Melt‐induced seismic anisotropy and magma assisted rifting in Ethiopia: Evidence from surface waves

摘要: [1] The East African rift in Ethiopia is unique worldwide because it captures the final stages of transition from continental rifting to seafloor spreading. A recent study there has shown that magma intrusion plays an important role during breakup, but mechanism by which incorporated into extending plate remains ambiguous: wide-angle seismic data and complementary geophysical tools such as gravity analysis are not strongly sensitive geometry subsurface melt intrusions. Studies shear wave splitting near-vertical SKS phases beneath transitional Main Ethiopian Rift (MER) provide strong consistent evidence for a rift-parallel fast anisotropic direction. However, difficult discriminate between oriented pocket (OMP) lattice preferred orientation (LPO) causes anisotropy based on alone. The speeds horizontally propagating Love (SH) Rayleigh (SV) waves vary similar fashions with azimuth LPO- OMP-induced anisotropy, their relative change distinctive each mechanism. This diagnostic exploited studying propagation surface suite azimuths across MER. Anisotropy roughly perpendicular absolute motion direction, thus ruling out due slowly moving Plate. Instead, three mechanisms act MER: periodic thin layering seismically slow material uppermost ∼10 km, OMP ∼20–75 km depth, olivine LPO upper mantle beneath. results explained best model low aspect ratio inclusions (dykes veins) being intruded late stage breakup. observations join growing body rifts passive margins shows accommodating extension without marked crustal thinning.