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Shallow Velocity Structure of Los Angeles Basin from ambient noise correlations with dense seismic arrays

Zhe Jia, Robert W. Clayton, & Jorge A. Castillo Castellanos

Published July 26, 2018, SCEC Contribution #8210, 2018 SCEC Annual Meeting Poster #098

It is important to understand the lateral variations in sediment structure of the Los Angeles (LA) Basin, since its shallow velocity structure can amplify strong ground motions. Existing sediment models of the LA Basin are generally derived from sonic logs and industry reflection profiles, but these models are limited by spatial coverage of well sites and seismic lines. There have been several dense seismic arrays that can be used to determine the shallow velocity structure. In this study, we show cross-correlations between five dense arrays and 21 continuous broadband stations of the Southern California Seismic Network (SCSN) in LA Basin. Each SCSN station is regarded as a virtual source, and all dense array stations are receivers. We observed clear fundamental and higher mode Rayleigh waves of 0.2~2.0 Hz from the noise correlation functions. These surface waves are sensitive to structure of depth less than 2 km, and their rays cover a large portion of LA Basin, and thus can provide improved resolution of the shallow LA Basin structure. However, Rayleigh wave dispersion curves show modal complexity and make automatic identification of particular mode branches challenging. We measured Rayleigh wave group velocities by fitting the peaks in frequency-time analysis, and use seismic tomography analysis for the shear-wave velocity structure.

Jia, Z., Clayton, R. W., & Castillo Castellanos, J. A. (2018, 07). Shallow Velocity Structure of Los Angeles Basin from ambient noise correlations with dense seismic arrays. Poster Presentation at 2018 SCEC Annual Meeting.

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