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1.
This paper compares the distribution of damage from the San Fernando, 1971, and Northridge, 1994, earthquakes. Both events had similar size, occurred on blind thrust faults beneath the densely populated San Fernando Valley of the Los Angeles metropolitan area, and hence offer a rare opportunity to compare the effects of the two earthquakes. In a previous study of the distribution of red-tagged (‘unsafe’) buildings and of breaks in the water distribution system caused by the Northridge earthquake, the authors discovered that buildings were damaged less where the soil response was not linear (as indicated by the breaks in the water pipes), except in localized areas of very severe shaking (peak ground velocity exceeding 150 cm/s). The study in this paper shows that the same applies to the damage caused by the San Fernando earthquake, and that the areas with severely damaged buildings (so called ‘gray zones’) for both earthquakes overlapped. This reoccurrence of damage within the same area is interpreted to result from some specific properties of local soil and geology. These properties are not fully understood at present, but should be explored to provide a basis for a new tool for forecasting microzonation maps, and reducing future seismic hazard.  相似文献   

2.
The areas that experienced large strains and differential motions in the soil (indicated by breaks in the water and gas pipe distribution systems) and the areas with severely damaged buildings showed remarkable separation during the March 10, 1933, Long Beach, California earthquake. With analogous results for the 1994 Northridge, California earthquake [Soil Dynam. Earthquake Engng. 17 (1998) 41], the observations summarized in this paper show the fallacy of simplistic and popular interpretations, such as those that hold that in the near field the damage to buildings is caused by ‘soft’ or ‘bad ground’ conditions. In fact, significant reduction in the potential damage to buildings may be expected in the areas where the soil experiences ‘moderate to large’ strains.  相似文献   

3.
The Northridge earthquake contributed unprecedented detail and quality of data on strong ground motion and on its effects on man-made structures. About 110 fires have been attributed directly to the effects of this earthquake. Two hypotheses for the principal causative agents leading to fire ignition were examined: differential motion and strains in the soil, and inertial forces. The fire-ignition frequency is described with respect to: (1) simple measures of strain in the soil (via density of water pipe breaks, n), (2) occurrence of severely damaged buildings (via density of red-tagged buildings, N), (3) site intensity of shaking, (IMM), and (4) inertial forces (via peak horizontal ground velocity, vm). It is shown that the rate of fires (per unit area) ignited by earthquake shaking can be predicted by several empirical equations of comparable accuracy and in terms of common scaling parameters of strong ground motion.  相似文献   

4.
The spatial distributions of severely damaged buildings (red-tagged) and of breaks in the water distribution system following the 1994 Northridge, California, earthquake (ML = 6·4) are investigated relative to the local characteristics of surficial geology. The pipe breaks are used as an indicator of nonlinear soil response, and the red-tagged buildings as indicator of severe shaking. The surficial geology is described by several generalized categories based on age, textural character and thickness of the near surface layer. Two regions are studied: the San Fernando Valley and Los Angeles-Santa Monica. The analysis shows that there is no simple correlation between damage patterns and surficial geology. Single family wood-frame buildings were damaged less when built on fine silt and clay (0–3 m thick) from the late Holocene.  相似文献   

5.
The 1994 Northridge earthquake occurred underneath a densely populated metropolitan area, and was recorded by over 200 strong motion stations in the metropolitan area and vicinity. This rare coincidence made it an ideal case to study, in statistical sense, the correlation of damage to structures with the level of strong shaking, in particular with respect to (1) instrumental characteristics of shaking and (2) the reported site intensity scale. In this paper, statistics for the incidence of red-tagged building in 1 × 1 km2 blocks in San Fernando Valley and Los Angeles is presented and analyzed, as function of the observed peak ground velocity or the local intensity of shaking. The ‘observed’ peak velocity is estimated from contour maps based on the recorded strong motion. The intensity of shaking is estimated from the published intensity map and from our modification of this map to make it more consistent with observed high damage to buildings in some localized areas. Finally, empirical scaling equations are derived which predict the average density of red-tagged buildings (per km2) as a function of peak ground velocity or site intensity of shaking. These scaling equations are specific to the region studied, and apply to Wooden Frame Construction, typical of post World War II period, which is the prevailing building type in the sample studied. These can be used to predict the density of red-tagged buildings per km2 in San Fernando Valley and in Los Angeles for a scenario earthquake or for an ensemble of earthquakes during specified exposure, within the framework of probabilistic seismic hazard analysis. Such predictions will be useful to government officials for emergency planning, to the insurance industry for realistic assessment of insured losses, and to structural engineers for assessment of the overall performance of this type of buildings.  相似文献   

6.
Empirical scaling equations are presented which relate the average number of water pipe breaks per km2, , with the peak strain in the soil or intensity of shaking at the site. These equations are based on contour maps of peak surface strain evaluated from strong motion recordings, and observations of intensity of ground shaking and damage following the Northridge, California, earthquake of 17 January 1994. Histograms for the number of pipe breaks per km2, n, are presented for several ranges of values of the horizontal peak strain and for several values of the site intensity. The observed distribution of pipe breaks is also used to speculate on possible more detailed geographical distribution of near surface strains in the San Fernando Valley and in central Los Angeles. The results can be used to predict number of pipe breaks in the San Fernando Valley and in Los Angeles, for a scenario earthquake or in probabilistic seismic hazard calculations, considering all possible scenarios that contribute to the hazard and the likelihood of their occurrence during specified exposure. Such predictions will be useful for emergency response planning (as the functioning of the water supply is critical for sanitation and in fighting fires caused by earthquakes), to estimate strains during future and past earthquakes in areas where no strong motion was recorded and in defining design guidelines for pipelines and other structures and structural systems sensitive to strains in the ground.  相似文献   

7.
The concept of in-plane and anti-plane shaking is introduced with a rigid block on a plane surface with Coulomb friction. Using a hypoplastic constitutive relation to model the mechanical behaviour of the soil, numerical solutions for a rigid block on a thin dry or saturated soil layer are obtained. The coupled nature of dynamic problems involving granular materials is shown, i.e. the motion of the block changes the soil state—skeleton stresses and density—which in turn affects the block motion. Motions of the block as well as soil response can be more realistically calculated by the new model. The same constitutive equation is applied to the numerical simulation of the propagation of plane waves in homogeneous and layered level soil deposits induced by a wave coming from below. Experiments with a novel laminar shake box as well as real seismic records from well-documented sites during strong earthquakes are used to verify the adequacy of the hypoplasticity-based numerical model for the prediction of soil response during strong earthquakes. The response of a homogeneous earth dam subjected to in-plane and anti-plane shaking is investigated numerically. In-plane and anti-plane shaking is shown to cause nearly the same spreading of a sand dam under drained conditions, whereas under undrained conditions anti-plane shaking causes stronger spreading of the dam. The dynamic behaviour of a breakwater founded on rockfill and soft clay during the 1995 Kobe earthquake is back-calculated to show the good performance of the proposed numerical model also with a structure. Section 9 deals with buildings on mattresses of densified cohesionless soils or fine-grained soils with granular columns, slopes with ‘hidden’ dams and structures on piles traversing clayey slopes to show the suitability of hypoplasticity-based models for the earthquake-resistant design and safety assessment of geotechnical systems.  相似文献   

8.
This paper presents a summary of uncorrected peak ground accelerations recorded during the Northridge, California, earthquake of 17 January 1994 and a preliminary analysis of these data. The presented contours of recorded accelerations agree well with observed patterns of damage. The paper also addresses the issue of how ‘unusual’ and ‘unexpected’ the recorded accelerations are relative to earlier predictions.  相似文献   

9.
A series of studies was conducted on three buildings of steel reinforced concrete structures with RC shear walls damaged in the 1995 Hyogo-ken Nanbu earthquake. These buildings are located in an area where structural damage centred around. Two of these buildings suffered severe damage, while the third was not structurally damaged. Our studies deal with site inspections, including micro-tremor measurement of buildings, the evaluation of input motions, and the response analyses considering soil–structure interaction. The results of simulation analyses of the two severely damaged buildings correspond to their actual damage state. From the response analyses of the one slender building with no structural damage, it was concluded that uplifting is the main reason it did not suffer any structural damage. Through these studies, the importance of soil–structure interaction and effective input motion is fully understood. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

10.
We study the seismic response of an idealized 2D ‘city’, constituted by ten non equally-spaced, non equally-sized, homogenized blocks (i.e. buildings or groups of buildings) anchored in a soft soil layer overlying a hard halfspace. Our results display strong response inside the blocks and on the ground which qualitatively match the responses observed in some earthquake-prone cities.  相似文献   

11.
The 1995 Kobe earthquake seriously damaged numerous buildings with pile foundations adjacent to quay walls. The seismic behavior of a pile group is affected by movement of quay walls, pile foundations, and liquefied backfill soil. For such cases, a three-dimensional (3-D) soil–water coupled dynamic analysis is a promising tool to predict overall behavior. We report predictions of large shake table test results to validate 3-D soil–water coupled dynamic analyses, and we discuss liquefaction-induced earth pressure on a pile group during the shaking in the direction perpendicular to ground flow. Numerical analyses predicted the peak displacement of footing and peak bending moment of the group pile. The earth pressure on the pile in the crustal layer is most important for the evaluation of the peak bending moment along the piles. In addition, the larger curvatures in the bending moment distribution along the piles at the water side in the liquefied ground were measured and predicted.  相似文献   

12.
Fourier spectrum amplitudes of horizontal and vertical earthquake accelerations recorded at the foundation levels of 57 buildings in the Los Angeles metropolitan area have been used to study the dependence of spectral amplitudes on the building foundation sizes. Comparison of these amplitudes with those predicted by empirical models for scaling ‘free field’ Fourier amplitude spectra does not indicate any significant dependence of the spectral amplitudes on the size of the foundation. Third degree polynomials have been employed to smooth the spectra of the accelerations recorded inside the buildings and their coefficients have been examined as functions of the foundation plan dimensions. These results also indicate no significant dependence of the spectral amplitudes on the foundation dimensions. A qualitative analysis of the spectral amplitudes for possible effects caused by the phenomena associated with soil-structure interaction indicates that the Fourier spectra of the recorded accelerations may experience some amplification as the relative ‘density’ of the foundation-structure system increases.  相似文献   

13.
Several new empirical equations of the frequency dependent duration of strong earthquake ground motion are presented. The duration is considered as being composed of two parts: (1) the duration of stong motion as it is observed at recording stations located on basement rocks, and (2) the prolongation of this duration for stations located on sediments. The first part, called the ‘basic duration’, is modelled in terms of the Modified Mercalli intensity and (in some cases) the hypocentral distance. The depth of the sediments under the station, the distance from the station to the rocks surrounding it, and the angular measure of the size of those rocks (as seen from the station) are chosen as the parameters for modelling the prolongation of the duration. The new empirical equations are compared (a) with each other, (b) with our previous models which used similar ‘prolongation’ terms, but the ‘basic duration’ was expressed in terms of the magnitude of the earthquake and the source-to-station distance, and (c) with models with ‘intensity-type’ ‘basic duration’, but with a simplified ‘prolongation’ term (the geological conditions at the stations are modeled by lumping all the sites into three groups: basement rock, sediments and intermediate geology). This collection of models is found to have good internal consistency. The choice of the proper model depends on the availability of the earthquake and site parameters. The residuals of the empirical regression equations are found to have similar distribution functions for all the models. An explicit functional form for such distributions is proposed, and the frequency dependent coefficients are found for all the models of duration. This allows one to predict (for each set of earthquake and site parameters) the probability of exceedance of any given level of duration of strong ground motion at a given frequency.  相似文献   

14.
The assessment of building damage caused by liquefaction-induced ground deformations requires the definition of building capacity and vulnerability as a function of the demand, as well as damage scales to describe the state of the damaged building. This paper presents a framework for resolving these issues within the context of earthquake loss estimations, where large variations in building stock and ground conditions must be considered. The principal modes of building response to both uniform and differential ground movements are discussed and the uncertainties in their evaluation are highlighted. A unified damage scale is proposed for use in both reconnaissance and assessment of all modes of building damage, including ‘rigid body’ response of structures on stiff foundations to uniform or differential ground movements. The interaction of ground shaking and liquefaction in the context of induced structural damage is also briefly considered. The paper raises important aspects of earthquake loss estimations in regions of liquefaction potential, which remain relatively poorly defined at present.  相似文献   

15.
The seismic risk is fairly high in Hong Kong even though it is located in an intreplate area with low to moderate seismicity. This is because of its high seismic vulnerability due to the presence of many steep loose fill slopes with a marginal static factor of safety, and a high consequence ‘value’ as a result of the dense population and intense economic activity in Hong Kong. In order to investigate the seismic stability and potential flow liquefaction of loose fill slopes, dynamic centrifuge tests in uni-axial and bi-axial directions were performed on saturated model embankments made of loose completely decomposed granite (CDG). Three windowed sinusoidal waves with peak shaking amplitudes ranging from 0.08 g to 0.3 g (prototype scale) were adopted. During the strong uni-axial shaking of 0.3 g, the measured maximum excess pore pressure ratios ranged from 0.70 to 0.85 and a relatively small crest settlement of 5.8 mm (0.22 m prototype) was measured. No soil liquefaction or flow slides were observed. Comparing the results between the strong uni-axial and bi-axial shaking, the maximum pore pressure ratios measured from the bi-axial test varied from 0.75 to 0.87, which were marginally larger than those obtained from the uni-axial test. Although the measured crest settlement during the bi-axial shaking was about 27% larger than that of the uni-axial test, soil liquefaction and flow slide did not occur. These test results suggest that loose CDG fill slopes are likely to be stable under the proposed design PGA ranging from 0.08 to 0.11 g in Hong Kong.  相似文献   

16.
The M w = 8.0 Wenchuan earthquake of May 12, 2008, caused destruction over a wide area. The earthquake cost more than 69,000 lives and the damage is reported to have left more than 5 million people homeless. It is estimated that 5.36 million buildings were destroyed and 21 million buildings were damaged in Sichuan and the nearby provinces. Economic losses due to the event are estimated to be 124 billion USD. From a field reconnaissance trip conducted in October 2008, it is evident that the combination of several factors, including mountainous landscape, strong ground shaking, extensive landslides and rock-falls, has exacerbated the human and economic consequences of this earthquake. Extensive damage occurred over a wide area due to the shear size of the earthquake rupture combined with poor quality building construction. In order to investigate the ground shaking during the earthquake, we have conducted a strong ground motion simulation study, applying a hybrid broadband frequency technique. The preliminary results show large spatial variation in the ground shaking, with the strongest ground motions along the fault plane. The simulation results have been calibrated against the recorded ground motion from several near-field stations in the area, and acceleration values of the order of 1 g are obtained, similar to what was recorded during the event. Comparison with the damage distribution observed in the field confirms that the effect of fault rupture complexity on the resulting ground motion distribution also controls to a large extent the damage distribution. The applied simulation technique provides a promising platform for predictive studies.  相似文献   

17.
To realistically assess the seismic risk relating to built infrastructures in Hong Kong and in the neighbouring coastal cities of southern Guangdong province, it is necessary to predict ground shaking induced by different earthquake scenarios with good accuracy. A companion paper has described the modelling of the spatial and temporal distribution of the diffused seismic activities in the region, based on the newly-developed ‘Expanding Circular Disc’ (ECD) method. Representative Magnitude–Distance (M–R) combinations for both near-field and far-field earthquakes (in relation to Hong Kong) have been derived using the ECD method. The present paper describes the modelling of the response spectrum on rock sites associated with the predicted M–R combinations, using the Component Attenuation Model (CAM) that was also developed recently by the authors, based on stochastic simulations of the seismological model. The significant effects of soil resonance on the response spectrum are described in a separate publication.The accuracy of CAM in modelling ground motion properties on rock sites has been tested here by comparisons with (i) strong motions recorded in Taiwan and South China from the 1999 ‘Chi-Chi’ earthquake in Taiwan (M=7.6), (ii) motions recorded in South China from another earthquake occurring in the southern Taiwan Strait in the same year (M=5.1), and (iii) historical seismic intensity data obtained within South China. The overall capability of CAM in modelling both near-field and far-field attenuation has been shown to be unmatched by existing empirical models. Results of the comparison studies confirm the accuracy of CAM, particularly within an epicentral distance of 300–400 km.This study shows that the developed serviceability response spectra (i.e. at short return periods) are controlled mainly by the earthquake recurrence behaviour of major distant seismic sources. In contrast, the ultimate response spectra (i.e. at long return periods) relate to events with magnitudes close to the maximum credible earthquake (MCE) limit, the effect of which may also be represented by the Characteristic Response Spectrum (CRS). Both types of earthquake scenario can be significantly affected by the regional crustal properties. The proposed response spectrum envelopes have been compared with previously developed recommendations, and a critical review has been conducted. The intrinsic advantages of the ECD–CAM modelling approach have been highlighted, emphasising its directness and transparency when compared with the more complex process required to implement traditional Probabilistic Seismic Hazard Assessment (PSHA).  相似文献   

18.
In a seismically active region, structures may be subjected to multiple earthquakes, due to mainshock–aftershock phenomena or other sequences, leaving no time for repair or retrofit between the events. This study quantifies the aftershock vulnerability of four modern ductile reinforced concrete (RC) framed buildings in California by conducting incremental dynamic analysis of nonlinear MDOF analytical models. Based on the nonlinear dynamic analysis results, collapse and damage fragility curves are generated for intact and damaged buildings. If the building is not severely damaged in the mainshock, its collapse capacity is unaffected in the aftershock. However, if the building is extensively damaged in the mainshock, there is a significant reduction in its collapse capacity in the aftershock. For example, if an RC frame experiences 4% or more interstory drift in the mainshock, the median capacity to resist aftershock shaking is reduced by about 40%. The study also evaluates the effectiveness of different measures of physical damage observed in the mainshock‐damaged buildings for predicting the reduction in collapse capacity of the damaged building in subsequent aftershocks. These physical damage indicators for the building are chosen such that they quantify the qualitative red tagging (unsafe for occupation) criteria employed in post‐earthquake evaluation of RC frames. The results indicated that damage indicators related to the drift experienced by the damaged building best predicted the reduced aftershock collapse capacities for these ductile structures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
Normal faults within the Ptolemais coal field and large seismogenic faults in the northwestern Aegean remain fractal for displacement values larger than about 1m. The kinematic parameters on reverse drag profiles such as length of rollover, footwall uplift and wavelength of footwall uplift show that all three parameters have a power law relationship, expressed by a c exponent of about 1, with the maximum displacement which take place across the fault. Footwall uplift/hanging wall subsidence ratio is about 1/2.The displacement analysis help us to propose a growth model for larger seismogenic faults in the NW Aegean, as is the ‘Hepiros fault set’ and the ‘Aliakmon fault zone’. Faults within the ‘Aliakmon fault zone’ were independently developed, at the first stages of deformation, by tip line deformation and out-of plane bifurcation, whereas later, deformation continued by segment linkage. One of these faults the ‘Sarakina fault’ was reactivated during the 1995 earthquake to produce a 25 km long surface rupture. A long term slip rate of about 0.3 mm a−1 has been estimated by taking into consideration that over the past 6 Ma a maximum displacement of 1700 m across this fault has taken place.  相似文献   

20.
It is recognized that soil improvement techniques are not economically feasible for mitigation of liquefaction-induced lifeline damages because of the large areas served. Instead, it is more practical to execute an emergency action immediately after an earthquake in order to prevent or minimize possible lifeline failures caused by the soil liquefaction. Essential element in the implementation of such a plan is the real-time identification of liquefied sites, which can be successfully achieved by analyzing surface strong motion records. In this paper, the thresholds of two ground motion parameters—the peak surface velocity and horizontal shaking frequency of the ground—that are associated with the soil liquefaction are assessed utilizing the theory of one-dimensional wave propagation in linearly elastic medium. Obtained simple expressions for both parameters are used to estimate their ranges and are examined against several case histories. Minimum level of peak ground velocity (PGV) is verified by experimental data from shaking-table test. Linear relationships between amplitude ground motion parameters at liquefied-soil sites are also developed. Results suggest that liquefaction is likely to take place when PGV exceeds 0.10 m/s and that the upper bound of horizontal ground vibration frequency after liquefaction occurrence is 1.3–2.3 Hz.  相似文献   

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