9412759 Dravinski The objective of this project is to obtain the predominant frequencies of vibration of ground motion in the San Fernando Valley area, and to compare them with the resonant frequencies of several key structures which suffered significant damage during the Northridge earthquake of January 17, 1994. This comparison permits the identification of "double resonance". (Double resonance occurs when the fundamental period of the ground coincides with the resonant frequency of the structure.) The specific tasks include: (1) the measurement of long-period microtremor response at highway bridges and overpasses which suffered severe damage during the earthquake (microtremors are naturally-occurring ground vibrations), and (2) measurement of long period microtremor response at seventy sites within the San Fernando Valley with simultaneous recordings at a reference bedrock site. ***
