Complex seismic anisotropy at the border of a very low velocity province at the base of the Earth's mantle

摘要: [1] We constrain the anisotropy associated with a very low velocity province (VLVP) at base of Earth's mantle using SKS and SKKS waves sampling region. Our selected high-quality data sets consist 415 111 waveforms for 127 deep earthquakes recorded distances between 90° 150° by seismic stations in three temporary broadband PASSCAL arrays: Kaapvaal array (1997–1999), Tanzania (1994–1995), Ethiopia/Kenya (1999–2001), as well permanent Global Seismographic Network. These provide good coverage some portion VLVP its surrounding areas. results show, when or phases sample regions away from border (inside outside VLVP), apparent splitting parameters inferred are consistent those phases, their variations strongly correlate but not exit points core-mantle boundary these phases. However, near VLVP, different, no longer stations. features indicate that part shear wave has to originate mantle, most likely VLVP. We assume shallow beneath horizontal hexagonal symmetry axis infer then obtain lowermost corrected stations, assuming medium also axis. reveal complex pattern Such may be explained lattice-preferred orientation anisotropic aggregates aligned flow margins. The margins strong interactions compositional anomaly, normal an explanation concentration hot spots geographically borders VLVPs mantle.