11:00 〜 11:15
[SCG52-08] Integrated 3D P-wave Tomography Reveals Forearc Structure of the Central NE Japan Subduction Zone
キーワード：Subduction, NE Japan, Megathust, Tokohu, Forearc structure
Recent studies have shown that crustal structure of the overlying plate may play an important role in modulating the slip behaviour of megathrust faults. Here, we present an integrated active- and passive-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 M9 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, which were recorded passively by ~150 seismographs located both onshore (Hi-net, F-net, Tōhoku University and Japan Meteorological Agency (JMA) networks) and offshore (S-net and temporarily deployed Ocean Bottom Seismometers). These data have been augmented by twenty years of earthquake travel-time arrivals recorded on >350 seismographs from the same networks, as documented by the JMA and relocated in this study.
Notably, in the central Miyagi-Oki forearc region, our model resolves a ~ 4 km increase in forearc crustal thickness and this coincides with a prominent increase in Vp within the underlying mantle wedge. Crustal rocks (estimated by the 5.5 km s-1 velocity contour) also extend further up-dip towards the trench in this part of the margin relative to adjacent regions. Consideration of the onshore basement terrane configuration suggests these characteristics may, to first order, represent the offshore expression of the allochthonous Palaeozoic Southern Kitakami terrane. The correlation of this region with a zone of high slip deficit rate prior to the 2011 Tōhoku earthquake corroborates previous results that variations in the structure of the upper plate may play a key role in modulating both the accumulation and release of elastic strain associated with megathrust events.
Notably, in the central Miyagi-Oki forearc region, our model resolves a ~ 4 km increase in forearc crustal thickness and this coincides with a prominent increase in Vp within the underlying mantle wedge. Crustal rocks (estimated by the 5.5 km s-1 velocity contour) also extend further up-dip towards the trench in this part of the margin relative to adjacent regions. Consideration of the onshore basement terrane configuration suggests these characteristics may, to first order, represent the offshore expression of the allochthonous Palaeozoic Southern Kitakami terrane. The correlation of this region with a zone of high slip deficit rate prior to the 2011 Tōhoku earthquake corroborates previous results that variations in the structure of the upper plate may play a key role in modulating both the accumulation and release of elastic strain associated with megathrust events.