Ratio Of Ground Motions Research Articles

Site amplification characteristics of bedrock using three reference site methods

ABSTRACTWith the growing interest in seismic hazards following the Gyeongju earthquake (ML 5.8; 2016), information on site amplification characteristics is essential for the effective analysis of seismic hazards in urban areas. To assess amplification characteristics, this study used three reference site methods. Two new modified reference methods were compared with the existing method, which relies on the horizontal/vertical (H/V) ratios of ground motions at the target and reference sites. For each type of seismic energy (S-wave, coda wave and background noise), similarities between the H/V spectral ratios (HVSR) for all three reference site methods were investigated. Site amplification characteristics were analysed using 216 acceleration ground motions of horizontal and vertical components for three earthquakes (Odaesan, Jeju and Gongju), observed simultaneously at four sites and having a magnitude > 3.4. Most electric substations showed similar HVSR behaviour for the three types of seismic energy and three reference site methods over a significant frequency range, with few exemptions. Although site amplification characteristics in the low- and high-frequency ranges, as well as the specific resonance frequency of each electric substation, varied greatly, the site amplification characteristics of the four sites could be classified into two groups: sites with a resonance frequency and those without. First, with the exception of New Taeback (NTB), the sites shared fundamental resonance frequencies in the range between ∼ 5 and ∼ 10 Hz. Second, NTB did not show any significant resonance, which may imply that it is located on a very firm rock formation. Considering all the resonance frequencies, the four sites can be classified as TB or harder rocks. By comparing the results with those from other regions, it is possible to provide insight into the site characteristics and the site classification methodology.

Amplification characteristics of seismic observation sites from S-wave energy, coda waves and background noise from the Fukuoka earthquake series

In Korea, several problems have been identified in the design standards for earthquake resistance, within a high-frequency range, due to the inappropriate characterisation of local site amplification characteristics. Among the methods that have been suggested for analysis of site amplification characteristics is one that uses the H/V spectral ratio of ground motions, which was used in this study. The method can be applied to S-waves, coda waves, and background noise. Based on a series of 15 aftershocks of the Fukuoka earthquake of 20 March 2005, analyses were conducted for a total of 267 sets of ground motion data observed at seismic stations in Korea. Most of the seismic stations suggested consistent site amplification characteristics among the three types of seismic energies despite a logarithmic difference of three or larger in the Fourier transform value of the observed waves, and also despite long epicentre distances, even greater than 600 km. The stations KHD, GSU, HSB and TJN showed no dominant resonance frequencies because they are located on solid bedrock or have borehole seismic sensors. It is necessary to use care when considering stations GKP1, KRA, and SNU, which have distinct resonance frequencies. The results of this study are essential for the effective design of earthquake-resistant structures and also for reliable seismic source and crustal attenuation studies.

Erratum to: A model for predicting vertical component peak ground acceleration (PGA), peak ground velocity (PGV) and 5% damped pseudospectral acceleration (PSA) for Europe and the Middle East

In this study, we present a ground-motion model for the vertical component of peak ground acceleration, peak ground velocity, and 5% damped pseudo acceleration response spectra at periods ranging from 0.01 to 4 s. The vertical model is based on the ground-motion models previously developed for the horizontal component and vertical-to-horizontal ratio of ground motion by Akkar et al. (Bull Earthq Eng 12:359–387, 2014a; 517–547, 2014b) rather than on an independent regression analysis of strong-motion data available for Europe and the Middle East. The proposed ground-motion model includes formulations for the median values as well as for the aleatory within-event, between-event, and total standard deviation values of the vertical ground motion. We validate the proposed model by comparing it against the strong-motion database of Europe and the Middle East. Our vertical ground-motion model is applicable for moment magnitudes ranging from 4.0 to 8.0, for source-to-site distances ranging from 0 to 200 km, average shear-velocity down to 30 m (Vs30) values ranging from 150 to 1200 m/s and for reverse, normal and strike-slip styles of faulting as is the case for the underlying horizontal component and vertical-to-horizontal ratio ground-motion models of Akkar et al. (2014a, b). Within the scope of this study, a method to develop a vertical spectrum that is fully consistent with the corresponding horizontal uniform hazard spectrum is also proposed.

Site-specific ground motion simulation and seismic response analysis for microzonation of Nanded City, India

We study strong ground motion characteristics and ground response analysis of different sites in Nanded City, India. Synthetic strong ground motion records are obtained for two scenario earthquakes of magnitude M 5.2 and M 6.8 in southern Peninsular India using the finite fault model. Shear-wave velocity averaged over top 30 m of the soil is obtained from multichannel analysis of surface wave survey at 60 sites at depths of 20–50 m below the ground surface. The sites in different parts of the city are characterized by peak ground acceleration (PGA) at the surface and bedrock level, 5 % damped response spectra at the ground surface and the amplification factor defined as the ratio of ground motion at the surface to that at the bedrock. The area east to the lineament is characterized by low V S30 values (<200 m/s), probably associated with Godavari River basin sediments with alluvial deposits, composed of brown clay with intercalated bands of sand and gravel. A relatively high PGA value at the surface of about 0.24 g for the M 5.2 target event and hence high ground motion amplification indicative of major damage are observed at sites E-NE to the lineament in the area that are associated with the top soil column consisting of unconsolidated river basin sediments with very low V S30 values (<200 m/s). The amplification factor for the city ranges from 3 to 8 for the highest target event of magnitude M 6.8. There is a strong lateral variation in PGA values at the surface for the part of the city lying to the east of the lineament and parallel to its trend, where a relatively high amplification factor of 6–8 is found at a dominant frequency of 1.5–2.5 Hz, which can be considered as a significant zone of amplification and hence areas with high seismic hazard. The site-specific response spectra show that the peak of spectral acceleration for different sites occurs around 3 Hz. There is a large spatial variation of spectral acceleration at any given frequency for the city. For example, site nos. 9 and 50 are characterized by a peak in spectral acceleration of 0.55 and 0.9 g, respectively, at 3 Hz frequency.

A Predictive Equation for the Vertical-to-Horizontal Ratio of Ground Motion at Rock Sites Based on Shear-Wave Velocity Profiles from Japan and Switzerland

Abstract Ratios of vertical-to-horizontal ( V / H ) ground motion are important for the computation of scenario-compatible vertical design spectra. They are therefore a crucial aspect of seismic hazard analysis. We characterize the V / H ratio at rock sites in terms of the recording site’s average quarter-wavelength velocity. A predictive equation is presented, which can be used for reconstructing the expected V / H ratio of the 5%-damped response and Fourier spectra for rock sites, given a known shear-wave velocity profile. The equation is based on the regression analysis of two datasets: one from Switzerland and one from Japan. The two datasets allow us to analyze well-characterized hard-rock sites in Switzerland using small earthquakes ( M w >2), while the magnitude range is increased up to events of M w 7.3 using strong-motion recordings from Japan’s KiK-net seismic network. It is shown that a correlation exists between the quarter-wavelength velocity at a given frequency and the V / H ground-motion ratio. Small differences, possibly due to velocity measurement bias or topographical and basin effects, existed when analyzing the individual regional datasets. Apart from near-source distances ( R V / H , no clear magnitude- or distance-dependence of the V / H ratios is present in either of the datasets of earthquake recordings. We show that the same correlation exists for response spectra and Fourier spectra of recorded ground motion. A similar correlation was derived for ambient vibrations recorded at Swiss station sites, resulting in larger values of V / H at a given frequency and thereby indicating that V / H is sensitive to the composition of the wave field. Finally, uncertainties in the V / H models are presented. We separate the sources of uncertainty into source and site-specific components and present the single-site sigma uncertainty measure for site-specific hazard analyses.

Spatial distribution of near-fault ground motion

Near-fault strong ground motion of strike-slip and dip-slip of vertical and inclined rectangular fault in half-space and layered half-space is analyzed by dislocation source model. The Fourier spectra ratio of ground motion is adopted to study the characteristics of near-fault ground motion. For both slip models, near-fault strong ground motion with high amplitude is located in a narrow belt area along the projection of the fault on the ground and mainly controlled by the sub-faults nearby. Directivity of strike-slip fault is more dominant in long period for components perpendicular to the fault, and more dominant in long period for components parallel to the fault for dip-slip fault. The deeper the location of the source is, the more slowly the amplitude of ground motion attenuates. There is obvious hanging wall effect in ground motion of inclined fault, and the spatial distribution of ground motion is asymmetric which coincides with observational data. Finally, a fitting function of spatial distribution for near-fault ground motion is proposed and compared with near source factors of the 1997 Uniform Building Code of USA.

GROUND MOTION DOMINANT FREQUENCY EFFECT ON THE DESIGN OF MULTIPLE TUNED MASS DAMPERS

Utilising the Kanai-Tajimi and Clough-Penzien spectrums and the pseudo-excitation algorithm in the frequency domain, parametric study is performed to examine the effect of the dominant frequency of ground motion on the optimum parameters and effective-ness of multiple tuned mass dampers (MTMD) with identical stiffness and damping coefficient but with unequal mass. The examination of the optimum parameters is con-ducted through the minimisation of the minimum values of the maximum displacement and acceleration dynamic magnification factors of the structure with the MTMD. The optimum parameters of the MTMD include the optimum frequency spacing reflecting the robustness, the average damping ratio and the tuning frequency ratio. Minimisation of the minimum values of the maximum displacement and acceleration dynamic mag-nification factors, nondimensionalised respectively by the maximum displacement and acceleration dynamic magnification factors of the structure without the MTMD, is used to measure the effectiveness of the MTMD. The results indicate that in the two cases where both the total mass ratio is below 0.02 and the total mass ratio is above 0.02, but the dominant frequency ratio of ground motion is below unity (including unity), the earthquake ground motion can be modelled by a white noise. It is worth noting, however, that for the total mass ratio above 0.02, the Kanai-Tajimi Spectrum or Clough-Penzien spectrum needs to be employed to design the MTMD for seismic structures in situations where the dominant frequency ratio of ground motion is beyond unity.

Replication of apparent nonlinear seismic response with linear wave propagation models

It is necessary to understand ground-motion amplification by sediment, defined as the ratio of ground motions at sediment sites to those at rock sites, to predict seismic loadings for earthquake engineering. At sediment sites, observed weak-motion amplifications from magnitude 3 to 4 aftershocks of the 1994 Northridge earthquake were twice as large as magnitude 6.7 mainshock amplifications. Amplitude-dependent (nonlinear) amplification by sediment is one explanation. However, earthquake simulations with empirical impulse responses and elastic finite-difference calculations with weakly heterogeneous, random three-dimensional (3D) crustal velocity variations show that linear wave propagation can explain observed (apparently nonlinear) sediment responses. Random 3D velocity variations also reproduce the observed log-normal dispersion of peak ground motions. Deterministic wave propagation models are not adequate to quantify the scaling and dispersion of near-source ground motions.

Engineering implication of ground motion A/V ratio

An earthquake data set consisting of 45 strong motion records was analyzed to investigate the significance of the peak ground acceleration-to-velocity (A/V) ratio as a parameter to indicate the dynamic characteristics of earthquake ground motions. It was found that the A/V ratio of ground motions is a viable indicator of the M (magnitude)-R (epicentral distance) relationships associated with the motions. Due to its tacit correlation with the M-R relationship, the A/V ratio provides useful information regarding the relative frequency content and duration of strong shaking for ground motions resulting from different seismic environments. In light of these observations, the implications of seismic ground motions having different A/V ratios on engineering design were discussed, and an example to incorporate this ratio into the specification of seismic design forces for building structures was illustrated.