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Inversion of Longer‐Period OBS Waveforms for P Structures in the Oceanic Lithosphere and Asthenosphere
Author(s) -
Takeuchi Nozomu,
Kawakatsu Hitoshi,
Shiobara Hajime,
Isse Takehi,
Sugioka Hiroko,
Ito Aki,
Utada Hisashi
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2019jb018810
Subject(s) - asthenosphere , geology , lithosphere , mantle (geology) , geophysics , low velocity zone , seismology , receiver function , anisotropy , tectonics , physics , quantum mechanics
We performed waveform inversion of the P waveforms recorded by our BroadBand Ocean Bottom Seismometers (BBOBSs) deployed in the Northwestern Pacific. Consequently, the depth profile of the P velocity of the oceanic upper mantle, which has not been well resolved by previous surface wave or receiver function analyses, was revealed. We considered the azimuthal anisotropy in the lithosphere, which significantly improved the variance reduction from 34 % to 44 % . The resulting P model exhibited higher and lower velocities in the lithosphere and asthenosphere, respectively. The velocity contrast was found to be second/third of that observed in the previous S models; however the obtained model appeared to have some trade‐off with the V S structures in the vicinity of the source. We compared our P model with the previous S model obtained using our BBOBSs and obtained the V P / V S model. The resulting V P / V S model has two notable features. First, the lithosphere is characterized by a rapid increase in the V P / V S values with depth, which implies chemical stratification. Second, the V P / V S values in the vicinity of the lithosphere‐asthenosphere boundary (LAB) are larger than the synthetic values of any major upper mantle mineral predicted by considering the anharmonic effects, which suggests the effects of anelasticity or melt.