Imaging upper mantle structures in regional, continental and global scales using long-period surface waves (50-300 sec) from ambient noise

Abstract:

Most of ambient noise tomography studies performed to date exploit surface waves at periods shorter than 40/50 sec. Two natural questions one may ask are (1) whether longer-period surface wave (>50 s) can also be extracted from ambient noise and (2) whether long-period dispersion curves from ambient noise are accurate enough for tomography to constrain upper-mantle structures. In this study, we investigate the capability of using teleseismic long-period surface waves from ambient noise in regional-, continental- and global-scale surface wave tomography and also evaluate the accuracy of long-period dispersion measurements at periods up to 300 sec. For regional and continental scale studies, we process ambient noise data from USArray to extract inter-station long-period surface wave dispersion curves and then perform surface wave tomography using the dispersion curves. For the global scale studies, we process ambient noise data from more than 1000 stations distributed around the globe, including both permanent FDSN stations and a number of PASSCAL transportable arrays. We observe clear, strong, and coherent long-period surface waves at 50-300 sec periods at both regional and teleseismic inter-station distances. Using long-period dispersion curves from ambient noise, we generate phase velocity maps at 50-300 sec periods and then compare them with those generated from earthquake data. The results show that long-period dispersion measurements from ambient noise are compatible with those from earthquake data and phase velocity maps from ambient noise data and earthquake data are similar to each other, verifying the feasibility and validity of using long-period surface waves from ambient noise in regional, continental and global surface wave tomography. Long-period surface waves from ambient noise are complementary to those from earthquakes. The inclusion of them in regional and global surface wave tomography could significantly increase both lateral and azimuthal path coverage, which is essential to improving the imaging of high resolution heterogeneities and azimuthal anisotropy, especially at regions with large gaps of azimuthal distributions of earthquakes.