During a three year-period, the participants of a NATO Science for Peace project performed ambient noise measurements inside buildings in four European countries. This paper reports the results relevant to reinforced concrete (RC) buildings with height in the range 1-20 floors. The total number of such buildings surveyed is 244. The most striking feature is the similarity of the height-period relationships in the four countries, which allowed the treatment of the all measurements as a single database. We found no significant correlation with other variables, and calculated a regression that is very similar to other empirical height-period relationships and quite different from code provisions and theoretical models.

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Slovenia with its neighbouring areas lies at the junction of the Alps, the Dinarides and the Pannonian basin. These belong to the three plates: Europe, Adria and Tisza. On the Slovenian territory itself converge the External Dinarides NW-SE oriented right lateral strike-slip faults, the Transdanubian Range NE-SW oriented left lateral strike-slip faults, and the Southern Alps E-W oriented thrusts. The direction of the principal stress | 1 (azimuth=6°, dip=8°) is determined under the assumption of uniform stress throughout the region. Dip of the least principal stress | 3 of 5°is consistent with the regional strike-slip regime. Listed structures form a pure shear structural mechanism on a regional scale.In spite of geologic evidence of tectonic displacements along mentioned structures in the past, there is no surface expression of their recent activity.The lithospheric units of the investigated area were amalgamated together during Tertiary. The seismicity is not concentrated along the primary plate boundaries but is rather spread in a broad zone along their deformed rims. The seismicity is moderate with the average depth of earthquakes in Slovenia of 6.5 km, and 9 to 20 km for stronger earthquakes (M LH \4.2). No surface rupture related to an earthquake has been detected to date in Slovenia.The territory of Slovenia and its neighbouring regions has been delineated into five seismogenic areas, i.e., the areas with similar and among themselves differentiable tectonic and seismological characteristics. They are the Eastern Alps, the Southern Alps, with the Friuli region as a separate unit, the External Dinarides, and the Transdanubian Range.

The city of Ljubljana is located in one of the three areas with the highest seismic hazard in Slovenia, and it is also the most densely populated. Site effects due to Quaternary sediments, which fill the up to 200 m-deep basin, are characteristic of the whole city area, but they can be especially strong in the southern part of Ljubljana, which is built on very soft lacustrine deposits. Existing microzonation studies of the city are inadequate, since there is a lack of borehole, geophysical and earthquake data. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied to a 200 m dense grid of free-field measurements over an area of 45 km 2 (1,223 measuring points) in order to assess the fundamental frequency of the sediments. The main difficulties in microtremor measurement arose from high levels of traffic and industrial noise, and from underground structures. Experimental conditions which can influence data quality, such as strong wind and water saturation of soil, were analysed. Very clear HVSR peaks were obtained in the entire southern part of the city, whereas in the northern part the site response is in general lower due to lower impedance contrast of gravel with the bedrock. The iso-frequency map of sediments shows a distribution in the range of 0.9-10 Hz. In the southern part of Ljubljana, sediment frequency correlates well with the thickness of soft sediments known from geophysical investigations and sparse drilling. Average amplitude of the HVSR peaks is considerably higher in the southern part (6.7 ± 2.4) than in the northern part (4.0 ± 2.0) of the city, indicating a high impedance contrast of lacustrine sediments with the bedrock. Microtremor measurements were also performed inside 122 buildings of various heights. We focused on important public buildings and selected blocks of flats and houses. To assess the longitudinal and transverse fundamental frequencies of each building, amplitude spectra and the spectral ratio between the upper floor A. Gosar (B) EARS, Seismology and Geology Office,