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Probabilistic seismic hazard analysis (PSHA) attempts to predict the occurrence rates of various ground motion parameters, and is therefore potentially verifiable. At very low probabilities, features that might bound past ground motions, such as surviving precarious rocks, often seem to be inconsistent with the predictions. The PSHA predictions at small probabilities are very sensitive to the way uncertainties are handled. One challenge is to separate uncertainties into their aleatory and epistemic components, which currently are mingled due to making an ergodic assumption when ground motion prediction equations are developed. At Lovejoy Buttes, California, there are several precarious rocks that have not been toppled by about 10,000 years of earthquakes. This paper shows a formal way to evaluate whether a particular probability distribution for peak acceleration from the largest earthquakes, M∼8 events on the nearby San Andreas fault, is consistent with existence of those rocks. The paper concludes with suggested data needs from strong motion observations, since the solution to these PSHA issues will ultimately be driven by new data.

Seismic hazard assessments provide quantitative evaluations of the nature of ground shaking at a specified location that could be induced by future earthquakes. Such evaluations serve to inform engineering decisions about the location and design of new projects and the safety of existing structures. In order to provide the engineers and planners with complete information on which to base their decisions, the assessments must identify and, to the extent that is possible, quantify the associated uncertainties. There are major uncertainties associated with both the seismicity model and the ground-motion model in any seismic hazard assessment, but the uncertainties associated with the latter will generally have the larger impact on the results. Uncertainties in ground-motion prediction equations can be characterized as aleatory variability and epistemic uncertainty; the former can be directly integrated into the hazard calculations, although for very low annual exceedance frequencies it can become necessary to impose physical limits on the distribution of residuals. Epistemic uncertainty can be handled using logic-tree formulations. Combining several ground-motion prediction equations in a logic tree often requires adjustments to be made to compensate for the use of different parameter definitions; without these adjustments, the epistemic uncertainty can be grossly over- or underestimated. However, the adjustments themselves, which are often empirically derived, carry their own uncertainty and this must be included in the analyses.

Digital strong-motion instruments allow routine recovery of ground motions at periods much longer than possible with older analog instruments, and under favorable conditions it may be possible to recover the residual displacements near earthquakes, particularly if both the rotational and translational components of motion are recorded (currently only the translational components are recorded). In practice, however, digital recordings are commonly plagued by drifts in the velocity and displacement traces obtained by integrating the recorded acceleration traces. Various baseline-correction schemes can be designed that give the appearance of removing these drifts. Although comparisons with independent measures of residual displacements, such as from GPS or InSAR measurements, show that such schemes can work, in general the sources of the drifts are such as to prevent routine corrections for the baseline problems; removal of low-frequencies by filtering is then required for many recordings. That is the bad news. The good news is that the filter corners can be so low that little of engineering interest is lost. Recent data from several earthquakes (e.g., 1999 Hector Mine and 2002 Denali) shows that for displacement response spectra, the transition from increasing to constant spectral levels occurs at significantly longer periods than in Eurocode 8; the transition period is in good agreement, however, with the recent 2003 NEHRP code.

This paper examines whether the extremely high ground motion values that are calculated for probabilistic seismic hazard analyses in critical facilities are physically attainable.

The improvement of understanding structural capacity against large displacement demand of near-fault conditions has become a subject of research interest for the last decade. Parallel to the developments in performance-based seismic design (PBSD) this issue has attracted researcher interest further, as assessment of structural displacement capacity has become one of the main issues for the procedures employed in this new concept. This study focuses on the near-fault ground motion demand on framed structures. We have used soil site, near-field records from various M > 6.5 events including the 1999 Turkey and Taiwan earthquakes. The spectral quantities were computed using a ground motion prediction relationship that is based partly on these near-fault ground motion records. The spectral quantities were evaluated for the global displacement demand definition of such ground motions. We employ this global demand definition to calculate the distance and magnitude dependent inter-story drift demand limits for frame-type structures. Comparison of these preliminary findings with code provisions is encouraging.

This contribution attempts to shed light on the important issues that affect the response of frame structures to near-fault ground motions with forward directivity. There is evidence that ground shaking near a fault rupture is characterized by a small number of pulses with high input energy. Pulse response characteristics are utilized to describe behavior attributes of structures subjected to near-fault ground motions. The ultimate objective is to develop improved design procedures and guidelines that take advantage of the equivalent pulses. Relationships are developed that relate equivalent pulse properties to earthquake magnitude and distance from the fault rupture. The results suggest that using near-fault factors introduced in current seismic codes may not provide consistent protection against near-fault effects. The need exists for an explicit consideration of the near-fault effects in seismic hazard analysis.

A new tool for rapid building response assessment is presented. By using a continuum model this new tool, named generalized interstory drift spectrum, provides estimates of maximum interstory drift demands in buildings responding to earthquakes. The continuous model consists of a combination of a flexural beam and a shear beam. By modifying a single parameter the model used in the generalized interstory drift spectrum can consider lateral deformations varying from those of a flexural beam to those of a shear beam. Therefore, it permits to account for a wide range of modes of deformation that represent more closely those of multistory buildings. Because of its computationally efficiency, and because it only requires a minimum of information about the building, the new spectrum provides a powerful tool for rapid assessment of many buildings. Examples of interstory drift demands from various ground motions recorded in the United States and Turkey are presented.

Fragility functions are determined for low- and mid-rise ordinary concrete buildings. A hybrid approach is employed where building capacities are obtained from field data and their dynamic responses are calculated by response history analysis. Lateral stiffness, strength and deformation capacities of the sample buildings are determined by pushover analyses. Uncertainties in lateral stiffness, strength and damage limit states are expressed by using statistical distributions. The seismic deformation demands of the subject buildings are calculated under 82 ground motions. Peak ground velocity is selected as the measure of seismic intensity since it has been observed that maximum inelastic displacements are better correlated with PGV. The results have revealed that the type of investigated buildings is highly vulnerable to strong ground shaking expected during the future earthquakes. Moreover, their fragility increases with the number of stories

An integrated set of four borehole arrays and ten surface installations is installed in the city of San Francisco, California to measure the response of soft-soil deposits to strong earthquake ground motions. The borehole arrays extend through thick layers of soft water-saturated soils of Holocene age and older more consolidated soils of Pleistocene age into bedrock at depths up to 90 m. The surface installations are configured in pairs to provide simultaneous comparative surface measurements of soft soils and nearby rock. The rock locations also permit comparative measurements of rock as observed at the surface and in nearby boreholes. The arrays are designed to address a wide variety of scientific and engineering issues, and especially the issue of anelastic and nonlinear soil response at high strain levels as might be recorded during a large regional earthquake. Recordings of ground motions from the largest regional earthquakes which have occurred since the installation of the arrays show marked evidence of amplification as measured on the borehole and surface arrays. Implications of the results for low-strain site coefficients in present U.S. building codes are discussed.

This paper presents a summary of the seismic monitoring issues as practiced in the past, as well as current applications and new developments to meet the needs of the engineering and user community. A number of examples exhibit the most recent applications that can be used for verification of design and construction practices, real-time applications for the functionality of built environment and assessment of damage conditions of structures.