor acceleration demands for the design of rigid and flexible acceleration-sensitive nonstructural components in buildings, calculated using the most recent Mexico City seismic design provisions, released in 2017. This evaluation includes two approaches: (1) a simplified continuous elastic model and (2) using recordings from 10 instrumented buildings located in Mexico City. The study found that peak floor elastic acceleration demands imposed on rigid nonstructural components into buildings situated in Mexico City might reach values of 4.8 and 6.4 times the peak ground acceleration at rock and soft sites, respectively. The peak elastic acceleration demands imposed on flexible nonstructural components in all floors, estimated using floor response spectra, might be four times larger than the maximum acceleration of the floor at the point of support of the component for buildings located in rock and soft soil. Comparison of results from the two approaches with the current seismic design provisions revealed that the peak acceleration demands and floor response spectra computed with the current 2017 Mexico City seismic design provisions are, in general, adequate.

scholarly journals Middle-Scale Ionospheric Disturbances Observed by the Oblique-Incidence Ionosonde Detection Network in North China after the 2011 Tohoku Tsunamigenic Earthquake

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 1000
Author(s):  
Jin Wang ◽  
Gang Chen ◽  
Tao Yu ◽  
Zhongxin Deng ◽  
Xiangxiang Yan ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Oblique Incidence ◽  
North China ◽  
Tohoku Earthquake ◽  
Ionospheric Disturbances ◽  
Doppler Measurement ◽  
The 2011 Tohoku Earthquake ◽  
Tsunamigenic Earthquake ◽  
The Pacific ◽  
The Pacific Ocean

The 2011 Tohoku earthquake and the following enormous tsunami caused great disturbances in the ionosphere that were observed in various regions along the Pacific Ocean. In this study, the oblique-incidence ionosonde detection network located in North China was applied to investigate the inland ionospheric disturbances related to the 2011 tsunamigenic earthquake. The ionosonde network consists of five transmitters and 20 receivers and can monitor regional ionosphere disturbances continuously and effectively. Based on the recorded electron density variations along the horizontal plane, the planar middle-scale ionospheric disturbances (MSTIDs) associated with the 2011 Tohoku tsunamigenic earthquake were detected more than 2000 km west of the epicenter about six hours later. The MSTIDs captured by the Digisonde, high-frequency (HF) Doppler measurement, and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellite provided more information about the far-field inland propagation characteristics of the westward propagating gravity waves. The results imply that the ionosonde network has the potential for remote sensing of ionospheric disturbances induced by tsunamigenic earthquakes and provide a perspective for investigating the propagation process of associated gravity waves.

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