Application of teleseismic long-period surface waves from ambient noise in regional surface wave tomography: A case study in western USA

Since the emerging of ambient noise tomography (ANT) in 2005, it has become a routine method to image the structures of crust and uppermost mantle because of its exclusive capability to extract short-period surface waves. Most of previous ANT studies focus on surface waves at periods shorter than 40/50 s. There are only a few studies of long-period surface wave tomography from ambient noise (longer than 50 s) in global scale. No tomography studies have been performed using teleseismic long-period surface waves from ambient noise in a regional scale, probably due to the two reasons that (1) energy of long-period ambient noise is weaker and it is harder to retrieve good signal-to-noise ratio long-period surface waves from portable stations with several years of ambient noise data and (2) long-period dispersion measurements from ambient noise may have larger uncertainties than those at shorter periods (<40/50 s). In this study, I investigate the feasibility of using teleseismic long-period surface waves from ambient noise in regional surface wave tomography and also evaluate the accuracy of longperiod dispersion measurements at periods up to 150 s. About 300 USArray/Transportable Array (TA) stations located in the Colorado Plateau and surrounding areas and 400 teleseismic stations relative to the TA stations are selected. Clear, strong, and coherent long-period teleseismic surface waves at periods much longer than 50 s are observed in the teleseismic cross-correlations between the TA stations and the teleseismic stations. Using long-period dispersion curves from ambient noise, I generate phase velocity maps at 50-150 s periods and then compare them with phase velocity maps from teleseismic earthquake data. The results show that phase velocity maps from ambient noise data and earthquake data are similar at the 50-150 s period range, verifying the validity of using long-period surface wave from ambient noise in regional surface wave tomography.