High-resolution seismic imaging in the Japan Trench axis area off Miyagi, northeastern Japan

Newly obtained high-resolution seismic data reveal the detailed structure of the Japan Trench axis off Miyagi, Japan, in the region of large shallow slip during the 11 March 2011 M9 Tohoku earthquake. Correlation of seismic images with previous drilling results identifies a possible basal chert-rich layer and hemipelagic/pelagic mudstones overlying igneous Pacific crust. Mapping of acoustic basement depicts the subduction of horst-and-graben topography. The basement and basal chert are subducted beneath a seismically chaotic frontal prism, but the majority of overlying hemipelagic mudstones is offscraped and imbricated at the trench axis as a result of plate boundary compression. A possible décollement is imaged as a seaward dipping reflection at landward part of the trench graben and was likely generated by loading and failure of underthrust sediments. Collectively, these analyses provide a structural framework for understanding sedimentary inputs and the localization of shallow plate boundary slip at the Japan Trench. Key Points Detailed structure in the Japan Trench axis is imaged with seismic dataDécollement and imbricate structure of sediments are clearly observedPossible scenario for the sequence of deformation in the trench is presented