2718 1 Earthquake Engineering Research Institute National University of San Juan Argentine Email:idia@unsj.edu.ar 2 Earthquake Engineering Research Institute National University of San Juan Argentine Email:idia@unsj.edu.ar 3 Department of Seismology National University of La Plata 1900 La Plata Argentine Email: nora@fcaglp.fcaglp.unlp.edu.ar 4 Earthquake Engineering Research Institute National University of San Juan Argentine Email:idia@unsj.edu.ar 5 Earthquake Engineering Research Institute National University of San Juan Argentine Email:idia@unsj.edu.ar 6 Earthquake Engineering Research Institute National University of San Juan Argentine Email:idia@unsj.edu.ar 7 Department of Seismology National University of La Plata 1900 La Plata Argentine Email: nora@fcaglp.fcaglp.unlp.edu.ar EFFECTS OF DISTANT AND LARGE MAGNITUDE EARTHQUAKES ON THE TALLEST BUILDINGS IN BUENOS AIRES CITY Juan S CARMONA 1 , Cristian SISTERNA 2 , Nora SABBIONE 3 , Marcelo MAGRINI 4 , Raquel PALAU 5 , Luisa GARCIA 6 And Roberto PINCIROLI 7 SUMMARY The evaluation of the motion amplitude of the highest buildings in Buenos Aires city, the capital of the Argentine Republic, generated by the seismic events whose magnitudes are over 7 and the epicenters of which are located at more than one thousand kilometers, are presented hereby. Buenos Aires city is located on an extended plane area. Because the seismic activity around this city is low, the motion due to distant and large magnitude seismic events with epicenters in western Argentina or in Chile, are more frequently perceived on the upper levels of tall buildings in Buenos Aires city, some of them generating strong alarm. In order to estimate the amplitudes of these motions, the fundamental periods of six tall buildings, including the tallest one 160m heigh, have been obtained by microvibrations on the one hand and on the other, the evaluation and anlysis have been made of the response spectra of the accelerogram with maximum horizontal ground acceleration of 0.75 gal, recorded in one broadband seismograph located at La Plata city, near Buenos Aires, during the Mw=7.1(USGS- NEIC) October 15, 1997 Chilean earthquake, whose epicenter was 1300 km from Buenos Aires. These horizontal components absolute acceleration response spectra analysed show important peaks at periods of 1.3 and 2.7 sec., while the period values of the tall buildings measured are larger than 1 sec and their maximun period reaches 2.7 sec for the tallest. In the upper levels of this tall buildings the absolute acceleration amplitudes of the motion generated by this eartquake reach nearly 10 gals and it lasts more than one minute. This explains why the distant and large magnitude seismic events have been perceived well and also with alarm on the uppermost floors of the tall buildings in Buenos Aires city. INTRODUCTION Buenos Aires city, the capital of the Argentine Republic, with a metropolitan population of nearly ten million inhabitants, is sited on the eastern side of an extended plane area formed by deep sedimentary alluvial soil layers, which are the Argentinian “pampas”. The seismic activity of the area is low. However, from the end of the past century when the number and height of the buildings increased, more occupants of the upper floors reported having felt the buildings motion caused by the large magnitude seismic events occurred in the western part of Argentina or in Chile, at distances longer than one thousand km from Buenos Aires. Although these motions have not damaged buildings yet, their amplitudes, frequencies and duration generated unpleasant emotions in their occupants and sometimes also strong alarm.