Poster Presentation

Non-uniform noise source distributions are common whenever seismic stations record data in proximity of a continental coast (Stehly et al., 2006). When seismic data in these areas are used to compute noise cross-correlations, it is possible to observe precursory energy preceding the direct arrivals. Such precursors can be theoretically explained by energy generated by scatterers present in the area (Snieder et al., 2008). These apparently unphysical events have been used to image scatterers in volcanic areas using an energy-based imaging condition (Ma et al., 2013). We present a novel imaging approach to quantitatively locate scatterers generating precursory signals within ambient noise cross-correlations. This method is based on a delay-and-sum algorithm in which the theoretical traveltimes of the precursors are computed using the Eikonal equation when complex surface-wave velocities characterize the area of interest. We describe the image properties using simple synthetic tests and apply the proposed method to the Long Beach and Seal Beach dense seismic arrays (Lin et al., 2013), with the goal of imaging faults and discontinuities located in the Los Angeles basin.