HR: 0800h
AN: S11A-0162    [Abstracts]
TI: Site Amplification and Attenuation Assessment through Downhole Seismogram Inversion
AU: * Assimaki, D
EM: dominic.assimaki@ce.gatech.edu
AF: Georgia Institute of Technology, School of Civil and Environmental Engineering 790 Atlantic Drive, Atlanta, GA 30332 United States
AB: This paper presents the theoretical framework of a downhole array seismogram inversion algorithm, and illustrates application of the numerical scheme for the assessment of site effects in North Japan, based on aftershock recordings from the 05/26/2003 M{_w} 7.0 and 08/16/2005 M{_w} 7.2 Miyagi Earthquakes. Based on a global optimization scheme in the wavelet domain complemented by a local least-square fit operator in the frequency domain, the hybrid inversion scheme can efficiently identify the optimal solution vicinity in the stochastic search space, whereas the best fit model detection is substantially accelerated through the local deterministic inversion. The algorithm is next implemented to assess the elastic shear wave velocity, attenuation and density profiles using low-amplitude, high quality seismic waveforms recorded by the Japanese Strong Motion Network Kik-Net. Using the inverted profiles, sites are first categorized according to the NEHRP seismic design provisions classification. Successively, elastic site amplification coefficients are computed for each local site category as the ratio of the recorded surface ground response to the corresponding rock-outcropping synthetic motion. Finally, weighted average shear wave velocity values are correlated to attenuation values in the near-surficial layers. By means of a regional study on site effects, this paper illustrates the use of downhole array recordings for the validity assessment of current methodologies and the understanding of in-situ transient soil response, and highlights both the shortcomings of the V_s,30-based site classification methodology and the effects of scattering on the attenuation estimation of near-surficial heterogeneous formations by means of deterministic seismogram inversion methodologies.
DE: 7203 Body waves
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: Fall Meeting 2005