Receiver Function Seismology

Аннотация

The results of application of the receiver function technique are briefly reviewed. In the mantle transition zone, the topography of the main seismic boundaries is evaluated with a resolution of about 3 km in depth and a lateral resolution of about 200 km. The variations of the depth of the main boundaries have the maximal amplitude reaching tens of kilometers. Thinning of the mantle transition zone 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 in the process of the olivine–wadsleyite phase transformation. The increase in the velocity of S-waves in the base of the second layer may explain the observations of the so-called 520-km boundary. The traditional approach to the studies of the structure of the crust and upper mantle is based on using the 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 study of the lunar crust. The joint inversion of P- and S-receiver functions provides robust estimates of the parameters of the seismic boundaries, including weak discontinuities such as the lithosphere–asthenosphere interface of cratons. The parameters determined from receiver functions include the P-wave to S-wave velocity ratio. In a few regions, a very high (>2.0) velocity ratio is observed in the lower crust that may indicate the presence of a fluid with a high pore pressure. Receiver functions allow estimating the parameters of the azimuthal anisotropy as a function of depth. The change of the parameters with depth makes it possible to distinguish the active anisotropy associated with recent deformations from the frozen anisotropy—the effect of the past tectonic processes.