Receiver function seismology

Abstract

The application results of the receiver function technique are briefly outlined. The topography of the main seismic boundaries in the mantle transition zone is evaluated with resolution of about 3 km in depth and about 200 km laterally. The maximal amplitudes of depth variations of the main boundaries reach tens of kilometers. The mantle transition zone thinning in the hot spots and the respective increase in temperature by ~100 °C is established. In several regions, two low-velocity layers are revealed in the mantle transition zone, one directly above the 410-km seismic discontinuity and another at a depth of 450 to 500 km. The origin of the first layer is associated with dehydration in the mantle plumes during olivine – walesite phase transformation. The increase in the S-wave velocity at the base of the second layer can explain the observations of the so-called 520-km boundary. The traditional approach to studying the structure of the crust and upper mantle is from surface waves. Receiver functions can provide higher resolution at the same depths when a combination of P- and S-wave receiver functions is used. This type of results was obtained for Fennoscandia, Kaapvaal craton, Indian shield, Central Tien Shan, Baikal rift zone, the Azores, Cape Verde Islands, and the western Mediterranean. S-receiver functions were used in the studies of the lunar crust. The joint P- and S-receiver function inversion provides robust estimates of the parameters of seismic boundaries including weak discontinuities such as the lithosphere – asthenosphere interface of cratons. The parameters determined from receiver functions include the P- to S-wave velocity ratio. In a few regions, a very high (> 2.0) velocity ratio is observed in the lower crust, probably indicating the presence of a fluid with high pore pressure. Receiver functions allow estimating the parameters of azimuthal anisotropy as a function of depth. The changes of the parameters with depth make it possible to distinguish the active anisotropy associated with recent deformations from the frozen anisotropy – the effect of the past tectonic processes.