Investigation of Relationship between the Response and Fourier Spectral Ratios Based on Statistical Analyses of Strong-Motion Records

2020 ◽  
pp. 2150008
Author(s):  
Haizhong Zhang ◽  
Yan-Gang Zhao
Keyword(s):  
Seismic Design ◽  
Site Effects ◽  
Epicentral Distance ◽  
Ground Motions ◽  
Scaling Law ◽  
Ground Surface ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Spectral Ratios ◽  
Earthquake Scenario

In both seismic design and probabilistic seismic-hazard analyses, site effects are typically characterized as the ratio of the response spectral ordinate on the ground surface to that on the bedrock based on the scaling law borrowed from the Fourier spectral ordinate. Recent studies have shown that different from the Fourier spectral ratio (FSR), the response spectral ratio (RSR) does not purely reflect the site effects but also depends on the earthquake scenario even for linear analysis. However, previous studies are limited to theoretical analysis. This study statistically compares the two spectral ratios by analyzing many actual seismic ground motions recorded at nearby soil and rock sites. It is observed that the average RSR and FSR have similar overall shapes, and their maximum values occur at approximately the same period; however, the values around the peak are clearly different with FSRs consistently exceeding the RSRs. The RSR–FSR relationship depends on the earthquake scenario and the oscillator damping; their difference at periods longer than the site’s fundamental period decreases as the magnitude and epicentral distance increase, and the RSRs generally approach the FSRs as the oscillator damping decreases.

scholarly journals Near-Source Simulation of Strong Ground Motion in Amatrice Downtown Including Site Effects

Geosciences ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 186
Author(s):  
Alessandro Todrani ◽  
Giovanna Cultrera
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Central Italy ◽  
Strong Motion ◽  
Seismic Source ◽  
Spectral Ratio ◽  
Intensity Measures ◽  
Standard Spectral Ratio ◽  
Heavy Damage ◽  
Strong Ground

On 24 August 2016, a Mw 6.0 earthquake started a damaging seismic sequence in central Italy. The historical center of Amatrice village reached the XI degree (MCS scale) but the high vulnerability alone could not explain the heavy damage. Unfortunately, at the time of the earthquake only AMT station, 200 m away from the downtown, recorded the mainshock, whereas tens of temporary stations were installed afterwards. We propose a method to simulate the ground motion affecting Amatrice, using the FFT amplitude recorded at AMT, which has been modified by the standard spectral ratio (SSR) computed at 14 seismic stations in downtown. We tested the procedure by comparing simulations and recordings of two later mainshocks (Mw 5.9 and Mw 6.5), underlining advantages and limits of the technique. The strong motion variability of simulations was related to the proximity of the seismic source, accounted for by the ground motion at AMT, and to the peculiar site effects, described by the transfer function at the sites. The largest amplification characterized the stations close to the NE hill edge and produced simulated values of intensity measures clearly above one standard deviation of the GMM expected for Italy, up to 1.6 g for PGA.

Two-parameter scaling of source spectra: Love waves from deep-focus Bonin Islands earthquakes

1977 ◽  
Vol 67 (2) ◽  
pp. 285-300
Author(s):  
R. James Brown
Keyword(s):  
Body Wave ◽  
Scaling Law ◽  
Spectral Ratio ◽  
Love Waves ◽  
Corner Frequency ◽  
Spectral Ratios ◽  
Bonin Islands ◽  
Deep Focus ◽  
Two Parameter ◽  
Fault Length

Abstract Starting with the one-parameter scaling law of Aki, a two-parameter expression is developed to model the source factor of the far-field spectrum from a dislocation fault source for both ω−2 and ω−3 high-frequency asymptotic types. Aki's assumption of similarity is relaxed in two respects: it is neither here assumed that wD0 ∞ L2 (L = fault length, w = fault width, D0 = average dislocation) nor that kT = v kL (kT−1 = correlation time, kL−1 = correlation length, v = velocity of rupture propagation), the latter being equivalent to allowing for Brune's fractional stress drop. From this two-parameter model a four-parameter model of spectral ratio is obtained and fitted to observed spectral ratios by computer optimization of the four parameters. Observed spectral ratios have been determined from the Love waves recorded at NORSAR from six deep-focus Bonin Islands earthquakes using a common-path method. From the optimal values of the four parameters, values are determined for corner frequency (f ≈ 0.2 Hz for m 6.0; f ≈ 0.3 Hz for m = 5.3; m = PDE body-wave magnitude), relative fault length, relative seismic moment (and magnitudes), and p, the slope of the corner-frequency locus. Values found for p are all greater than 3 and such p, in combination with an ω−3 scaling law, can yield a reasonable m:M relation, i.e., with no ceiling imposed on m. A slightly better fit is obtained by starting with an ω−3 model than with ω−2.

Continuous measurements of microtremors on sediments and basement in Los Angeles, California

1993 ◽  
Vol 83 (5) ◽  
pp. 1595-1609 ◽  
Author(s):  
Hiroaki Yamanaka ◽  
Marijan Dravinski ◽  
Hiroshi Kagami
Keyword(s):  
Los Angeles ◽  
Continuous Measurement ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Earthquake Ground Motion ◽  
Spectral Amplitude ◽  
Spectral Ratios ◽  
Long Period ◽  
Short Period ◽  
Deep Sediments

Abstract Continuous measurement of microtremors at two sites on basement rock and sediments was carried out in Los Angeles, California, in order to understand the fundamental characteristics of microtremors. A predominant peak with a period of about 6.5 sec was found in the microtremor spectra in both media. The spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites. Their time-variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of Los Angeles. This suggests that they originate from an oceanic disturbance. On the other hand, a clear daily variation of spectral amplitudes at a period of 0.3 sec indicates that short-period microtremors are caused by cultural noises. It was found that the spectral ratio of long-period microtremors between the basement and the sediments was repeatable, although the spectral amplitudes at the two sites were time-variant. The spectral ratio of the long-period microtremors was similar to that derived from strong motion records. This suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long-period earthquake ground motion.

Implementing horizontal-to-vertical Fourier spectral ratios and spatial correlation in a ground-motion prediction equation to predict site effects

2020 ◽  
pp. 875529302095244
Author(s):  
Shu-Hsien Chao ◽  
Che-Min Lin ◽  
Chun-Hsiang Kuo ◽  
Jyun-Yan Huang ◽  
Kuo-Liang Wen ◽  
...  
Keyword(s):  
Spatial Correlation ◽  
Ground Motion ◽  
Prediction Accuracy ◽  
Site Effects ◽  
Strong Motion ◽  
Prediction Equation ◽  
Motion Prediction ◽  
Ground Motion Prediction Equation ◽  
Ground Motion Prediction ◽  
Spectral Ratios

We propose a methodology to implement horizontal-to-vertical Fourier spectral ratios (HVRs) evaluated from strong ground motion induced by earthquake (EHVRs) or ambient ground motion observed from microtremor (MHVRs) individually and simultaneously with the spatial correlation (SC) in a ground-motion prediction equation (GMPE) to improve the prediction accuracy of site effects. We illustrated the methodology by developing an EHVRs-SC-based model which supplements Vs30 and Z1.0 with the SC and EHVRs collected at strong motion stations, and a MHVRs-SC-based model that supplements Vs30 and Z1.0 with the SC and MHVRs observed from microtremors at sites which were collocated with strong motion stations. The standard deviation of the station-specific residuals can be reduced by up to 90% when the proposed models are used to predict site effects. In the proposed models, the spatial distribution of the predicted station terms for peak ground acceleration (PGA) from MHVRs at 3699 sites is consistent with that of the predicted station terms for PGA from EHVRs at 721 strong motion stations. Prediction accuracy for stations with inferred Vs30 is similar to that of stations with measured Vs30 with the proposed models. This study provides a methodology to simultaneously implement SC and EHVRs, or SC and MHVRs in a GMPE to improve the prediction accuracy of site effects for a target site with available EHVRs or MHVRs information.

Site Effects of Onna during the 2009 L’Aquila (Central Italy) Seismic Sequence: Constraints on Bedrock Depth and 1D Local Velocity Structure from Aftershock Seismograms

2020 ◽  
Vol 110 (2) ◽  
pp. 399-409
Author(s):  
Giuliana Mele ◽  
Antonio Rovelli ◽  
Antonio Fodarella ◽  
Marco Mancini
Keyword(s):  
Velocity Structure ◽  
Transfer Functions ◽  
Ground Motions ◽  
Central Italy ◽  
Spectral Ratio ◽  
Spectral Ratios ◽  
Linear Approach ◽  
Bedrock Depth ◽  
The Village ◽  
Sequence Constraints

ABSTRACT After the 2009 L’Aquila Mw 6.1 earthquake, particular attention was paid to the large difference of Mercalli–Cancani–Sieberg (MCS) macroseismic intensity between the nearby villages of Onna (9.5 MCS) and Monticchio (6 MCS). Several authors estimated that in Onna, settled in the Aterno river valley, ground motions were amplified at 2–3 Hz by up to a factor of 5 with respect to Monticchio, settled on more competent rocks. Although there was a general agreement that the spectral peak was caused by the resonance of the uppermost 40 m layer, a satisfactory fit of the amplitudes was not provided. Here, we apply spectral ratio techniques to 1437 aftershock seismograms (magnitude between 1.8 and 3.9) to compare ground motions within Onna and between Onna and Monticchio. Spectral amplitudes at stations located outside and inside the “red zone” of Onna show that the seismic response was uniform, confirming that vulnerability was crucial for the heavier damage of the ancient part of the village. We have also estimated the empirical transfer function of Onna through the spectral ratios between Onna and Monticchio. Although in a 1D simplification, a model with a further velocity contrast of ∼2 at 200 m of depth produces a more accurate fit of observations. Using the new velocity profile, we modeled the mainshock ground motion at Onna in an equivalent-linear approach. Accelerations are amplified by a factor of 2 and spectral ordinates increase from 0.7g at 0.2 s to 1g at 0.5 s, a shaking level that can be destructive for nonductile ancient buildings. This study shows that accurate estimates of empirical transfer functions, even in a simplified 1D approach, provide useful constraints to the deeper velocity structure where measurements are shallow or lacking.

The attenuation of seismic shear waves in quaternary alluvium in Santa Clara Valley, California

1994 ◽  
Vol 84 (1) ◽  
pp. 76-90 ◽  
Author(s):  
James F. Gibbs ◽  
David M. Boore ◽  
William B. Joyner ◽  
Thomas E. Fumal
Keyword(s):  
Attenuation Factor ◽  
Shear Waves ◽  
Ground Surface ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Mean Value ◽  
Depth Range ◽  
Nonlinear Wave Propagation ◽  
Surface Source ◽  
Frequency Spectra

Abstract We used shear waves, generated by an air-powered source at the ground surface and recorded in a borehole, to estimate the shear-wave quality factor at strong-motion station Gilroy no. 2. We find similar values of Q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths; we find no evidence of a frequency dependence of Q. The mean value of Q over the depth range 10 to 115 m is close to 10. The use of this value over the depth of the borehole and the observed travel time of 0.358 sec gives a cumulative attenuation factor t* of 0.036 sec for the upper 180 m of the Quaternary alluvium. This is comparable to the differential decay between Gilroy no. 2 and a rock site 1.9 km away (Gilroy no. 1), as measured from the decay of the high-frequency spectra of accelerograms from large earthquakes, plotted on a log-linear scale: t* = 0.05, 0.04, and 0.03 sec for the 1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta earthquakes, respectively. The similarity between the attenuations measured from the low-strain surface source and those from the larger amplitude earthquake sources suggests that increases of damping due to nonlinear wave propagation effects are limited.

The Effect of Site Condition on Ground Motion in Gansu Province during the Wenchun Ms8.0 Earthquake

2012 ◽  
Vol 594-597 ◽  
pp. 1658-1667
Author(s):  
Zhi Jian Wu ◽  
Lan Min Wang ◽  
Ping Wang ◽  
Hang Shi ◽  
Tuo Chen
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Seismic Design ◽  
Site Effects ◽  
Strong Motion ◽  
Gansu Province ◽  
Response Analysis ◽  
Site Condition ◽  
Seismic Response Analysis ◽  
Ground Acceleration

Based on mobile strong motion array observation, borehole exploration and site seismic response analysis, the site effects of mountainous topography in southeastern Gansu and the topography of loess tableland on ground motion were investigated in details. The analysis on acceleration records of aftershocks showed that the peak ground acceleration at top of the mountain is nearly 2 times of that at the foot of it. The seismic response analysis of sites shows that the loess tableland may amplify PGA by 1.44-2.0 times. Therefore, site effects of mountains and loess topography on ground motion should been taken account into seismic design.

Bi-Directional Pseudo-Acceleration Response Spectra

2016 ◽  
Vol 10 (04) ◽  
pp. 1650007
Author(s):  
Anat Ruangrassamee ◽  
Chitti Palasri ◽  
Panitan Lukkunaprasit
Keyword(s):  
Seismic Design ◽  
Response Spectrum ◽  
Ground Motions ◽  
Strong Motion ◽  
Response Spectra ◽  
Acceleration Response ◽  
Acceleration Response Spectra ◽  
Acceleration Response Spectrum ◽  
Two Degree Of Freedom ◽  
Ratio Response

In seismic design, excitations are usually considered separately in two perpendicular directions of structures. In fact, the two components of ground motions occur simultaneously. This paper clarifies the effects of bi-directional excitations on structures and proposes the response spectra called “bi-directional pseudo-acceleration response spectra”. A simplified analytical model of a two-degree-of-freedom system was employed. The effect of directivity of ground motions was taken into account by applying strong motion records in all directions. The analytical results were presented in the form of the acceleration ratio response spectrum defined as the bi-directional pseudo-acceleration response spectrum normalized by a pseudo-acceleration response spectrum.

Site effect evaluation using spectral ratios with only one station

1993 ◽  
Vol 83 (5) ◽  
pp. 1574-1594
Author(s):  
Javier Lermo ◽  
Francisco J. Chávez-García
Keyword(s):  
Transfer Function ◽  
Rayleigh Waves ◽  
Site Effects ◽  
Spectral Ratio ◽  
Site Effect ◽  
Reference Station ◽  
Effect Evaluation ◽  
Spectral Ratios ◽  
S Wave ◽  
Dominant Period

Abstract The spectral ratio technique is a common useful way to estimate empirical transfer function to evaluates site effects in regions of moderate to high seismicity. The purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station. The technique, originally proposed by Nakamura to analyze Rayleigh waves in the microtremor records, is presented briefly and it is discussed why it may be applicable to study the intense S-wave part in earthquake records. Results are presented for three different cities in Mexico: Oaxaca, Oax., Acapulco, Gro., and Mexico City. These cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city. Each time we compare the results of Nakamura's technique with standard spectral ratios. In all three cases the results are very encouraging. We conclude that, if site effects are caused by simple geology, a first estimate of dominant period and local amplification level can be obtained using records of only one station.

EVALUATION OF S-WAVE AMPLIFICATION SPECTRUM USING MICROTREMORS

2014 ◽  
Vol 1 (1) ◽  
Author(s):  
Hayato Nishikawa ◽  
Tomiya Takatani
Keyword(s):  
Site Effects ◽  
Estimation Method ◽  
Ground Surface ◽  
Spectral Ratio ◽  
S Wave ◽  
Wave Amplification ◽  
Measurement Results ◽  
Microtremor Measurement ◽  
Microtremor Measurements ◽  
Amplification Spectrum

To evaluate the site effects above the engineering base rock with an S-wave velocity of 300m/s, microtremor measurements on the ground surface were conducted in Maizuru, Japan. An estimation method of S-wave amplification spectrum using the microtremor H/V spectral ratio was applied at the ground surface, estimating S-wave amplification spectrum without any ground information based on the microtremor measurement results. It was found that the evaluation of S-wave amplification spectrum needs a revision on the microtremor H/V spectral ratio, using some coefficients on the microtopography classification and the shape of the microtremor H/V spectral ratio.

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