[S-SS08] Crustal Structure

[SSS08-02] 3D active-source tomography reveals crustal structure of the central NE Japan subduction zone

*Brook Tozer¹, Dan Bassett¹, Shuichi Kodaira², Adrien Arnulf³, Ayako Nakanishi², Seiichi Miura², Gou Fujie², Kimihiro Mochizuki⁴ (1.GNS Science, 2.Japan Agency for Marine-Earth Science and Technology, 3.The University of Texas at Austin, 4.Earthquake Research Institute, the University of Tokyo)

Keywords:Subduction, Tōhoku, Megathrust, Earthquake, Crustal, P-wave

Recent studies have shown that crustal structure of the overlying plate plays an important role in modulating the slip behaviour of megathrust faults. Here, we present a preliminary active-source three-dimensional tomographic model of crustal structure in the central part of the NE Japan subduction zone – spanning the rupture area of the 2011 great Tōhoku earthquake. This model has been constructed using seismic travel-time data generated by over two decades of offshore seismic surveys undertaken by JAMSTEC, ERI and others, that were recorded passively by ~150 seismographs from the Hi-net, F-net, Tōhoku University, JMA and S-net networks as well as temporary deployed OBS networks. Our preliminary model resolves a reduction in P-wave velocity of the forearc crust, which coincides with a pre-identified forearc segment boundary interpreted to mark the offshore extension of the Median Tectonic Line. This interpretation attributes differences in wavespeeds to lithologic heterogeneity in the forearc, with higher velocity volcanic rocks in the north to accretionary sediments in the south. It also suggests upper-plate structure may have played a key role in the accumulation and release of elastic strain during the 2011 Tōhoku earthquake.