Showing papers on "Peak ground acceleration published in 1990"

A new attenuation relation for peak horizontal acceleration of strong earthquake ground motion in Japan

Abstract: A new attenuation relation for peak horizontal acceleration applicable to the near source region in Japan is developed. The data base consists of 1372 horizontal components of peak ground acceleration from 28 earthquakes in Japan and 15 earthquakes in the United States and other countries. Coefficients describing the decrease in acceleration with increasing distance found by most previous studies of Japanese data are significantly smaller than those found by analyzing individual earthquakes. This phenomenon is examined and found to result from use of general nonstratified multiple regression analyses. The present analysis uses a two-step stratified regression procedure and an attenuation model that accounts for geometrical spreading and anelastic attenuation but has magnitude-independent shape at very short distances. The resulting relation in Japan is log ⁡ 10 A = 0.41 M − log ⁡ 10 ( R + 0.032 ⋅ 10 0.41 M ) − 0.0034 R + 1.30 where A is the mean of the peak acceleration from two horizontal components at each site (cm/sec 2 ), R the shortest distance between site and fault rupture (km), and M the surface-wave magnitude. The median estimate of peak horizontal acceleration at the source region is 620 cm/sec 2 , independent of earthquake magnitude. Effects of four different ground condition (rock, hard-, medium- and soft-soils) on the attenuation relation are also examined. Average peak horizontal accelerations for the rock and the soft-soil sites are 60 and 140 per cent respectively of the value predicted from the equation.

Probabilistic earthquake risk maps of Australia

Abstract: New earthquake risk maps, based on the Cornell‐McGuire methodology, have been prepared for the Australian continent and continental margins. The risk is depicted as contours of peak ground velocity, acceleration and ground intensity with a 10% probability of being exceeded in 50 years. The earthquake process was assumed to be Poissonian and consequently foreshocks and aftershocks were eliminated. The estimated maximum earthquake magnitude likely to be expected in each zone was assumed to be half a magnitude unit greater than the largest recorded Richter magnitude for that zone. For areas outside the defined source zones, normalized background seismicity levels were used in the risk estimates. Separate relationships for the attenuation of ground intensity with hypocentral distance using a scaling law of the Kanai form were obtained for western, southeastern and northeastern Australia and for Indonesian earthquakes felt in northern Australia. These were based on the determination of mean isoseismal radii fr...

Attenuation models inferred from intraplate earthquake recordings

Abstract: Strong-motion recordings at 87 sites from 56 different intraplate earthquakes from North America, Europe, China and Australia have been used through a two-step regression analysis to develop new attenuation models for peak ground acceleration, and for pseudo-relative velocity for frequencies of 0.25, 0.5, 1.0, 2.0, 5.0 and 10.0 Hz, all for 5 per cent of critical damping. The estimates are obtained along with an analysis of residuals and scatter. A similar regression analysis has been performed also for Fourier spectra of acceleration, in which case the coefficient for the anelastic term has been interpreted in terms of a frequency dependent quality factor Q. The resulting Q-model shows a strong frequency sensitivity with values around 600–700 at 1 Hz, around 2000 at 10 Hz and around 5200 at 25 Hz. These PGA, PSV and Q results depend, however, on the underlying assumption for geometrical spreading, in particular for low frequencies.

Localization of intermediate‐term earthquake prediction

Abstract: Relative seismic quiescence within a region which has already been diagnosed as having entered a “Time of Increased Probability” (TIP) for the occurrence of a strong earthquake can be used to refine the locality in which the earthquake may be expected to occur. A simple algorithm with parameters fitted from the data in Northern California preceding the 1980 magnitude 7.0 earthquake offshore from Eureka depicts relative quiescence within the region of a TTP. The procedure was tested, without readaptation of parameters, on 17 other strong earthquake occurrences in North America, Japan, and Eurasia, most of which were in regions for which a TIP had been previously diagnosed. The localization algorithm successfully outlined a region within which the subsequent earthquake occurred for 16 of these 17 strong earthquakes. The area of prediction in each case was reduced significantly, ranging between 7% and 25% of the total area covered by the TIP.

Stochastic response of suspension bridges to earthquake forces

Abstract: The purpose of the paper is to study the applicability of stochastic methods for determining the response in the vertical plane of long-span bridges to earthquakes. The bridges are of the modern type, with flexible towers, box-decks and inclined hangers, Humber and Bosporus being used as the main examples, although some useful information is obtained by studying a small suspension footbridge. The input ground acceleration is that of the Pacoima Dam record of the 1971 San Fernando event, but use is also made of filtered white noise. Because the stochastic approach is essentially an attempt to abstract usable information which could otherwise be obtained from a lengthy time-history approach, the procedure adopted here is to compare the same parameters obtained in these two ways, as far as possible. In particular, the maximum values of displacements and bending moments are considered. The essential question to be answered is whether the short length of earthquake records, coupled with the large natural periods of vibration of long-span bridges, allows sufficient response information to be generated to make statistical parameters meaningful. The short-span (50 m) footbridge gives no cause for concern here, but the detailed comparison with time-history solutions shows that the stochastic approach for both Bosporus and Humber has to be cautiously assessed, particularly if some trailing zeros are not added to the earthquake record. However, general conclusions are not made, because only one earthquake record has been used.

Floor response spectra for base‐isolated multi‐storey structures

Abstract: A study of floor response spectra for a base-isolated multi-storey structure under sinusoidal and seismic ground excitations is carried out. Several base isolation systems including the laminated rubber bearing, the pure-friction, the resilient-friction, the Electricite de France and the sliding resilient-friction systems are considered. A sinusoidal ground acceleration and several earthquake accelerograms (including those of El Centro 1940, Pacoima Dam 1971 and Mexico City 1985) are used to evaluate the floor response spectra. The characteristics of the spectra generated by different base isolation systems are studied, and the results are compared with those for the fixed-base structure. It is shown that the structural contents can be protected against earthquakes by the use of properly designed base isolation systems. In particular, the laminated rubber bearing system appears to be remarkably effective in protecting the secondary systems under a variety of conditions.

Stochastic Characterization of Strong Ground Motion and Applications to Structural Response

Abstract: This study addresses the problem of characterizing strong ground motion for the purpose of computing the dynamic response of structures to earthquakes. A new probabilistic ground motion model is proposed which can act as an interface between ground motion prediction studies and structural response studies. The model is capable of capturing, with at most nine parameters, all those features of the ground acceleration history which have an important influence on the dynamic response of linear and nonlinear structures, including the amplitude and frequency content nonstationarities of the shaking. Using a Bayesian probabilistic framework, a simple and effective statistical method is developed for extracting the "optimal" model from an actual accelerogram. The proposed ground motion model can be efficiently applied in simulations as well as analytical response and reliability studies of linear and inelastic structures. The random response of linear and nonlinear oscillators subjected to the proposed stochastic excitation is considered. The nonlinearity of the oscillator is accounted for by equivalent linearization. A formulation is developed which approximates the original lengthy expressions for the second-moment statistics of the transient response by much simpler expressions. The results provide insight into the characteristics of the nonstationary response and the effect of the ground motion nonstationarities. It is found that the temporal nonstationarity in the frequency content of the ground motion significantly influences the response of both linear and nonlinear structural models. Simulations are also used to study the sensitivity of inelastic structural response parameters to the details of the ground motion which are left "random" by the model. The results can also be used to provide a quantitative assessment of the expected structural damage associated with the ground motion described by the model.

Intermediate term earthquake prediction in the area of Greece: Application of the algorithm M8

Abstract: The 3 strongest earthquakes,M≥70, which have occurred since 1973 in the area of Greece were preceded by a specific increase of the earthquake activity in the lower magnitude range This activation is depicted by algorithm M8 This algorithm of intermediate term earthquake prediction was originally designed for diagnosis by Times of Increased Probability (TIPs) of the strongest earthquake,M≥80 worldwide (Keilis-Borok andKossobokov, 1984) At present the algorithm is retrospectively tested for smaller magnitudes in different seismic regions (Keilis-Borok andKossobokov, 1986, 1988) A TIP refers to a time period of 5 years and an area whose linear size is proportional and several times larger than that of the incipient earthquake source Altogether the TIPs diagnosed by the algorithm M8 in the area of Greece occupy less than 20% and the Times of Expectation (TEs) about 10% of the total space-time domain considered Also there is a current TIP for the southeastern Aegean sea and 1988–1992 It may specify the long-term prediction given inWyss andBaer (1981a,b)

The Influence of the Coastal Plain Sedimentary Wedge on Strong Ground Motions from the 1886 Charleston, South Carolina, Earthquake

Abstract: The effect of Atlantic Coastal Plain sediments on ground motion from the 1886 Charleston, South Carolina, earthquake was studied using linear regression analysis and ground motion modeling. Statistical tests applied to 264 Modified Mercalli intensity reports at epicentral distances less than 400 km showed that intensities within the Lower Coastal Plain (near the coast) averaged from 0.5 to 1.0 units less than intensities within other areas over comparable distances. Simulated ground acceleration time histories were generated along two profiles: one trending northeast from the epicenter along the coast and another trending northwest toward the Fall Line. The modeling results (which assume linear behavior) indicate that the thick coastal sediments attenuate high frequency motions (>3‐10 Hz), while amplifying lower frequency motions. In contrast, locations on thinner sediments to the northwest experience amplification of high frequency motions. The overall effect is that peak acceleration decays mor...

The global geodynamic effect of the MacQuarie Ridge Earthquake

Abstract: The coseismic effect of the Macquarie Ridge earthquake on the earth's length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are compared. It is found that this earthquake should have caused the length-of-day to decrease by 0.06, the position of the mean rotation pole to shift 0.11 milliarcsec towards 323 E longitude, and selected degree l = 2-5 gravitational field coefficients to change by about 1 part in 10 to the 13th.

A Probabilistic Comparative Study of Base Isolation Systems

Abstract: A probabilistic comparative study of base isolation systems is carried out. Laminated rubber bearing with and without lead plug, resilient friction, and EDF base isolation systems is studied. Nonstationary stochastic models for earthquake ground acceleration are considered and the method of equivalent linearization is used for response analysis. The root-mean-square displacement, velocity, and acceleration responses of a rigid structure with various base isolation systems are evaluated. The results are compared with those obtained from several Monte Carlo digital simulations and good agreement is observed. Probabilistic analysis of displacement limit crossing is also carried out.

Seismic design of bridge abutments and retaining walls (summary volume)

Abstract: The behaviour of retaining walls under earthquake loading has been studied by both experimental and theoretical investigations. Free standing walls, ranging from rigid or walls with low flexibility, to walls that can respond by outward sliding on soil failure planes, have been investigated. Analysis and design procedures for special forms of construction, including reinforced earth and tied-back walls, have been developed. The research has shown the validity of using the limiting equilibrium approach for many types of free standing walls. Provided outward movements can be tolerated under severe ground shaking, this method enables the wall to be designed for accelerations lower than the peak ground acceleration. Results of the studies show that the outward movements are not particularly large under inertia loads corresponding to about one-half of usual design level peak ground accelerations. This finding should result in a significant reduction in the costs of many high walls. For smaller walls, a static design for gravity and superimposed loads alone may provide sufficient strength to resist earthquakes. One method of simplifying bridge abutment structures is to build them monolithic with the superstructure rather than to separate them with sliding bearings, expansion joints, seismic gaps and restrainers. Abutment studies have been mainly directed towards the prediction and measurement of pressures that develop on these types of abutments as they displace under inertia forces imposed by the superstructure. The research results have increased the reliability of methods for predicting the soil stiffening effect of abutments and have shown how this influences the dynamic response of the bridge during earthquakes.

Regional seismic slope failure probability matrices

Abstract: A method for constructing seismic slope failure probability matrices is presented. The core of the method is a probabilistic sliding block model which allows for systematic incorporation of the uncertainties associated with both the ground excitation and the strength of the slope materials. The extent of damage to a slope is defined in terms of the magnitude of the earthquake-induced permanent displacement. The intensity of the ground shaking is characterized by a peak ground acceleration as well as an earthquake magnitude, and the possible scatter in the ground motion details is included through the use of an equivalent stationary motion model. After the effects of essential contributing factors are discussed, regional seismic slope failure probability matrices are presented for general applications.

Ground Acceleration near St. Michael's Church During the 1886 Charleston, SC, Earthquake

Abstract: The historic and continuing seismicity in the southeastern U.S. indicate the seismic threat to the population. However, little is known about the engineering characteristics of eastern U.S. earthquakes because there are no strong motion recordings of them. In particular, the peak ground acceleration, needed for structural design, is not available except through correlations with western U.S. earthquakes or MMI data of unknown uncertainty. This paper estimates the peak ground acceleration experienced by St. Michael's Church during the 1886 Charleston, SC, event based on conventional and probabilistic structural analysis. The 1886 event, rated as MMI X and magnitude 7, is the only historic strong motion event greater than mb = 5 that affected Charleston. The analysis concluded that the peak ground acceleration for the 1886 event was 0.33g. The coefficient of variation of this acceleration was 24%, remarkably small when considering the uncertainty in the input parameters.

Strong Ground Motions from Intermediate-Depth Earthquake : A Study of Site Effects

Abstract: In this paper we study the site effects on long-period (1 to 10 sec) ground motions at various sites in Hokkaido, Japan, using JMA strong motion records from near-by, intermediate-depth earthquakes. First the source parameters of the events are determined from a study of teleseismic body waves. Then synthetic strong-motion seismograms are calculated for the source parameters obtained, assuming a plausible plane-layered earth model, and they are compared with the observed records to investigate the site effect. Body waves from intermediate-depth events can be explained fairly well by the synthetics. However, the long-period coda waves with a period of several seconds, which appear after S arrival at stations within the alluvial plains, cannot be explained by the simple synthetics. They are considered to be surface waves locally generated on the irregular, sediment-bedrock interface due to the incident S wave. We investigate the mode of excitation of the long-period coda waves by means of the envelope shape of the coda. The envelope shape varies from station to station and may represent an index of the site effect.

Ground-motion and source parameters of the Coalinga earthquake sequence

Abstract: Ground-motion and seismic-source parameters, determined from acceleration measured in the epicentral region of the May 2 earthquake, were analyzed with regard to the scaling of source processes responsible for the seismic radiation, as well as the effect of the crustal environment at the hypocenter on these processes. The 30 events, including the M{sub L} = 6.7 main shock, studied here were especially well suited to an investigation of how the various parameters scale with earthquake size, in that nearly six orders of magnitude in seismic moment M{sub 0} were represented, extending over a range from about 4 {times} 10{sup 18} down to 7 {times} 10{sup 12}. The observations at Coalinga have revealed substantial complexities in the earthquake scaling that appear to be general features of individual earthquake sequences. The paper describes: ground-motion-data processing; source parameters, including magnitude-moment relation, seismic deformation, source radius and stress drop, and P- and S-wave corner frequencies; and ground-motion parameters.

Parametric effect of vertical ground acceleration on the earthquake response of elastic structures

Abstract: An analytical procedure is presented for the calculation of the statistical properties of the response of a linear elastic tall building under earthquake excitation. Emphasis is placed on the effect of the vertical ground motion. The restoring force in each story of the structural model is assumed to arise from the bending deformation of the columns whose rigidities are subjected to a general reduction due to the combined action of gravitational forces and the random variations due to vertical ground acceleration. Since earthquakes are random phenomena, stochastic modelling of ground motion seems appropriate. Both the vertical and the horizontal accelerations are treated as amplitiude-modulated Gaussian random processes. With these models, the techniques developed herein, using the concept of Markov processes and Ito's stochastic differential equations, may be applied. To illustrate the application of the method, numerical results are presented for a 6-story building. For computational purposes, the structural properties are evaluated using the finite element method. Within the limit of linear elastic deformation for this moderately tall building. The percentage is expected to be larger for a taller building and much larger when the deformations exceed the elastic limit.

Increasing seismicity as an earthquake precursor in Israel

Abstract: SUMMARY The possibility that changes in the seismicity in and around Israel are precursors is examined. The data available for the period 1982-1987 show that the probability of the occurrence of a relatively strong earthquake (ML > 4.0) increases significantly after the occurrence of an earthquake swarm. A proposed alarm procedure, based on the identification of an increase in the seismic activity for at least two successive days, is applied to four seismically active zones in the region. The results indicate that there is a high probability (more than 40 per cent) of a successful earthquake prediction. Nevertheless, a great deal more data is required to support these observations before the suggested alarm procedure may be incorporated in an earthquake prediction scheme in Israel.

Earthquake Ground Motions Consistent with Probabilistic Seismic Hazard Analysis

Abstract: The present study deals with the new methodology for simulation of earthquake ground motion for the probabilistic risk assessment (PRA) of structures. Peak ground acceleration, acceleration response spectra, and ground motion duration are selected as the parameters to characterize earthquake ground motions. In the proposed method, the seismic hazard curve in terms of peak ground acceleration is calculated and normalized response spectrum and ground motion duration are probabilistically evaluated given that the ground motion intensity exceeds a certain acceleration level. Correlation coefficients between the spectral values at different natural periods are also examined using observed earthquake records. The Monte Carlo technique is adopted to generate sample normalized response spectra in which the correlation relation is taken into account, and the earthquake ground motions for the dynamic response analyses are simulated to fit the sample spectra.

FRACTURE SYSTEM MODELS OF EARTHQUAKE SEQUENCES OF M_s≥7.0 IN NORTH CHINA AND SYNTHETIC INVERSION OF FRACTURE PROCESSES

Abstract: Four large earthquake sequences of Ms≥70 occurred in North China during 1966-1976 They are the Xingtai earthquake of 1966,Bohai earthquake of 1969,Haicheng earthquake of 1975 and Tangshan earthquake of 1976 The occurrence processes of these earthquakes are studied from the view point of fracture system propagation in this paper In terms of the analyses of their activity patterns of foreshock-mainshock-aftershock,it is found that the occurrence of each earthquake sequence is the results from the propagation of the associated fracture system in which the length and geometric distribution of fractures may be different Based on the theory of fracture propagation,four mechanical models of fracture systems suited to each earthquake sequence respectively are presented The geometric and mechanical parameters of these models are corrected once more by means of the synthetic inversion for the data of focal mechanism solutions,variations of aftershock activity patterns during different periods and geodetic deformation using the fracture finite element method Then,the best solutions modelling the fracture processes of the four earthquake sequence are selected It is also found that the pattern of aftershock distribution of a large strike-slip earthquake sequence always show a Z-shape as a whole due to the propagation and combination of fracture branches when an earthquake sequence is at its final stage It can be a mark to recognize the termination time of an earthquake sequence

Geological-Seismological Evaluation of Earthquake Hazards at Hartwell and Clemson Upper and Lower Dams, South Carolina

Abstract: : Seismic source zones have been developed for the southeastern United States that are based on the geology and historic seismicity. A floating earthquake was assigned to each source zone and earthquake motions were attenuated to Hartwell and Clemson Upper and Lower Dams. A maximum credible earthquake at each dam is a far field, MM VII (M = 5.5) earthquake. Horizontal ground motions for this earthquake are as follows: acceleration 190 cm/sec2, velocity 14 cm/sec, and duration 11 sec. Acceleration and response spectra appropriate to these values were selected and are included. Where vertical motions are considered, they may be taken at two-thirds of the horizontal. (SDW)

Reliability-Based Design Codes

Abstract: Reliability analysis for code-designed simple structures subjected to earthquake loading are being determined using both static and dynamic methods and strength-based and damage-related limit states. Seismic hazard is incorporated by assuming a filtered Poisson process model for earthquakes. Ground motion in different seismic events are modeled as independent identically distributed stationary Gaussian processes with band-limited white spectrum. Results suggest that designs by Uniform Building Code at sites with frequent small earthquakes have different reliability than at sites with rare large earthquakes, although the sites are characterized by the same value a 10 of 10% upper fractile of peak ground acceleration.

Three-dimensional analysis of pressures on dams

Abstract: A study is reported of a span-wise variation of nonlinear hydrodynamic pressures on dams during earthquakes. The study used a finite-difference approximation of Euler's equations coupled with the nonlinear free-surface boundary condition. The analysis is useful for calculating hydrodynamic pressures on a dam when the direction of the ground acceleration is no longer in the upstream or downstream direction and when the effect of geometry of a dam-reservoir system must be considered. It is noted that the inviscid flow calculation is effective for this earthquake engineering problem.

A Seismic PRA Procedure in Japan and its Application to a Building Perforance Safety Estimation: Part 1. Seismic Hazard Analysis

Abstract: A method for seismic hazard evaluation which deals with response spectrum information is presented. A local city near Tokyo facing the Pacific Ocean is selected for the case study. It serves as a model of earthquake sources which, in turn, are based on summarized historical earthquake and geological data. Using the model, PGA-dependent spectral shapes as well as seismic hazard curves of PGA are consistently evaluated on the surface of the bed rock, with the hazard curves regarding absolute acceleration response spectra being obtained. Through application of this method, the effects of surface layer profile can be properly treated.

A study on the stochastic characteristics of earthquake response spectra in seismic hazard analysis

Abstract: For the purpose of establishing seismic design criteria for engineering structures, it is desirable to assess the expected intensity of seismic strong ground motion at a site for various probability levels (i.e., Seismic Hazard Analysis). In order to consider the seismic hazard at a site, the predictive equations of ground motion are needed. A number of predictive relationships derived from regression analysis of strong‐motion data are available for horizontal peak acceleration, response spectral value, and Fourier amplitude value. Of the earthquake data recorded in the Taiwan area, the “rock site” data are chosen for the determination of ground motion parameters. By using the predictive equation of peak ground acceleration, the seismic hazard curve at a site can be calculated, and by using the model of spectral acceleration attenuation, the uniform hazard spectrum is developed. Finally, by using the proposed Fourier amplitude attenuation model and the mathematical theory of the maximum response ...