Journal of Earthquake Engineering

We reappraise the material needed to assess the 20th-century seismicity of Switzerland and of the adjacent areas of the Alps in terms of magnitude. For this we make use of macroseismic reports and literature and by calculating the surface-wave magnitude from the Prague formula of all significant earthquakes in the region. No attempt is made to relocate earthquake positions; instead their reliability is ranked using existing solutions and macroseismic observations. We find that for small earthquakes (M_S<4.5), which constitute the bulk of the events in the region, the calculation of M_S observed at relatively short distances, requires station and distance corrections which can be significant. Also we find that recomputed Ms estimates differ from those reported in other earthquake catalogues. From this reappraisal of M_S and from a uniform re-evaluation of the associated macroseismic data, we derive a stable correlations between M_S and felt areas that can be used to assess the magnitude of historical, pre-instrumental, events for which only isoseismal radii (r_i) and the associated intensities (I_i) are available. We examined the conversion of surface-wave magnitude into moment magnitude, a conversion that presents some interesting problems for relatively small events for which the M_S-log(M₀) scaling changes. We conclude that the rate of moment release derived from events of M_S>4.0 is small, and that it should be associated with horizontal and vertical velocity rates of less than 1 mm/yr, too small to be confirmed by GPS measurements over short periods of time so that can be used to constrain hazard assessment.

This paper presents response spectral attenuation laws used in the new French Safety Rule, which is the reference for nuclear safety studies in France. Attenuation laws were derived from 965 horizontal and 485 vertical components from a two-step inversion method and accounts for geometrical spreading, anelastic attenuation and geological site condition. The datasets are mainly constituted of European strong motion records (83%) recently collected and homogeneously processed. In order to complete the distribution data beyond magnitude 6, a few American records were added, representing 17% of the datasets. The magnitude type and source-to-site distance definitions chosen to derive the laws are tested with respect to other definitions. These parametric tests induce a conservative law, for some magnitude and distance ranges of interest. The residual values between observed and predicted spectral accelerations are studied and do not exhibit any bias. The inferred laws are in good agreement with classical strong motion attenuation laws.

The objective of the present work is to examine advantages and drawbacks of different types of isolation systems, when seismic isolation is used as a protection strategy against damage to internal equipment and contents. The starting point of the study is the big experimental program of table tests on reduced-scale R/C structural models, carried out within the MANSIDE (Memory Alloys for New Seismic Isolation DEvices) project. Seven identical 1:3.3-scaled, 3-storey frames were tested, including two fixed-base models and four base-isolated models with different isolation systems, namely: (1) rubber isolators, (2) steel-hysteretic system and (3), re-centring SMA (Shape Memory Alloy) system. In this study the internal equipment is regarded as an elastic single degree of freedom, with 2% equivalent viscous damping. Therefore, the capability of fixed-base and base-isolated models with different isolation systems to protect light secondary systems is evaluated by comparing the floor response spectra obtained from the storey accelerations recorded during shaking table tests. Three different PGA's are considered, about 0.15g, 0.3g and 0.5g, respectively. All the shaking table tests are also simulated with an accurate numerical model, to validate and better understand the experimental results. It is found that each type of isolation system reduces considerably the seismic effects on internal equipments in wide frequency regions. However, tuning effects may arise in specific frequency ranges, corresponding to the first mode in structures equipped with quasi-elastic (rubber) isolation systems, and to higher modes in structures equipped with elasto-plastic (steel) and nonlinear re-centering (SMA) isolation systems.

Understanding the dynamic behaviour of soil in the Anchorage basin in southcentral Alaska is essential for seismic hazard assessment of this highly seismically active region. The analysis of site responses for 40 sites from weak-motion and strong-motion data with amplitudes less than 0.1 g showed a strong influence of subsurface geological conditions on the characteristics of ground motion. Particularly, the sites in the central part of the city, including the downtown area, showed prominent resonance peaks around 1 Hz with amplification values up to about 4. The numerical analysis, based on one-dimensional multi-layer soil models shows that site response characteristics, and especially aforementioned peaks, are largely related to the thick, soft layer of Quaternary deposits, particularly cohesive facies of Bootlegger Cove Formation. The computed transfer functions for soil profiles of six representative sites are in accord with the site responses in the frequency range from 1 to 5 Hz. There is no significant change in amplification values below 2 Hz corresponding to large-amplitude (up to 0.38 g) ground motions; however, above 2–3 Hz the amplification values are greatly reduced in this case.

This paper summarises the results of comprehensive statistical study of response and design spectra in which a total of 106 Iran's horizontal acceleration components recorded during various earthquakes was considered. Special emphasis is given to the influence of effective duration of strong motion, soil condition and damping ratio of structure on elastic response and design spectra. The study included both deterministic and probabilistic approaches. The records with peak ground accelerations greater than 0.05 g from 23 stations in 47 seismic events are divided into four soil categories in accordance with Iranian seismic code. For each soil group, mean and mean plus one standard deviation spectral ordinates were computed for: effective duration of strong motion and damping ratio of structures and also a design spectra for different soil conditions has been constructed by deterministic and probabilistic approaches and results have been compared with code provisions (i.e. NEHRP, UBC, EC8 and seismic code of Iran). The influence of effective duration of strong motion has been studied by definition based on energy of accelerogram. The paper also presents an evaluation of the damping ratios on the response spectra. Results and conclusions from this study can be directly used for the evaluation of the present Iranian seismic code in order to construct new design spectra and also for the evaluation of seismic design provisions.

In recent years, current seismic codes started contemplating the design of structures with passive energy dissipating devices. One important issue for the rational seismic design of these devices and the structure that contains them is the formulation of numerical methods to estimate their design seismic forces. From the study of the dynamic response of single-degree-of-freedom systems subjected to accelerograms recorded in Mexico during the last two decades, expressions to estimate the strength reduction factor that should be used to reduce the elastic design strength spectra for 5 percent damping, to establish the design seismic forces for structures having different combinations of plastic and viscous energy dissipating capacities, are formulated.

The reply consists of two main sections, the second one having five sub-sections:

(1) the definition of archaeoseismology;

(2) the basic data used and their interpretations.