Site amplification, attenuation, and scattering from noise correlation amplitudes across a dense array in Long Beach, CA

Daniel C. Bowden, Victor C. Tsai, & Fan-Chi Lin

Published March 6, 2015, SCEC Contribution #6068

For accurate seismic hazard evaluation, both the spatial and frequency-dependent variabilities in the amplitudes of earthquake ground motions are needed. While this information is rarely fully available due to the paucity of relevant seismic data, dense arrays like the 5200-geophone array in Long Beach, California provide the opportunity to study this amplitude variability. Here we show that ambient noise correlation amplitudes from the Long Beach array can be used to directly determine frequency-dependent site amplification factors. We analyze Rayleigh-wavefield amplitude gradients from ambient noise correlations that are processed so that relative amplitudes satisfy the wave equation and are therefore meaningful. Ultimately, we construct maps of site amplification across Long Beach at frequencies of 0.67, 1.0, and 2.0 Hz. These maps correlate well with local structure, notably the Newport-Inglewood Fault and also to known velocity structure. Through this process, we also obtain constraints on average attenuation structure and local scattering.

Key Words
seismology, site amplification, ambient noise, wavefront tracking

Citation
Bowden, D. C., Tsai, V. C., & Lin, F. (2015). Site amplification, attenuation, and scattering from noise correlation amplitudes across a dense array in Long Beach, CA. Geophysical Research Letters, 42(5), 1360-1367. doi: 10.1002/2014GL062662.

Related Projects & Working Groups
Ground-Motion Prediction