Source Effects in Higher‐Order Ambient Seismic Field Correlations

Abstract

Ambient seismic noise interferometry is widely used for surface wave imaging. It typically requires synchronous station recordings and assumes uniform noise source distributions. Higher‐order correlations, such as the re‐correlation of the reconstructed direct waves , enable imaging with asynchronous data and can improve an incomplete source distribution. We show with field data and simulations that surface wavefields are, however, highly sensitive to the original source distribution and even amplify the effects associated with directional incidence. This can lead to systematic errors in the obtained velocity estimates and the downstream subsurface images. A range of auxiliary station distributions tested for the re‐correlation process can not mitigate this bias but introduce additional wavefield distortions. We find that both local and far‐field imaging approaches using higher‐order correlation wavefields are affected by significant and systematic velocity estimation errors. Our results show that the re‐correlation of direct waves is not an all‐purpose correlation wavefield enhancement technique, which highlights the need for a careful consideration of source effects for improved imaging.