METHODS TO ASSESS THE SITE EFFECTS BASED ON IN SITU MEASUREMENTS IN BUCHAREST CITY, ROMANIA

摘要

In seismic microzonation we want to display the variation in seismic response of the subsurface and subsequently determine where the soil is being amplified to a level that may damage existing buildings or other structures. Frequently peak ground acceleration (PGA) is used to determine the maximum horizontal forces that can be expected. The method is not always adequate, because PGA often corresponds to high frequencies, which are out of range of the natural frequencies of most structures. The largest amplification of the soil will occur at the lowest natural frequency or its fundamental frequency, which corresponds to the characteristic site period. In situ measurements of shear wave velocity in the soil and the soil thickness, provide a direct measure of the characteristic site period. Extensively seismic noise measurements provides a more accessible method and computed H/V spectral ratios can also provide a good indication on the fundamental frequency of the site. Average shear wave velocity in the first 30 m depth (V_(S 30)) as defined in EUROCODE 8 and Romanian Code P100-1 is a useful indicator in seismic microzonation, showing zones with low values of average seismic velocities in Bucharest.