Site response estimation from earthquake data

1992 ◽  
Vol 82 (6) ◽  
pp. 2308-2327
Author(s):  
Stephen H. Hartzell
Keyword(s):  
Shear Wave ◽  
San Francisco ◽  
Model Comparison ◽  
Site Response ◽  
Response Spectra ◽  
Source Model ◽  
Source Spectrum ◽  
Spreading Factor ◽  
Linear Inversion ◽  
Q Model

Abstract Aftershocks of the 1989 Loma Prieta, California, earthquake are used to estimate site response along the San Francisco Peninsula. A total of 215 shear-wave records from 24 sources and 21 sites are used in a linear inversion for source and site response spectra. The methodology makes no assumptions about the shape of the source spectrum. However, to obtain a stable, unique inverse a Q model and geometrical spreading factor are assumed, as well as a constraint on site response that sets the site response averaged over two specific stations to 1.0. Site responses calculated by this formulation of the problem are compared with other studies in the same region that use different methodologies and / or data. The shear-wave site responses compare favorably with estimates based on an ω2-constrained source model. Comparison with coda amplification factors is not as close, but still favorable considering that the coda values were determined for nearby locations with similar geology, and not the same sites. The degree of agreement between the three methods is encouraging considering the very different assumptions and data used.

Sensitivity Analysis for Finite‐Difference Seismic Basin Modeling: A Case Study for Kinburn Basin, Ottawa, Canada

2019 ◽  
Vol 109 (6) ◽  
pp. 2305-2324 ◽  
Author(s):  
Amin Esmaeilzadeh ◽  
Dariush Motazedian
Keyword(s):  
Sensitivity Analysis ◽  
Finite Difference ◽  
Shear Wave ◽  
Fourier Spectrum ◽  
Large Earthquake ◽  
Source Model ◽  
Frequency Content ◽  
Gaussian Source ◽  
Q Model ◽  
The Waves

Abstract We used a finite‐difference modeling method to investigate the sensitivity of the ground‐motion simulation results to the main input parameters, including the source model, regional path properties, and local site conditions. We used a spectral frequency range of 0.1–1 Hz for the Kinburn bedrock topographic basin, Ottawa, Canada, for the Ladysmith earthquake (Mw 4.7). Some findings are known facts; however, the unique geophysical conditions in the Ottawa area, such as the high contrast between the shear‐wave velocities of the bedrock and the shear‐wave velocity of the soil, were the reason for a comprehensive sensitivity analysis. Using a Gaussian source function with a short half‐duration increased the peak ground velocities (PGVs) and the amplitude of the velocity Fourier spectrum. Relaxation times and relaxation coefficients for the viscoelastic simulation significantly increased the amplitude of later arrivals at the soil site, which, consequently, led to an increase in PGV, the amplitude of the pseudospectral acceleration (PSA) ratio, and the velocity Fourier spectrum for a small earthquake. Employing a small soil Q model damped a significant amount of energy of the waves in the basin; thus, PGV, the PSA of soil to rock ratios, and the velocity Fourier spectrum were dependent on the soil Q model. Also, using a high‐velocity contrast between soil and rock increased PGVs and the amplitude of the PSA of the soil to rock ratios, whereas the frequency content of the waves shifted toward lower frequencies. Using a finite‐fault source model for a scenario large earthquake (Mw 7) significantly reduced the PGV values relative to a point‐source model. Using nonlinear‐viscoelastic simulation for a large earthquake (Mw 7) reduced the amplitude of the later arrivals and the amplitude of the PSA of the soil to rock ratios, and shifted the frequency content of waves toward lower frequency.

scholarly journals The seismic analysis of sandy sites

1994 ◽  
Vol 27 (2) ◽  
pp. 114-123 ◽  
Author(s):  
T. J. Larkin ◽  
S. Marks
Keyword(s):  
Case Studies ◽  
San Francisco ◽  
Effective Stress ◽  
Seismic Analysis ◽  
Site Response ◽  
Response Spectra ◽  
Correlated Data ◽  
Specific Information ◽  
Liquefaction Resistance ◽  
Ground Acceleration

This paper presents an approach for performing one dimensional effective stress site response analyses for sandy sites, including the evaluation of liquefaction potential. This type of analysis differs from the more common total stress response analyses in that induced pore pressures in saturated sandy soils are accounted for, including the resulting influence on soil properties. This analytical method has been refined to the point where the need for complex and expensive laboratory soil testing is no longer required, a factor which has traditionally held back developments in the effective stress area. The effective stress analysis requires the determination of five soil specific parameters. A trial and error backfitting procedure was developed to successfully determine these parameters from traditional site investigation data rather than detailed laboratory testing. This procedure was investigated using two case studies, the Edgecumbe earthquake of 1987 and the Loma Prieta event of 1989, which both exhibited significant liquefaction damage. The Edgecumbe analysis produced useful results. The predicted ground acceleration required to initiate liquefaction was 2.8 m/s2 (0.29g) which is close to the estimated value of 3 m/s2 (0.31g). This was a good result as a reasonable amount of estimated and correlated data had to be used due to a lack of specific site data. The case study of Treasure Island, in the San Francisco Bay area, also produced encouraging results with both the prediction of liquefaction and surface response spectra in good agreement with recorded data. Both case studies used liquefaction resistance curves determined empirically from SPT blow count data. While this data proved acceptable it was discovered that care must be taken in the use of such overseas derived empirical data, particularly if no corroborating site specific information is available.

Empirical Models for Site- and Region-Dependent Ground-Motion Parameters in the Taipei Area: A Unified Approach

2001 ◽  
Vol 17 (2) ◽  
pp. 313-331 ◽  
Author(s):  
Vladimir Yu Sokolov ◽  
Chin-Hsiung Loh ◽  
Kuo-Liang Wen
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Seismic Hazard Assessment ◽  
Response Spectra ◽  
Source Model ◽  
Empirical Models ◽  
Ground Motion Parameters ◽  
Taipei Basin ◽  
Scenario Earthquakes ◽  
Motion Parameters

We calculated peak ground accelerations and response spectra for the Taipei area using stochastic simulation technique on the basis of recently obtained empirical models. The source, path and site effects were characterized separately on the basis of the analysis of a large collection of ground-motion recordings obtained since 1991 in the Taiwan area. The simple ω-squared Brune's point-source model combined with regional anelastic attenuation ( Q) and duration (τ0.9) models provide a satisfactory estimation of ground-motion parameters for rock sites. Effects of local site response are considered by means of empirical soil/bedrock spectral ratios calculated as ratios between spectra of actual earthquake records and those modeled for hypothetical “hard rock” site. The results of the simulation demonstrate that this combination of source, path and site response models provides an accurate prediction of “site- and region-dependent” ground-motion parameters for the Taipei basin for the broad range of earthquake magnitudes, distances and site conditions. The model, with a set of generic soil profiles, can be considered as an efficient tool for estimating of design input ground motion parameters in the Taipei basin both in deterministic (scenario earthquakes) and probabilistic (“site- and region-dependent” Uniform Hazard response spectra) seismic hazard assessment.

scholarly journals Experimental and analytical study of seismic site response of discontinuous permafrost

2016 ◽  
Vol 53 (9) ◽  
pp. 1363-1375 ◽  
Author(s):  
Behrang Dadfar ◽  
M. Hesham El Naggar ◽  
Miroslav Nastev
Keyword(s):  
Shear Wave ◽  
Site Response ◽  
Free Field ◽  
Frozen Soil ◽  
Shaking Table ◽  
Experimental Program ◽  
Small Scale ◽  
Seismic Site Response ◽  
Discontinuous Permafrost ◽  
Spectral Accelerations

Seismic site response of discontinuous permafrost is discussed. The presence of frozen ground in soil deposits can significantly affect their dynamic response due to stiffer conditions characterized by higher shear-wave velocities compared to unfrozen soils. Both experimental and numerical investigations were conducted to examine the problem. The experimental program included a series of 1g shaking table tests on small-scale models. Nonlinear numerical analyses were performed employing FLAC software. The numerical model was verified using the obtained experimental results. Parametric simulations were then conducted using the verified model to study variations of the free-field spectral accelerations (on top of the frozen and unfrozen soil blocks) with the scheme of frozen–unfrozen soil, and to determine the key parameters and their effects on seismic site response. Results show that spectral accelerations were generally higher in frozen soils than in unfrozen ones. It was found that the shear-wave velocity of the frozen soil as well as the assumed geometry of the blocks and their spacing have a significant impact on the site response.

A Numerical Study on the Seismic Site Response of Rocky Valleys with Irregular Topographic Conditions

2019 ◽  
Vol 10 (04) ◽  
pp. 1850011 ◽  
Author(s):  
Mohammad Katebi ◽  
Behrouz Gatmiri ◽  
Pooneh Maghoul
Keyword(s):  
Seismic Analysis ◽  
Numerical Study ◽  
Site Response ◽  
Slope Angle ◽  
Response Spectra ◽  
Topographic Effects ◽  
Combined Effects ◽  
Acceleration Response ◽  
Vertically Propagating ◽  
Maximum Amplification

This paper investigates topographic effects of rocky valleys with irregular topographic conditions subjected to vertically propagating SV waves of Ricker type using a boundary element code. Valleys with two intersecting slopes, [Formula: see text] and [Formula: see text], are modelled in order to study their combined effects on ground motion. Presented in the form of pseudo-acceleration response spectra, results of this work can be extended to similar topographies. The main findings are: (i) [Formula: see text] (the first slope angle) and [Formula: see text] (L is the half width of the valley and [Formula: see text] is its corresponding height) have amplifying effects, and [Formula: see text] (the second slope angle) has de-amplifying effects on the site response. (ii) [Formula: see text] has a straight effect on intensifying the effects of both [Formula: see text] and [Formula: see text]. (iii) The combined effects of slope angles have been found to be important in modifying the response so more than a single slope should be considered for seismic analysis. (iv) Engineers should use the maximum amplification of 2.4 in case of valleys with the first and second slope angles below [Formula: see text].

scholarly journals Preliminary results of ground-motion characteristics

2012 ◽  
Vol 55 (4) ◽  
Author(s):  
Francesca Bozzoni ◽  
Carlo Giovanni Lai ◽  
Laura Scandella
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Response Spectrum ◽  
Field Tests ◽  
Response Spectra ◽  
Ground Acceleration ◽  
Preliminary Results ◽  
Emilia Earthquake ◽  
Particle Orbit ◽  
2012 Emilia Earthquake

The preliminary results are presented herein for the engineering applications of the characteristics of the ground motion induced by the May 20, 2012, Emilia earthquake. Shake maps are computed to provide estimates of the spatial distribution of the induced ground motion. The signals recorded at the Mirandola (MRN) station, the closest to the epicenter, have been processed to obtain acceleration, velocity and displacement response spectra. Ground-motion parameters from the MRN recordings are compared with the corresponding estimates from recent ground-motion prediction equations, and with the spectra prescribed by the current Italian Building Code for different return periods. The records from the MRN station are used to plot the particle orbit (hodogram) described by the waveform. The availability of results from geotechnical field tests that were performed at a few sites in the Municipality of Mirandola prior to this earthquake of May 2012 has allowed preliminary assessment of the ground response. The amplification effects at Mirandola are estimated using fully stochastic site-response analyses. The seismic input comprises seven actual records that are compatible with the Italian code-based spectrum that refers to a 475-year return period. The computed acceleration response spectrum and the associated dispersion are compared to the spectra calculated from the recordings of the MRN station. Good agreement is obtained for periods up to 1 s, especially for the peak ground acceleration. For the other periods, the spectral acceleration of the MRN recordings exceeds that of the computed spectra.<br />

Regional propagation characteristics and source parameters of earthquakes in northeastern North America

1994 ◽  
Vol 84 (1) ◽  
pp. 1-15 ◽  
Author(s):  
John Boatwright
Keyword(s):  
Site Response ◽  
Source Parameters ◽  
Low Frequency ◽  
Response Spectra ◽  
Spectral Shape ◽  
Propagation Characteristics ◽  
S Wave ◽  
Data Set ◽  
Wave Trains ◽  
Source Site

Abstract The vertical components of the S wave trains recorded on the Eastern Canadian Telemetered Network (ECTN) from 1980 through 1990 have been spectrally analyzed for source, site, and propagation characteristics. The data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from M ≈ 3 to 6. The epicentral distances range from 15 to 1000 km, with most of the data set recorded at distances from 200 to 800 km. The recorded S wave trains contain the phases S, SmS, Sn, and Lg and are sampled using windows that increase with distance; the acceleration spectra were analyzed from 1.0 to 10 Hz. To separate the source, site, and propagation characteristics, an inversion for the earthquake corner frequencies, low-frequency levels, and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km. The iteration between these two parts of the inversion converges in about 60 steps. The average attenuation parameters obtained from the inversion were Q = 1997 ± 10 and γ = 0.998 ± 0.003. The most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 Hz, which shallows with increasing frequency and increasing distance out to 200 km. The site-response spectra obtained for the ECTN stations are generally flat. The source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events (Mo &lt; 3 × 1021 dyne-cm) in the data set, whose Brune stress drops range from 5 to 150 bars. For the five events in the data set with Mo ≧ 1023 dyne-cm, however, the source spectra obtained by regressing the residuals suggest that an ω2 spectrum is an inadequate model for the spectral shape. In particular, the corner frequencies for most of these large events appear to be split, so that the spectra exhibit an intermediate behavior (where |ü(ω)| is roughly proportional to ω).

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