The high-frequency shape of the source spectrum for earthquakes in eastern and western Canada

1996 ◽  
Vol 86 (1A) ◽  
pp. 106-112 ◽  
Author(s):  
Gail M. Atkinson
Keyword(s):  
High Frequency ◽  
Fourier Spectrum ◽  
Response Spectrum ◽  
Ground Motions ◽  
Source Spectrum ◽  
Western Canada ◽  
Eastern Canada ◽  
Ground Acceleration ◽  
Kappa Effect ◽  
Key Parameter

Abstract The high-frequency shape of the earthquake spectrum strongly influences the amplitude of the peak ground acceleration and of the response spectrum at frequencies of 10 Hz and greater. A key parameter for the description of high-frequency ground motions is “kappa,” which is the decay slope of the Fourier spectrum of acceleration at near-source distances (Anderson and Hough, 1984; note Anderson and Hough originally referred to this parameter as kappa (0)). Kappa may be attributed to site effects (fmax; Hanks, 1982), source processes (Papageorgiou and Aki, 1983), or both. Seismographic data place weak but significant constraints on kappa values. On average, there is no resolved kappa effect on spectra recorded at rock sites in eastern Canada, in the frequency range f ≦ 30 Hz. Four firm-soil sites in southwestern Ontario also show no kappa effect. An implied upper bound for kappa is 0.004 (or lower bound of 30 Hz for fmax). By contrast, source spectra from earthquakes in the Cascadia region, recorded on hard-rock sites in southwestern British Columbia (B.C.), appear to be well described by a kappa of 0.011 ± 0.002. The B.C. spectra are thus intermediate to the eastern case, with zero apparent kappa, and the typical California case, for which kappa is about 0.04.

scholarly journals Smooth Crustal Velocity Models Cause a Depletion of High-Frequency Ground Motions on Soil in 2D Dynamic Rupture Simulations

2021 ◽  
Author(s):  
Yihe Huang
Keyword(s):  
Shear Wave ◽  
High Frequency ◽  
Ground Motions ◽  
Velocity Model ◽  
Dynamic Rupture ◽  
Ground Acceleration ◽  
Velocity Models ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Crustal Velocity

ABSTRACT A depletion of high-frequency ground motions on soil sites has been observed in recent large earthquakes and is often attributed to a nonlinear soil response. Here, I show that the reduced amplitudes of high-frequency horizontal-to-vertical spectral ratios (HVSRs) on soil can also be caused by a smooth crustal velocity model with low shear-wave velocities underneath soil sites. I calculate near-fault ground motions using both 2D dynamic rupture simulations and point-source models for both rock and soil sites. The 1D velocity models used in the simulations are derived from empirical relationships between seismic wave velocities and depths in northern California. The simulations for soil sites feature lower shear-wave velocities and thus larger Poisson’s ratios at shallow depths than those for rock sites. The lower shear-wave velocities cause slower shallow rupture and smaller shallow slip, but both soil and rock simulations have similar rupture speeds and slip for the rest of the fault. However, the simulated near-fault ground motions on soil and rock sites have distinct features. Compared to ground motions on rock, horizontal ground acceleration on soil is only amplified at low frequencies, whereas vertical ground acceleration is deamplified for the whole frequency range. Thus, the HVSRs on soil exhibit a depletion of high-frequency energy. The comparison between smooth and layered velocity models demonstrates that the smoothness of the velocity model plays a critical role in the contrasting behaviors of HVSRs on soil and rock for different rupture styles and velocity profiles. The results reveal the significant role of shallow crustal velocity structure in the generation of high-frequency ground motions on soil sites.

Generation of seismic excitations compatible with target spectrum: application to Eurocode 8

2020 ◽  
Vol 18 (1) ◽  
pp. 122-135
Author(s):  
Abdellah Boudina ◽  
Malek Hammoutene
Keyword(s):  
Epicentral Distance ◽  
Response Spectrum ◽  
Ground Motions ◽  
Environmental Parameters ◽  
Eurocode 8 ◽  
Ground Acceleration ◽  
Content Type ◽  
Strong Ground Motions ◽  
Acceleration Time Histories ◽  
Strong Ground

Purpose This paper aims to artificially generate seismic accelerograms compatible with the response spectrum imposed as a function of the given environmental parameters such as magnitude, epicentral distance and type of soil. This study is necessary for the non-linear dynamic analysis of structures in regions where real seismic records are not available. Design/methodology/approach First, a stochastic iterative method is used to estimate the spectral densities of acceleration power from the respective target response spectra. Thereafter, based on the superposition of seismic waves, a subsequent iterative procedure, which implicitly takes into account the non-stationary character of temporal intensity content of strong ground motions, is developed to synthesize, from these power spectral density, the corresponding acceleration time histories. The phase contents of the ground acceleration samples, thus obtained, are generated using a probability density function of phase derivatives with characteristic parameters estimated from seismological considerations. When based on seismic codes spectrum compatible criteria, this procedure can be used to generate strong ground motions for structural design. Findings The results found show that the forms of acceleration of the target and the simulated signals have similar characteristics in terms of strong motion durations, the peak ground acceleration values, corresponding time of occurrence and also, the corresponding cumulative energy functions follow practically the same pattern of variations. Originality/value The aim of this study is to generate seismic accelerograms compatible with regulatory spectra by the composition of the three acceleration duration segments based on environmental parameters (magnitude, epicentral distance and type of soil) and which subsequently serves to control the time envelope of the generated signals, and therefore the random generation of phase derivatives, which has not been previously treated.

SEA99: A revised ground motion prediction relation for use in extensional tectonic regimes

1999 ◽  
Vol 89 (5) ◽  
pp. 1156-1170 ◽  
Author(s):  
P. Spudich ◽  
W. B. Joyner ◽  
A. G. Lindh ◽  
D. M. Boore ◽  
B. M. Margaris ◽  
...  
Keyword(s):  
Response Spectrum ◽  
Ground Motions ◽  
Geometric Mean ◽  
Strike Slip ◽  
Normal Faulting ◽  
Step Method ◽  
Ground Acceleration ◽  
Data Set ◽  
Extensional Tectonic ◽  
One Step

Abstract We present SEA99, a revised predictive relation for geometric mean horizontal peak ground acceleration and 5%-damped pseudovelocity response spectrum, appropriate for estimating earthquake ground motions in extensional tectonic regimes, which we demonstrate to have lower ground motions than other tectonic regimes. SEA99 replaces SEA96, a relation originally derived by Spudich et al. (1996, 1997). The data set used to develop SEA99 is larger than that for SEA96, and minor errors in the SEA96 data set have been corrected. In addition, a one-step regression method described by Joyner and Boore (1993, 1994) was used rather than the two-step method of Joyner and Boore (1981). SEA99 has motions that are as much as 20% higher than those of SEA96 at short distances (5-30 km), and SEA99's motions are about 20% lower than SEA96 at longer periods (1.0-2.0 sec) and larger distance (40-100 km). SEA99 dispersions are significantly less than those of SEA96. SEA99 rock motions are on the average 20% lower than motions predicted by Boore et al. (1994) except for short distances at periods around 1.0 sec, where SEA99 motions exceed those predicted by Boore et al. (1994) by as much as 10%. Comparison of ground motions from normal-faulting and strike-slip events in our data set indicates that normal-faulting horizontal ground motions are not significantly different from extensional regime strike-slip ground motions.

scholarly journals Frequency-dependent site factors for the Icelandic strong-motion array from a Bayesian hierarchical model of the spatial distribution of spectral accelerations

2021 ◽  
pp. 875529302110369
Author(s):  
Sahar Rahpeyma ◽  
Benedikt Halldorsson ◽  
Birgir Hrafnkelsson ◽  
Sigurjón Jónsson
Keyword(s):  
Ground Motion ◽  
Hierarchical Model ◽  
Response Spectrum ◽  
Ground Motions ◽  
Strong Motion ◽  
Bayesian Hierarchical Model ◽  
Site Factors ◽  
Ground Acceleration ◽  
Small Aperture ◽  
Bayesian Hierarchical

The earthquake ground motions of over 1700 earthquakes recorded on a small-aperture strong-motion array in south Iceland (ICEARRAY I) that is situated on a relatively uniform site condition characterized as rock, exhibit a statistically significant spatial variation of ground-motion amplitudes across the array. Both earthquake and microseismic horizontal-to-vertical spectral ratios (HVSR) have been shown to exhibit distinct and in some cases, bimodal peaks in amplification, indicating site resonance at periods of 0.1–0.3 s, a phenomenon that has been attributed to a surface layer of lava rock lying above a sedimentary layer, a structure that is then repeated with depth under the array. In this study, we implement a Bayesian hierarchical model (BHM) of the seismic ground motions that partitions the model residuals into earthquake event term, station term, and event–station term. We analyzed and compared peak ground acceleration (PGA) with the 5% damped pseudo-acceleration response spectrum (PSA) at oscillator periods of T = 0.05–1.0 s. The results show that the event terms, dominate the total variability of the ground-motion amplitudes over the array. However, the station terms are shown to increase in the period range of 0.1–0.3 s on most stations and to different extents, leading to an increase in the overall variability of ground motions at those periods, captured by a larger inter-station standard deviation. As the station terms are a measure of how much the ground motions at those stations deviate from the array average, they act as proxies for localized site effects and amplification factors. These results, improve our understanding of the key factors that affect the variation of seismic ground motions across the relatively small area of ICEARRAY I. This approach can help to improve the accuracy of earthquake hazard assessments on local scales, which in turn could contribute to more refined seismic risk assessments and engineering decision-making.

A Comparison of Eastern North American ground Motion Observations with Theoretical Predictions

1990 ◽  
Vol 61 (3-4) ◽  
pp. 171-180 ◽  
Author(s):  
Gail M. Atkinson
Keyword(s):  
Stochastic Model ◽  
Ground Motion ◽  
North American ◽  
High Frequency ◽  
Ground Motions ◽  
Source Spectrum ◽  
Regression Analyses ◽  
Specific Effects ◽  
Model Predictions ◽  
Theoretical Predictions

Abstract Theoretical predictions of eastern North American (ENA) ground motion parameters based on a stochastic model (Boore and Atkinson, 1987; Atkinson and Boore, 1990) are evaluated in light of recent data, including data from the 1988 Saguenay, Quebec earthquake. The evaluation is based on visual comparisons of predicted and observed ground motion amplitudes, and on regression analyses of the data. Data are consistent with the theoretical model on average, although high-frequency ground motions from the Saguenay earthquake are underpredicted. It is hypothesized that differences between the observations and the stochastic model predictions may be explained by the presence of two corner frequencies in the source spectrum. Any single earthquake may exhibit ground motions significantly higher or lower than predicted due to local or earthquake-specific effects not accounted for in predictions of ‘average’ motions.

Use of ray theory to calculate high-frequency radiation from earthquake sources having spatially variable rupture velocity and stress drop

1984 ◽  
Vol 74 (6) ◽  
pp. 2061-2082
Author(s):  
Paul Spudich ◽  
L. Neil Frazer
Keyword(s):  
Stress Drop ◽  
High Frequency ◽  
Slip Velocity ◽  
Green’S Functions ◽  
Ground Motions ◽  
Spatial Variations ◽  
Body Waves ◽  
Ray Theory ◽  
Rupture Velocity ◽  
Ground Acceleration

Abstract We analyze the problem of calculating high-frequency ground motions (>1 Hz) caused by earthquakes having arbitrary spatial variations of rupture velocity and slip velocity (or stress drop) over the fault. We approximate the elastic wave Green's functions by far-field body waves, which we calculate using geometric ray theory. However, we do not make the traditional Fraunhofer approximation, so our method may be used close to large faults. The method is confined to high frequencies (greater than about 1 Hz) due to the omisson of near-field terms, and must be used at source-observer distances less than a few source depths, due to the omission of surface waves. It is easily used in laterally varying velocity structures. Assuming a simple parameterization of the slip function, the computational problem collapses to the evaluation of a series of line integrals over the fault, with one line integral per each time ti in the observer seismogram. The path of integration corresponding to observation time ti consists of only those points on the fault which radiate body waves arriving at the observer at exactly time ti. This path is an isochron of the arrival time function. An isochron velocity may be defined that depends on rupture velocity and resembles the usual directivity function. Observed ground motions are directly dependent upon this isochron velocity. Ground velocity is proportional to isochron velocity and ground acceleration is proportional to isochron acceleration in dislocation models of rupture. Ground acceleration may also be related to spatial variations of slip velocity on the fault, using the square of isochron velocity as a constant of proportionality. We show two rupture models, one with variable slip velocity and the other with variable rupture velocity, that cause the same ground acceleration at a single observer. The computational method is shown to produce reasonably accurate synthetic seismograms, compared to a method using complete Green's functions, and requires about 0.5 per cent of the computer time. It may be very effective in calculating ground motions in the frequency band 1 to 10 Hz at observers within a few source depths of large earthquakes, where most of the high-frequency motions may be caused by direct P and S waves. We suggest a possible method for inverting ground motions for both slip velocity and rupture velocity over the fault.

Use of Discrete Orthonormal S-Transform to Simulate Earthquake Ground Motions

2020 ◽  
Vol 110 (2) ◽  
pp. 565-575 ◽  
Author(s):  
Xi Zhong Cui ◽  
Han Ping Hong
Keyword(s):  
Power Distribution ◽  
Fourier Spectrum ◽  
Response Spectrum ◽  
Ground Motions ◽  
Frequency Resolution ◽  
Average Amplitude ◽  
Time Frequency ◽  
S Transform ◽  
Practical Tool ◽  
The Fourier Transform

ABSTRACT The S-transform and discrete orthonormal S-transform (DOST) produce time–frequency representations, which is in contrast to the wavelet transformations. Similar in the Fourier transform, the use of the S-transform and DOST provides frequency-dependent resolution with absolutely referenced phase information. Although the decomposed signal using DOST is expressed as a sum of orthonormal basis function, this is not the case if the S-transform is used. In the present study, a procedure to simulate nonstationary ground motions based on DOST is proposed based on a seed record or given a target amplitude of DOST coefficients. It is shown that the model has zero mean, and its variance equals the assigned target. Using five real records, each from a larger earthquake, the application of the DOST and S-transform to the records is carried out. Although the time–frequency resolution obtained from DOST is coarse as compared to that obtained using the S-transform, its use identifies clearly time–frequency characteristics. Samples of ground motions are simulated using the proposed method based on the amplitude of the DOST coefficients of a seed record or on the average amplitude of the DOST coefficients of a set of actual records. The comparison of the time–frequency resolution, Fourier spectrum, time-varying power distribution, and response spectrum of the simulated and seed records indicates that the proposed simulation model is a useful and practical tool to simulate nonstationary ground motions.

scholarly journals Combination of Spectral Representation and Wavelet Packets for Generating Long-Period Ground Motions

2020 ◽  
Vol 2020 ◽  
pp. 1-24
Author(s):  
Minghui Dai ◽  
Yingmin Li
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
Spectral Representation ◽  
Response Spectrum ◽  
Ground Motions ◽  
Time History ◽  
Wavelet Packets ◽  
Velocity Spectrum ◽  
Long Period ◽  
Frequency Components

Far-field long-period ground motions (hereafter long-period ground motions) featuring low-frequency components are responsible for the resonant responses of high-rise buildings. In this context, it is beneficial to assess the dynamic performance of these buildings under long-period ground motions with the aid of time history analysis. This paper proposes a method for generating long-period motions by combining long-period components synthesized by spectral representation with high-frequency components simulated by wavelet packets. Later-arriving long-period surface waves (LALP surface waves), which are determined on the grounds of phase dispersion, represent the main long-period properties in sense of velocity spectrum at longer periods of interest. An analytical expression for power spectrum density is employed to capture the narrowband properties of LALP velocity surface waves. Meanwhile, modification of the Gaussian random process is performed in time and frequency domains to attain a modulated initial seed motion, which shows the variability of the targeted ground motion. A simulation of high-frequency components is accomplished by means of iteration, in which wavelet coefficients of the modulated seed motion are adjusted to match the targeted response spectrum and cumulative energy plot. Furthermore, comparisons between an ensemble of realizations and target motions demonstrate the feasibility of the proposed method to generate long-period simulations sharing similar properties to target motions.

Synthesis of Strong Ground Motions at Two Dam Sites during the Great Wenchuan Earthquake

2013 ◽  
Vol 353-356 ◽  
pp. 1934-1940
Author(s):  
Hai Ming Liu ◽  
Xia Xin Tao ◽  
Li Yuan Wang ◽  
Wei Jiang
Keyword(s):  
Wenchuan Earthquake ◽  
Peak Ground Acceleration ◽  
Ground Motions ◽  
Source Spectrum ◽  
Ground Acceleration ◽  
Mean Values ◽  
Strong Ground Motions ◽  
Finite Fault ◽  
Source Models ◽  
Strong Ground

The ground motions on two dam sites during the great Wenchuan earthquake with magnitude 8.0, motions are synthesized from 30 finite fault based hybrid source models and inversed regional parameters of source spectrum and motion attenuation. The results show that the peak ground acceleration values are less than those estimated directly from the Intensities Ⅹ and Ⅺ at the two sites, with mean values 259 and 716 gals. The motion at Shapai is much stronger than that at Zipingpu, and the spectrum is also wider than the latter, but the corresponding duration is shorter during the earthquake.

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