oa Temporal Change in Reflected Waves from Deep Crust Possibly Synchronized with the Activity of DLFTs Detected Using ACROSS

ACROSS stands for Accurately Controlled, Routinely Operated Signal System. Repeated transmission of a controlled seismic signal and long-term continuous observation of the seismic waves enable precise monitoring of time-evolving physical properties of the Earth’s interior. An observation using the ACROSS source was conducted in the Tokai distinct, Japan to establish a method to monitor the state of coupling of the plate boundary and to understand the time-evolving phenomena such as slow-slip and deep low-frequency tremors (DLFTs). A seismic signal emitted from the ACROSS source was observed by a short-span surface seismometer array and a Hi-net station (N.HOUH) located at the distance of 57 km from the source for 10 months. The transfer function clearly shows the P-wave, S-wave and their later-phases. Coherent later phases were detected using the semblance analysis of the array of transfer functions. They were interpreted as the reflections from the Moho and the plate boundary. The temporal changes of these phases were examined using Hi-net data which were free from environmental effects. The temporal changes of these phases show correlation with the episodic activity of the DLFTs in 2005. This implies the possibility of seismic monitoring of seismogenic plate-subduction zone using ACROSS.