Equivalent Shear Wave Velocity Research Articles

Geomorphological site classification for the Fujian province

Geomorphological classification of the Fujian province was done based on remote-sensing imaging, digital elevation maps, and slope gradient data acquired by ArcGIS 9.2. The engineering geological units in the Fujian province were divided into five types by the geomorphologic shape and genesis. The relationship among geomorphological type, engineering geological unit, and site category was determined using engineering geological data and site category data. Then, after making a preliminary site classification adjusted by drill hole data, the site was classified into four types: I0, I1, II, and III according to site classification standards of equivalent shear-wave velocity and overburden thickness. The results showed that the site categories in the Fujian province mainly consist of type II, which accounts for 85.26 % of the land area. The percentage of I0 was the smallest, which accounts for only 2.44 % of the total area.

Reply to comment on ‘Shear wave profile from surface wave inversion: the impact of uncertainty on seismic site response analysis’

Socco et al (2012 J. Geophys. Eng. 9 241) comment on our study about the effect of non-uniqueness of surface wave solutions on seismic site response analysis. In particular, they refer to the approach we adopted for the selection of equivalent shear wave velocity profiles and argue that it leads to overestimation of the uncertainty due to the inherent ill-posedness of the problem. Moreover, for one of the synthetic cases of our original paper, they calculate a different set of equivalent velocity profiles, retrieving the corresponding amplification spectra. From these results, Socco et al claim that their general conclusion that the impact of solution non-uniqueness on seismic response simulations is negligible. In this reply we demonstrate that (a) the uncertainty bounds used by Socco et al in their prediction analysis, as a consequence of their surface wave inversion procedure, are unreasonably narrow; (b) consequently, their shaking predictions appear to suffer no impact from their underestimated uncertainty; and (c) their presented case shows an amplification spectrum that is only the result of assuming the existence of a bedrock at 150 m that causes resonance of the overlying layer—practically independent of the details of the S-wave velocity distribution.

Modeling shear rigidity of stratified bedrock in site response analysis

Where a distinct soil–rock interface exists, the bedrock medium is commonly treated as elastic half-space and the bedrock surface as the lower boundary of the soil-column model for site response analyses (or the lower boundary of the finite element model for soil-structure interaction analyses). While shear wave velocity in bedrock varies with depth, there has been no consensus amongst scientists and practitioners over the value of “effective depth” into bedrock at which the “half-space” shear wave velocity value should be taken for modeling purposes. This paper reports an interesting and important observation that the effective depth into bedrock is sensitive to the shear wave velocity profile of the overlying soil sediments. A simple and heuristic method, namely Resonant Period Equivalence ( RPE) Method, is proposed herein for representing a stratified elastic bedrock of inhomogeneous properties by an equivalent homogeneous elastic half-space medium, which is characterized by a single equivalent shear wave velocity ( V R) value. The proposed calculation method has been verified by extensive comparative analyses involving the use of programs SHAKE and NERA and employing the complete shear wave velocity models of both the soil sediments and the underlying stratified bedrock.

Amplification based on shear wave velocity for seismic zonation: comparison of empirical relations and site response results for shallow engineering bedrock sites

Amplification based on empirical relations is widely used for seismic microzonation of urban centers. Amplifications are used to represent the site effects of a particular soil column. Many empirical correlations are available to estimate the amplification of seismic waves. These correlations are based on the ratio of shear wave velocity of foundation/rock to soil velocity or 30 m equivalent shear wave velocity (<TEX>$Vs^{30}$</TEX>) and are developed considering deep soil data. The aim of this work is to examine the applicability of available amplification relations in the literature for shallow engineering bedrock sites by carrying out site response studies. Shear wave velocity of thirteen sites having shallow engineering bedrock have been selected for the study. In these locations, the depth of engineering bedrock (> 760 <TEX>${\pm}$</TEX> 60 m/s) is matched with the drilled bore hole. Shear wave velocity (SWV) has been measured using Multichannel Analysis of Surface Wave survey. These sites are classified according to the National Earthquake Hazards Reduction Program (NEHRP) classification system. Amplifications for an earthquake are arrived for these sites using empirical relations and measured SWV data. Site response analysis has been carried out in SHAKE using SWV and using synthetic and real earthquake data. Amplification from site response analysis and empirical relations are compared. Study shows that the amplification arrived using empirical relations does not match with the site response amplification. Site response amplification is much more than empirical values for same shear wave velocity.

Effect of Vibrating Buildings on Free-Field Motion and on Adjacent Structures: The Bonefro (Italy) Case History

Abstract During the 2002 Molise sequence, a shock was recorded in a building that suffered heavy damage (Mucciarelli et al. , 2004). The availability of this data, along with other similar data, led to the organization of an international workshop for structural engineers aimed at the reproduction of the staged evolution of damage observed (A. Goretti and M. Mucciarelli, unpublished manuscript, 2007). The aim of this present work is to model the damaged building; the adjacent, less damaged building; and a large section of the subsoil. The model should provide some insight into two possible phenomena: (1) the soil–structure interaction (SSI), that is, the modification of the free-field seismic response induced by the presence of the buildings located on soft soil; and (2) the possible interaction between the two buildings. The study was performed using the 2D Chebyshev spectral element method (SPEM) for a 2D section. The model, with topography, includes the bedrock (limestone) with the overlaying clay layer, circa 30 m. The building is modeled by an equivalent shear-wave velocity, which is calculated from its identified mechanical properties. First, the model’s ability to reproduce the motions recorded inside and outside the building was verified. Then, one or both of the buildings were removed to study their effect. The influence of the presence of buildings on the free-field motion is about 40% on spectral values, and it is felt up to a distance of about 250 m from the buildings. The results also suggest the presence of resonance between buildings.

Preliminary site classification of free-field strong motion stations based on Wenchuan earthquake records

During the great Wenchuan earthquake, about 460 permanent free-field stations in National Strong Motion Observation Network System (NSMONS) of China captured the main shock acceleration records. These records can be applied to site effect analyses, and then the site classification of those permanent stations can be carried out firstly, which will served as the fundamental information for further research. In this paper, the site of near-fault stations is classified by horizontal-to-vertical spectral ratio (HVSR) method according to the site class description of Japan earthquake resistant design code and response spectral shapes (RSS) method following the site class description of the 1997 Uniform Building Code (UBC) provisions. Then based on the detailed borehole data of those free-field stations, the equivalent shear wave velocity and overburden thickness are calculated and the site classifications are given by Chinese code for seismic design of buildings. Furthermore, for the stations having successful microtremor test data, the site dominant periods are computed to verify the results of site classification. Finally, combined with all the above results, the recommended site classes of near-fault permanent free-field stations are given.

Non-uniqueness in surface-wave inversion and consequences on seismic site response analyses

Surface-wave tests are based on the solution of an inverse problem for shear-wave velocity profile identification from the experimentally measured dispersion curve. The main criticisms for these testing methodologies are related to the inverse problem solution and arise from the possible equivalence of different shear-wave velocity profiles. In this paper, some implications of solution non-uniqueness for seismic response studies are investigated using both numerical simulations and experimental data. A Monte Carlo approach for the inversion problem has been used to obtain a set of equivalent shear-wave velocity models. This selection is based on a statistical test which takes into account both data uncertainty and model parameterization. This set of solutions (i.e., soil profiles) is then used to evaluate the seismic response with a conventional one-dimensional analysis. It is shown that equivalent profiles with respect to surface-wave testing are equivalent also with respect to site amplification, thus countering the criticism related to inversion uncertainty for the engineering use of surface-wave tests.

応答スペクトル法による表層地盤の非線形増幅特性の解析法

This paper proposes a response spectrum method (RSM) for evaluating nonlinear amplification of surface strata (SS) overlying an engineering bedrock (EBR). The proposed RSM follows the procedures below. (1) Represent the response characteristics of SS on EBR by a multi-lumped mass model with shear springs and damping coefficients. (2) Calculate a period T1, a mode shape {U1} and a modal damping factor ƒA1 for the first vibration mode. (3) Evaluate the equivalent shear wave velocity Vse of SS. (4) Evaluate the amplification factor R1 of the surface to EBR at T1 using the Haskell matrix of two strata consisting of an equivalent SS with Vse and ƒA1 on EBR. (5) Evaluate the displacements in SS from R1{U1}, and hence evaluate the shear strains. (6) In accordance with nonlinear relations between shear modulus (G), damping factors (h) and shear strains, replace soil constants G and h by those corresponding to strains. (7) Return to step (1) with revised G and h. Iterate these procedures until T1 becomes stable. (8) After T1 is converged, calculate the response distributions in SS. The results obtained by the proposed RSM are compared with those by “SHAKE” in terms of the response spectrum at the surface as well as distributions of displacement, shear wave velocity and damping factor in SS. The applicability of the proposed RSM for evaluating the nonlinear amplification of SS is confirmed through the comparative studies.