Strong Earthquake Ground Motion Research Articles

PRELIMINARY ANALYSIS OF THE PEAKS OF STRONG EARTHQUAKE GROUND MOTION--DEPENDENCE OF PEAKS ON EARTHQUAKE MAGNITUDE, EPICENTRAL DISTANCE, AND RECORDING SITE CONDITIONS

Analyses of peak amplitudes of strong earthquake ground motion have been carried out with the emphasis on their dependence on earthquake magnitude, epicentral distance, and geological conditions at the recording site. Approximate empirical scaling functions have been developed which, for a selected confidence level, yield an estimate of an upper bound of peak accelerations, velocities, and displacements. The parameters in these scaling functions have been computed by least-squares fitting of the recorded data on peak amplitudes which are now available for a range of epicentral distances between about 20 and 200 km and are representative for the period from 1933 to 1971 in the Western United States. The possibility of extrapolating the derived scaling laws to small epicentral distances where no strong-motion data are currently available has been tested by comparing predicted peak amplitudes with related parameters at the earthquake source. These source parameters (average dislocation and stress drop) can be derived from other independent studies and do not contradict the inferences presented in this paper. It has been found that for an approximate 90 per cent confidence level the presently available data suggest that peak accelerations, velocities, and displacements at the fault and for the frequency band between 0.07 and 25 Hz probably do not exceed about 3 to 5 g, 400 to 700 cm/sec, and 200 to 400 cm, respectively. The logarithms of the peaks of strong ground motion seem to depend in a linear manner on earthquake magnitude only for small shocks. For large magnitudes this dependence disappears gradually and maximum amplitudes may be achieved for M ≈ 7.5. The influence of geological conditions at the recording site appears to be insignificant for peak accelerations but becomes progressively more important for peaks of strong-motion velocity and displacement.

A Note on the Range of Peak Amplitudes of Recorded Accelerations, Velocities and Displacement With Respect to the Modified Mercalli Intensity Scale

Correlations of the logarithms of acceleration, velocity and displacement peak amplitudes of recorded strong earthquake ground motion with the Modified Mercalli Intensity scale, I MM , are characterized by large scatter of data points. For a given I MM this scatter is equal to about one order of magnitude on the linear amplitude scale. Correlations have been presented that are valid for the range of intensities IV ≤ I MM ≤ VIII, which correspond to 187 strong-motion accelerograms recorded during 57 earthquakes in the Western United States. Extrapolation of these correlations on the logarithmic scale to the largest Modified Mercalli intensity level I MM = XII lead to strong-motion amplitudes which are not contradicted by other independent estimates of these largest amplitudes.

A STUDY ON THE DURATION OF STRONG EARTHQUAKE GROUND MOTION

A simple definition of the duration of strong earthquake ground motion based on the mean-square integral of motion has been presented. It is closely related to that part of the strong motion which contributes significantly to the seismic energy as recorded at a point and to the related spectral amplitudes. Correlations have been established between the duration of strong-motion acceleration, velocity, and displacement and Modified Mercalli intensity, earthquake magnitude, the type of recording site geology, and epicentral distance. Simple relations have been presented that predict the average trend of the duration and other related parameters as a function of Modified Mercalli intensity, earthquake magnitude, site geology and epicentral distance.

Steel design

Structural steel has proved to be a suitable material for ductile moment-resisting space frames in buildings subjected to strong earthquake ground motion.
 The material properties buckling criteria and connection design considered necessary to avoid premature unloading before the inelastic potential of the material is achieved are discussed. Consideration is also given to the behaviour of full size steel frames, lamellar tearing and deformation of the panel zone.

Time and amplitude dependent response of structures

AbstractAn understanding of the precise nature of the non‐linear response of structures is essential for future improvement of earthquake resistant design procedures. This paper presents a summary of observations of dynamic behaviour which were made on two typical modern buildings during a period of about ten years. These structures underwent numerous tests and experienced three strong earthquake ground motions. The data presented should prove useful for calibration of parameters in theoretical non‐linear modelsFor buildings having an apparent soft‐spring‐type non‐linearity, a partial or complete recovery of the structural stiffness appears to occur following the large strains created by strong ground shaking. The rate and extent of this recovery appear to depend strongly on the strain levels throughout the excitation.

Analysis of strong earthquake ground motion for prediction of response spectra

AbstractPrediction of response spectra for earthquake engineering purposes is considered from a new point of view based on the dislocation theory of earthquakes. It is shown that the traditional scaling of response spectra by the predicted peak acceleration should be limited to the high‐frequency end of the spectrum, and that the peak acceleration in the near field is not strongly correlated with earthquake magnitude. The amplitude of the long‐period end of response spectrum at source to station distances greater than about 10 source dimensions should be scaled with seismic moment, while for distances less than about one source dimension this amplitude should be proportional to the permanent ground displacement. To reconcile the existing extensive data on seismicity of active regions based on magnitude scale, it is shown that magnitude can be used to determine approximately the seismic moment.

Local distribution of strong earthquake ground motions

abstract Twenty ground stations distributed over a 40-square-mile area in Pasadena recorded strong ground shaking during the San Fernando earthquake of February 9, 1971. Relative responses at 10 of these same stations as measured for small earthquakes by standard Wood-Anderson torsion seismometers are available for comparison from a study made by Gutenberg in the 1950's. Frequency spectra of strong ground motions as calculated for four sites having time-recording accelerographs assist in the interpretation of seismoscope results at the other stations. Attempts to correlate local distributions with known features of local geology such as thickness of alluvium, distance from known faults, etc., indicate that no single feature plays a dominant role in the resulting patterns. The implications of such complicated distributions for the preparation of seismic risk maps are discussed, and it is concluded that it would not be possible in the present state of knowledge to assess meaningful variations in the seismic risk throughout the Pasadena area.

Stress estimates for the San Fernando, California, earthquake of February 9, 1971: Main event and thirteen aftershocks

AbstractThe strong earthquake ground motion recorded in the center of and above the fault plane is combined with field evidence of faulting and instrumental studies of aftershocks to deduce stresses during and after the San Fernando earthquake of February 9, 1971. Stress computations based on Brune's near-field, shear-wave spectra, peak velocity of ground motion, energy calculated from the strong-motion record, and a model of circular dislocation give mutually consistent stress estimates, which suggest that the effective stress operating during the earthquake was approximately 100 bars, while during the earthquake it dropped several tens of bars. The energy of the main event is estimated to be 1022 dyne cm.Thirteen aftershocks, recorded during the first 6 min, were associated with stress drops ranging from 10 to 500 bars, these events clustering along the north-eastern end of the dislocation surface.The strong-motion accelerograms provide invaluable data for detailed investigations of the pattern of earthquake energy release during and immediately after an earthquake. Used for the first time in this study, strong-motion accelerograms gave an excellent picture of stress history and migration of seismic activity during the first 6 min.

Response envelope spectrum and interpretation of strong earthquake ground motion

abstract A multiple filter technique is developed using a single-degree-of-freedom lightly-damped oscillator as a narrow band-pass filter. It provides for a physically simple approach to the analysis of accelerograph records from the point of view of structural engineering. The analysis of several typical accelerograph records indicates that a significant portion of strong earthquake ground motion consists of surface waves. It is concluded that the duration of intense shaking will be determined predominantly by the dispersion properties of the ground.

Response of Multi-Story Structures to Earthquake

Behavior of multistory buildings responding to strong earthquake ground motion has been computed by high-speed digital computer; response curves and tables and data on effects of certain structural parameters on response are presented.

Integrated velocity and displacement of strong earthquake ground motion

Abstract The earthquake ground accelerations recorded at El Centro, 30 December 1934; El Centro, 18 May 1940; Olympia, Washington, 13 April 1949; and Taft, California, 21 July 1952, have been integrated with a digital computer to obtain at each location the three components of ground velocity and ground displacement. Maximum horizontal displacements of 10 and 20 inches are indicated, and maximum vertical displacements of 5 inches are indicated.

Response of Multi-Story Structures to Earthquake

The behavior of multi-story buildings responding to strong earthquake ground motion has been computed by a high-speed digital computer. Response curves and tables are presented, and the effects of certain structural parameters on the response are studied.