Spatial variation of lithospheric heterogeneity on the globe as revealed from transverse amplitudes of short-period teleseismic P-waves

We systematically characterized the medium heterogeneity of the lithosphere by analyzing transverse-component amplitudes of teleseismic P-waves from shallow earthquakes in short periods of 0.5 to 4 Hz. Normalized transverse amplitudes, which are less affected by a layered structure, were measured at each station of the IRIS GSN network. The data revealed significant regional differences in lateral heterogeneity of the lithosphere, with small amplitudes observed at stations on stable continents and large normalized transverse amplitudes observed in seismically active regions, such as island arcs or collision zones. These spatial changes are consistent with the tectonic settings of each station. However, large normalized transverse amplitudes were also observed in regions of very low seismicity and in regions where no seismic activity has been recognized, which may indicate the existence of medium heterogeneity in the lithosphere that has been formed in ancient times.