Multipathing Rayleigh Waves From Long‐Distance Noise Cross Correlation Along an Ocean‐Continent Boundary (Alaska to California)

Seismic interferometry can reliably extract interstation surface waves in homogeneous or smooth media. We test the validity of this technique in the case of sharp lateral heterogeneity, by examining paths along the western edge of continental North America. After cross correlating several years of time series of ambient seismic noise, we extract interstation Rayleigh waves with different arrivals in the frequency of 0.04 to 0.06 Hz (periods 17 to 25 s). Using beamforming and seismic wavefield simulations, we show that the different Rayleigh wave arrivals are related to the oceanic and continental paths, respectively. This multipathing of Rayleigh waves that is identified from ambient noise is also identified from earthquakes. Our results demonstrate that seismic noise interferometry is capable of extracting realistic surface waves for complex structural paths such as along the continental margin of North America. Additional studies from other regions may demonstrate the potential for using multipathing surface waves within full waveform inversion. Plain Language Summary Various studies demonstrate that empirical Green's function (usually Rayleigh wave) can be extracted from noise correlation and empirical Green's function revolutionize travel time tomography. In these studies, usually one group of Rayleigh wave is observed. In this manuscript, we report that two groups of Rayleigh waves are found in noise correlation between seismic stations in Alaska and California. We figure out that the sharp boundary between ocean and continent causes the multipathing via comparison with earthquake data and wavefield simulation. The mulitpathing noise Rayliegh wave can be used to image sharp lateral variation, thus improving noise travel time tomography. Key Points Rayleigh waves from noise correlation between stations in Alaska and California manifest two different propagation paths The multipathing of noise Rayleigh waves due to sharp lateral variations are confirmed with earthquake waveforms and simulations Our study suggests that noise Rayleigh waves are reliable approximate of Green's function for regions of strong lateral variation