Testing the Waveguide Effect in the Los Angeles Area using Ambient Seismic Noise

ABSTRACT
Numerical simulations modeling a M 7.7 earthquake on the southern San Andreas fault predict that a channel of narrow sedimentary basins along the southern edge of the San Gabriel and San Bernardino Mountains acts as a waveguide that channels Love waves into the Los Angeles Basin (Olsen and Day, 2006). Our study tests the behavior of seismic waves in the proposed waveguide using ambient seismic noise. If the sedimentary channel does act as a waveguide, long term reverberations are expected. Station RUS (located at the western end of the waveguide) was correlated with 50 stations in the Los Angeles area at four different frequency bands (0.1 - 0.2 Hz, 0.2 - 0.333 Hz, 0.333 - 0.5 Hz, and 0.5 - 1 Hz). Before correlation, data underwent coordinate rotation, one-bit normalization, and spectral whitening. The results were ~600 station-to-station Green's functions. Long term reverberations are seen in Green's functions whose station paths run through the waveguide; however, many of these are polluted with noise, keeping any convincing conclusions from being drawn.