HR: 0830h
AN: S51E-0099    [PDF]
TI: Study of Nonlinear Site Effect on Ground Motion Response Spectra From the Chi-Chi and Northridge Earthquakes
AU: * Su, F
EM: feng@seismo.unr.edu
AF: Seismological Laboratory, University of Nevada, Reno, NV 89557
AU: Zeng, Y
EM: zeng@seismo.unr.edu
AF: Seismological Laboratory, University of Nevada, Reno, NV 89557
AU: Anderson, J G
EM: jga@seismo.unr.edu
AF: Seismological Laboratory, University of Nevada, Reno, NV 89557
AB: We have investigated the nonlinear site effect on ground motion response spectra from the Chi-Chi and Northridge earthquakes. We found that nonlinearity affects ground motions from both earthquakes significantly. This was demonstrated by comparing the average ground motion response spectra from different site conditions within the same distance ranges. At large distances, the average soil site shows higher amplitudes in spectra at all frequencies than that of rock sites, but at short distances, in the presence of nonlinearity, the high frequency part of the spectra shows smaller amplitudes on soil sites than that on rock sites. The crossover between response spectra of soil and rock sites occurs at about 1 Hz for both earthquakes. The distance for nonlinearity to appear is different between the Northridge and the Chi-Chi earthquakes. We found the threshold for nonlinearity is at peak velocity of about 20 cm/s. This result is consistent with an early result of Su et al (1998), in which they studied nonlinearity in the Northridge earthquake using seismograms from the mainshock and aftershocks recorded at co-located stations. We have also examined ground motions of other recent large earthquakes in California, Japan and Turkey and found that the threshold of nonlinearity is quite consistent with the results from the Chi-Chi and Northridge earthquakes.
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2003 Fall Meeting