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The occurrence of a damaging earthquake provides an opportunity to compare observed and estimated damage, provided that detailed observations of the earthquake effects are made in the field. A question that arises is whether such comparisons can provide the basis for validation of an earthquake loss model. In order to explore this issue, a case study loss model for the northern Marmara region has been set up and the losses have been calculated for various ground-motion fields that arise when different assumptions are made about the ground-motion variability. In particular, the influence of removing the inter-event variability for a scenario earthquake and modeling spatial correlation among ground motions is studied. Further analyses are conducted assuming that a number of accelerograms are available within the region and that knowledge of spatial correlations among ground motions can therefore be used to better predict the motions at sites in the vicinity of the recording stations. The results demonstrate that unless one has a dense network of accelerographs (commensurate with the geographical resolution of exposure), then the variability in the losses cannot be sufficiently reduced to allow validation of the loss model. [ABSTRACT FROM AUTHOR]

This article summarizes recent work investigating the sensitivity of loss estimates for the northern Marmara region to various representations of ground-motion variability. Issues that are discussed include the partitioning of the total ground-motion variability into inter- and intra-event components, macrospatial correlations among ground motions, and the propagation of the ground-motion variability into damage and loss calculations. The issue of whether an earthquake loss model can be validated using field observations is also considered. Recent findings suggest that, regardless of how one treats the ground-motion variability when conducting loss estimation analyses, unless a close network of accelerograms and a high spatial resolution of exposure data exists, the ground-motion variability precludes the validation of loss models. [ABSTRACT FROM AUTHOR]

The Bojnurd region of NE Iran experienced a Mw 6.4 earthquake on February 4, 1997. By combining results from teleseismic body-waveform analysis, field observations of structural damage, coseismic deformation, geomorphology, and analysis of the resulting strong ground-motions, we build a coherent picture of the faulting associated with this earthquake. The earthquake resulted from almost pure right-lateral strike-slip motion (0.5-1.0 m), which ruptured a ∼15 km long section of fault, striking ∼340° at its northern end, which changes to ∼320° at its southern end. This fault can be seen clearly on the geological map and satellite imagery. The village of Sheikh lies ∼10-15 km SE of the fault rupture, yet was severely damaged during the earthquake. Analysis of strong-motion records, recorded by the Building and Hazard Research Center of Iran, particularly their significant duration, the polarization of the fault-normal component, and the velocity pulse, indicates a probable directivity effect, in which the rupture propagated from north to south, towards the village of Sheikh. [ABSTRACT FROM AUTHOR]

The seismic behavior of asymmetric building structures is often complex and reductions to plane problems which can be analyzed with a single horizontal ground-motion component are often deemed unsatisfactory. As a consequence, dynamic structural analyses with both horizontal ground-motion components become more common, both in research as well as in practice. A review of code provisions regarding selection and scaling of ground motions for bi-directional analysis has, however, revealed that the guidelines provided are frequently inconsistent or are lacking transparency regarding the underlying assumptions. The aim of this study is to shed some light on a number of aspects involved when selecting and scaling records for bi-directional analysis and post-processing results of such analyses. [ABSTRACT FROM AUTHOR]

Dynamic nonlinear analysis of structures requires the seismic input to be defined in the form of acceleration time-series, and these will generally be required to be compatible with the elastic response spectra representing the design seismic actions at the site. The advantages of using real accelerograms matched to the target response spectrum using wavelets for this purpose are discussed. The program RspMatch, which performs spectral matching using wavelets, is modified using new wavelets that obviate the need to subsequently apply a baseline correction. The new version of the program, RspMatch2005, enables the accelerograms to be matched to the pseudo-acceleration or displacement spectral ordinates as well as the spectrum of absolute acceleration, and additionally allows the matching to be performed simultaneously to a given spectrum at several damping ratios. [ABSTRACT FROM AUTHOR]

Peak ground velocity (PGV) has received much less attention in the technical literature than more widely-used parameters such as peak ground acceleration (PGA) and response spectral ordinates. However, there are many examples of the use of PGV in engineering seismology and earthquake engineering, including as a parameter from which to estimate macroseismic intensity and structural damage. PGV is also employed in some methods for the assessment of liquefaction potential and, because of its relationship to ground strains, in the seismic design and assessment of buried pipelines. One of the most important uses of PGV has been in the construction of elastic response spectra. There are relatively few predictive equations for PGV, compared to those for PGA and spectral ordinates, but 25 such equations are reviewed and summarised. The issue of scaling PGV from response spectral ordinates is explored and it is shown that the common practice of scaling PGV from spectral accelerations at 1.0 second should not be continued because the ratio of the two quantities is highly variable. A more stable relationship exists between PGV and the spectral acceleration at 0.5 second response period; however, it is clearly preferable to estimate peak velocities directly and PGV equations should be derived together with equations for spectral ordinates in the same way as PGA. [ABSTRACT FROM AUTHOR]

The increasing availability of strong-motion accelerograms, and the relative ease with which they can be obtained compared to synthetic or artificial records, makes the use of real records an ever more attractive option for defining the input to dynamic analyses in geotechnical and structural engineering. Guidelines on procedures for the selection of appropriate suites of acceleration time-series for this purpose are lacking, and seismic design codes are particularly poor in this respect. Criteria for selecting records in terms of earthquake scenarios and in terms of response spectral ordinates are presented, together with options and criteria for adjusting the selected accelerograms to match the elastic design spectrum. The application of both geophysical and response spectral search criteria is illustrated using compatible scenarios, and the selected records are analysed and adjusted to produce suites of acceleration time-series suitable for dynamic analyses. The paper concludes with suggestions for making use of real records in engineering analysis and design, and recommendations are given for improving the current guidelines provided in seismic design codes. [ABSTRACT FROM AUTHOR]

This paper reviews the modelling of the scatter in ground-motion prediction equations, and also explores the nature of scatter in strong ground-motion, using an extended database of European accelerograms and newly derived predictive equations. Several statistical tests are used to confirm that the distribution of the residuals is genuinely lognormal over a certain range but appears to deviate from this model significantly in the tails of the distribution. An alternative model, the upper limit lognormal (ULLN) distribution is found to provide a good fit to the data; the parameters of this model include an upper-bound on the distribution, which is effectively inferred from the statistics of the data itself. However, it is clear that upper bounds established in this way do not provide a reliable ceiling on ground-motion amplitudes and physical constraints are required. Investigative tools that could be used to explore the physical limits of ground-motion amplitudes are discussed. In line with the underlying focus of the work, which is to explore the sometimes almost dominant influence that the scatter can exert on PSHA, and also to provide new data to prevent the overestimation of strong-motion parameters for design, the covariance in the scatter of different strong-motion parameters is also explored. [ABSTRACT FROM AUTHOR]

Deterministic and probabilistic seismic hazard assessment are frequently represented as irreconcilably different approaches to the problem of calculating earthquake ground motions for design, each method fervently defended by its proponents. This situation often gives the impression that the selection of either a deterministic or a probabilistic approach is the most fundamental choice in performing a seismic hazard assessment. The dichotomy between the two approaches is not as pronounced as often implied and there are many examples of hazard assessments combining elements of both methods. Insistence on the fundamental division between the deterministic and probabilistic approaches is an obstacle to the development of the most appropriate method of assessment in a particular case. It is neither possible nor useful to establish an approach to seismic hazard assessment that will be the ideal tool for all situations. The approach in each study should be chosen according to the nature of the project and also be calibrated to the seismicity of the region under study, including the quantity and quality of the data available to characterise the seismicity. Seismic hazard assessment should continue to evolve, unfettered by almost ideological allegiance to particular approaches, with the understanding of earthquake processes. [ABSTRACT FROM AUTHOR]

The major hazard posed by earthquakes is often thought to be due to moderate to large magnitude events. However, there have been many cases where earthquakes of moderate and even small magnitude have caused very significant destruction when they have coincided with population centres. Even though the area of intense ground shaking caused by such events is generally small, the epicentral motions can be severe enough to cause damage even in well-engineered structures. Two issues are addressed here, the first being the identification of the minimum earthquake magnitude likely to cause damage to engineered structures and the limits of the near-field for small-to-moderate magnitude earthquakes. The second issue addressed is whether features of near-field ground motions such as directivity, which can significantly enhance the destructive potential, occur in small-to-moderate magnitude events. The accelerograms from the 1986 San Salvador (El Salvador) earthquake indicate that it may be unconservative to assume that near-field directivity effects only need to be considered for earthquakes of moment magnitude M 6.5 and greater. [ABSTRACT FROM AUTHOR]

The duration of strong ground shaking during earthquakes can play an important rôle in the response of foundation materials and structures, particularly when strength or stiffness degradation is encountered. A thorough seismic hazard assessment should therefore include an estimation of the expected duration of strong motion, which first requires criteria to define the part of an accelerogram considered to represent the duration of strong ground motion. Some 30 different definitions of strong motion duration are reviewed and classified into generic groups. Problems that arise with the use of these definitions for duration are highlighted. A new definition of duration is presented using a previously unexplored option which identifies the part of the record where the main energy is contained and constrains this strong shaking phase by absolute criteria. This new definition is shown to give consistently meaningful durations for strong earthquake accelerograms from an engineering viewpoint. The correlations between the new definition of duration and magnitude, soil conditions and distance are explored as a first step towards the development of predictive equations. [ABSTRACT FROM AUTHOR]

Displacement-based seismic design and assessment of structures require the reliable definition of displacement spectra for a wide range of periods and damping levels. The displacement spectra derived from acceleration spectra in existing seismic codes do not provide a suitable answer and there are no existing frequency-dependent attenuation relationships derived specifically for this purpose. Using a carefully processed dataset of European strong motion records, attenuation relationships have been derived for horizontal displacement response spectral ordinates. The results have been simplified into a parametric form that allows the straightforward construction of displacement design spectra for rock, stiff soil and soft soil sites at distances of up to 50 km from earthquakes with magnitudes between 5.5 and 7.5, for six damping levels and up to response periods of 3.0 seconds. Results from recent studies linking levels of ductility to equivalent damping, using a complex hysteretic model and the same strong motion databank, are also reported. [ABSTRACT FROM AUTHOR]