Multiple estimates of soil structure at a vertical strong motion array: Understanding uncertainties from different shear wave velocity profiles

Raptakis, Dimitrios; Makra, Konstantia

doi:10.1016/j.enggeo.2015.03.016

Cited by 9 publications

(5 citation statements)

References 42 publications

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“…For stations BUT and SCT the information is inadequate, so we infer V s30 through correlation with neighbouring stations. For TST-196, the V s30 is based on Raptakis & Makra (2015). In Fig.…”

Section: Correlation With Shallow Geology (First 30 M)mentioning

confidence: 99%

Understanding the physics of kappa (κ): insights from a downhole array

et al. 2015

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S U M M A R YAt high frequencies, the acceleration spectral amplitude decreases rapidly; this has been modelled with the spectral decay factor κ. Its site component, κ 0 , is used widely today in ground motion prediction and simulation, and numerous approaches have been proposed to compute it. In this study, we estimate κ for the EUROSEISTEST valley, a geologically complex and seismically active region with a permanent strong motion array consisting of 14 surface and 6 downhole stations. Site conditions range from soft sediments to hard rock. First, we use the classical approach to separate local and regional attenuation and measure κ 0 . Second, we take advantage of the existing knowledge of the geological profile and material properties to examine the correlation of κ 0 with different site characterization parameters. κ 0 correlates well with V s30 , as expected, indicating a strong effect from the geological structure in the upper 30 m. But it correlates equally well with the resonant frequency and depth-to-bedrock of the stations, which indicates strong effects from the entire sedimentary column, down to 400 m. Third, we use our results to improve our physical understanding of κ 0 . We propose a conceptual model of κ 0 with V s , comprising two new notions. On the one hand, and contrary to existing correlations, we observe that κ 0 stabilizes for high V s values. This may indicate the existence of regional values for hard rock κ 0 . If so, we propose that borehole measurements (almost never used up to now for κ 0 ) may be useful in determining these values. On the other hand, we find that material damping, as expressed through travel times, may not suffice to account for the total κ 0 measured at the surface. We propose that, apart from material damping, additional site attenuation may be caused by scattering from small-scale variability in the profile. If this is so, then geotechnical damping measurements may not suffice to infer the overall crustal attenuation under a site; but starting with a regional value (possibly from a borehole) and adding damping, we might define a lower bound for site-specific κ 0 . More precise estimates would necessitate seismological site instrumentation.

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Section: Correlation With Shallow Geology (First 30 M)mentioning

confidence: 99%

Understanding the physics of kappa (κ): insights from a downhole array

et al. 2015

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“…Where each layer has its unique characteristics such as the seismic velocity, thickness and geotechnical parameters (Cai et al, 2014;Sopaci and Akgun, 2015;Raptakis and Makra, 2015). Azwin et al (2013b) confirmed the possibility of applying seismic refraction method in the production of 2D profiles of the subsurface for site characterization.…”

Section: Introductionmentioning

confidence: 72%

Evaluation of geotechnical parameters of reclaimed land from near-surface seismic refraction method

Adewoyin

Joshua

Akinyemi

et al. 2021

Heliyon

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Correct execution of civil engineering structures depends largely on the adequate and detailed mapping of the subsurface. This can be achieved by the application of appropriate geophysical or geotechnical methods in association with a detailed information on the geological sequence of the subsurface structure. In this study, a combination of near surface seismic refraction method, cone penetration test and borehole logs were used to obtain 2-dimensional (2D) information of the subsurface geological features. These methods were used to characterize the subsurface condition of a reclaimed land in Ajah area of Lagos for the purpose of construction. The seismic refraction method revealed three geologic layers with seismic velocities ranging between 258 and 3544 m/s. Additionally, the cone penetration test revealed that the geologic formation from the topsoil to a depth of 6 m was an alluvium of soft and highly compressible property. Furthermore, the percussion drilling test also confirmed the geologic formation from the topsoil to a depth of about 6 m to be highly compressible. However, a geologic formation with good geotechnical characteristics, such as a low compressibility potential, was encountered at a depth between 7 and 16 m, which coincides with the third layer of the seismic refraction method. The results of the three methods confirmed that the depth to most competent layer must be located before the foundations of engineering constructions are sited.

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“…Recordings from 8 earthquakes at the vertical accelerometric array were used to determine VS velocity of soil layers (figure 1a) using seismic interferometry of ground motion (Raptakis and Makra, 2015). Raw data have been corrected for instrument response and baseline offset.…”

Section: Vs Profiles At Tst Sitementioning

confidence: 99%

“…All these surface measurements together with cross-hole (CH) and down-hole (DH) tests are performed in a limited area (of about 0.25 km 2 ) around TST site and their analysis led to a total of 26 VS profiles ( Figure 2). Details could be found in Raptakis and Makra (2015). Field measurements of different lengths, geophone spacings and offsets are performed in order to achieve good resolution VS profiles at depths from top to 10-50 m ( Ambient noise array measurements (AMN).…”

Section: Vs Profiles At Tst Sitementioning

confidence: 99%

“…liquefaction, soilfoundation-structure interaction etc.). On the other hand, the exploration of Vs velocity is a rather non-straightforward task due to the nature of the demands of the anticipated study and its non-unique evaluation from different techniques (for details see also Raptakis, 2012, 2013and Raptakis and Makra, 2015. Then, in such cases of different VS estimates available at a site, it is necessary to understand the differences and not simply compute an average.…”

Section: Introductionmentioning

confidence: 99%

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