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Localized seismic anisotropy associated with long‐term slow‐slip events beneath southern Mexico
Author(s) -
Song TehRu Alex,
Kim YoungHee
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl051324
Subject(s) - geology , transition zone , subduction , seismology , shear zone , mylonite , slip (aerodynamics) , crust , seismic anisotropy , anisotropy , shear (geology) , oceanic crust , episodic tremor and slip , low velocity zone , geophysics , petrology , tectonics , mantle (geology) , lithosphere , physics , quantum mechanics , thermodynamics
Slow slip events (SSEs) are recently discovered in the transition zone downdip of the locked zone where megathrust earthquakes repeatedly occur at subduction zone interface. Structural changes from the locked zone to the transition zone and the nature of in situ deformation in the transition zone, however, remain unclear. We model teleseismic converted P‐to‐S waves to investigate seismic structural transition and anisotropy associated with shear deformation near the deep locked zone and the transition zone beneath southern Mexico. The deep locked zone appears to be consistent with normal oceanic crust velocity. In the transition zone, we find that seismic anisotropy larger than 5% is associated with the ultra‐slow velocity layer (USL) near the top of the subducted oceanic crust. The foliation plane is plunging 20 ± 10 degrees steeper than the plate interface, and it is consistent with crystallographic preferred orientation developed in S‐C mylonites. We suggest that long‐term SSEs likely coincide with a near‐lithostatic semiductile talc‐rich shear zone.