Multiscale regionalised Rayleigh-wave group and phase velocity maps for East Asia

Abstract

East Asia comprises multiple tectonic domains and has been the subject of many regional and local broadband seismic investigations in recent years, especially the ChinArray experiments. These studies have improved the overall seismic data coverage for East Asia, although the distribution of data is extremely uneven. While regionalised group or phase velocity dispersion curves from surface-wave tomography are particularly important for deriving deep shear-wave velocities, calibrating phase velocity measurements and joint analyses with other geophysical data, they are normally derived using quadrilateral cells with a fixed latitude and longitude spacing, such that the cell spacing varies with latitude but not with data coverage. For a region with extremely uneven data coverage, closely spaced cells will worsen the ill-posedness of tomographic problems, whereas widely spaced cells will lower the lateral resolution capability of regions with dense data. Here we propose a new model discretisation approach for two-dimensional surface-wave tomography that divides the study area into triangular cells with variable sizes based on data coverage and apply it to East Asia, where seismic observations are numerous but unevenly distributed. The updated regionalised Rayleigh-wave group and phase velocity maps detect small sedimentary basins with low velocities and large cratons with high velocities, implying that our approach can simultaneously image local-, regional- and large-scale structures in one tomographic system. The regionalised dispersion curves can be used to invert for deep structure directly or jointly with other geophysical observations across East Asia.