Correlations of peak acceleration, velocity and displacement with earthquake magnitude, distance and site conditions (original) (raw)
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Soil Dynamics and Earthquake Engineering, 2013
Variations of average and maximum power of strong earthquake ground motion during the 1994 Northridge, California earthquake were gradual and smooth over distances as large as tens of kilometers. Correlation of the contours of recorded power with the depth of sediments and vertical offsets of the basement rocks along the faults in the Los Angeles basin implies a horizontal flow of earthquake wave energy through the deep waveguides of this basin. If the fault-to-station distances were to be measured along the three-dimensional wave paths through these sedimentary waveguides, rather than along straight lines emanating from the source, as is common in empirical studies of strong motion amplitudes, the accuracy of empirical-scaling equations for the prediction of the power of strong shaking could improve significantly.
Soil Dynamics and Earthquake Engineering, 1997
Plots of smoothed contours of peak amplitudes and of areas with the same peak sign are presented for the radial, transverse and vertical components of acceleration, velocity and displacement. These were drawn by hand based on strong motion recordings, and represent direct observational evidence of the nature of the attenuation of strong motion with distance at high, intermediate and low frequencies. The contours of peak amplitudes indicate that, close to the source, those are affected by the source radiation pattern, and away from the source, by the geological structure. Slower attenuation of peak amplitudes with distance IS observed for waves travelling through the sediments of the Los Angeles basin. Large areas with consistent peak polarity are observed, often tens of kilometers in size, indicating that the sign of the peak is not random. The time of the peak amplitude, relative to first arrivals of S-waves, was also calculated; the areas where this time was greater than 7s were contoured and shaded, indicating peak occurrence later than the direct arrivals from the source. These plots show that, at distances larger than about 20.--30 km, for acceleration, the largest peak occurs mostly before, and, for displacement, mostly after the arrival of surface waves. This indicates that the attenuation of strong ground motion is governed by body waves at short periods and by surface waves at long periods. The presented plots will be useful in refinement of attenuation laws for ground motion peak amplitudes, and for frequency dependent response spectrum ordinates. ({3 1997 Elsevier Science Limited.
An investigation into earthquake ground motion characteristics in eastern North America
Bulletin of the Seismological Society of America, 1987
A random-vibration model of the Hanks-McGuire type is used to predict peak ground motions at rock sites in eastern North America. The assumed geometric decay and distance-dependent duration approximate the propagation of direct body waves (at short distances) and Lg waves (at regional distances). The model predicts peak acceleration and velocities, as well as response spectra and magnitude for a given seismic moment and corner frequency. To predict ground motions for a given Lg magnitude (mLg), the model is first used to calculate the seismic moment corresponding to that magnitude, assuming a source scaling law. Then, knowing the moment and corner frequency, the model is used to calculate peak ground motions. Available data from strong motion recordings and from the ECTN and LRSM networks, modified to estimate horizontal ground motions on rock where appropriate, are used to verify the model's assumption and predictions. Modified Mercalli intensity data are also used. Ground motions predicted by the model with a stress drop of 50 to 200 bars agree with the ground motion data, but the mLg values computed by the model for given seismic moments do not agree with Nuttli's (1983) moment versus mLg data for large earthquakes. Resolution of the latter disagreement awaits the collection of instrumental data from large events in eastern North America.
Analysis of accelerograms—Parkfield earthquake
Bulletin of the Seismological Society of America, 1967
Integrated velocities and displacements show that near the fault at Cholame the surface motion exhibited a transient horizontal displacement pulse of approximately ten inches amplitude and one and one-half seconds duration, normal to the fault. Although 50 per cent of g ground acceleration was recorded at the fault, the ground motion attenuated rapidly with distance and at ten miles from the fault the maximum acceleration was reduced to one-tenth of its near-fault value. The ground motion also changed its character with distance, losing its pulse-like directional characteristic and becoming isotropic. Computed response spectra are presented and the large spectrum ordinates for this shock of relatively small magnitude and moderate destructiveness indicate that in an engineering sense the Parkfield ground motion is in a different class from such large destructive ground motions as El Centro 1940, Tehachapi 1952, and Olympia 1949.
1976
An empirical model for scaling Fourier Amplitude Spectra of strong earthquake ground acceleration in terms of magnitude, M, epicentral distance, R, and recording site conditions has been presented. The analysis based on this model implies that: (a) the Fourier amplitude spectra of strong-motion accelerations are characterized by greater energy content and relatively larger amplitudes for long-period waves corresponding to larger magnitudes M, (b) the shape of Fourier amplitude spectra does not vary appreciably for the distance range between about 10 and 100 km, and (c) long-period spectral amplitudes (T > 1 sec) recorded on alluvium are on the average 2.5 times greater than amplitudes recorded on basement rocks, whereas short-period (T < 0.2 sec) spectral amplitudes tend to be larger on basement rocks. It has been shown that the uncertainties which are associated with the forecasting of Fourier amplitude spectra in terms of magnitude, epicentral distance, site conditions, and component direction are considerable and lead to the rhnge of spectral amplitudes which for an 80 per cent confidence interval exceed one order of magnitude. A model has been presented which empirically approximates the distribution of Fourier spectrum amplitudes and enables one to estimate the spectral shapes which are not exceeded by the presently available data more than 100 (1-p) per cent of time where p represents the desired confidence level (0 < p <1). No. of Accelerograms Earthquake Used in No.* this Study Magnitude Caltech Report No.
Peak displacement demand of small to moderate magnitude earthquakes in stable continental regions
Earthquake Engineering & Structural Dynamics, 2005
A theoretical fault-slip model has been developed for predicting the notional peak displacement demand (PDD) of earthquakes based on a limiting natural period of 5 s, for application in stable continental regions (SCRs). The developed theoretical expression is simple and robust. Importantly, it envelops predictions arising from a number of existing empirical and seismological (stochastic) models included in the comparison. The notional PDD prediction has been made initially for hard rock crustal conditions and at a reference source-site distance of 30 km. Factors have accordingly been introduced to correct for di erent distances and geological conditions in completing the PDD prediction model. Assuming displacement-controlled behaviour, the predicted notional PDD may be compared with the displacement capacity of a structure, or component, for purposes of seismic stability assessment. Figure 1. Peak displacement demand (PDD) and displacement response spectrum: (a) displacement spectrum of a single pulse; and (b) idealized bi-linear displacement spectrum.
Statistical analysis of peaks and directivity of earthquake ground motion
Earthquake Engineering & Structural Dynamics, 1995
Conversion factors are useful for attenuation and damage estimation relationships. These factors among different definitions of peaks (i.e. larger, average and resultant) for peak ground motion indices and acceleration response spectrum were investigated. A large number of horizontal acceleration records recorded at 76 free-field sites of the Japan Meteorological Agency were used in this study. Two orthogonal horizontal components were combined in the time domain to get the maximum resultant peak ground motion indices and acceleration response spectrum in the horizontal plane. From the analysis, the means of the larger/resultant ratio were found to be 0.934 for acceleration, 0926 for velocity, and 0.913 for displacement. A similar decreasing trend was observed for the means of the average/resultant ratio of the ground motion indices and acceleration response spectrum. The directivity of peak ground motion indices was also examined. It was found that the peak ground motion is more likely to occur in the transverse direction than in other directions. This trend is more prominent in the long-period contents of ground motion.